water stress

environmental stresses such as water stress and allelopathic stress. Biotic and abiotic stresses disrupt the equilibrium between ROS production and their degradation by the defense system of plants. Oxidative damage is caused by accumulation of superoxide and hydroxyl radicals. The production of superoxide radicals increased under allelochemicals and water deficiency which caused lipid peroxidation resulting in membrane damage (Halliwell and Gutteridge, 1999). The ROS generated are removed with the help of antioxidant enzymes viz. SOD, CAT, APX and GPX. Allelochemicals induced SOD activities in maize (Singh et al., 2009) and mung (Singh et al., 2010). Drought stress in presence of allelochemicals enhanced SOD activities in maize (Singh et al., 2009). SOD converts free oxygen radical

Using infrared thermometers is a fast, practical, reliable and non-destructive technique that allows to adjust irrigation management and measure crop water stress index (CWSI), which varies from zero (plant under no water stress) to one (plant under severe water stress). Canopy temperature, under both water stress and no stress conditions, may provide information on crop water status and favor irrigation management (Idso et al, 1981; Jackson et al., 1981, 1988; López et al., 2009a, b; Sezen et al., 2014; Ghaemi et al., 2015).

For solving this impasse, four categories about the behaviour of families in relation to water stress were established in this paper by Instituto Agronômico, Campinas (IAC) sugarcane breeding program: tolerant, responsive, non-responsive and susceptible. The categories are defined by the means of all the families for irrigated and unirrigated conditions. A tolerant family would be one that has an above average value in both favourable (irrigated) as well as unfavourable (unirrigated) conditions. Responsive is the family that has below average yields in dry conditions but, when the environment gets better, in this case irrigated, its value increases to above average. A non-responsive family is one that has an above average value in an inferior environment but a below average value in an improved environment. And finally, a susceptible family shows below average values in both superior and inferior environments. To assess the performance of a given family its mean expression is compared to the average of all families. So, if its average is above the mean of all families it is considered adapted to that environment and the opposite is true if its mean expression is below the average of all families.

The results of ANOVA (Table 2) showed that significant statistic differences (p<0.05) were verified in Genotype (G), Year (Y) and Water Treatment (WT) to all traits, excepting to boll weight (BW) in year (Y) and water treatment (WT). For these source of variation, the F test uses the interaction Y x WT. As it was very high and significant for this trait, it caused no-significance effect for them (Y and WT). The same results were seen for G x WT, that uses G x Y x WT interaction to test it, indicating different behavior of cultivars submitted to water treatments. On the other hand, the interaction G x Y did not demonstrate significant effect indicating that the genotypes had similar behaviors in both years (2014 and 2015). The CV values ranged from 2.14 for LP to 10.48% for CSY, and they are in accordance with the results found by Carvalho et al. (2015), Carvalho et al. (2016) and Zonta et al. (2016) for this crop. The means of traits (Table 3), obtained from different hybrid combinations submitted to two water treatments, demonstrate that the water suppression influenced the growth and production of plants at different levels. For all traits, some hybrid averages showed good potential to develop new genotypes with better performance in water stress condition. The number of groups formed by Scott- Knott test ranged from two groups (PH) to seven groups (LP). These results are expected due to the differences among the genetic variability and the influence of the environment in each trait. The reduction in height ranged from 12.88 to 24.71%. This difference promoted a direct impact in yield, with losses ranging from 3.08 to 44.78%. These results explain the effect seen in G x WT, in which some combinations were more negatively impacted by water stress, such as FMT 705 x BRS Seridó (1 x 9) with yield reduced of 44.78%, revealing a highly sensitive genotype. In contrast, BRS 286 x CNPA

