Effect of potassium deficiency on growth, antioxidants, ionome and metabolism in rapeseed under drought stress

Abstract

Previous studies have reported that potassium plays important roles in rapeseed drought tolerance, however, the interrelationship between potassium and metabolism under drought stress remains unclear. In this study, physiological and metabolic responses were investigated in two cultivars Youyan57 (YY57) and Chuanyou36 (CY36) exposed to 7% PEG6000 simulated drought stress with two potassium levels (0.01 and 1.0 mM K2SO4, referred to LK and NK, respectively). Compared to NK, LK caused a more dramatic reduction in biomass and led to significant lower enzymatic activities of antioxidants under drought stress for both the two cultivars. Moreover, potassium concentration in plant tissues decreased by 29.1% in LK compared to NK averagely and induced metabolic disorder. Totally 51 metabolites changed significantly under LK compared to NK, in which amino acids and amines increased dramatically. Most carbohydrates and carbohydrate conjugates decreased at LK, while organic acids increased, including α-ketoglutaric acid, succinic acid, l-malic acid and oxalacetic acid, which could participate in tricarboxylic acid cycle (TCA) and synthesis of amino acids. The results suggested that potassium deficiency under drought stress induced the accumulation of amino acids for osmotic adjustment and balance of electric charge, while resistance related biosynthesis of amino acids and enhanced TCA cycle were high demands of carbon skeletons which affected plant growth. Cultivar YY57 kept much higher potassium concentration and antioxidant capacity than CY36 at LK, and showed less disturbance of metabolism, consequently resulting in higher biomass. Therefore, potassium uptake and retention was closely associated with rapeseed drought tolerance.