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HYDROGEN PEROXIDE AS SALT STRESS ATTENUATOR IN SOUR PASSION FRUIT

PERÓXIDO DE HIDROGÊNIO COMO ATENUANTE DO ESTRESSE SALINO EM MARACUJAZEIRO-AZEDO

ABSTRACT

Sour passion fruit is a fruit crop widely cultivated throughout Brazil, due to its adaptation to the tropical climate. However, in semi-arid regions its development is limited by the high concentration of soluble salts in the waters commonly used in irrigation. In this context, exogenous application of low concentrations of hydrogen peroxide can attenuate the damage caused by salt stress. The objective of this study was to evaluate electrolyte leakage, photosynthetic pigments and photochemical efficiency in sour passion fruit cv. BRS Rubi do Cerrado under irrigation with saline waters and foliar application of hydrogen peroxide. A completely randomized design was used, with treatments arranged in split plots, corresponding to five levels of irrigation water salinity - ECw (0.6; 1.2; 1.8; 2.4 and 3.0 dS m−1) and four concentrations of hydrogen peroxide - H2O2 (0; 15; 30 and 45 μM of H2O2) in plots and subplots, respectively. Irrigation with saline water reduced chlorophyll a and total chlorophyll contents of sour passion fruit plants cv. BRS Rubi do Cerrado, at 240 days after transplanting. Hydrogen peroxide at concentration of 15 μM stimulated chlorophyll a and total chlorophyll biosynthesis and, at 45 μM, relieved the effect of 3.0 dS m−1 water salinity on electrolyte leakage in the leaf blade of sour passion fruit. Salt stress did not affect the initial, maximum, variable fluorescence and quantum efficiency of photosystem II of sour passion fruit cv. BRS Rubi do Cerrado.

Keywords
Passiflora edulis Sims; Reactive oxygen species; Photochemical efficiency; Oxidative stress

RESUMO

O maracujazeiro-azedo é uma fruteira amplamente cultivada em todo Brasil, devido sua adaptação ao clima tropical. No entanto, em regiões semiáridas seu desenvolvimento é limitado devido água alta concentração de sais solúveis nas águas comumente utilizadas na irrigação. Neste contexto, a aplicação de baixas concentrações de peróxido de hidrogênio de forma exógena pode atenuar os danos provocados pelo estresse salino. Objetivou-se com esta pesquisa avaliar o extravasamento de eletrólitos, os pigmentos fotossintéticos e a eficiência fotoquímica em maracujazeiro-azedo cv. BRS Rubi do Cerrado sob irrigação com águas salinas e aplicação foliar de peróxido de hidrogênio. Foi utilizado o delineamento inteiramente casualizados, com os tratamentos dispostos em parcelas subdivididas, sendo cinco níveis de salinidade da água de irrigação - CEa (0,6; 1,2; 1,8; 2,4 e 3,0 dS m−1) e quatro concentrações de peróxido de hidrogênio - H2O2 (0; 15; 30 e 45 µM de H2O2) nas parcelas e subparcelas, respectivamente. A irrigação com água salina reduziu os teores de clorofila a e total das plantas de maracujazeiro-azedo cv. BRS Rubi do Cerrado, aos 240 dias após o transplantio. O peróxido de hidrogênio na concentração de 15 µM estimulou a biossíntese de clorofila a e total e de 45 µM aliviou o efeito da salinidade da água de 3,0 dS m−1 sobre o extravasamento de eletrólitos no limbo foliar do maracujazeiro-azedo. O estresse salino não afetou a fluorescência inicial, máxima, variável e eficiência quântica do fotossistema II do maracujazeiro-azedo cv. BRS Rubi do Cerrado.

Palavras-chave
Passiflora edulis Sims; Espécie reativa de oxigênio; Eficiência fotoquímica; Estresse oxidativo

INTRODUCTION

Sour passion fruit (Passiflora edulis Sims) is a crop that adapts well to the conditions of cultivation in the Brazilian semi-arid region; however, with the great temporal and spatial variability of the rains, it is necessary to use irrigation and the water used for it often comes from artesian wells that have high salinity. Passion fruit is classified as sensitive to salinity, that is, it has salinity threshold of only 1.3 dS m−1 for electrical conductivity of the soil saturation extract, which enables the use of water with maximum electrical conductivity of 0.9 dS m−1. The national production of sour passion fruit in 2019 was 593,429 ton; the Northeast accounted for 64.50% of this production, Bahia was the largest national producer (168,457 ton), and Paraíba occupied the 13th place in the national ranking, with a production of 9,967 ton (IBGE, 2019IBGE - Instituto Brasileiro de Geografia e Estatística. Produção agrícola municipal: culturas temporárias e permanentes. 2019. Disponivel em: <https://sidra.ibge.gov.br/tabela/5457#resultado>. Acesso em: 30 set. 2020.
https://sidra.ibge.gov.br/tabela/5457#re...
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It is a crop well known and exploited throughout the world and can be consumed in various ways, being highly valued and easy to trade. Its cultivation is a source of job and income generation for many family farmers. The Northeast region has great potential in the exploitation of this crop, mainly due to its edaphoclimatic characteristics. As sour passion fruit is a crop well known and accepted by the consumer market, its cultivation has been growing throughout the country, thus generating employment and income.

