Abstract
Abstract： Phaseolus vulgaris L., common bean (Pv), is adapted to subtropical and water-welled area; Phaseolus acutifolius A. Gray, tepary bean (Pa) is adapted to hot arid climates of desert areas in the U. S., and Mexico. Field observations and physiological studies suggest that Pv is very sensitive to drought and heat stress, and its yield is significantly reduced under these conditions; but Pa doesn't. In the original study, we found there are many starch granules in the extract solutions. To easily and quickly quantify chloroplasts and starch granules, flow cytometry was employed using intrinsic chlorophyll fluorescence as gauge. We found that the number of starch granules per chloroplast is dependent on the leaf developmental stage, the age of plants as well as day/night cycle. It was also noted that Pa specially accumulated a large quantity of starch granules during leaf development, and the granules persisted even after a long dark period. When growth temperature was increased from 25℃ to 32℃, the removal of starch in the dark was abolished in Pv, whereas starch even increased in the young leaves of Pa. It seems that the starch content of Pa chloroplasts remain very high all the time. We have also studied the electron transport rate (ETR) and quantum yield of the two beans grown under normal condition, high temperature, water stress, as well as temperature and water double stress . Under normal condition and high temperature, photosynthetic activity of Pv is a little better than Pa, but under the double stress condition, Pa is better than Pv. The results suggest that Pa can keep good photosynthetic ability and high level's starch in any condition. Whether these characters have anything to do with its heat tolerance remain to be elucidated.