Physiological responses and yield performance of selected rice (Oryza sativa L.) genotypes under deficit moisture stress.

Rice is an important food crop, while it is severely affected by drought stress. Viewing this point in mind we conducted an experiment to see the physiological responses and yield potential of selected rice genotypes under inadequate moisture condition. Two soil moisture condition: one is sufficient moisture condition (control; 95-100% field capacity (FC)) and another is deficit moisture condition (moisture stress; 40-45% FC) with five replications was maintained. Six drought tolerant one susceptible genotype and one standard check variety were used. Results revealed that tolerant genotypes BU Acc 37 and BU Acc 32 showed the highest RWC, WRC, rate of photosynthesis, conductance of stomata, transpiration rate, total chlorophyll content, proline and soluble sugar content, while susceptible genotype BU Acc 5 showed the lowest value of those parameters during water stress condition. In contrast, the lowest WSD, WUC, accumulation of H2O2 and malondialdehyde were noticed in tolerant genotypes BU Acc 37 and BU Acc 32, whereas those were the highest in susceptible genotype BU Acc 5 under deficit moisture condition. Tolerant genotype BU Acc 37 and BU Acc 32 also showed the higher antioxidant enzyme activity than the susceptible genotype BU Acc 5. Regardless of genotypes, yield contributing characteristics and yield were severely affected by deficit water stress. However, tolerant genotype BU Acc 37 showed the highest grain yield per hill, while susceptible genotype BU Acc 5 showed the lowest grain yield per hill. Hence, better accumulation ability of osmoprotectants, and the higher activity of antioxidant enzymes in the tolerant genotypes reduce the oxidative stress, enhance water relation and gas exchange attributes, and protect the yield reduction of rice.

Combined Effect of Salicylic Acid and Proline Mitigates Drought Stress in Rice (Oryza sativa L.) through the Modulation of Physiological Attributes and Antioxidant Enzymes.

Salicylic acid (SA) and proline exhibit protective effects against a wide range of stresses. However, the combined impact of SA and proline on rice under drought stress is still unknown. Therefore, we investigated the protective roles of SA and/or proline in conferring drought tolerance in rice. There were eight treatments comprising the control (T1; 95-100% FC), 1.5 mM SA (T2), 2 mM proline (T3), 0.75 mM SA + 1 mM proline (T4), 45-50% FC (T5, drought stress), T5 + 1.5 mM SA (T6), T5 + 2 mM proline (T7), and T5 + 0.75 mM SA + 1 mM proline (T8), and two rice varieties: BRRI dhan66 and BRRI dhan75. Drought stress significantly decreased the plant growth, biomass, yield attributes, photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), photosynthetic pigments (chlorophyll and carotenoids content), relative water content (RWC), membrane stability index (MSI), soluble sugar and starch content, and uptake of N, P and K+ in roots and shoots. Drought-induced oxidative stress in the form of increased hydrogen peroxide (H2O2) production and lipid peroxidation (MDA) was observed. The combined application of SA (0.75 mM) + proline (1 mM) was found to be more effective than the single application of either for drought stress mitigation in rice. A combined dose of SA + proline alleviated oxidative stress through boosting antioxidant enzymatic activity in contrast to their separate application. The application of SA + proline also enhanced proline, soluble sugar and starch content, which resulted in the amelioration of osmotic stress. Consequently, the combined application of SA and proline significantly increased the gas exchange characteristics, photosynthetic pigments, RWC, MSI, nutrient uptake, plant growth, biomass and yield of rice. Therefore, the combined application of SA and proline alleviated the detrimental impacts of drought stress more pronouncedly than their separate application did by increasing osmoprotectants, improving nutrient transport, up-regulating antioxidant enzyme activity and inhibiting oxidative stress.

Exogenous Application of Calcium Ameliorates Salinity Stress Tolerance of Tomato (Solanum lycopersicum L.) and Enhances Fruit Quality.