A limiting factor for the production of this fruit crop in the semi-arid region of northeastern Brazil is the occurrence of low rainfall, temporal and spatial variability, and high temperatures and evapotranspiration (LIMA et al., 2016LIMA, G. S. de et al. Irrigação com águas salinas e aplicação de prolina foliar em cultivo de pimentão ‘All Big’. Comunicata Scientiae, 7: 513-522, 2016.; SANTOS et al., 2016SANTOS, J. B. et al. Morfofisiologia e produção do algodoeiro herbáceo irrigado com águas salinas e adubado com nitrogenio. Comunicata Scientiae, 7: 86-96, 2016.). In this region, water scarcity makes it impossible to grow fruit crops under a rainfed regime (SILVA et al., 2016da SILVA, J. M. et al. Profitability of yellow passion fruit as a function of irrigation depths under semiarid conditions. African Journal of Agricultural, 11: 1079-1085, 2016.), so irrigation becomes necessary. However, the occurrence of water sources with high concentrations of salts is a barrier to the expansion of irrigated agriculture (BEZERRA et al., 2018BEZERRA, I. L. et al. Morphophysiology of guava under saline water irrigation and nitrogen fertilization. Revista Brasileira de Engenharia Agricola e Ambiental, 22: 32-37, 2018.).

The use of saline water in irrigation can cause deleterious effects on plants, by reducing water availability due to the decrease in the osmotic potential of the soil solution, leading to stomatal closure and compromising transpiration and photosynthesis (SILVA et al., 2015SILVA, F. G. et al. Trocas gasosas e fluorescencia da clorofila em plantas de berinjela sob laminas de irrigação. Revista Brasileira de Engenharia Agricola e Ambiental, 10: 946-952, 2015.). In addition, the use of waters with high concentrations of salts causes photoinhibition, photooxidation in chloroplasts, enzyme inactivation, degradation of photosynthetic pigments and lipid peroxidation of membranes (ASHRAF; HARRIS, 2013ASHRAF, M.; HARRIS, P. J. C. Photosynthesis under stressful environments: an overview. Photosynthetica, 51: 601-639, 2013.).

Considering that most crops are sensitive to the presence of salts either in irrigation water or in soil, it is necessary to conduct research to investigate the technical and economic feasibility of strategies capable of minimizing the deleterious effects of salinity on plants (FREIRE et al., 2014FREIRE, J. L. O. et al. Rendimento quântico e trocas gasosas em maracujazeiro amarelo sob salinidade hidrica, biofertilização e cobertura morta. Revista Ciência Agronômica, 45: 82-91, 2014.). Thus, hydrogen peroxide (H2O2), which is a reactive oxygen species capable of causing oxidation of lipid and proteins, DNA changes and modulation of gene expression, has been studied as an attenuating agent of abiotic stresses in plants (FERNANDO; SOYSA, 2015FERNANDO, C. D.; SOYSA, P. Optimized enzymatic colorimetric assay for determination of hydrogen peroxide (H2O2) scavenging activity of plant extracts. Methods, 2: 283-291, 2015.), functioning as a signaling molecule to mediate stress responses (LI et al., 2016LI, Q. et al. Putrescine protects hulless barley from damage due to UV-B stress via H2S and H2O2 mediated signaling pathways. Plant cell reports, 35: 1155-1168, 2016.).

Andrade et al. (2019)ANDRADE, E. M. G. et al. Gas exchanges and growth of passion fruit under saline water irrigation and H2O2 application. Revista Brasileira de Engenharia Agricola e Ambiental, 23: 945-951, 2019. investigated the effect of irrigation water salinity (0.7 to 2.8 dS m−1) and exogenous application of hydrogen peroxide (0 to 60 μM) on the passion fruit variety ‘Guinezinho’ and observed a higher number of leaves in plants irrigated using water with electric conductivity of 1.5 dS m-1 and under H2O2 application of 40 μM, with reduction as irrigation water salinity increased.

Silva et al. (2019)SILVA, A. A. et al. Salt stress and exogenous application of hydrogen peroxide on photosynthetic parameters of soursop. Revista Brasileira de Engenharia Agricola e Ambiental, 23: 257-263, 2019. observed that, when the soursop cv. ‘Morada Nova’ is irrigated using water with electrical conductivity of up to 3.5 dS m−1 and is under exogenous application of H2O2 (0 to 100 μM) via seed soaking and foliar spraying, the application of 25 and 50 μM attenuated the deleterious effects of salinity on stomatal conductance, CO2 assimilation rate and chlorophyll a contents.