The accumulation of soluble sugars is a common fea- ture of the desiccation process, in both desiccation-tolerant and desiccation-susceptible plants. Sugars have a role in os- motic adjustment, but also have indirect protective effects, such as protein stabilization (Carpenter et al., 1990). In the desiccation-tolerant plant C. plantagineum, dehydration in- duces the conversion of 2-octulose, an eight-carbon sugar, to sucrose (Bianchi et al., 1991). This conversion correlates to increases in the gene expression for sucrose synthase (SUS) and sucrose phosphate synthase (SPS) (Ingram et al., 1997; Kleines et al., 1999), which are considered key en- zymes of sucrose synthesis/metabolism. Under conditions of dehydration/osmotic stress, the expression of genes cod- ing for SUS isoforms is upregulated in several plants (Pelah et al., 1997; Déjardin et al., 1999). Similarly, antisense ex- pression of the SPS coding sequence in potato plants com- pletely suppressed the water stress-induced stimulation of sucrose synthesis (Geigenberger et al., 1999). Thus, SUS and SPS in plants are crucial steps in the acclimation pro- cess of dehydration. Highly soluble sugars, such as the polyfructose molecules fructans, are involved in plant and bacterial adaptation to osmotic stress. Transgenic tobacco and sugar beet plants, overexpressing the gene SacB that codes for a levan sucrase from Bacillus subtillis, accumu- lated higher levels of fructans and performed better than the untransformed controls under water deficit conditions (Pilon-Smits et al., 1995; Pilon-Smits et al., 1999). Similar results were obtained with transgenic tobacco plants over- expressing a gene encoding the trehalose synthase subunit (TPS1) of the yeast trehalose synthase enzyme (Holmstrom et al., 1996) and bacterial trehalose-6-phosphate synthase and trehalose-6-phosphate-phosphatase genes (Pilon-Smits et al., 1998). The function of trehalose, a non-reducing disaccharide of glucose, in desiccation is hypothesized to involve the stabilization of membrane proteins and lipids and its use as a reserve metabolite. The accumulation of the methylated sugar alcohol, D-ononitol, in transgenic to- bacco plants overexpressing the IMT1 gene from Mesem- bryanthemum crystallinum, has led to increased salt and drought tolerance (Sheveleva et al., 1997).

ABSTRACT - The goal of this work was to determine the combining ability of three white oat parental genotypes (UPF 18, URS21 and URS 22) and to estimate the heterosis of F 1 hybrids in two conditions, with and without water stress. The results indicate a large effect of the environment on the evaluated characters (cycle, leaf area, plant stature, grain yield per plant, main panicle weight and number of grains of the main panicle). The condition without stress was the most efficient for the selection of superior genotypes. Based on the general and specific combining ability, the cultivar URS 22 was shown to be indicated for cycle and stature reduction, while UPF 18 lead to increases in leaf area, main panicle weight and number of grains of the main panicle. The specific cross URS 22 x URS 21 was the best for the selection of superior genotypes.

collected during the 2015 harvest during a period of severe water stress for the producers of the State of São Paulo by the IEA (2015) and CTC (2015) that showed losses up to 25.0% in crop yield and by Vieira et al. (2014), who observed a reduction in stalk yield of 21.5% in treatments without irrigation. De Moraes Nogueira et al. (2016) showed that treatments maintained under a water regime had better technological parameters for the production of ethanol and recoverable total sugars during the harvest than the cultivation with dry farming.

Studies on how plants respond to, and recover from drought stress can reveal differences in plasticity among genotypes and could be a useful tool for screening for stress tolerance. Plant physiological/phenotypic plasticity or the ability of the plant to alter its physiology, morphology and/or behavior in response to a change in the environmental conditions has not been extensively studied in relation to drought tolerance. Following re- watering, plants could immediately show a high rate of biological activity, including photosynthetic capacity and new organ growth, which can be considered as alternative functional states that may overcompensate for the limitation to plant growth and metabolic activity due to previous drought (Cai et al., 2004; Montanaro et al., 2007; Efeoglu et al., 2009; Flexas et al., 2009; Xu et al, 2009). Such overcompensation has also been reported in sugarcane (Ashton, 1956; Inman-Bamber, 1995). Even after several weeks of severe stress, it took only few days (3 to 5 days) for leaf extension rates to resume to those rates under normal conditions (Inman-Bamber, 1995). Genetic variation in physiological/phenotypic plasticity with respect to drought has not been explored in sugarcane. The objective of this study was to characterize and compare morphophysiological responses of two sugarcane genotypes during water stress exposure and during a recovery period after re-watering. The two genotypes used had previously been classified as drought tolerant and drought susceptible based on yield performance tests in a field study.

