Physiological Effects of Ascorbic and Gallic Acids on Growth and Metabolic Activities of Cowpea (Vigna unguiculata L.) Plants

A pot experiment was performed at Helwan University Experimental Farm, Cairo, Egypt during the season of 2016-2017. This experiment aimed to study the response of vegetative growth criterea, seed yield (weight) and some metabolic activities and constituents of cowpea (Vigna unguiculata L.) plants to foliar spray of ascorbic acid (AA; 100, 150 and 200 ppm) and gallic acid (GA; 100, 150 and 200 ppm), two antioxidant compounds. The foliar application of AA and GA significantly increased all growth criteria (i.e. length of roots and stem, the root and stem fresh and dry weights, No. of leaves and total leaves area cm2/plant), as well as seed weight and quality compared to the untreated control plants. Total photosynthetic pigments (TPP), total carbohydrate (TC), total soluble proteins (TSP), crude protein (CP) and different minerals in leaves were increased accompanied by decrease in total soluble sugars (TSS) by application of AA and GA, especially at 100 ppm concentration. Furthermore, GA at 100 ppm was more effective than ascorbic acid at 100ppm in increasing the levels of the growth hormones indole acetic acid (IAA), cytokinins (CKs) and gibberellic acid (GA3) in cowpea leaves, with lower abscisic acid (ABA) content. In conclusion, nutritional value and quality of cowpea plants could be improved by application of AA and GA at 100 ppm concentration.