Tomato is affected by various biotic and abiotic stresses, especially salinity, which drastically hinders the growth and yield of tomato. Calcium (Ca) is a vital macronutrient which plays physiological and biochemical roles in plants. Hence, we studied the protective roles of Ca against salinity stress in tomato. There were eight treatments comprising control (nutrient solution), 5 mM Ca, 10 mM Ca, 15 mM Ca, 12 dS m-1 NaCl, 12 dS m-1 NaCl + 5 mM Ca, 12 dS m-1 NaCl + 10 mM Ca and 12 dS m-1 NaCl + 15 mM Ca, and two tomato varieties: BARI tomato-2 and Binatomato-5. Salinity significantly decreased the plant-growth and yield attributes, relative water content (RWC), photosynthetic pigments (SPAD value) and the uptake of K, Ca and Mg in leaves and roots. Salinity-induced oxidative stress was present in the form of increased Na+ ion concentration, hydrogen peroxide (H2O2) content and lipid peroxidation (MDA). Ca application reduced oxidative stress through the boosting of antioxidant enzymatic activity. Exogenous Ca application enhanced proline and glycine betaine content and reduced Na+ uptake, which resulted in the inhibition of ionic toxicity and osmotic stress, respectively. Hence, Ca application significantly increased the growth and yield attributes, RWC, SPAD value, and uptake of K, Ca and Mg. Calcium application also had a significant effect on the fruit quality of tomato and the highest total soluble solid, total sugar, reducing sugar, ß-carotene, vitamin C and juice pH were found for the combined application of NaCl and Ca. Therefore, application of Ca reversed the salt-induced changes through increasing osmoprotectants, activation of antioxidants enzymes, and by optimizing mineral nutrient status.

Integrated Nutrient Management for Rice Yield, Soil Fertility, and Carbon Sequestration.

Reliance on inorganic fertilizers with less or no use of organic fertilizers has impaired the productivity of soils worldwide. Therefore, the present study was conducted to quantify the effects of integrated nutrient management on rice yield, nutrient use efficiency, soil fertility, and carbon (C) sequestration in cultivated land. The experiment was designed with seven treatments comprising of a zero input control, recommended inorganic fertilizers (RD), poultry manure (PM) (5 t ha-1) + 50% RD, PM (2.5 t ha-1) + 75% RD, vermicompost (VC) (5 t ha-1) + 50% RD, VC (2.5 t ha-1) + 75% RD, and farmers' practice (FP) with three replications that were laid out in a randomized complete block design. The highest grain yield (6.16-6.27 t ha-1) was attained when VC and PM were applied at the rate of 2.5 t ha-1 along with 75% RD. Uptake of nutrients and their subsequent use efficiencies appeared higher and satisfactory from the combined application of organic and inorganic fertilizers. The addition of organic fertilizer significantly influenced the organic carbon, total carbon, total nitrogen, ammonium nitrogen, nitrate nitrogen, soil pH, phosphorus, potassium, sulfur, calcium, and magnesium contents in post-harvest soil, which indicated enhancement of soil fertility. The maximum value of the organic carbon stock (18.70 t ha-1), total carbon stock (20.81 t ha-1), and organic carbon sequestration (1.75 t ha-1) was observed in poultry manure at the rate of 5 t ha-1 with 50% RD. The soil bulk density decreased slightly more than that of the control, which indicated the improvement of the physical properties of soil using organic manures. Therefore, regular nourishment of soil with organic and inorganic fertilizers might help rejuvenate the soils and ensure agricultural sustainability.

Reactive Carbonyl Species Mediate Methyl Jasmonate-Induced Stomatal Closure.

Production of reactive oxygen species (ROS) is a key signal event for methyl jasmonate (MeJA)- and abscisic acid (ABA)-induced stomatal closure. We recently showed that reactive carbonyl species (RCS) stimulates stomatal closure as an intermediate downstream of hydrogen peroxide (H2O2) production in the ABA signaling pathway in guard cells of Nicotiana tabacum and Arabidopsis thaliana. In this study, we examined whether RCS functions as an intermediate downstream of H2O2 production in MeJA signaling in guard cells using transgenic tobacco plants overexpressing A. thaliana 2-alkenal reductase (n-alkanal + NAD(P)+ ⇌ 2-alkenal + NAD(P)H + H+) (AER-OE tobacco) and Arabidopsis plants. The stomatal closure induced by MeJA was impaired in the AER-OE tobacco and was inhibited by RCS scavengers, carnosine and pyridoxamine, in the wild-type (WT) tobacco plants and Arabidopsis plants. Application of MeJA significantly induced the accumulation of RCS, including acrolein and 4-hydroxy-(E)-2-nonenal, in the WT tobacco but not in the AER-OE plants. Application of MeJA induced H2O2 production in the WT tobacco and the AER-OE plants and the H2O2 production was not inhibited by the RCS scavengers. These results suggest that RCS functions as an intermediate downstream of ROS production in MeJA signaling and in ABA signaling in guard cells.

Reactive Carbonyl Species Function as Signal Mediators Downstream of H2O2 Production and Regulate [Ca2+]cyt Elevation in ABA Signal Pathway in Arabidopsis Guard Cells.

