A Protein Hydrolysate Mitigates the Adverse Effect of Chilling Stress on Cucumber Plants

Chilling has been recognized as a stress factor adversely impacting plant growth and productivity. Even a slight decrease in temperature may significantly reduce crop yield. Recently, biostimulants have emerged as a new tool for enhancing the chilling tolerance of cold-sensitive plants. The early stages of cucumber growth often occur under suboptimal temperatures, which motivated the aim of the current study to assess the effect of a protein hydrolysate (PH) on the physiological performance of young cucumber plants subjected to chilling stress. The results showed that low temperatures caused severe chilling stress by inducing changes in growth, photosynthesis, and nitrogen assimilation. These adverse effects were mitigated when the PH was supplied. The ameliorating effect could be due to a remedial influence on photosynthetic pigment content, facilitating light harvesting and energy utilization. The potential impact of the PH treatment on the redox balance was demonstrated by the activation of the G6PD gene. The possible effect of the biostimulant on nitrate assimilation was tested by measuring nitrate reductase activity, which improved after application of the biostimulant. Moreover, the activity of phenylalanine ammonia-lyase (PAL) in PH-supplied plants was also increased, further confirming the enhanced protective capacity of the plants. All obtained results indicate the beneficial effect of PH application on cucumber plants and their chilling resilience.