Exogenous Abscisic Acid Priming Modulates Water Relation Responses of Two Tomato Genotypes With Contrasting Endogenous Abscisic Acid Levels to Progressive Soil Drying Under Elevated CO2

Plants have evolved multiple strategies to survive and adapt when confronting the changing climate, including elevated CO2 concentration (e[CO2]) and intensified drought stress. To explore the role of abscisic acid (ABA) in modulating the response of plant water relation characteristics to progressive drought under ambient (a[CO2], 400 ppm) and e[CO2] (800 ppm) growth environments, two tomato (Solanum lycopersicum) genotypes, Ailsa Craig (AC) and its ABA-deficient mutant (flacca), were grown in pots, treated with or without exogenous ABA, and exposed to progressive soil drying until all plant available water in the pot was depleted. The results showed that exogenous ABA application improved leaf water potential, osmotic potential, and leaf turgor and increased leaf ABA concentrations ([ABA]leaf) in AC and flacca. In both genotypes, exogenous ABA application decreased stomatal pore aperture and stomatal conductance (gs), though these effects were less pronounced in e[CO2]-grown AC and gs of ABA-treated flacca was gradually increased until a soil water threshold after which gs started to decline. In addition, ABA-treated flacca showed a partly restored stomatal drought response even when the accumulation of [ABA]leaf was vanished, implying [ABA]leaf might be not directly responsible for the decreased gs. During soil drying, [ABA]leaf remained higher in e[CO2]-grown plants compared with those under a[CO2], and a high xylem sap ABA concentration was also noticed in the ABA-treated flacca especially under e[CO2], suggesting that e[CO2] might exert an effect on ABA degradation and/or redistribution. Collectively, a fine-tune ABA homeostasis under combined e[CO2] and drought stress allowed plants to optimize leaf gas exchange and plant water relations, yet more detailed research regarding ABA metabolism is still needed to fully explore the role of ABA in mediating plant physiological response to future drier and CO2-enriched climate.

Expression Pattern and Functional Analyses of Arabidopsis Guard Cell-Enriched GDSL Lipases

There are more than 100 GDSL lipases in Arabidopsis, but only a few members have been functionally investigated. Moreover, no reports have ever given a comprehensive analysis of GDSLs in stomatal biology. Here, we systematically investigated the expression patterns of 19 putative Guard-cell-enriched GDSL Lipases (GGLs) at various developmental stages and in response to hormone and abiotic stress treatments. Gene expression analyses showed that these GGLs had diverse expression patterns. Fifteen GGLs were highly expressed in guard cells, with seven preferentially in guard cells. Most GGLs were localized in endoplasmic reticulum, and some were also localized in lipid droplets and nucleus. Some closely homologous GGLs exhibited similar expression patterns at various tissues and in response to hormone and abiotic stresses, or similar subcellular localization, suggesting the correlation of expression pattern and biological function, and the functional redundancy of GGLs in plant development and environmental adaptations. Further phenotypic identification of ggl mutants revealed that GGL7, GGL14, GGL22, and GGL26 played unique and redundant roles in stomatal dynamics, stomatal density and morphology, and plant water relation. The present study provides unique resources for functional insights into these GGLs to control stomatal dynamics and development, plant growth, and adaptation to the environment.

FOLIAGE APPLIED SILICON AMELIORATES DROUGHT STRESS THROUGH PHYSIO-MORPHOLOGICAL TRAITS, OSMOPROTECTANTS AND ANTIOXIDANT METABOLISM OF CAMELINA (Camelina sativa L.) GENOTYPES