In this context, the objective of this study was to evaluate the electrolyte leakage, photosynthetic pigments and photochemical efficiency of sour passion fruit cv. BRS Rubi do Cerrado under irrigation with saline waters and foliar application of hydrogen peroxide.

MATERIAL AND METHODS

The experiment was conducted between May 2019 and January 2020 in an arch-type greenhouse, 30 m long and 21 wide, with ceiling height of 3.0 m, 150-micron low-density polyethylene cover, sides covered with white screen, with openings of 4 mm × 7 mm, belonging to the Academic Unit of Agricultural Engineering – UAEAg of the Federal University of Campina Grande – UFCG, in Campina Grande, Paraíba, Brazil (7º15’18” S, 35º52’28” W and average altitude of 550 m). The average monthly temperature inside the greenhouse was monitored throughout the experiment with a digital thermometer (Figure 1).

Figure 1
Maximum and minimum monthly average temperatures inside the greenhouse during the experimental period.

The treatments consisted of five levels of electrical conductivity of irrigation water - ECw (0.6; 1.2; 1.8; 2.4 and 3.0 dS m−1) and four concentrations of hydrogen peroxide - H2O2 (0; 15; 30 and 40 μM). The experimental design adopted was completely randomized in split plots, with the levels of electrical conductivity of irrigation water considered the plots and the concentrations of hydrogen peroxide considered the subplots, with three replicates. Water salinity levels and H2O2 concentrations were established based on a study conducted by Andrade et al. (2019)ANDRADE, E. M. G. et al. Gas exchanges and growth of passion fruit under saline water irrigation and H2O2 application. Revista Brasileira de Engenharia Agricola e Ambiental, 23: 945-951, 2019., who found that the 20 μM concentration promoted the highest values for variable and maximum fluorescence and carotenoid content, constituting an alternative to induce acclimatization of sour passion fruit.

The seeds were obtained from the cv. BRS Rubi do Cerrado provided by the orchard of the Federal Institute of Paraíba - IFPB, campus of Sousa, PB. The fruits of this cultivar are round, with a predominantly red, purplish or yellowish rind, weighing from 120 to 300 g, with soluble solids content ranging from 13° to 15° Brix, averaging 14° Brix, juice yield around 35%, higher resistance to transport, strong yellow pulp color, greater amount of vitamin C, and resistance to diseases such as those caused by viruses and bacteria, and scabs (EMBRAPA, 2012EMBRAPA - Empresa Brasileira de Pesquisa Agropecuária. BRS Rubi do Cerrado: Hibrido de maracujazeiro-azedo de frutos avermelhados e amarelos para indústria e mesa. 2 ed. Brasília, DF: EMBRAPA CERRADO, 2012. 2 p.).

The seedlings were grown in plastic bags with capacity for 3 kg (35 × 10 cm), filled with substrate in the 84:15:1 ratio of soil (volume based), washed sand and earthworm humus, respectively. The moisture content of the substrate was increased to the level corresponding to the maximum water holding capacity through the weighing lysimetry principle (BERNARDO; SOARES; MANTOVANI, 2013ASHRAF, M.; HARRIS, P. J. C. Photosynthesis under stressful environments: an overview. Photosynthetica, 51: 601-639, 2013.), and then 4 seeds were sown at a depth of 1.0 cm in each bag of seedlings. The water used was local-supply water from the Paraíba State Supply and Sewage Company, with electrical conductivity of 0.4 dS m−1.

At 10 days after emergence, thinning was performed leaving only one plant per bag of seedlings. At 70 days after emergence, that is, when the plants had tendrils, the seedlings were transplanted to pots that functioned as drainage lysimeters. Each lysimeter was perforated at the base and a drain was installed; above each drain, a nonwoven geotextile (Bidim) was placed to avoid clogging. The lower end of each drain was connected to a plastic container to collect the drained water, in order to determine the water consumption by the plant and electrical conductivity of the soil solution (EC).

The spacing adopted was 2.20 m between rows and 1.50 m between plants, using the vertical trellis system with smooth wire Nº 14 installed inside the greenhouse, at 2.40 m height from the floor and 1.60 m height from the soil of the lysimeter.

The lysimeters (height of 70 cm, bottom diameter of 57 cm and upper diameter of 57 cm) were filled with 0.5 kg of crushed stone Nº 0 and 250 kg of soil classified as Luvissolo crômico (Alfisol) (EMBRAPA, 2018EMBRAPA - Empresa Brasileira de Pesquisa Agropecuária. Sistema Brasileiro de Classificação de Solos. 5 ed. Brasilia, DF: EMBRAPA SOLOS, 2018. 353 p.), from Alagoa Nova, PB. The soil was collected at 0-30 cm depth (A horizon), before the experiment started, and was characterized for chemical and physical-hydraulic attributes (Table 1) according to the methodology of Teixeira et al. (2017)TEIXEIRA, P. C. et al. Manual de métodos de análise de solo. 3. ed. Brasilia, DF: Embrapa, 2017. 573 p.. Before the transplanting, the moisture content of the soil contained in the lysimeters was increased to the level corresponding to the maximum water holding capacity through the drainage lysimetry principle (BERNARDO; SOARES; MANTOVANI, 2013BERNARDO, S.; SOARES, A. A.; MANTOVANI, E. C. Manual de irrigação. 8 ed. Viçosa, MG: UFV. 2013. 625 p.).

