High temperature is a common constraint during anthesis and grain-filling stages of wheat leading to huge losses in yield. In order to understand the mechanism of heat tolerance during monocarpic senescence, the present study was carried out under field conditions by allowing two well characterized Triticum aestivum L. cultivars differing in heat tolerance, Hindi62 (heat-tolerant) and PBW343 (heat-susceptible), to suffer maximum heat stress under late sown conditions. Senescence was characterized by measuring photosynthesis related processes and endoproteolytic activity during non-stress environment (NSE) as well as heat-stress environment (HSE). There was a faster rate of senescence under HSE in both the genotypes. Hindi62, having pale yellow flag leaf with larger area, maintained cooler canopy under high temperatures than PBW343. The tolerance for high temperature in Hindi62 was clearly evident in terms of slower green-leaf area degradation, higher stomatal conductance, higher stability in maximum PSII efficiency, Rubisco activity and Rubisco content than PBW343. Both the genotypes exhibited lower endopeptidase activity under HSE as compared to NSE and this difference was more apparent in Hindi62. Serine proteases are the predominant proteases responsible for protein degradation under NSE as well as HSE. Flag leaf of both the genotypes exhibited high-molecular-mass endoproteases (78 kDa and 67 kDa) isoforms up to full grain maturity which were inhibited by specific serine protease inhibitor in both the environments. In conclusion, the heat-tolerant Hindi62 exhibited a slower rate of senescence than the heat-susceptible PBW343 during HSE, which may contribute towards heat stability. and S. Chauhan ... [et al.].