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

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Abstract
A collection of chlorophyll (Chl)-deficient mutants of sweetclover (Melilotus alba) with defects in eight nuclear loci were grown at 17 or 26° C. Plants grown at either temperature were examined for Chl content, Chla/b ratio, expression of the light-harvesting complex II (LHC-II) apoproteins, and protochlorophyllide (Pchlide) biosynthetic capacity. Except for thech4 mutant, the parental strain and all mutants accumulate more Chl when grown at 26° C than at 17° C. Thech5 mutants, lacking Chl b under any growth condition, and thech12 mutant showed little temperature-dependent phenotypic plasticity, whereas this was a marked phenomenon in the other mutants. Thech10 andch11 mutants demonstrated extreme temperature sensitivity with regard to the production of Chlb and the Chlb-binding LHC-II apoproteins. When excised trifoliolates were supplemented with exogenously supplied δ-aminolevulinic acid, only thech4 mutant was markedly impaired in the ability to produce Pchlide. These data indicate that temperature-sensitive phenotypic plasticity is a common phenomenon of chlorophyll-deficient mutants and substantiate that only a minority of Chl-deficient mutants is impaired in the biosynthesis of Chl.