Photosynthetic rates, the activities of key enzymes associated with the C4 cycle and ribulose-l,5-bisphosphate carhoxylase (RuBPCase), and the levels of metabolites involved in the C4 cycle were compared between the two phosphoenolpyruvate carboxykinase (PCK) type C4 species Spartina anglica, which is cold-tolerant, and Zoysia japonica, which is cold-sensitive, during exposure to low temperature. Plants of both species grown outside in summer were placed in a growth chamber at 27/20 °C day/night temperatures. After 1 week, plants were exposed to 20/17 °C for 1 week and then to 10/7 °C for 2 weeks. Photosynthetic rates in Z. japonica decreased progressively to about 25% during the chilling treatments. In contrast, S. anglica exhibited a 43% increase in photosynthetic rates after exposure to 20 °C for 1 week, which remained relatively constant thereafter. Consistent with these observations, most of the C4 enzymes and RuBPCase in Z. japonica declined. Phosphoenolpyruvate carboxylase (PEPC) and PCK activities declined particularly drastically during the treatments. However, the activities of these enzymes in S. anglica showed either a slight increase or decrease upon a mild cold treatment, and remained relatively constant during further chilling treatments. There was a sharp decline in phosphoenolpyruvate in Z. japonica after exposure to 10 °C. On the other hand, metabolite levels in S. anglica were largely unaffected by the chilling treatments. These results suggest that the drastic declines of both PEPC and PCK activities may be important limiting factors responsible for cold sensitivity in C4 photosynthesis of Z. japonica.
There are two growth types of plants for the number of developed leaves, heading time, and culm and panicle lengths within a population of a homozygous rice cultivar. However, this phenomenon has not been deeply investigated, because of lack of concrete data. Rice breeders and physiologists have paid little attention to it, regarding it as a genetically uncontrollable environmental variation. To study more details of the phenomenon, we grew two near-isogenic lines of rice with each one of the alleles for the Se1 locus conferring photoperiod sensitivity on chromosome 6 under natural long and short day-length conditions. In the line ER homozygous for the earliness allele Se1-e, and the line LR with the lateness allele Se1-u, N-leaf plants headed several days earlier than N+1-leaf plants. The N-leaf plants had shorter culms and longer panicles and were the upper-internode elongation type, whereas the N+1-leaf plants had opposite values of these characters. The proportion of these two kinds of plants changed in lines, plots and experiments. We discuss the meanings of this phenomenon from the viewpoints of rice cultivation to attain the uniform growth of plants, breeding to select individual plants with environmental variation, and fixation test to evaluate the uniformity needed as a cultivar.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.