Scielo RSS <![CDATA[Theoretical and Experimental Plant Physiology]]> vol. 25 num. 4 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>The future of water relations of plants</b>]]> <![CDATA[<b>Will we have enough to eat in the near future?</b>: <b>what the Brazilian Society of Plant Physiology and The Global Plant Council have to do with it?</b>]]> <![CDATA[<b>Enhanced salt tolerance in maize plants induced by H<sub>2</sub>O<sub>2</sub> leaf spraying is associated with improved gas exchange rather than with non-enzymatic antioxidant system</b>]]> Hydrogen peroxide (H2O2) is an essential signaling molecule that mediates plant responses against several biotic and abiotic stresses. H2O2 pretreatment has emerged as a signaling way, inducing salt stress acclimation in plants. Here, we analyzed the effects of H2O2 leaf pretreatment on the non-enzymatic defense system (ascorbate and glutathione), plant growth, relative water content (RWC), relative chlorophyll content, H2O2 content, and gas exchange in maize plants under NaCl stress. The results showed that salinity reduced the leaf area and shoot and root dry mass as compared to control, and the leaf spraying with H2O2 significantly improved the growth of salt stressed plants. Photosynthesis and transpiration, stomatal conductance and intercellular CO2 concentration were strongly decreased by salinity after 7 and 14 days of salt exposure; however, the decrease was lower in plants sprayed with H2O2. The improved gas exchange in H2O2-sprayed stressed plants correlated positively with higher RWC and relative chlorophyll content and lower leaf H2O2 accumulation under NaCl stress conditions. Ascorbate and glutathione did not play any obvious effects as non-enzymatic antioxidants in the ROS scavenging. In conclusion, the salt tolerance induced by H2O2 leaf pretreatment is attributed to a reduction in the H2O2 content and maintenance of RWC and chlorophyll in maize leaves. These characteristics allow maize plants to maintain high rates of photosynthesis under salt stress and improve the growth. <![CDATA[<b>Ethylene response factors gene regulation and expression profiles under different stresses in rice</b>]]> Stresses can cause large yield reductions in cultivated plants. The response to these stresses occurs via a plethora of signalling pathways, where a large number of genes is induced or repressed. Among the environmental stress responsive genes, there are the members of the ethylene response factors (ERF) gene family. The mRNA levels of different ERF are regulated by many hormones and molecules produced under different stress conditions. In this study, with the goal of identifying the response of rice ERF genes to environmental stress, it was analysed the transcriptional expression profile of 114 of these genes under stress by anoxia, salt and Magnaporthe grisea. Also, aiming to characterize how the regulation of ERF genes occurs, the amount of known cis regulatory elements in the promoter region of these genes and their association with the expression profiles under the tested conditions were also assessed. The results indicate that some ERF members present the same specific expression profiles under different environmental stresses, while others do not. Within the ERF family, the regulation of gene expression is complex for some genes which have many cis elements in their promoters, but simple for others, demonstrating high levels of divergence among them. The findings demonstrate the importance of the study of each ERF separately, since it is not possible to establish general rules for regulation and probably for the function of these genes. <![CDATA[<b><b>Resistance to cyanide by salicylate pretreatment in <i>Salix babylonica</i> L.</b></b>]]> Cyanide is uncontrollably produced in some industrial operations and has lethal effects on humans and the environment. Since removing processes of cyanide are complicated and costly, the phytoremediation has recently been extensively considered. To achieve an increased cyanide resistance, which is needed for an efficient phytoremediation of the mediums with high concentrations of cyanide, the effects of salicylate as a phytohormone were studied. Cuttings of Salix babylonica, as a model plant, were used in a completely randomized design with three replicates in hydroponics using a modified Hoagland nutrient solution. Plants were pretreated with sulfosalicylate (0, 5, 10 and 15 mg L-1) for 21 days and then were treated with toxic concentration of cyanide (9 mg CN- L-1); some of the physiological indices which show cyanide toxicity/resistance were measured. Favorable responses to salicylate toward the increase in resistance to cyanide were concentration dependent which were observed at 10 mg L-1 sulfosalicylate and it was accompanied with an increase in superoxide dismutase activity and reducing the capacity of root extract. Dehydrogenase activity and electrolyte leakage from roots were decreased relating to control plants. It also prevented the cyanide inhibitory effect on oxygen consumption. The observed effects could be attributed to redox status and alteration of production and scavenging of reactive oxygen species by salicylate and cyanide. The results indicated that a proper concentration of salicylate could be used as a cyanide resistance stimulator in willows. <![CDATA[<b>Ploidy levels in Citrus clementine affects leaf morphology, stomatal density and water content</b>]]> The objective of the present study was to understand the relationship among leaf morphology, stomatal characteristics and water relations in triploids generated through anther culture and their counterpart diploid plant of C. clementina. Triploid plants possessed small and narrow leaves as compared to diploid plant as evident by less leaf length, leaf width and leaf area. By contrast, the leaf index was observed to be more in triploids than haploid ones. Flow cytometric analysis re-confirmed the ploidy levels of heterozygous plant Hd as diploid and the ploidy of Th1, Th2, Th3 and Th4 plants as triploids. A positive relation was found between ploidy level and stomatal guard cell length and width, whereas a negative relation was observed between the stomata density and ploidy level. The stomatal density was reported to be 6.2±0.2 stomata per µm² in diploid plant, while stomatal density varied between 3.0 and 3.6 stomata per µm² in triploids. Leaf relative water content (RWC) was slightly higher in triploids (90.8 to 93.1%) than diploid (89.5%). The leaf water loss was found to be marginally higher in diploid than in triploid plants. Our results show that increase in ploidy level from diploids to triploids caused an effect on leaf morphology and stomatal characteristics with probable consequences to water relations of leaves. This research will serve as an important basis for future work on complete analysis of both morphological and behavioural traits of the leaf stomata and transpiration rates in relation to diploid versus triploid plants. <![CDATA[<b>Abscisic acid-mediated leaf phenolic compounds, plant growth and yield is strawberry under different salt stress regimes</b>]]> The present research was conducted to evaluate the interaction effects of exogenous abscisic acid (ABA) and salt stress on phenolic compounds, growth and yield of two short day strawberry cvs "Queen Elisa" and "Kurdistan". Plants were subjected to control, gradual salt stress (up to 20 mmol L-1 over 5 weeks) and salinity shock (20 mmol L-1). ABA treatments included: 0 (control), 5, 10, 20 and 40 µmol L-1. The experiment was carried out based on a complete randomized design in factorial experiment. The highest level of ferulic acid was observed by applying 40 µmol L-1 ABA in "Queen Elisa" under salt stress shock but effective increase in caffeic acid and p-coumaric acid was shown at gradual salt stress for both cultivars at the same ABA level. Maximum level of ABA led to the highest gentisic acid and gallic acid at gradual salt stress in "Kurdistan". Methyl gallate and flavonoid content showed a striking increase at the same conditions in "Queen Elisa". The interaction effect of salt stress regimes and ABA resulted in an increase in ellagic acid content for both cultivars. The interaction effect of ABA and salt shock caused higher reduction in root and shoot fresh dry weights and decrease in fruit yield in "Kurdistan". The results of this experiment accounts for the important role of exogenous ABA in the activation of antioxidant defense mechanism, growth and yield maintenance under gradual salt stress in strawberry.