We have focused here on the apparent role of carbon in regulating the mutualistic exchange between trees and ants (Figure 1). Two alternative hypotheses to explain the negative relationship between scale-insect abundance and annual precip- itation deserve consideration. First, water availability could have independent, direct effects on both plants and ants. If ants are directly water stressed, they might tend more scales to obtain water at drier sites. Our results indicate that this is unlikely, because ant- colony size and the number of scale insects increased concomi- tantly with water stress, such that ants at drier sites actually tended fewer scale insects per ant (see Results). Second, a currency besides carbon could regulate ant–plant mutualistic exchange. For example, ants can provide plants with nitrogen and other nutrients (e.g., [38]), and arboreal ants may themselves be nitrogen-limited [39]. We have suggested previously that A. pittieri ants obtain their nitrogen primarily from dead insects and guano [19], sources that could vary substantially among sites. Arguing against a key role for nutrients other than carbon, however, is that our data have consistently shown nonsignificant differences in nutrient content of both plants and ants between sites (Figures S3 and S8; Table S3). Figure 4. Tree NSC pools and water stress. Total NSCs, starch and sucrose pools in main stems in (A) the late dry season (April 2009) at a wetter site (Santa Rosa; black bars) and a drier site (Chamela; white bars) and (B) the early dry season (October 2009; gray bars) and the late dry season (April 2009; white bars) at the drier site. Bars indicate means, and error bars indicate SE; values are based on plant dry weights. Starch bars are open, glucose (free sugars) bars have diagonal lines, and sucrose bars have vertical lines. Asterisks (*) indicate p,0.05 by two-tailed t tests.

The values found for the WSDI were also relatively low, ranging from 0.05 to 0.3 MPa, which could be related to the lower tensions observed during the experiment. Another possible explanation is that the method used to obtain the WSDI was adapted for essential oil and total flavonoid content, which have lower values in comparison to the production of FM, for example. Essential oil and total flavonoid contents decreased linearly, following the water stress magnitude, with daily decreases of approximately 50% for oil content and 60% for total flavonoids due to the reduction of 0.3 MPa in leaf water potential (Figure 2). Oliveira et al. (2005) observed production losses of about 10% for beans, for this same range of water stress, while Garcia et al. (2009) reported values of daily water stress with production losses of nearly 25%, at about 0.8 MPa. These results indicate that pepper-rosmarin plants are sensitive to water stress.

The population increase and the need of intensifying food production, coupled with the scarcity of water resources, have led to the search of alternatives that reduce consumption and optimize the water use during cultivation. In this context, hydrogels become a strategy in agricultural management, due to their water retention capacity in the soil and availability to plants. This study aimed at evaluating the efficiency of hydrogels on the development and production of cowpea bean (‘Sempre-verde’ cultivar) under water stress, in a greenhouse. The experiment was performed in a randomized block design, with five replications, in a 4 x 5 factorial scheme, consisting of four types of hydrogel (Hydroplan-EB HyA, with granulometry of 1-3 mm; Hydroplan-EB HyB, with granulometry of 0.5-1 mm; Hydroplan-EB HyC, with granulometry < 0.5 mm; Polim-Agri, with granulometry of 1-0.5 mm) and five concentrations (0 g pot -1 ; 1.5 g pot -1 ;

