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Two Sweetclover (Melilotus alba Desr.) Mutants Temperature Sensitive for Chlorophyll Expression
M. A. Bevins1, S. Madhavan, J. Markwell
1Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68583.
Plant Physiology
|December 1, 1993
Summary
Temperature-sensitive sweetclover mutants reveal how chlorophyll (Chl) biosynthesis and assembly are regulated. These mutants demonstrate that internal factors, not just environmental ones, influence carbon isotope fractionation in plants.
Area of Science:
- Plant Molecular Biology
- Photosynthesis Research
- Biochemistry
Background:
- Sweetclover mutants U371 and U372 exhibit temperature-dependent chlorophyll deficiency.
- These mutants are derived from the wild-type U389 strain, providing a genetic basis for studying pigment synthesis.
Purpose of the Study:
- To investigate the regulation of chlorophyll biosynthesis and assembly in response to temperature changes.
- To explore the relationship between photosynthetic apparatus development and carbon isotope fractionation.
Main Methods:
- Comparative growth analysis of wild-type and mutant sweetclover at different temperatures (17°C and 26°C).
- Biochemical analysis of chlorophyll and carotenoid content, including chlorophyll a/b ratios.
- Assessment of light-harvesting complex apoprotein expression and chloroplast ultrastructure.
- Measurement of leaf carbon isotope fractionation during temperature-induced greening.
Main Results:
- Mutant plants showed severe chlorophyll deficiency at 17°C, with reduced carotenoids and negligible chlorophyll b.
- Transferring mutants to 26°C induced progressive greening, increasing chlorophyll content, chlorophyll a/b ratio, and apoprotein expression over 20 days.
- Greening correlated with changes in chloroplast ultrastructure and leaf carbon isotope fractionation, suggesting internal factors influence CO2 fixation limitations.
Conclusions:
- Temperature-sensitive sweetclover mutants are valuable tools for studying photosynthetic apparatus assembly and biosynthesis.
- Internal metabolic and structural factors, alongside environmental cues, play a significant role in regulating carbon isotope fractionation during photosynthesis.