Chlorophyll Expression Varies with Development State in the Temperature-Sensitive ch4 Mutation of Melilotus alba.

The ch4 mutant of sweetclover (Melilotus alba) has previously been demonstrated to be temperature- and photoperiod-sensitive for the accumulation of chlorophyll. Pigment content of ch4 mutant leaves was examined as a function of trifoliolate mass, an index of leaf development. Inhibition of chlorophyll accumulation caused by increased growth temperature or decreased photoperiod can be attenuated during the earliest leaf development stages but is almost complete after the trifoliolates have reached 10 milligrams in size. Once this size is reached, the total amount of chlorophyll per trifoliolate remains constant, and the amount of chlorophyll per gram of leaf decreases as the leaf expands. We have evidence for several other sweetclover mutants with this general phenotype, all with alterations previously determined to be located in different genes as evidenced by complementation following genetic crosses. This mutant phenotype may represent lesions in the chlorophyll biosynthetic pathway or the assembly of the photosynthetic apparatus.