ABSORPTION OF SUCROSE BY TISSUES OF ADULTTUBERS OF POTATO (SOLANUM-TUBEROSUM L) - MODALITIES AND INFLUENCE OF PHYTOHORMONES

Sugar uptake by potato tuber discs was studied. Discs were used ''fres h'' or after a 24-h ageing period. It was shown that ageing increases (by 3 to 4 times) the rate of glucose and sucrose uptake. Sucrose upta ke by fresh tissues was insensitive to the presence of glucose or fruc tose while a competitive effect was observed after ageing. This indica tes the development of an invertase activity, which was inhibited by t ris-buffer. Sucrose and glucose uptake by aged discs was dependent on cellular metabolism as shown by the sensitivity to low temperature and metabolic inhibitors (NaCN, DNP, CCCP). Involvement of thiol groups w as demonstrated by the inhibition with NEM and PCMBS. Orthovanadate, w hich decreases phosphate uptake by 85 % (Poder et al 1986) did not pro duce any effect on glucose and sucrose uptake by aged tissues. Fusicoc cin produced only a slight stimulation (15 %). These results argue in favour of the involvement of specific ATPases in ion and sugar uptake. No involvement of a redox system was observed. ABA and BAP inhibited the uptake induced by ageing but had no effect on the endogenous sugar content. BAP would act by its effect on the amount of ATP while ABA w ould act at the membrane level. The results are discussed in relation to the mechanisms of transfer of glucosyl groups and to the transport of sucrose by the symplasmic pathway.