PLANT PHYSIOLOGY , Vol 103, Issue 4 1123-1131, Copyright © 1993 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Two Sweetclover (Melilotus alba Desr.) Mutants Temperature Sensitive for Chlorophyll Expression
M. A. Bevins, S. Madhavan and J. Markwell
Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68583
The nonallelic sweetclover (Melilotus alba Desr.) mutants U371 (ch10/ch10
genotype) and U372 (ch11/ch11 genotype) are derived from the U389 (+/+
genotype) parental strain. Growth of the U389 strain at a temperature of 17
or 26[deg]C results in plants normally green in appearance. The U371 and
U372 mutant plants grown at 26[deg]C are slightly to moderately chlorophyll
(Chl) deficient and have decreased Chl b/a ratios. Growth of the mutants at
17[deg]C results in plants severely deficient in Chl a, with markedly
reduced levels of carotenoids except for violaxanthin, and with negligible
amounts of Chl b or apoproteins for the light-harvesting complex of
photosystem II. If mutant plants grown at 17[deg]C are transferred to
26[deg]C, during the next 20 d the amount of Chl per fresh weight will
increase 5-fold and both the Chl b/a ratio and the expression of the
light-harvesting complex apoproteins will progressively increase. Studies
of the U371 mutant during the temperature-induced greening demonstrate
progressive changes in chloroplast ultra-structure and leaf carbon isotope
fractionation that parallel the increases in Chl. Changes observed in the
leaf carbon isotope fractionation in the mutant suggest that, in addition
to the already known effects of various abiotic factors, structural and
metabolic internal factors can also influence whether the limitation in CO2
fixation is at the level of diffusion or carboxylation. Such
temperature-initiated progressive greening in these and similar mutants may
make them useful tools to elucidate not only the biosynthesis and assembly
of the photosynthetic apparatus, but also physiological phenomena such as
the influence of light-driven energy production on the overall carbon
isotope fractionation during photosynthesis.
