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

Abstract

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.

Characterization of a Family of Chlorophyll-Deficient Wheat (Triticum) and Barley (Hordeum vulgare) Mutants with Defects in the Magnesium-Insertion Step of Chlorophyll Biosynthesis

“…Temperature sensitivity has been postulated to be a general phenomenon in Chl-deficient mutants of sweetclover (Yang et al, 1990) and Arabidopsis (Markwell and Osterman, 1992). We postulate that the bottleneck in the Chl synthesis pathway in these mutants, seen especially early in development, could simply exaggerate the low-temperature slowdown in de novo protein synthesis (Greer et al, 1991) required for the processes of development and repair and thereby enhance the mutational effects.…”

Severity of Mutant Phenotype in a Series of Chlorophyll-Deficient Wheat Mutants Depends on Light Intensity and the Severity of the Block in Chlorophyll Synthesis

“…In addition, the total amount of Chl and the Chl alb ratio vary greatly in response to changes in the light environment (similar to sun and shade plants) and to changes in temperature (Yang et al, 1990;Markwell and Osterman, 1992). Concomitant light-and temperature-dependent changes in LHCs, grana stacks, and general organization of the thylakoids have also been observed, with losses in peripheral LHCs in general paralleling reductions in the size and number of grana stacks (Greene et al, 1988a(Greene et al, , 1988bKnoetzel and Simpson, 1991).…”

Two Sweetclover (Melilotus alba Desr.) Mutants Temperature Sensitive for Chlorophyll Expression

“…have been identified in which the restrictive growth temperature producing the Chl-deficient phenotype is either lower or higher than the temperature producing more normal Chl content (Markwell et al, 1986;Yang et al, 1990;Markwell and Osterman, 1992). For some of the mutants such as the sweetclover ch4, the Chl deficiency is not reversed when the plant is placed at a nonrestrictive temperature (Markwell and Chelgren, 1988), whereas initial studies indicated that mutants such as the sweetclover chlO and chll will markedly green when transferred to the nonrestrictive temperature (Yang et al, 1990). In this report we will examine the phe-Plant Physiol.…”