The uptake of glucose, fructose and sucrose into the lower epidermis of leaf discs of pea (Pisum sativum L. cv. Argenteum)



The pea mutant, Pisum sativum L. cv. Argenteum, has been used to investigate the sugar uptake characteristics of leaf epidermal tissue. The uptake rates from either 1 mol m−3 glucose, fructose or sucrose into whole leaf discs of cv. Argenteum and of P. sativum cv. Onward were very similar; uptake was linear over a 3 h period, with glucose taken up faster than the other two sugars in both cultivars. A similar pattern for uptake was observed into the lower epidermis of cv. Argenteum. Furthermore, uptake from 1 mol m−3 3-O-methylglucose was markedly slower than from 1 mol m−3 glucose. The epidermal tissue showed some day to day variation in uptake rates; however, the basic pattern of uptake was consistent. Kinetic analysis of sugar uptake revealed the presence of two transport components. At concentrations greater than 1 mol m−3 a linear component predominated with fructose entering the epidermis faster than glucose and sucrose. An increase in the pH of the exogenous medium from 5 to 8 caused a slight but steady drop in the rate of uptake of glucose, fructose and sucrose; glucose uptake had a pH optimum of about 5. Glucose and fructose competed with one another and also with sucrose for uptake into the epidermis. Sucrose was not, however, an effective competitor against glucose and fructose. The uptake of glucose, fructose and sucrose was inhibited by about 20–30 % by 0.05 mol m−3 erythrosin B and 1 mol m−3 parachloro-mercuribenzene sulphonic acid (PCMBS). Carbonyl cyanide m-chlorophenylhydrazone (CCCP) at 0.05 mol m−3inhibited the uptake of glucose and fructose (60–70%) but did not substantially inhibit sucrose uptake.