[Effects of sunlight and temperature on ultrastructure and functions of chloroplast of cucumber in solar greenhouse].
ABSTRACT Studies on the effects of sunlight and temperature on the ultrastructure and functions of leaf chloroplasts of cucumber (Cucumis sativus L.) in solar greenhouse showed that the size of cells, chloroplasts, and starch grains and the number of chloroplast, grana, grana lamella and grana thickness of leaf chloroplast of cucumber increased with lowering leaf position. The microstructure of leaves and the ultrastructure of chloroplast of cucumber leaves were different because of the difference of temperature and sunlight among different months. In January, the light intensity was lower, and the cell size of cucumber leaves was larger than that in May, but the number of chloroplasts was less than that in May. The relationships between photosynthetic rate (Pn) and ultrastructure of chloroplast of cucumber leaves were not direct and very close. The Pn of the fourth leaf of cucumber was the highest, that of the first spreading out leaf was the second, and the near ground leaves had the lowest Pn. The primary reasons of the difference of Pn among different position leaves were that the leaf age and accepted light intensity were different. If different position leaves of cucumber accepted the same sunlight intensity, the difference of Pn among leaves of different positions would be smaller. Less efficient light hours and lower light intensity were the main factors influencing cucumber growth and yield in solar greenhouse. Comparatively, under sunny circumstance, the restriction of temperature on cucumber growth was very small, but in cloudy days, lower temperature induced by low light intensity became a key factor that restricted cucumber growth.