Table 1
Chemical and physical-hydraulic characteristics of the soil, before application of the treatments.

Basal fertilization was performed according to the recommendation of São José (2000)SÃO JOSÉ, A. R. Maracujá: Práticas de cultivo e comercialização. 1. ed. Vitória da Conquista, BA: UESB-DFZ, 2000. 316 p., applying 250 g of single superphosphate (18.9% P2O2) and 100 g of potassium chloride (60% K2O) monthly until the beginning of flowering; at the beginning of this stage, nitrogen and potassium fertilization was performed monthly, according to the methodology proposed by Santos (2001)SANTOS, J. B. Estudo das relações nitrogênio: potássio e cálcio: magnésio sobre o desenvolvimento vegetativo e produtivo do maracujazeiro amarelo. 2001. 88 p. Dissertação (Mestrado em Manejo de Solo e Agua: Area de concentração Solos e Nutrição de plantas). Universidade Federal da Paraiba, Areia, 2001., using urea (45.9% N) as nitrogen source and potassium chloride (60% K2O) as potassium source.

In the crop formation stage, the 1N:1K ratio was used, based on a reference of 10 g of nitrogen; from the beginning of flowering, the N dose was raised to 20 g and the K dose to 30 g, increasing the N:K ratio to 1:1.5. Fertilization with micronutrients was performed according to the recommendation of Costa et al. (2008)COSTA, A. F. S. et al. Recomendações técnicas para o cultivo do maracujazeiro. Vitória, ES: Incaper, 2008. 56 p. (Incaper. Documentos, 162). at 15-day intervals after transplanting, by spraying the plants with a solution containing 2.5 g L−1 of commercial fertilizer with the following characteristic: N (15%), P2O5 (15%), K2O (15%), Ca (1%), Mg (1.4%), S (2.7%), Zn (0.5%), B (0.05%), Fe (0.5%), Mn (0.05%), Cu (0.5%) and Mo (0.02%). Throughout the experiment, each plant received 250 g of single superphosphate, 150 g of urea and 200 g of potassium chloride.

The levels of electrical conductivity of the irrigation water were prepared with Na:Ca:Mg in the equivalent proportion of 7:2:1, using the salts NaCl, CaCl2.2H2O and MgCl2.6H2O, adjusting them to the concentrations of the available supply water. This is a proportion of salts commonly found in the water bodies of the semi-arid region of northeastern Brazil. The irrigation waters were prepared considering the relationship between ECw and the concentration of salts according to Richards (1954)RICHARDS, L. A. Diagnosis and improvement of saline and alkali soils. Washington: U.S, Department of Agriculture, 1954. 160 p., as shown in Equation 1:

(1)Q=640×ECw

Where:

Q = Quantity of salts to be applied (mg L−1);

ECw = Electrical conductivity of water (dS m−1)

After transplanting, irrigation was performed daily according to Rhoades, Kandiah and Mashali (2000)RHOADES, J. D.; KANDIAH, A.; MASHALI, A. M. Uso de águas salinas para produção agrícola. 1. ed. Campina Grande, PB: UFPB, 2000. 117 p. (Estudos da FAO. Irrigação e Drenagem, 48)., applying in each lysimeter a volume of water corresponding to that obtained by the water balance, determined by Equation 2:

(2)VI=(Va-Vd)(1-LF)

Where:

VI = volume of water to be used in the next irrigation event (mL);

Va = volume applied in the previous irrigation event (mL);

Vd = volume drained (mL) and LF = leaching fraction of 0.15.

The salinized waters were stored in five boxes with capacity for 500 L, one for each salinity level, protected from the weather and covered with a lid to reduce evaporation and contamination by external agents. The salinized waters began to be applied at 15 days after transplanting and, during this period, the plants were irrigated with water of low electrical conductivity (0.4 dS m−1).

Hydrogen peroxide - H2O2 concentrations were prepared with deionized water. At the end of each application, the volume used in each treatment was quantified, and an average volume of 63.75 mL of H2O2 was applied per plant, in each application event, until the beginning of flowering. To avoid drift of the H2O2 solution, the plants of each treatment were isolated using plastic curtains.

Hydrogen peroxide concentrations were applied by foliar spraying (on the adaxial and abaxial sides) from 17:00 h, due to the lower incidence of light, because its degradation in the presence of light is very fast, using a manual sprayer, with 1-cm-diameter adjustable metal conical nozzle, operating pressure of 2.07 MPa, and flow rate of 1.1 L min−1 at 15-day intervals, starting at 15 days after the beginning of irrigation with the salinized waters until the flowering stage of the crop.

