Common bean seedlings show increased tolerance to cool temperatures when treated with progesterone, β-oestradiol, abscisic acid, and salicylic acid

Cold stress has a significant effect on plant physiology inducing growth hindrance and reduced yields. This study was aimed to evaluate the effect of mammalian sex hormones (progesterone and β-estradiol), abscisic acid (ABA), and salicylic acid (SA) on plant growth, chlorophyll, malondialdehyde (MDA), hydrogen peroxide (H2O2) and the activities of anti-oxidative and nitrate assimilation enzymes in common bean (Phaseolus vulgaris L.) seedlings under cold stress. For this purpose, cold stress was conducted to 11-day-old seedlings in a climate chamber at 9/5°C (day/night), but for control, the temperature was set at 25/20°C (day/night). Progesterone (Pro) 10-9 M, βoestradiol (ES) 10-6 M, ABA 10-4 M, and SA 10-4 M were applied to 11-day-old seedlings using a handheld sprayer. The results of this experiment showed that cold stress significantly decreased plant growth, and it was followed by an increase in MDA and H2O2 content in common bean seedlings. However, the exogenous application of Pro, ES, ABA, and SA mitigated the adverse effect of cold stress in common bean seedlings. In this respect, cold stress decreased the activities of nitrate reductase (NR), nitrite reductase (NiR), and glutamine synthetase (GS) by 41.03%, 35.20%, and 47.54%, respectively, compared to control. However, under cold stress, Pro, ES, ABA, and SA treatments significantly increased NR, NiR, and GS activities by 41.87%, 14.80%, 33.87%, and 64.82 % for NR, 3.4%, 30.10%, 12.75%, and 33.12% for NiR, and 83.00%, 50.10%, 83.14%, and 9.34% for GS, respectively, compared to the plants treated with cold stress. These results suggest that exogenous application of Pro 10-9 M, ES 10-6 M, ABA 10-4 M, and SA 10-4 M after three days mitigate the unfavourable impact of cold stress in common bean seedlings by enhancing nitrate metabolism and antioxidant enzyme activities; their spraying on the leaves is beneficial for plant recovery and growth under cold stress.