F. Perezalfocea et F. Larher, SUCROSE AND PROLINE ACCUMULATION AND SUGAR EFFLUX IN TOMATO LEAF DISCS AFFECTED BY NACL AND POLYETHYLENE-GLYCOL-6000 ISOSMOTIC STRESSES, PLANT SCI, 107(1), 1995, pp. 9-15
The effect of phlorizin, a reversible inhibitor for glucose transporte
rs and that of PCMBS, a non-permeant water soluble chemical modifier o
f membrane sulphydryl groups, on proline and sugar accumulation and su
gar efflux have been studied in tomato leaf discs (Lycopersicon escule
ntum L. Mill. cv. Volgogradskij) subjected to stress conditions when i
ncubated in 300 mM NaCl or iso-osmotic solution of non-permeant PEG 60
00. The amounts of proline and sucrose found in the tissue were mainly
related to the structure of the osmoticum used for the treatment: 12.
5 and 56 mu mol of proline per gram of dry weight were registered unde
r saline and PEG conditions respectively, while 49.4 and 91.7 mu mol o
f sucrose were found under these conditions. The application of inhibi
tors provoked a different sugar efflux to the bathing medium: PCMBS en
hanced the sugars efflux up to 10 times in saline medium and up to thr
ee times under PEG conditions. Surprisingly, the sucrose content in th
e tissue was always similar to that of the same treatment in the absen
ce of the inhibitor. When exogenous sucrose was supplied to the treate
d leaf discs, it was found that it exerts two opposite effects on prol
ine accumulation since (1) it prevented the inhibitory effect of both
phlorizin and PCMBS in some treatments and (2) it enhanced proline acc
umulation provoked by these inhibitors in control discs and those trea
ted with PEG. The proline response in relation to the accumulation of
sugars for osmotic adjustment and the possibility of an osmoregulated
process concerning sucrose synthesis and carbohydrate export under str
ess conditions are discussed.