When the plants reached 10 cm above the trellis, their apical bud was pruned, aiming to stimulate the growth of secondary branches, which were trained one to each side up to a length of 1.10 m, and then a new pruning was performed to stimulate the growth of tertiary branches and, consequently, the formation of curtains and production of inflorescences. Pruning of the tertiary branches was performed at 30 cm from the soil to avoid their contact with the soil and the possible attack of pests or diseases. During pruning, Bordeaux mixture was applied to promote healing of injuries (MAZARO et al., 2013MAZARO, S. M. et al. Produção e qualidade de morangueiro sob diferentes concentrações de calda bordalesa, sulfocálcica e biofertilizante supermagro. Semina: Ciências Agrárias, 34: 3285-3294, 2013.).

At 240 days after transplanting, photosynthetic pigments were determined after collecting three fully expanded leaves, in the third order of three tertiary branches, and taking them to the Plant Physiology Laboratory of UFCG. Nine discs were collected to quantify the contents of chlorophyll a (Chl a), chlorophyll b (Chl b), total chlorophyll (Chl total) and carotenoids (Car), according to the methodology proposed by Arnon (1949)ARNON, D. I. Copper enzymes in isolated cloroplasts: polyphenoloxidases in Beta vulgaris. Plant Physiology, 24: 1-15, 1949.. From the extracts, the chlorophyll concentration was determined in the solutions using a spectrophotometer at absorbance wavelength (ABS) (470, 646, and 663 nm), according to Equations 3, 4 and 5.

(3)Chlorophylla(Chla)=(12.21×ABS663)(2.81×ABS646)
(4)Chlorophyllb(Chlb)=(20.13×ABS646)(5.03×ABS663)
(5)Carotenoids(Car)=[(1000×ABS470)(1.82Chla85.02Chlb)]198

The values obtained for chlorophyll a, chlorophyll b and carotenoids contents in the leaves were expressed in milligram per gram of fresh matter (mg g−1 FM).

Photosynthetic efficiency was determined using an Opti Science OS5p pulse-modulated fluorometer; first, the Fv/Fm protocol was used to determine the fluorescence induction variables: initial fluorescence (Fo), maximum fluorescence (Fm), variable fluorescence (Fv = Fm - Fo) and quantum efficiency of photosystem II (Fv/Fm); this protocol was performed after adaptation of the leaves to the dark for a period of 30 min, using a clip of the device, in order to ensure that all the primary acceptors are oxidized, that is, the reaction centers are open (MONTEIRO et al., 2018MONTEIRO, D. R. et al. Chlorophyll a fluorescence in saccharine sorghum irrigated with saline water. Revista Brasileira de Engenharia Agricola e Ambiental, 22: 673-678, 2018.).

Electrolyte leakage (EL) in the leaf blade was also determined according to the methodology proposed by Scotti-Campos et al. (2013)SCOTTI-CAMPOS, P. et al. Physiological responses and membrane integrity in three Vigna genotypes with contrasting drought tolerance. Emirates Journal of Food and Agriculture, 25: 1002-1013, 2013. by the relationship between the initial (Ci) and final (Cf) electrical conductivity, according to Equation 6.

(6) EL = Ci Cf × 100

Where:

EL = Electrolyte leakage in the leaf blade (%);

Ci = initial electrical conductivity (dS m−1);

Cf = final electrical conductivity (dS m−1).

Shapiro-Wilk test was applied to the obtained data to verify the assumption of normality. Next, the data were subjected to analysis of variance by the F test at p ≤ 0.05 and, when significant, linear and quadratic polynomial regression analysis was performed, using the statistical program SISVAR ESAL (FERREIRA, 2019FERREIRA, D. F. SISVAR: A computer analysis system to fixed effects split plot type designs. Revista Brasileira de Biometria, 37: 529-535, 2019.). When heterogeneity occurred in the data, verified through the values of the coefficient of variation, they were subjected to exploratory analysis, with transformation to square root.

RESULTS AND DISCUSSION

Chlorophyll a, chlorophyll b, total chlorophyll and carotenoid contents were significantly affected (p ≤ 0.05) by the salinity levels of irrigation water and by the foliar application of hydrogen peroxide - H2O2. The interaction between the factors (SL × H2O2) significantly affected (p ≤ 0.05) the chlorophyll b and carotenoid contents of sour passion fruit (Table 2).

Table 2
Chlorophyll a (Chl a), chlorophyll b (Chl b), total chlorophyll (Chl total) and carotenoids (Car) contents of sour passion fruit cv. BRS Rubi do Cerrado under irrigation with saline waters and foliar application of hydrogen peroxide - H2O2, at 240 days after transplanting.

