SUPPRESSION OF THE OSMOINDUCED PROLINE RESPONSE OF RAPESEED LEAF DISCS BY POLYAMINES

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.