Damage to plants in response to abiotic and biotic stresses is a worldwide ecologic and economic concern. Recent and predicted climate changes exacerbate this concern (Lobell & Gourdji, 2012). Environmental stresses not only have adverse effects on plant growth and productivity but also are expected to become more variable, severe, and widespread in decades to come. Prolonged and repeated severe environmental stresses affecting plant growth and development would bring down long-lasting effects in woody plants as a result of its long-term growth period. Plant tolerance to stress englobes a variation in the detail network and cascade of events or reactions leading to alleviation of potential stress-induced cellular injuries depending on the plant species that have evolved through environmental changes. The development of lignin biosynthesis has been considered to be one key factor that allowed plants to flourish in terrestrial ecosystems. Therefore, to understand and improve water stress tolerance in plants by manipulating lignin in wood plant tissues becomes a necessity if tree survival and biomass production are to be increased and profitable in face of future climate changes. Plasticity in lignin biosynthesis may be an important feature in understanding future species distribution as impacted by changing water stress patterns.

Our results showed significant differences between stressed and control group, in regard to both observed parameters (F v /F m and T ½ ). When the effect of water shortage was compared in stressed and control group after 15 days of treatment, it was approved that F v /F m decreased significantly in both groups (for 14.2% and 18.2% in WS and C group, respectively). These data indicate that water shortage hasn’t the crucial effect to decrease of photosynthetic efficiency. These results could be supported with the previous studies on the same species. In the comprehensive study on the effects of water and light sup- plies on three oak species (Quercus robur, Q. petraea and Q. rubra), pedunculate oak was the least sensitive to water shortage (Wag ne r, D reye r, 1997). Furthermore, this species showed decline in all photosynthetic parameters, including F v /F m , in the condi- tions of waterlogging. Other studies also demonstrated that Q. robur is, among other oak species, particularly efficient in water usage, even in the conditions of severe water stress (Molcha nov, 2009, Rosenqu ist , 2010). From our results, it could be concluded that the photosynthetic efficiency of seedlings of Pedunculate oak was more affected by suf- ficient watering than by short-term water stress.

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tween 0 and 3 m (Fig. 3) at both sites for the CTL plots, but the model tends to be too wet during the dry season. The low correlations (around 0.65) between observations and simula- tions at Tapajós are potentially due to the use of reconstructed forcing data, that were necessary to cover the entire experi- mental period. Despite a wetter climate (Fig. 2), the simula- tion at Caxiuanã produces a drier soil, in line with a sandier texture. Due to higher evapotranspiration, the SiB3 and lin- ear WSF reduce the wet bias and improve the seasonality of simulated SWC. When throughfall exclusion is applied to the model, the observed reduction in SWC is also better captured by the linear and the SiB3 WSF (Fig. 3). The SWI remains close to 1 (field capacity) with the drought-avoiding and drought-tolerant WSFs, while it drops below 0.5 with the linear and SiB3 WSFs (Fig. 4). The unstressed transpira- tion fluxes (at SWI > 1) are lower with the drought-avoiding and drought-tolerant WSFs and the soil moisture is not de- pleted quickly enough. Therefore, the edaphic water stress is not captured and we expect little impact on the vegetation fluxes. With the linear and SiB3 WSFs, the stomatal conduc-

The tolerance of crops to salinity is greater in hydroponic systems due to the low contribution of the matric potential to the total potential of the water. The objective of this study was to evaluate the use of brackish water, to prepare the nutrient solution and replace the evapotranspired volume, and rates of application of this solution on the water stress index, water potential, leaf succulence and water consumption of cauliflower cv. ‘Piracicaba Precoce’. The experimental design was completely randomized in a 6 x 2 factorial scheme, with six salinity levels used to prepare the nutrient solutions (0.2, 1.5, 2.5, 3.5, 4.5 and 5.5 dS m -1 ) and

Studies on the growth and development of species capable of adapting to water stress conditions caused by excess water can play a key role in understanding the strategies developed by plants to survive and grow under these conditions (Costa et al., 2006). Thus, despite the great economic and environmental importance of bracatinga, information on the responses of plants under water saturation conditions is still scarce. Therefore, aiming to contribute to the knowledge about the use of bracatinga in riparian forest recovery programs and to provide information on plant responses to this ecological condition, the objective of this study was to verify the effect of different levels of water saturation of the substrate on the development of Mimosa scabrella Benth seedlings.

