Effect of Benzyladenine Treatment Duration on δ-Aminolevulinic Acid Accumulation in the Dark, Chlorophyll Lag Phase Abolition, and Long-Term Chlorophyll Production in Excised Cotyledons of Dark-Grown Cucumber Seedlings

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Abstract
Cotyledons excised from dark-grown cucumber (Cucumis sativus L. cv. Aonagajibai) seedlings were incubated in the dark with the cytokinin benzyladenine for different time periods. Then, various greening parameters were examined, including protochlorophyll(ide) to chlorophyll(ide) photoconversion and δ-aminolevulinic acid accumulations in the dark, both triggered by a 5-minute red-light pulse. Benzyladenine rapidly stimulates δ-aminolevulinic acid accumulation, protochlorophyll(ide) regeneration, and lag-phase abolition. The red-light-pulse-induced protochlorophyll(ide) to chlorophyll(ide) photoconversion does not appear to be affected by benzyladenine treatment. Long-term chlorophyll production in the light is stimulated after longer incubations with the cytokinin. Rates of δ-aminolevulinic acid accumulation in the dark were similar to chlorophyll production rates in the light (maximum rates of 20 and 19 to 23 nanomoles per gram fresh weight per hour, respectively, in mole equivalents). The data strongly suggest that benzyladenine abolishes the lag phase by triggering δ-aminolevulinic acid synthesis potentiation and that the cytokinin has other stimulatory effects on chlorophyll production after longer incubations.