Enhancing the performance of leafy greens under nutrient deficiency and salinity stress through the application of protein hydrolysates

As plants live through stressful times, their sessile nature prevents them from fleeing, therefore putting the onus on farmers to discover the most apt strategies to fend off stresses. Through 2019’s 1009 regulation the EU has defined plant biostimulants as products which enhance plant resilience to stresses, therefore providing a valuable addition to farmers’ toolset. Protein hydrolysates (PH) biostimulants, which derive from the degradation of protein matrices, adhere to this definition by regulating the minute metabolic processes that decrease the effect of stressors on plant performance. The presence of peptides of specific mass and composition, or signaling peptides, make for root growth increase capability, which increases nutrient acquisition in suboptimal conditions. Furthermore, literature shows that PH biostimulants modulate plants’ defence mechanisms via the increase the contents of antioxidants like polyphenols and carotenoids, which provide double duty as safeguards against stresses (i.e. nutrient deficiency and salt) and human health enhancers. This paper seeks to elucidate PH-derived effects on plants by reviewing the literature on nutrient and salt stress on the widely consumed leafy vegetables group, which include lettuce, spinach and rocket. Further research areas relevant to PHsbased biostimulants are then identified to harness the biostimulants activity of these bioactive signaling molecules in controlled environments.