The increase in the electrical conductivity of irrigation water reduced the chlorophyll a contents in the sour passion fruit cv. BRS Rubi do Cerrado and, according to the regression equation (Figure 2A), there was a quadratic reduction, with maximum and minimum values estimated at 8.91 and 6.11 mg g−1 FM, respectively, in plants irrigated using waters with electrical conductivity of 0.6 and 3.0 dS m−1. In relative terms, in the comparison of plants irrigated with water of higher salinity level (3.0 dS m−1) with those that received the lowest ECw level (0.6 dS m−1), there was a reduction of 32.72% (3.03 mg g−1 FM) in Chl a content. The reduction in chlorophyll a content can be attributed to the increase in the activity of the chlorophyllase enzyme, which acts by degrading photosynthesizing pigments (FREIRE et al., 2013FREIRE, J. L. et al. Teores de clorofila e composição mineral foliar do maracujazeiro irrigado com águas salinas e biofertilizante. Revista de Ciências Agrárias, 36: 57-70, 2013.). Lima et al. (2020)LIMA, G. S. et al. Gas exchange, chloroplast pigments and growth of passion fruit cultivated with saline water and potassium fertilization. Revista Caatinga, 33: 184-194, 2020., when studying the contents of photosynthetic pigments in passion fruit cv. BRS Rubi do Cerrado irrigated using water with electrical conductivity of 0.3 to 3.5 dS m−1 and under two doses of potassium - K2O (50 and 100% of the recommendation) in a protected environment, concluded that chlorophyll a synthesis was significantly reduced with the use of 3.5 dS m−1 water.

Figure 2
Chlorophyll a - Chl a (A) and total chlorophyll (B) contents of sour passion fruit plants cv. BRS Rubi do Cerrado as a function of irrigation water salinity; Chl a (C) and total chlorophyll (D) contents as a function of hydrogen peroxide concentrations; and chlorophyll b - Chl b (E) and carotenoids - Car (F) contents as a function of the interaction between irrigation water salinity and hydrogen peroxide concentrations, at 240 days after transplanting.

As observed for Chl a (Figure 2A), the total chlorophyll content of sour passion fruit plants decreased quadratically with increasing salinity of irrigation water (Figure 2B), and the maximum and minimum values were estimated at 10.86 and 7.71 mg g−1 FM, respectively, when the plants were grown under irrigation with ECw of 0.6 and 3.0 dS m−1. When comparing the Chl total contents of plants irrigated using water with lower salt concentration (0.6 dS m−1) with that of plants that received ECw of 3.0 dS m−1, there was a decrease of 30.16% (3.39 mg g−1 FM). This reduction in chlorophyll synthesis may be associated with inhibition of chlorophyll biosynthesis and instability of protein complexes caused by the effects of salt stress (HOUIMLI et al., 2010HOUIMLI, S. I. M. et al. Effects of 24-epibrassinolide on growth, chlorophyll, electrolyte leakage and proline by pepper plants under NaC1-stress. Eurasia Journal of BioSciences, 4: 96-104, 2010.).

Regarding the effects of hydrogen peroxide concentrations on chlorophyll a contents of sour passion fruit plants (Figure 2C), the regression showed that the highest estimated value of 7.609 mg g−1 FM was obtained in plants that received the estimated H2O2 concentration of 24 μM and, from this point on, there was a reduction in Chl a contents. In relative terms, plants that received 45 μM of H2O2 increased their chlorophyll contents by 0.162 mg g−1 FM compared to those that did not receive hydrogen peroxide (0 μM of H2O2). According to Farooq et al. (2017)FAROOQ, M. et al. Foliage applied sodium nitroprusside and hydrogen peroxide improves resistance against terminal drought in bread wheat. Journal of Agronomy and Crop Science, 203: 473-482, 2017., hydrogen peroxide is the reactive oxygen species with greatest stability in cells and, at high concentrations, can rapidly diffuse through the subcellular membrane, resulting in oxidative damage to the cell membrane.

Regarding the Chl total contents (Figure 2D), it was verified that the exogenous application of 15 μM of H2O2 promoted the highest value (9.74 mg g−1 FM). According to the regression equation (Figure 2D), the highest Chl total content (9.41 mg g−1 FM) was reached when the H2O2 concentration of 23.86 μM was applied. When comparing the total chlorophyll contents of plants that received foliar application of 45 μM of H2O2 with that of plants subjected to the control treatment (0 μM), there was an increase of 5.61% (0.49 mg g−1 FM). Despite the action of this reactive oxygen species in the plant defense system in the production of antioxidative biochemical agents such as superoxide dismutase, catalase and ascorbate peroxidase that seek to find redox homeostasis (YAO et al., 2021YAO, X. et al. Pretreatment with H2O2 Alleviates the Negative Impacts of NaC1 Stress on Seed Germination of Tartary Buckwheat (Fagopyrum tataricum). Plants, 10: 1-14, 2021.), its effect on plants depends on the H2O2 concentration applied.

