Biochemical changes, yield, and quality of gram under boron stress

Gram (Cicer arietinum L.) cv. Avrodhi was grown in refined sand at levels of boron (B) ranging from deficiency to excess (0.0033-6.6mgBL(-1)). At low (< 0.33 mg B L-1) B, apart from marked depression in growth at day 28, deficiency symptoms were initiated as chlorosis of young leaflets. With increase in age, these chlorotic leaflets turned necrotic and shed premature. Biomass weight of pods and seeds was maximum at 0.33 mg B L-1. At 6.6 mg B L-1, toxicity symptoms appeared as marginal necrosis of old leaflets along with growth depression. Later, the necrotic leaflets became completely dry and shed. In low B, activity of acid phosphatase, starch phosphorylase, and ribonuclease increased and that of polyphenol oxidase decreased in leaves of gram. Excess B at 6.6 mg BL-1 increased the activity of starch phosphorylase and acid phosphatase and decreased that of ribonuclease and polyphenol oxidase. Deficiency (< 0.33mgL(-1)) as well as excess (> 0.33mgL(-1)) of B deteriorated the quality of gram seeds by lowering seed yield, starch and protein concentration, and increasing the accumulation of phenols and sugars. The concentration of B increased in leaves and seeds with an increase in B supply. The values of deficiency, threshold of deficiency, threshold of toxicity and toxicity are, respectively, 13.5, 32, 190, and 310 mu g B g(-1) in leaves of grain.