EFFECTS OF NACL AND GABACULINE ON CHLOROPHYLL AND PROLINE LEVELS DURING GROWTH OF RADISH COTYLEDONS

Radish (Raphanus sativus L.) cotyledons subjected to NaCl display a significant accumulation of proline concomitant with a decline in chlorophyll setting. The NaCl-dependent proline synthesis is closely related to the storage glutamate. Addition of ornithine in the culture medium discloses the occurrence of an additive source of proline, via ornithine aminotransferase, in saline conditions. Nevertheless, when seeds are sown on a medium containing gabaculine, a potent inhibitor of both Beale and ornithine aminotransferase pathways, the proline content increases in cotyledons. This proline accumulation might arise from glutamate molecules which are not converted into chlorophyll. The use of gabaculine indicates that chlorophyll and proline syntheses compete for glutamate, their common precursor.