Photosynthetic efficiency, temperature induction response, carbon isotope discrimination correlate with expression profiling in Indian wheat cultivars

In the backdrop of global warming and increase in temperatures, wheat productivity worldwide would be limited. This study was therefore undertaken to analyze the heat stress response in 12 different cultivars of Indian wheat. Three developmental stages were used i.e. germination stage, seedling stage and anthesis stage, to characterize thermotolerant and thermosusceptible cultivars on the basis of different physiological and molecular parameters. Lethal temperature stress on germinating seeds showed a clear reduction in percentage germination. At the seedling stage, higher decrease in Fv/Fm, total chlorophyll content, membrane injury and carbon isotope discrimination was observed in thermosusceptible cultivars. Results similar to seedling stage were obtained at anthesis stage. PSII efficiency of late-sown cultivars and timely-sown cultivars also indicated that thermosusceptible cultivars are more prone to terminal heat stress than thermotolerant cultivars. Heat Susceptibility Index (HSI) was calculated on the basis of physiological parameters. Based on HSI, thermotolerant and thermosusceptible cultivars were identified. HSI revealed comparatively low heat susceptibility in <i>K7903, CBW12</i> and <i>C306</i> and high heat susceptibility in <i>PBW343, HD2329</i> and <i>HD2428</i>. On the basis of HSI, expression analysis of stress induced genes was performed between 2 tolerant cultivars <i>C306</i> and <i>K7903</i> along with 2 susceptible cultivars, <i>HD2329</i> and <i>PBW343</i>. Higher expression of stress induced genes was observed in the 2 thermotolerant cultivars <i>C306</i> and <i>K7903</i> as compared to the 2 thermosusceptible cultivars <i>HD2329</i> and <i>PBW343</i>. Thus further reconfirms that stress inducible genes can be employed for categorizing cultivars into susceptible and tolerant groups.