Tomato is a climacteric fruit susceptible to rapid softening and ripening after harvest. In this study, the changes of physicochemical characters, cell wall‐degrading enzymes, cell wall compositions and ethylene production of ‘Hisar Arun’ and ‘BSS‐488’ tomato fruits were investigated under the influence of salicylic acid treatment. Salicylic acid treatment effectively delayed firmness decline and increase in PLW, TSS and lycopene content. The treated fruits maintained the integrity of cell wall composition by delay in increase in activities of cell wall‐degrading enzymes (pectin methylesterase, polygalacturonase and cellulose) and cell wall components (cellulose, hemicellulose, lignin and pectin) decline. Moreover, salicylic acid treatments significantly suppress expression level of ethylene‐producing genes (ACO1 and ACS2) and inhibited ethylene production during storage. Overall, the salicylic acid‐induced delay in the ripening process occurs via the strong inhibition of ethylene biosynthesis, lowered cell wall‐degrading enzyme activities and slowed cell wall degradation.
Tolerance to water deficit in relation to activities of sucrose-to- starch metabolizing enzymes and starch accumulation was studied in the grains of contrasting wheat (Triticum aestivum L.) genotypes (WH1021 and WH1080; tolerant) and (WH711 and HD2687; susceptible) under late planting conditions. The activities of starch metabolizing enzymes i.e. sucrose synthase (SuSase), ADP-glucose pyrophosphorylase (AGPase), soluble starch synthase (SSS) and starch branching enzymes (SBE) were substantially enhanced by water deficit in all genotypes at early to mid-grain filling stage showing peaks at 14 to 21 days after anthesis (DAA); while decreased significantly at mid-late grain filling stage with maximum decline at 35 DAA. Activities of all the enzymes under study showed maximum decline in activity (28.4–60%) in susceptible genotype WH711; whereas WH1021 proved to be most tolerant one with minimum decline in enzyme activity (14.9–32.8%). Starch content was also markedly reduced (21%) in WH711 due to drought while WH1021 reported 12% decline corresponding well with enzyme activity. A faster pre-mature cessation of starch deposition occurred in susceptible wheat genotypes compared to tolerant ones. A significant and positive correlation of the enzyme activities with starch accumulation (r = 0.491–0.555 at P0.05 for SuSase, AGPase, SSS and r = 0.638 at P0.01 for SBE) under well watered conditions indicated that enhancing the activities of the enzymes would lead to increase in starch accumulation and thus faster grain filling. Genotype WH1021 proved to be most efficient based on comparatively higher enzyme activity and least yield penalty under late planting conditions combined with water scarcity.
The investigation was conducted to evaluate the effect of drought stress on role of proline, hydrogen peroxide and total antioxidant activity (TAA) of two wheat varieties viz. WH 1105 (Drought sensitive) and WH 1025 (Drought sensitive) after anthesis. Drought was given by only pre sown irrigation. Analysis of data revealed that drought stress results an increase in proline and hydrogen peroxide (H2O2) contents in leaves and developing grains of both wheat varieties after anthesis, however more increase in imino amino acid proline was observed in WH 1025 which is ascribed to improved drought tolerance through osmotic adjustment of cellular contents. Drought sensitive wheat variety WH 1105 had accumulated higher hydrogen peroxide (H2O2) than WH 1025. Stress tolerance to plants is determined by the pool size of antioxidants and protective plant pigments particularly carotenoids. This study also revealed that the total antioxidant activity (TAA) was increased in leaves and developing grains of both wheat varieties with higher and significant increase in WH 1025 than WH 1105.
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