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Regulation of Synthesis of Chlorophyll, Carotene, Ribulosel,5‐diP Carboxylase and Phosphoribulokinase in a Temperature‐sensitive Chlorophyll Mutant of Medicago sativa
Author(s) -
Huffaker R. C.,
Cox E. L.,
Kleinkopf G. E.,
Stanford E. H.
Publication year - 1970
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1970.tb06430.x
Subject(s) - phosphoenolpyruvate carboxylase , pyruvate carboxylase , carbon fixation , chlorophyll , photosynthesis , biochemistry , malate dehydrogenase , rubisco , biology , chemistry , enzyme , botany
The activities of several enzymes were studied in a temperature‐sensitive chlorophyll mutant of alfalfa ( Medicago saliva ). In leaves grown at 10°C photosynthetic capacity was essentially nil with ribulose‐1,5‐diP carboxylase, chlorophyll, and carolene present in greatly limiting concentrations. The activity of phosphoribulokinase was 3.5 times lower at 10°C than at 27°C, but was still sufficiently high at 10°C to not limit the rate of CO 2 fixation. Activities of phosphoriboisomerase, phosphoenolpyruvate carboxylase, glucose‐6‐P dehydrogenase and malate dehydrogenase were not different at 10°C and 27°C. The low fraction I protein content (which also accounts for the ribulose‐1,5‐dip carboxylase activity in alfalfa) indicated that synthesis of the carboxylase was effectively blocked at 10°C. A large, comparable increase in carboxylase activity and in concentration of fraction I protein in alfalfa leaves grown at 27°C indicated that the carboxylase was synthesized de novo . The initial induction of the carboxylase, chlorophyll, and carotene may be related, but after induction the carboxylase was not linearly correlated with the other two and had a different temperature optima. Nevertheless, the synthesis of each appeared to be regulated by the temperature‐sensitive gene of this mutant.