From the moment photooxidation occurs, an irreversible process that directly involves photosynthesizing pigments that absorb light and become excited, producing free radicals such as superoxide and/or hydrogen peroxide, which can destroy the pigments (VERNON; SEEL, 2014VERNON, L. P.; SEEL, Y, G. R. The chlorophylls. 1 ed. New York, USA: Academic Press, 2014. 679 p.), it is believed that the exogenous application of low concentrations of hydrogen peroxide stimulates biochemical defenses of plants, hence producing enzymes such as superoxide dismutase, which endogenously destroys free radicals of H2O2.

The increase in chlorophyll b and carotenoid contents in sour passion fruit plants may be related to the physiological defense process of plants against photooxidation to avoid a reduction in photosynthetic efficiency (SILVA et al., 2014SILVA, M. A. et al. Pigmentos fotossintéticos e índice Spad como descritores de intensidade do estresse por deficiência hídrica em cana-de-açúcar. Bioscience Journal, 30: 173-181, 2014.). Plants use a number of enzymatic antioxidants (catalase – CAT, ascorbate peroxidase – APX, glutamine reductase – GR) and non-enzymatic antioxidants (ascorbic acid, carotenoids, flavonoids and phenolic compounds) to prevent oxidative damage and maintain the concentrations of reactive oxygen species within a functional range (OZGUR et al., 2013OZGUR, R. et al. Reactive oxygen species regulation and antioxidant defence in halophytes. Functional Plant Biology, 40: 832-847, 2013.).

Qiao et al. (2021)QIAO, T. et al. Hydrogen peroxide and salinity stress act synergistically to enhance lipids production in microalga by regulating reactive oxygen species and calcium. Algal Research, 53, e102017, 2021., when studying the effect of the combined treatment of NaCl (85.56, 171.12 and 342.23 mM) and hydrogen peroxide - H2O2 (0.5, 1, 2 and 4 mM) on lipid accumulation in Monoraphidium sp. (microalgae), verified that chlorophyll contents decreased with the application of hydrogen peroxide and NaCl, indicating that there was a change in physiological and biochemical metabolism from normal growth to biosynthesis of lipids.

Regarding the chlorophyll b contents of sour passion fruit (Figure 2E), plants that received foliar application of H2O2 at concentrations of 15, 30 and 45 μM showed a quadratic reduction, with maximum estimated values in plants irrigated with ECw of 3.0, 1.21 and 2.26 dS m−1, respectively. When considering the effect of irrigation water salinity with the foliar application of hydrogen peroxide on chlorophyll b contents, it was verified that the foliar application of 45 μM of H2O2 promoted an increase of 22.64% (0.48 mg g−1 FM) in plants irrigated with water of lower salinity (0.6 dS m−1) compared to those receiving the same concentration of hydrogen peroxide under irrigation with water of 3.0 dS m−1. It is assumed that the application of hydrogen peroxide at high concentrations associated with irrigation with saline water can induce oxidative stress.

Regarding the carotenoid contents of sour passion fruit plants (Figure 2F), it is verified that the data were described by a quadratic model, whose estimated maximum values (360.04, 347.73, 564.04 and 526.47 mg−1 FM) were obtained in plants that received 0, 15, 30 and 45 μM of H2O2 and were irrigated using water with ECw of 2.08, 2.01, 1.71 and 1.58 dS m−1, respectively. Plants irrigated with the lowest salinity level (0.6 dS m−1) showed the highest contents of carotenoids (689 mg g−1 FM) for H2O2 concentration of 15 μM. The lowest carotenoid content (1.34 mg g−1 FM) was observed when sour passion fruit plants cv. BRS Rubi do Cerrado were irrigated with ECw of 1.2 dS m−1 and subjected to 0 μM of hydrogen peroxide.

It is suggested that, for photosynthetic pigments, hydrogen peroxide at the concentration of 30 μM can act as a signaling molecule of abiotic stress, through the action of enzymatic and non-enzymatic components, promoting an increase in carotenoid contents, induced by the production of β-carotene, which are integrated components of thylakoids, acting in the absorption and transfer of light to chlorophyll (SILVA et al., 2017SILVA, A. R. A. et al. Pigmentos fotossintéticos e potencial hidrico foliar em plantas jovens de coqueiro sob estresses hídrico e salino. Revista Agro@mbiente On-line, 10: 317-325, 2017.), since the excess of salts causes imbalances in chloroplast activities, such as reduction in the synthesis of 5-aminolevulinate acid, which is a chlorophyll precursor molecule, inducing an increase in oxidative activity, resulting in the degradation of molecules of photosynthesizing pigments such as chlorophyll b (CAVALCANTE et al., 2011CAVALCANTE, L. F. et al. Clorofila e carotenoides em maracujazeiro-amarelo irrigado com águas salinas no solo com biofertilizante bovino. Revista Brasileira de Fruticultura, 33: 699-705, 2011.).

