Benzyladenine‐induced stimulation of 5‐aminolevulinic acid accumulation under various light intensities in levulinic acid‐treated cotyledons of etiolated cucumber

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Abstract
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 (−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.