RESPONSE TO WATER DEFICIT OF Ipomoea cairica ( L . ) SWEET Resposta de Ipomoea cairica ( L . ) Sweet à deficiência hídrica

Green spaces require frequent watering, increasing the pressure on water resources. The use of native plants in landscaping reduces the risks of biological contamination, contributing to preservation of Brazilian biodiversity and provides the value of sustainability in urban green areas. Of these native plants, a restricted number are native lianas which are adapted to Brazilian climate and available on the market. In this regard, the selection and recommending of native plants which are efficient in use of water for planting in urban areas constitute an effective strategy for conservation of water resources. Thus, the purpose of this study was to evaluate the growth and development of I. cairica plants submitted to water deficit. For a period of 100 days after transplanting, plants of this species were grown with watered at pot capacity except for 30 days (from the 30th to the 60th day) when four water deficits (25, 50, 75 and 100% pot capacity) were applied. During all regimes of water deficiency applied, there was a 100% survival rate. After reestablishment of water regime the species recovered its growth, even that was submitted to the 25% of pot capacity. It testify that I. cairica is resistant to low water availability.


INTRODUCTION
Climbing plants are important for gardens, because they may be used in beautifying walls, frontages, pergolas and arbors (PAIVA, 2008).The number of native plants available on the market for this purpose is quite small, mainly due to the lack of research (BARROSO et al., 2007).In the Brazilian floriculture market, only some native species are available, such as: Allamanda cathartica, Philodendron hederaceum, Cuspidaria convoluta, Pyrostegia venusta, Combretum fruticosum, Turbina corymbosa, Bougainvillea spectabilis and B. glabra (LORENZI;SOUZA, 2001).
Due to anthropic pressure, many native species run the risk of extinction (CUQUEL et al., 2009).The growing of native plants is a manner of preservation of these species (LEAL;BIONDI, 2006).In addition, the use of native plants for ornamentation reduces the risks of biological contamination by exotic species (BARROSO et al., 2007) and contributes to preservation of biodiversity and sustainable use of green areas (YOUNIS et al., 2010).
For maintenance of urban landscaping, frequent watering is performed which raises the cost and does not collaborate with sustainable use of water resources.Due to the capacity of native species for adaptation to diverse environmental conditions (FRANCO et al., 2006), including low water availability (HITCHMOUGH, 2010), has recommended the use of these plants in landscaping.For that reason, the use of native species with ornamental potential is a trend in contemporary landscaping (HEIDEN et al., 2006;BRETZEL;PEZZAROSSA, 2010).Thus, studies Ciênc. agrotec., Lavras, v. 36, n. 3, p. 318-324, maio/jun., 2012 on drought tolerance, based on physiological parameters related to the state of water in the plant, may assist in the selection of the right plants for use in gardens (CHYLINSKI et al., 2007).
The species I. cairica or morning glory is a climbing, herbaceous, branched plant with exuberant lilac-colored flowers, and may be used as an ornamental plant (LORENZI; SOUZA, 2001).It is native from Brazil and is found in various types of environments: open fields, vacant lots, edges of forested areas and roadsides (FERREIRA; MIOTTO, 2009).The purpose of this study was to evaluate the growth and development of I. cairica plants submitted to water deficit.
Pot capacity (PC) was determined according to the methodology proposed by Sinclair et al. (2005).During the first 29 days after transplant all pots were watered with 100% PC.From 30 to 60 days after transplant pots were submitted to the water regimes of 25%, 50%, 75% and 100% PC.From 61 to 100 days after transplant pots were watered with 100% PC.Watering was manual on a daily basis, and under the highest water amount supplied no water drained.
Water deficit were evaluated from 30 to 60 days after transplant by measuring fresh mass and dry mass of leaves, stems and roots.Water mass (WM) all these structures were calculated by the difference of the fresh mass and dry mass.Throughout the 100 days of this study number of leaves and branches per plant; and length of the largest branch were evaluated.The water relations (WR), water status (WS) and water deficit (WD) were obtained by the methodology of Cruiziat and Bodet (1974) modified by Petry (1992): Water status (WS) of each organ, regarded as a qualitative type (water content in relation to dry mass): WS = dry mass -fresh mass / fresh mass (g/g).
Water deficit (WD): Where WM t is the water mass in the organ in full turgescence, WM def is the water mass in the organ in deficit, and WM is the variation of water mass in the organ.
Tolerance indexes (I T ) were obtained by the relation of dry mass production and physiological and morphological determinations of the treatments under stress in relation to the results of the control (I t = Productivity in 75, 50 and 25% of PC/ productivity in 100% of PC x 100) (VIDAL; ARNOUX, 1981).
Plants were grown inside a greenhouse with curved ceiling covered with low density polyethylene (LDPE) of 150 µm arranged externally at a height of 2.5 m, and a black shading screen, with 75% shade index.Temperature was measured by using a thermometer installed inside the greenhouse.The maximum daily temperatures were between 22 and 34° C, and minimum daily were between 9 and 21° C.
Experimental design was completely randomized with four water regimes (25%, 50%, 75% and 100% PC), with nine replications of each water regimes, evaluated from 30 to 60 days after transplant.Data were submitted to analysis of variance with posterior regression analysis through the statistical program SISVAR (FERREIRA, 2011).

