Abstract

A variety of environmental issues are threatening crops all across the world, but high temperatures are posing the most significant threat. As a master growth regulator, polyamines help plants grow and develop optimally and are more resilient to stress. The current study aims to clarify how putrescine and cadaverine contribute to Brassica juncea’s ability to withstand heat stress. Brassica juncea L.cv. RH 1566, RH 1999-42, RH 1708 & RH 1707 seedlings were grown under controlled conditions (Irradiance 75 W m2, RH 60–70%, and temperature 25°C) and field conditions. Ten days old seedlings exposed to heat shock treatment at 42–45°C for 2–3 hours. Before exposing the seedlings to heat shock (42–45°C for 2-3 h), putrescine and cadaverine (1 mM) were given as a pre-treatment at the usual temperature of 25–2°C for 2-3 h. The results revealed that polyamines treatment significantly attenuates heat-induced damage by promoting root length, shoot length, and fresh weight.  At field level, 1 mM polyamines foliar spray effectively mitigates the harmful effects of heat stress in Brassica juncea L. The most significant effect was observed in RH-1707 and RH-1708, which were higher sensitive to cellular damage under heat stress. Anatomical examinations revealed enlarged xylem vessels in RH-1707 and RH-1708 under early sowing, while late-sown plants showed less developed vessels. Polyamine application partially reduced vessel size under early heat stress, though its effects were minimal during late heat stress. Further this study demonstrated that heat stress markedly decreased the chlorophyll content in the brassica leaves. However, polyamines-treated brassica plants alleviated heat stress by reducing lipid peroxidation, hydrogen peroxide, electrolyte leakage, transpiration rate, stomatal conductance, and stomatal density, while boosting antioxidant enzyme activities, chlorophyll content, relative water content, proline content and overall yield. The MDA content in heat-stressed seedlings was higher and was significantly reduced in polyamines-treated seedlings under heat-stress conditions. This study suggested that polyamines significantly reduced oxidative stress biomarkers, membrane damage and transpiration water loss.