The salinity of irrigation water significantly affected (p ≤ 0.05) only electrolyte leakage (EL), while hydrogen peroxide concentrations significantly affected the quantum efficiency of photosystem II (Fv/Fm). There was interaction between the factors (SL × H2O2), significantly affecting the electrolyte leakage (EL) of sour passion fruit cv. BRS Rubi do Cerrado (Table 3).

Table 3
Summary of the analysis of variance for initial fluorescence (Fo), maximum fluorescence (Fm), variable fluorescence (Fv), quantum efficiency of photosystem II (Fv/Fm), and electrolyte leakage (EL) of sour passion fruit cv. BRS Rubi do Cerrado under irrigation with saline waters and foliar application of hydrogen peroxide - H2O2, at 240 days after transplanting.

Quantum efficiency of photosystem II was also significantly affected by the exogenous application of hydrogen peroxide (Figure 3A). According to the regression equation, there was higher Fv/Fm (0.72) with the application of 10 μM of H2O2. In relative terms, there was a reduction of 2.73% (0.02) in Fv/Fm when the hydrogen peroxide concentration increased from 0 to 45 μM. The decrease in Fv/Fm possibly stands out as a defense mechanism to reduce the absorption of light energy and thus decrease the flow of electrons in the electron transport chain (WILLADINO et al., 2011WILLADINO, L. et al. Estresse salino em duas variedades de cana-de-açúcar: enzimas do sistema antioxidativo e fluorescencia da clorofila. Revista Ciência Agronomica, 42: 417-422, 2011.).

Figure 3
Quantum efficiency of photosystem II - Fv/Fm (A) of sour passion fruit plants cv. BRS Rubi do Cerrado, as a function of the application of hydrogen peroxide - H2O2 and electrolyte leakage - EL (B) as a function of the interaction between the levels of irrigation water salinity – ECw and concentrations of H2O2, at 240 days after transplantation.

According to Seon et al. (2000)SEON, J. H. et al. Influence of in vitro conditions on photosynthetic competence and survival rate of Rehmannia glutinosa plantets during acclimatization period. Plant Cell, Tissue and Organ Culture, 61: 135-142, 2000., the ideal Fv/Fm ratio should be between 0.75 and 0.85, and the photoinhibitory damage to the reaction centers of photosystem II in plants cultivated with high-salinity water also varies according to the phenological stage of the crop. Freire et al. (2014)FREIRE, J. L. O. et al. Rendimento quântico e trocas gasosas em maracujazeiro amarelo sob salinidade hidrica, biofertilização e cobertura morta. Revista Ciência Agronômica, 45: 82-91, 2014. evaluated the cultivation of yellow passion fruit under irrigation with saline water (ECw: 0.5 and 4.5 dS m−1) and observed that the increase in water salt content until the beginning of flowering reduced Fv/Fm from 0.82 to 0.77, with depletion of 6.1%.

The use of saline waters in the irrigation of the sour passion fruit cv. BRS Rubi do Cerrado with foliar application of hydrogen peroxide led to an increase in electrolyte leakage in the leaf blade and consequently a reduction in cell integrity. By the regression equation (Figure 3B), it can be observed that the lowest EL (64.62%) was obtained when plants were irrigated with water of electrical conductivity estimated at 1.16 dS m−1 and with foliar application of 15 μM. However, the highest EL occurred when hydrogen peroxide was not applied (0 μM) and under saline water of 1.38 dS m−1.

H2O2 is a molecular signaling agent that contributes to regulating the size of the antenna of photosystem II, leading to the long-term acclimatization response of the photosynthetic apparatus under excessive light conditions. Therefore, it is proposed that H2O2 is a molecule released by the set of molecules of the plastoquinone group, which is one of the main agents through which from its redox state it is an isoprenoid quinone molecule involved in the electron transport chain in light-dependent reactions of photosynthesis, providing regulatory effect on abiotic stress (BORISOVA-MUBARAKSHINA et al., 2015BORISOVA-MUBARAKSHINA, M. M. et al. Long-term acclamatory response to excess excitation energy: evidence for a role of hydrogen peroxide in the regulation of photosystem II antenna size. Journal of Experimental Botany, 66: 7151-7164, 2015.).

CONCLUSIONS

Irrigation with saline water reduces chlorophyll a and total chlorophyll contents of sour passion fruit plants cv. BRS Rubi do Cerrado, at 240 days after transplanting.

Hydrogen peroxide at the concentration of 15 μM stimulates chlorophyll a and total chlorophyll biosynthesis and, at 45 μM, relieves the effect of 3.0 dS m−1 water salinity on electrolyte leakage in the leaf blade of sour passion fruit.

Salt stress does not affect the initial, maximum and variable fluorescence and quantum efficiency of photosystem II of the sour passion fruit cv. BRS Rubi do Cerrado.

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Publication Dates

  • Publication in this collection
    13 May 2022
  • Date of issue
    Apr-Jun 2022

History

  • Received
    07 Jan 2021
  • Accepted
    24 Sept 2021
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