FOLIAR ABSORPTION—AN ACTIVE UPTAKE PROCESS

Abstract

Mechanisms of foliar absorption of phosphate and rubidium in primary leaves of bean seedlings were resolved by a newly developed leaf‐immersion and leaf‐washing technique. Uptake was expressed as “specific absorption,” defined as mμmoles/cm2 leaf X 24 hr from a known concentration of substance in an external solution maintained in a known environment. Criteria for active uptake included time‐course analysis, temperature, oxygen, and energy dependence, sensitivity to metabolic inhibitors, accumulation against a concentration gradient, irreversibility, and pH dependence. The results suggest that the over‐all process of foliar absorption of rubidium and phosphate by bean leaves, beginning with zero time and extending over a 24‐hr period, is metabolic. It is proposed that carriers play an important role in uptake and that they are proteinaceous.