Silicon (Si) is one of the best plant defense elements against the biotic and abiotic stresses. Camelina plants accumulate Si which serves in protection against drought stress. The present study was conducted to investigate the impact of different doses of foliage applied Si (0, 3, 6 and 9 mM) under water stress (40% field capacity, FC) and non-stress conditions (100% FC) on camelina genotypes (Canadian and Australian). The imposed drought drastically decreased the growth parameters like root-shoot length and plant fresh and dry weight and also had negative impact on the chlorophyll content along with water relation attributes (water potential, osmotic potential and turgor pressure). In contrast, total free amino acids, total soluble proteins, proline and antioxidants such as ascorbic peroxidase (APX), superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were enhanced especially in water stressed Canadian genotype, while osmoprotectants (flavonoids, anthocyanins and glycinebetaine) and phenolics contents were decreased. On the other hand, the foliar application of Si was instrumental in enhancing the growth of camelina by increasing the chlorophyll contents and water relation of stressed and non-stressed plants. Similarly, the biochemical, osmoprotectants and antioxidant metabolism was also improved in camelina stressed plants through the application of foliar Si. In conclusion, foliar application of 6 mM Si at vegetative growth stage played a vital role in alleviating the drastic impact of water stress on camelina growth by improving the water status, chlorophyll content, accumulation of phenolics and osmoprotectants and activating antioxidants. Therefore, the foliar application of Si could be developed as an important biologically viable strategy for boosting the tolerance in camelina plants to water stress conditions.

How Do Different Cocoa Genotypes Deal with Increased Radiation? An Analysis of Water Relation, Diffusive and Biochemical Components at the Leaf Level

The cultivation of cocoa (Theobroma cacao L.) is traditionally managed under shade because of its photosynthetic characteristics; however, its behavior can vary according to the genotype and environmental conditions where it is grown. In this sense, here, we explore the possible mechanisms of protection against radiation stress and how these mechanisms are affected by variation between cocoa genotypes. Therefore, we evaluate the effect of the radiation level (HPAR, 2100 ± 46 mol m−2 s−1; MPAR, 1150 ± 42 mol m−2 s−1; LPAR, 636 ± 40 mol m−2 s−1) on the water status and gas exchange in plants of different cocoa genotypes (CCN-51, ICS-1, ICS-95, LUKER-40 and LUKER-50), and the occurrence of photoinhibition of PSII (as a marker of photodamage), followed by a characterization of the protection mechanisms, including the dynamics of photosynthetic pigments and enzymatic and non-enzymatic antioxidant systems. We found significant changes in the specific leaf area (SLA) and the water potential of the leaf (ΨL) due to the level of radiation, affecting the maximum quantum yield of PSII (Fv/Fm), which generated dynamic photoinhibition processes (PIDyn). Cocoa genotypes showed the lowest Light-saturated maximum net carbon assimilation rate (Amax) in HPAR. Moreover, the maximum carboxylation rate (Vcmax) was negatively affected in HPAR for most cocoa genotypes, indicating less RuBisCO activity except for the ICS-95 genotype. The ICS-95 showed the highest values of Vcmax and maximum rate of regeneration of ribulose-1,5-bisphosphate (RuBP) controlled by electron transport (Jmax) under HPAR. Hence, our results show that some genotypes were acclimated to full sun conditions, which translated into greater carbon use efficiency due to the maximization of photosynthetic rates accompanied by energy dissipation mechanisms.

Elevated CO2 Modulates Plant Hydraulic Conductance Through Regulation of PIPs Under Progressive Soil Drying in Tomato Plants

Increasing atmospheric CO2 concentrations accompanied by abiotic stresses challenge food production worldwide. Elevated CO2 (e[CO2]) affects plant water relations via multiple mechanisms involving abscisic acid (ABA). Here, two tomato (Solanum lycopersicum) genotypes, Ailsa Craig (AC) and its ABA-deficient mutant (flacca), were used to investigate the responses of plant hydraulic conductance to e[CO2] and drought stress. Results showed that e[CO2] decreased transpiration rate (E) increased plant water use efficiency only in AC, whereas it increased daily plant water consumption and osmotic adjustment in both genotypes. Compared to growth at ambient [CO2], AC leaf and root hydraulic conductance (Kleaf and Kroot) decreased at e[CO2], which coincided with the transcriptional regulations of genes of plasma membrane intrinsic proteins (PIPs) and OPEN STOMATA 1 (OST1), and these effects were attenuated in flacca during soil drying. Severe drought stress could override the effects of e[CO2] on plant water relation characteristics. In both genotypes, drought stress resulted in decreased E, Kleaf, and Kroot accompanied by transcriptional responses of PIPs and OST1. However, under conditions combining e[CO2] and drought, some PIPs were not responsive to drought in AC, indicating that e[CO2] might disturb ABA-mediated drought responses. These results provide some new insights into mechanisms of plant hydraulic response to drought stress in a future CO2-enriched environment.