RESULTS AND DISCUSSION
For WS, water storage capacity in the different plant organs showed differential behavior among the organs and the water deficits (Figure 1).Leaves WS was greater in the 100% PC treatment, followed by the treatments of 50, 75 and 25% PC.The greatest WS for the stem was observed in the 75% treatment.The root was the organ that exhibited the greatest WS for the 25% treatment (8.1 g/g).According to Sinclair et al. (2005) water reserves in the different plant organs may vary for the same water situation in a different way among species and even among cultivars.The study of the WS dynamic of the plant is complex and involves metabolic interactions, but the tendency upon applying the deficit is to reduce the water status, and if the species or cultivar is more tolerant, there are increases in its water status (CRUZIAT; BODET, 1974;PETRY, 1992).Increase in the WS of the plants found in I. cairica during the study, showed this specie is tolerant to water stress.
Upon analyzing the WD there was an increase in water deficit in the leaves and decrease in the roots, showing that the plant stored more water in the roots during the stress period (Table 1).After water reestablishment, the plants inverted the response, with

∆WM
´ greater water deficit in the leaves and less in the roots.
Plants capable of tolerating periods of water deficit are those that make frugal use of water, conserving part in the soil and making osmotic adjustment, reducing water potential and turgor pressure in the leaves (FRANCO et al., 2006;TAIZ;ZEIGER, 2009).Ciênc.agrotec., Lavras, v. 36, n. 3, p. 318-324, maio/jun., 2012 Upon establishing the tolerance indexes (I T ) (Table 1) it was observed that to the extent that water restriction increases, the tendency was for reduction in the quantity of water in the leaves and increase in the roots.The I T of consumption also decr eased in accordance with the water deficit.With 25% of PC, the plants consumed less; however, upon returning to the normal water deficit, they resumed normal consumption.Increase in water deficit in the leaves of I. cairica during the period of stress proves this characteristic of drought tolerance.These characteristics are also present in other ornamental species considered resistant to drought periods, such as Penstemon barbatus, Penstemon x mexicali and Lavandula angustifolia (ZOLLINGER et al., 2006), and which are recommended for use in landscaping.
The different water deficit applied from 30 to 60 days after transplant did not affect the number of shoots.Reduction in the water level of the substrate from 100% to 25% of PC caused a decrease in the length of the shoots (Figure 2).One of the first responses to water stress is reduction in plant growth (YIN et al., 2005).In studies with two varieties of I. batatas, water stress proved to have a significant effect on growth of the above ground part of the plants ( VAN HEERDEN;LAURIE, 2008).Carvalho et al. (2003) also observed less height in Artemisia plants maintained at a low water level.For other ornamental species, like Impatiens walleriana, Petunia x hybrida and Pelargonium hortorum, water stress proved to be a decisive factor for growth (CHYLINSKI et al. 2007;ANDERSSON, 2011).This was likewise observed in I. cairica, which reduced its growth through reduction in the length of branches.
The number of leaves decreased with the increase of water restriction (Figure 3).The same results were found by Figueirôa et al. ( 2004) in young Myracrodruon urundeuva plants and by Carvalho et al. (2004) in eggplant.Water stress limits not only the size, but also the number of leaves, because it reduces the number and the growth rate of the branches (TAIZ; ZEIGER, 2009).´ Another common evolutional characteristic of plants tolerant to water stress is the production of a thick cuticle and increase of wax deposition over the leaf surface, which reduces water loss through the epidermis (cuticular transpiration) (TAIZ; ZEIGER, 2009).According to Procópio et al. (2003) I. cairica plants exhibit these important tolerance characteristics, having a thick cuticle in the adaxial part, as well as being covered with epicuticular wax.These characteristics may have contributed to drought tolerance capacity observed during this study.
