Sucrose Suppression of Chlorophyll Synthesis in Tissue Culture: Changes in the Activity of the Enzymes of the Chlorophyll Biosynthetic Pathway

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Abstract
Chlorophyll synthesis in carrot root tissue cultures grown on a medium containing sucrose is inhibited. Examination of the activities of the first enzymes in the chlorophyll biosynthetic pathway shows that the major effect of sucrose upon chlorophyll synthesis occurs at the stage controlling 5-aminolevulinic acid (ALA) synthesis. The toxic nature of ALA in this tissue precluded its use to alleviate the sucrose inhibition effect but the utilization of various other precursors for chlorophyll synthesis was consistent with a block occurring at the level of ALA synthesis. The activities of other enzymes involved in chlorophyll synthesis decreased in activity paralleling decreases in chlorophyll amount. These latter changes are thought to result as a consequence of chloroplast degeneration rather than representing a prime cause in the loss of greening.

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