BENZYLADENINE-INDUCED STIMULATION OF 5-AMINOLEVULINIC ACID ACCUMULATION UNDER VARIOUS LIGHT INTENSITIES IN LEVULINIC ACID-TREATED COTYLEDONS OF ETIOLATED CUCUMBER

Benzyladenine (BA) stimulated 5-aminolevulinic acid (ALA) accumulation in the presence of levulinic acid during illumination with 43 .mu.mol m-2 s-1 light in excised etiolated cotyledons of cucumber (Cucumis sativus L. cv. Aonagajibai). A short dark-pretreatment (6h) with BA eliminated the lag phase of ALA accumulation. The rate of ALA accumulation during the steady-state phase in cotyledons pretreated with BA for a long period (14 h) was considerably accelerated compared to that in cotyledons pretreated with BA for 6 h. The rate of ALA accumulation during the lag phase was saturated at a very low light fluence (< 1.4 .mu.mol m-2 s-1) in both BA-pretreated and water-control cotyledons. The steady-state rate of ALA accumulation increased with increasing light fluence up to 43 .mu.mol m-12 s-1 (parallel to that of chlorophyll[Chl] formation) in water-control cotyledons. In cotyledons pretreated with BA for either 6 or 14 h, the steady-state rate reached a plateau at a very low light fluence. Possible intermediate steps of Chl biosynthesis pathway affected by BA and light intensity are discussed.