Silicon triggers the signalling molecules and stress-associated genes for alleviating the adverse effect of terminal heat stress in wheat with improved grain quality

Terminal heat stress severely affects the growth of wheat crop causing drastic reduction in the yield and nutritional quality of the grains. Various technologies have been developed in the past to alleviate the effect of terminal heat stress (HS) in wheat, but with limited success. Silicon (Si), being quasi-essential element, has many beneficial advantages to the plants. Here, we observed exogenous application of 2.5 mM Si to be very effective in modulating the thermo-tolerance and quality of the grains. The application of Si has been observed to trigger the expression of signalling molecules (MAPK, CDPK), and stress-associated genes (SAGs) like HSFs (HD97, HSFA6e), HSPs (HSP17, HSP23, HSP70 and HSP90) and genes of antioxidant enzyme (GPX and SOD) under HS. Thermo-tolerant wheat cv. HD3086 showed more abundance of SAGs transcripts, as compared to thermo-susceptible cv. BT-Schomburgk. We observed increase in the accumulation of photosynthetic enzyme (RuBisCo activase) in leaves and storage protein (gliadin) in wheat grains under Si treatment. Heat stress downregulates the expression of genes linked with starch biosynthesis pathway; the percent decrease observed was minimum under Si treatment. Improved grain quality in both cvs. in response to Si under HS was observed. Si inhibits the activity of starch-degrading enzyme in endospermic tissue of grains. Si application was very effective, cheap and non-hazardous for mitigating the effect of terminal HS in wheat, stabilizing yield without compromising the quality of the grains.