F. Larher et al., SUPPRESSION OF THE OSMOINDUCED PROLINE RESPONSE OF RAPESEED LEAF DISCS BY POLYAMINES, Physiologia Plantarum, 102(1), 1998, pp. 139-147
Rapeseed leaf discs (RLD) subjected to upshock osmotic stress accumula
te proline (Pro). Di- and polyamines (PA) supplied to the external med
ium suppressed Pro accumulation. These effects were dependent not only
on diamine and PA concentrations but also on their cationic charge. T
he suppression of Pro accumulation required that diamine and PA be tak
en up and further accumulated in the leaf tissues. Glycine betaine (GB
) also inhibited Pro accumulation, with the effects of GB and PA being
additive. Experiments to elucidate the mechanism(s) responsible for t
he inhibitory effect of spermine (Spm) indicated that it could be simu
lated with methionine sulfoximine (MSG), a potent inhibitor of glutami
ne synthetase. The inhibitory effects of Spm and MSO were both allevia
ted by supplying glutamine to the RLD. In addition, Spm as well as MSO
increased glutamate content, indicating that these compounds could in
hibit the conversion of glutamate to proline. A comparison of the chan
ges in chlorophyll and protein content of RLD osmotreated with or with
out added Spm indicates that this PA behaves as an antisenescent compo
und, preventing chlorophyll breakdown and proteolysis and hence the co
nversion of amino acids to Pro. Since the PA concentrations used in th
is work were much higher than the endogenous concentrations in RLD, th
e significance of PA under osmotic stress remains unclear. This study
shows, however, that PA can suppress Pro accumulation.