Showing papers on "Portulaca published in 1973"
TL;DR: In general the seeds of the narrowly obovate leaf ecotype were more sensitive to light than those of the obovates leaf ecotypes, and the seeds that showed significant temperature-dependent dark germination with a single light exposure given at high temperatures exhibited the loss of photo-thermoperiodic requirement.
Abstract: SUMMARY
The effect of various temperature and light conditions on the germination of freshly harvetesd and 1-year-old seeds of obovate leaf and narrowly obovate leaf ecotypes of Portulaca oleracea L. is reported. These plants are common weeds of moist cultivated fields in the Upper Gangetic Plain. Freshly harvested seeds showed insignificant germination in darkness at any temperature between 10–40° C, and required specific photoperiodic and thermoperiodic conditions for germination. In contrast 1-year-old seeds showed significant temperature-dependent dark germination, and almost complete germination with a single light exposure given at high temperatures; they thereby exhibited the loss of photo-thermoperiodic requirement. In general the seeds of the narrowly obovate leaf ecotype were more sensitive to light than those of the obovate leaf ecotype. The possible significance of the germination requirements in relation to the success of the plant in Nature and to its essentially tropical distribution is discussed.
TL;DR: It appears as if the stage of leaf development is one of the most important factors determining the operation of a particular enzyme system in C4 plants.
Abstract: The photosynthetic products of Portulaca oleracea differ greatly depending on leaf age and length of exposure to 14CO2. Mature leaves of P. oleracea fix 14CO2 primarily into organic and amino acids during a 10-s exposure period. Less than 2% of the 14CO2 fixed appears in phosphorylated compounds. In contrast, incorporation into amino acids can account for over 60% of the total 14CO2 fixed by young leaves in an equal time period, and incorporation into alanine alone can account for up to one half of this amount. Senescent leaves display a quantitative shift of primary products toward phosphorylated compounds with a concomitant reduction of the label residing in malate and asparate. About 8 times more phosphoglyceric acid is produced in senescent leaves than in mature leaves. The aspartate/ malate ratio is not constant and depends on the length of time the leaves are exposed to 14CO2 and the age of the leaves under study. It appears as if the stage of leaf development is one of the most important factors determining the operation of a particular enzyme system in C4 plants.