text: In plants, production of 5-ALA is the step on which the speed of synthesis of chlorophyll is regulated.  Plants that are fed by external 5-ALA accumulate toxic amounts of chlorophyll precursor, protochlorophyllide, indicating that the synthesis of this intermediate is not suppressed anywhere downwards in the chain of reaction. Protochlorophyllide is a strong photosensitizer in plants. Controlled spraying of 5-ALA at lower doses (up to 150 mg/L) can however help protect plants from stress and encourage growth.