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 μmol m−2 s−1 light in excised etiolated cotyledons of cucumber (Cucumis sativus L. cv. Aonagajibai). A short dark‐pretreatment (6 h) 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 μmol 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 μmol m−2 s−1 (parallel to that of Chl formation) in water‐control cotyledons. In contrast, in cotyledons pretreated with BA for either 6 or 14 h, the steady‐state rate reached a plateau at a very low light fluence. Based on the above results together with our finding that there are two components of Chl formation (M. Dei, 1984. Physiol. Plant. 62: 521–526) possible intermediate steps of Chl biosynthesis pathway affected by BA and light intensity are discussed.