Responses of Mungbean to Water Deficit, Water use Efficiency and Drought Resistance

Backround: Legumes are the second important agricultural crop of great prominence to humans. Among 20000 legume species the mungbean is one of the most important grain cultivated in India. Drought is a major environmental stress that affects mungbean in the sub-humid, dry and intermediate zones of India. The present study records the response of mung bean varieties to water stress during its growth stage.Methods: The impact of drought stress imposed on the crop was evaluated by measuring the water relation parameters and the biochemical progresses like osmolyte accumulation, nitrate assimilation and antioxidant system in Mung bean during 2017-2018 in Avinashilingam Institute for Home Science and Higher Education for Women, Coimbatore.Result: Drought stress altered the water status of the crop by reducing the RWC, which was enhanced in drought susceptible varieties. Increased amount of proline denotes the osmoregulatory mechanism in the crop to bring about resistance and the elevated levels of antioxidant enzymes shows the protective mechanism in the crop at cellular level.

Quality Differences between Fresh and Dried Buckwheat Noodles Associated with Water Status and Inner Structure

Buckwheat noodles are mainly sold in the form of fresh and dried noodles in China. Among the noodles with varied proportions of extruded buckwheat flour (20% to 80%), the cooking or textural qualities of fresh and dried buckwheat noodles (FBN and DBN, respectively) were significantly different, and FBN showed a lower cooking loss and breakage ratio and were more elastic than DBN. FBN-20% showed the highest sensory score, followed by DBN-50%. The mechanisms causing the quality differences were investigated using water mobility and the internal structures of the noodles were investigated with low-field nuclear magnetic resonance and scanning electron microscopy, respectively. Compared with FBN, DBN showed a denser internal structure, which explained its higher hardness. The water within FBN and DBN was mainly in the form of softly bound water and tightly bound water, respectively. FBN with highly mobile softly bound water (longer T22) and a more uniform internal structure had a lower breakage ratio, whereas the trends of water relation with texture properties were different for FBN and DBN. The drying process and added extruded buckwheat flour together contributed to the varied cooking and textural properties.

Influence of Potassium on Growth, Yield, Water Relation and Chlorophyll Content of Greeengram [Vigna radiate (L.) Wilczek] in Inceptisols

Background: Mung bean (Vigna radiata L.) is an important edible bean in the human diet worldwide. However, its growth, development, and yield may be restricted or limited by insufficient or unbalanced nitrogen (N), phosphorus (P) and potassium (K) fertilization. Under intensive cropping systems, large amounts of K are removed, leading to serious depletion of soil K reserves. Therefore this study was conducted to generate the high yield and to improve yield components via effective and balanced fertilization.Methods: In this field experimentation during 2014-2016 different levels of potassium through soil application and foliar spray were studied. Three locations were selected on the basis dominance of the crops under rainfed condition.Result: In the present experimentation there was a significant effect of potash levels on plant height, number of pods per plant, 100-grain weight and grain yield. Significantly the highest grain yield (1120 kg ha-1) was recorded with 20 kg K2O ha-1, which was at par with 30 kg K2O ha-1. However, the grain yield with 20 kg K2O ha-1 was reported statistically equivalent yield with two foliar spray of muriate of potash (KCL) at flowering and pod filling stage. The pigments responsible for photosynthesis such as chlorophyll was favourably influenced by soil and foliar application of potassium. The K use efficiency parameters of AE, AR, ENUE and VCR were relatively high with potash application @ 20 kg ha-1 thereafter it declines. The positive balance of K is highly predominant in almost all the potassium applied plots which imply that the use of K fertilizers is optimal.