Benzyladenine Partially Restores the Normal Phenotype in a Chlorophyll Mutant of Maize

Summary Several maize mutants with reduced pigment content and altered chloroplast stucture are known. Since cytokinins promote chloroplast development we supposed that some of these mutants have either a reduced level of endogenous cytokinins or a defect in their mechanism of action. In both cases repair of the mutant phenotype could be expected after cytokinin administration. Accordingly, we tested five chlorophyll mutants for response to exogenous benzyladenine (BA). One of them (l-11) showed a strong enhancement in chlorophyll and carotenoid content as well as in PEP carboxylase activity. Chloroplast structure that is badly altered in this mutant was greatly improved by BA, especially in the mesophyll cells. Endogenous content of the cytokinins dHZR and tZR (tested immunologically) was not lowered in the mutant. Taken together, these results suggest that the l-11 mutation affects some step in the pathway of cytokinin action rather than causing a reduction in the endogenous cytokinin level.