Sharma, Kanu Priya2017-04-242017-04-242012http://krishikosh.egranth.ac.in/handle/1/5810010043The present study was conducted to understand the biochemical changes in rice (Oryza sativa L.) genotypes viz., heat tolerant (N22), moderately heat susceptible (IR8) and fine grain rice variety (PR116) in response to different transplanting time. Constitutive level of peroxidase (PO), phenylalanine ammonia lyase (PAL), tyrosine ammonia lyase (TAL), superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) was found to be significantly higher in N22 than in IR8 at very early (D1) and early transplanting (D2) times. Heat stress caused a significant increase in the level of the phenolics constituents and the activities of PO, PAL and TAL in N22. In contrast, the hydrogen peroxide (H2O2) and malondialdehyde (MDA) content was maximum in IR8 and was found to be the highest at D1. Total free amino acid and proline content was significantly higher in N22 than in PR116 and IR8. Total sugars and reducing sugars decreased at D1 and maximum content was found in IR8. The starch content was found to be maximum in N22. Total chlorophyll, chlorophyll a and chlorophyll b content decreased with heat stress and minimum content was present in PR116. Total amino acid content showed an increase with increase in heat stress in IR8 and PR116. No difference was noticeable in the electrophoretic pattern of protein bands in all the three cultivars. The 1000-grain weight of paddy, brown rice and milled rice decreased at D1 and D2, particularly in IR8. Grain dimensions were unaffected by different transplanting dates. A significant decrease was observed in the head rice recovery at D1 and D2 in all the three cultivars with the maximum head rice recovery being obtained at normal transplanting time. Higher expression of PO, PAL, TAL, SOD, GR, CAT, APX, ascorbate content and phenolic constituents in N22 than in the IR8 and PR116 is suggestive of their significant role in development of tolerance exhibited by the cultivar N22 under heat stressed conditions, during D1.ennullThesis