Ascorbic acid at pre-anthesis modulate the thermotolerance level of wheat (Triticum aestivum) pollen under heat stress

摘要

The reproductive stage of wheat is highly sensitive to the heat stress, especially pollen viability. Here, we report the alterations in the expression of heat shock proteins and antioxidant enzymes in wheat pollen of thermotolerant (C-306) and susceptible (HD2329) cultivars under the heat shock (42 A degrees C, 2 h) with or without ascorbic acid (400 mM) treatment. A significant fold change in expression of catalase (CAT) and ascorbate peroxidase (APX) was observed in the pollens of HD2329 in response to 400 mM ascorbic acid (AsA) before heat stress (T-1). The SOD transcript was observed significantly high in C-306 pollens compared to HD2329 in response to T-1. The transcripts of high and low molecular weight HSPs (HSP70, HSP90, HSP17 and HSP26) were very high in pollens of C-306 as compared to HD2329. Semi-quantitative RT-PCR showed marked variations in the transcript of HSPs and antioxidant enzymes in pollens of C-306 and HD2329 under T-0 and T-1 treatments. 1D and 2D polyacrylamide gel electrophoresis of pollens showed more differentially expressed proteins in C-306 than in HD2329 in response to T-1. A significant increase in the accumulation of osmolyte (proline), H2O2 and endogenous AsA levels were observed in the pollens of C-306 than in HD2329, in response to T-0 and T-1 treatments. Immunoblot analysis using monoclonal antibodies of HSP70 and HSP90 showed abundance of HSP70 proteins in the pollens of C-306 and HSP90 proteins in pollens of HD2329. Scanning electron microscopy of pollen under the heat stress showed disintegrated and dehydrated exine layer and alteration in pollen structure from spheroid to ovoid in both the cultivars. The pollen viability was found to be less in HD2329 than in C-306 in response to T-1 treatment. A significant increase in the total antioxidant capacity was observed in pollens of C-306 as compared to HD2329 in response to the treatments. Findings indicate that pre-anthesis treatment of 400 mM AsA before HS (42 A degrees C, 2 h) enhances the thermotolerance capacity of wheat pollens, as assessed through biochemical markers; further investigations on similar elicitors may yield useful information on mitigating the effect of the terminal heat on reproductive system of wheat