Effects of 6-Benzylaminopurine and Potassium on δ-Aminolevulinate Dehydratase Activity of Excised Cucumber Cotyledons

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Changes in δ-aminolevulinate dehydratase (ALAD) activity were followed in 7-day excised cotyledons maintained on water or treated with 6-benzylaminopurine (BA 1 μg・ml^<-1>), KCl (10 mM) or a combination of BA + KCl. Cotyledons were incubated for 3 days in the dark or in the light, or preincubated for 18 h in the dark before illumination. Cycloheximide treatments (10μg・ml^<-1>) were performed to differenciate between ALAD biosynthesis or activation. The excision entailed an increase in ALAD activity. Then a decrease appeared after a 24-h incubation on water in the dark. It was more precocious in the light, but was delayed when the cotyledons were illuminated after a dark preincubation. BA had little effect on ALAD activity in the dark. In the light, BA completely prevented the decrease in ALAD activity observed in the control, and enhanced this activity when a dark preincubation preceded illumination. KCl had a slight stimulating effect in the dark, but was uneffective in the light. The combination BA + KCl was always devoid of stimulating effect. Stimulating effects of BA or KCl seemed to be due to an increase in ALAD biosynthesis. No treatment markedly affected ALAD exportation from cytoplasm to plastids. These results are discussed in relation with cotyledon greening.
日本植物生理学会の論文