Temperature sensitivity as a general phenomenon in a collection of chlorophyll-deficient mutants of sweetclover (Melilotus alba).

A collection of chlorophyll (Chl)-deficient mutants of sweetclover (Melilotus alba) with defects in eight nuclear loci were grown at 17 or 26 degrees C. Plants grown at either temperature were examined for Chl content, Chl a/b ratio, expression of the light-harvesting complex II (LHC-II) apoproteins, and protochlorophyllide (Pchlide) biosynthetic capacity. Except for the ch4 mutant, the parental strain and all mutants accumulate more Chl when grown at 26 degrees C than at 17 degrees C. The ch5 mutants, lacking Chl b under any growth condition, and the ch12 mutant showed little temperature-dependent phenotypic plasticity, whereas this was a marked phenomenon in the other mutants. The ch10 and ch11 mutants demonstrated extreme temperature sensitivity with regard to the production of Chl b and the Chl b-binding LHC-II apoproteins. When excised trifoliolates were supplemented with exogenously supplied delta-aminolevulinic acid, only the ch4 mutant was markedly impaired in the ability to produce Pchlide. These data indicate that temperature-sensitive phenotypic plasticity is a common phenomenon of chlorphyll-deficient mutants and substantiate that only a minority of Chl-deficient mutants is impaired in the biosynthesis of Chl.