Plants submitted to the lowest water level exhibited symptoms of water deficiency; however, the survival rate at the end of the 30 days of application of water deficit was 100%.After returning to the normal water condition, they resume their growth processes, issuing forth new branches and leaves.The same results were found for Nerium oleander grown in a pot and submitted to low water availability, which during the stress period exhibited symptoms of deficiency, but after the restricted water deficit, the plants returned to normal appearance (LENZI et al., 2009).The same may be said for other ornamental species such as Gallardia aristada and Leucanthemum x superbum that resumed their growth when watered once more (ZOLLINGER et al., 2006).
There were no differences among the water treatments for fresh mass, dry mass and water mass of roots.The water level that exhibited the greatest accumulation of fresh mass of the above ground part (92.7g) was that of 100% of PC, and in the period of water deficit, the plants submitted to 25% of PC obtained the lowest value (52.8g).The fresh mass, dry mass and water mass variables of the above ground part (Figure 4) had linear growth throughout the experimental period.For fresh mass, dry mass, water mass of leaves, and fresh mass and water mass of stems (Figure 5) there were differences among the water deficits; the greater the moisture of the substrate, the greater the resulting masses.I. cairica plants exhibited greater accumulation of fresh mass and water mass in the stem in relation to the leaves; these masses may be related to the accumulation of compounds like amino acids and sugars arising from water restriction.Another fact that may be related to the greater accumulation of dry mass in the stem is the habit of the plant under study; since it is a climbing species, it needs to guarantee sufficient reserves to this sustaining organ.
The rate of 100% survival observed in all water regimes applied in I. cairica testify its rusticity.Other ornamental species used in landscaping as Penstemon x mexicali, Lavandula angustifolia (ZOLLINGER et al., 2006), and Gladiolus x grandiflorus (PEREIRA et al. 2009), do not show this survival capacity like I. cairica.
The results obtained in this study agree with those found in environmental conditions of habitat where I. cairica arises spontaneously, since this species is able to survive in locations which are quite rustic and with low water availability.Under environmental conditions where scarcity of water is a constant problem, and where water restrictions are more and more common, I. cairica clearly proves to be an excellent landscaping alternative.

Figure 1 -
Figure 1 -Water status of the leaves (WSL), water status of the stems (WSS) and water status of the roots (WSR) during the application of different water deficits (25, 50, 75 and 100% of pot capacity (PC) from 30 to 60 days after transplant.

Figure 2 -
Figure 2 -Length of the longest shoot of Ipomoea cairica submitted to 25, 50, 75 and 100% of pot capacity (PC) from 30 to 60 days after transplant.

Figure 4 -
Figure 4 -Fresh mass of the above ground part (FMGP), dry mass of the above ground part (DMGP), and water mass of the above ground part (WMGP) of Ipomoea cairica submitted to 30 days of water regimes (25, 50, 75 and 100% of pot capacity) evaluated during 100 days.

Table 1 -
Water deficit (%) in relation to the control and tolerance indexes for the physiological parameters in each plant organ of Ipomoea cairica during (30-60 days) and after (61-100 days) application of the different water.