Studies on seed germination in artificial stress conditions are particularly important for physiological ecology, providing an assessment of the limits of tolerance and adaptation of species to natural stress conditions (Guedes et al., 2013). Z. sylvatica seeds seem to be tolerant to osmotic stress, showing the best results when germinated in -0.4 MPa, with values around 90% germination and normal seedlings and 70% in distilled water (Figures 5 A, B). The germination kinetics showed unexpected results. Seeds germinated in -0,8 MPa had much higher average germination speed than those germinated in distilled water, reducing the average germination time in more than three days (Figures 5C, D). Water stress can affect germination, causing delay in the initiation or decrease in the final stand. Therefore, the ability

Dehydration of plants during moderate water stress can cease physiological functions, such as transpiration, photosynthesis, which are mostly restricted by other functions sensitive to water deficit, in this case, by closing stomata. After rehydration, these functions reached the same level. On the contrary, at severe water stress induced by prolonged dehydration of plant tissue, water content can reach the critical value for physiological functions, important for plant viability. After rehydration from this critical value, the physiological activity of some functions is mostly unrecoverable. This critical water content can be reached by primary water stress, occurring during the drought period. It can occur also as a secondary stress acting simultaneously with other stresses e.g. during freezing stress, when the water content in plant cells reaches the critical water content by extracellular freezing of intracellular water. The life strategy of some plant parts such as seeds, pollen, tree buds, and/or resurrection plants is to survive at low water content close to the critical water content. During dehydration of plant tissue the changes of solvent concentration affect kinetics of reaction and the thermodynamic interaction (hydrogen bonding). Since the critical water content occurs at the low water content, it is not easy to measure its thermodynamic activity. Water content, close to the critical water content, is called non-osmotic water volume or unfrozen water or simply bound water. The bound mononolayer of water can be calculated from water vapour isotherms by BET (Brunauer- Emmett-Teller) model. This model defines the bound water thermodynamically, what is important for recognizing various parts of bound water. Thermodynamic characteristics of water activity, characterised by equilibration at relative humidity over different saturated salt solutions of known water activity, or by water potential, are not able to explain fully all limits of dehydration tolerance. The concept of vitrification (from Latin, vitreus, glassy) of cell solution to glasses and rubbers as amorphous solids has been introduced to explain the kinetics of chemical reaction at low water contents. The glass transition temperature of dehydrated samples is mostly measured by differential scanning calorimeters in various modifications. Measurements of vitrification in the plant can help to explain how water activity participates on plant survival in various stresses. Similarly, it can help us to manage experimentally the water status of plants with the aim to store the meristems and seeds in viable state to preserve plant biodiversity.

Sugarcane (Saccharum officinarum L.) is a crop of vital importance to Brazil, in the production of sugar and ethanol, power generation and raw materials for various purposes. Strategic information such as topography and canopy temperature can provide management technologies accessible to farmers. The objective of this study was to determine water stress indices for sugarcane in irrigated areas, with different exposures and slopes. The daily water stress index of the plants and the water potential in the soil were evaluated and the production system was analyzed. The experiment was carried out in an “Experimental Watershed”, using six surfaces, two horizontal and the other ones with 20 and 40% North and South exposure slopes. Water stress level was determined by measuring the temperatures of the vegetation cover and the ambient air. Watering was carried out using a drip irrigation system. The results showed that water stress index of sugarcane varies according to exposure and slope of the terrain, while areas whose water stress index was above 5.0 °C had lower yield values.