Mutants of Sweetclover (Melilotus alba) Lacking Chlorophyll b

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Abstract
Mutants of sweetclover with defects in the nuclear ch5 locus were examined. Using TLC and absorption spectroscopy, 3 of these mutants lacked chlorophyll (Chl) b. One of these 3 mutants, U374, possessed thylakoid membranes lacking the 3 Chl b-containing pigment-protein complexes (AB-1, AB-2 and AB-3) while still containing A-1 and A-2, Chl a complexes derived from photosystems I and II, respectively. Complete solubilization and denaturation of the thylakoid proteins from this mutant revealed very little apoprotein from the Chl b-containing light-harvesting complexes, the major thylakoid proteins in normal plants. The normal and mutant sweetclover plants had active thylakoid protein kinase activities and numerous polypeptides were labeled following incubation with [.gamma.-32P]ATP. With the U374 mutant, there was very little detectable label co-migrating with the light-harvesting complex apoproteins on polyacrylamide gels. The Chl b-deficient chlorina-f2 mutant of barley (Hordeum vulgare) also had an active protein kinase activity capable of phosphorylating numerous polypeptides, including ones migrating with the same mobility as the light-harvesting complex apoproteins. The sweetclover mutants may be useful systems for studies on the function and organization of Chl b in thylakoid membranes of higher plants.