We have demonstrated that reactive carbonyl species (RCS) function as an intermediate downstream of hydrogen peroxide (H2O2) production in abscisic acid (ABA) signaling for stomatal closure in guard cells using transgenic tobacco plants overexpressing alkenal reductase. We investigated the conversion of the RCS production into downstream signaling events in the guard cells. Both ABA and H2O2 induced production of the RCS, such as acrolein and 4-hydroxy-(E)-2-nonenal (HNE), in epidermal tissues of wild-type Arabidopsis thaliana plants. Application of the RCS scavengers, carnosine and pyridoxamine, did not affect the ABA-induced H2O2 production but inhibited the ABA- and H2O2-induced stomatal closure. Both acrolein and HNE induced stomatal closure in a plasma membrane NAD(P)H oxidase mutant atrbohD atrbohF as well as in the wild type, but not in a calcium-dependent kinase mutant cpk6. Acrolein activated plasma membrane Ca2+-permeable cation channels, triggered cytosolic free Ca2+ concentration ([Ca2+]cyt) elevation, and induced stomatal closure accompanied by depletion of glutathione in the guard cells. These results suggest that RCS production is a signaling event between the ROS production and [Ca2+]cyt elevation during guard cell ABA signaling.

Green manuring effects on crop morpho-physiological characters, rice yield and soil properties.

A field experiment was carried out to evaluate the effect of green manure and nitrogen fertilizer on morpho-physiological traits, yield and post-harvest nutrient status of the soil during kharif season of 2017. The experiment was laid out with a randomized complete block design with twelve treatments, and was replicated thrice. The treatments were T1 [Control (no green manure + no fertilizer)], T2 (Sesbania aculeata + N0), T3 (Sesbania aculeata + N15), T4 (Sesbania aculeata + N30), T5 (Sesbania aculeata + N45), T6 (Sesbania aculeata + N60), T7 (Crotalaria juncea + N0), T8 (Crotalaria juncea + N15), T9 (Crotalaria juncea + N30), T10 (Crotalaria juncea + N45), T11 (Crotalaria juncea + N60), and T12 (N60). Incorporation of green manure with nitrogen fertilizer generated consistently positive responses in important morpho-physiological traits such as chlorophyll content (SPAD value), leaf area index (LAI), light interception percent (%LI), and net assimilation rate (NAR), which may result in higher grain yield compared to control, and N60 due to greater contribution of yield determining traits. Treatment comprising green manure with N60 produced significantly the higher grain yield even over the N60. The results of this research indicated that balanced nutrients supply increased leaf chlorophyll content, LAI, %LI, NAR, and finally led to higher dry matter production and yield of rice. Incorporation of green manure also had significantly increased the macro- and micronutrient content of post-harvest soil. These results suggest that continuous use of fertilizer might lead to a yield loses of rice, and that situation could be escaped by a combined application of green manure and judicial nitrogen fertilizer management.

Reactive Carbonyl Species Mediate ABA Signaling in Guard Cells.

Drought is responsible for a massive reduction in crop yields. In response to drought, plants synthesize the hormone ABA, which induces stomatal closure, thus reducing water loss. In guard cells, ABA triggers production of reactive oxygen species (ROS), which is mediated by NAD(P)H oxidases. The production of ROS is a key factor for ABA-induced stomatal closure, but it remains to be clarified how the production of ROS is transduced into downstream signaling components in guard cells. We investigated roles of reactive carbonyl species (RCS) in ABA-induced stomatal closure using transgenic tobacco (Nicotiana tabacum) overexpressing Arabidopsis 2-alkenal reductase (AER-OE), which scavenges RCS. ABA and hydrogen peroxide (H2O2) induced accumulation of RCS including acrolein and 4-hydroxy-(E)-2-nonenal in wild-type tobacco but not in AER-OE. Stomatal closure and RCS accumulation in response to ABA and H2O2 were inhibited in AER-OE unlike in the wild type, while ABA-induced H2O2 production in guard cells was observed in AER-OE as well as in the wild type. Moreover, ABA inhibited inward-rectifying K+ channels in wild-type guard cells but not in AER-OE guard cells. These results suggest that RCS is involved in ABA-induced stomatal closure and functions downstream of H2O2 production in the ABA signaling pathway in guard cells.

Inhibition by acrolein of light-induced stomatal opening through inhibition of inward-rectifying potassium channels in Arabidopsis thaliana.

Acrolein is a reactive α,ß-unsaturated aldehyde derived from lipid peroxides, which are produced in plants under a variety of stress. We investigated effects of acrolein on light-induced stomatal opening using Arabidopsis thaliana. Acrolein inhibited light-induced stomatal opening in a dose-dependent manner. Acrolein at 100 µM inhibited plasma membrane inward-rectifying potassium (Kin) channels in guard cells. Acrolein at 100 µM inhibited Kin channel KAT1 expressed in a heterologous system using Xenopus leaves oocytes. These results suggest that acrolein inhibits light-induced stomatal opening through inhibition of Kin channels in guard cells.