Studies on the time course of photosynthetic rate of mulberry leaves after illumination

Abstract

A single leaf showing differnt stage of growth was kept in the dark for 10 to 12 hours and, immediately after the dark treatment, it was illuminated by the artificial light for approximately about 2 hours, during which measurement was made on photosynthetic rate at about 5 minutes intervals.
The results are as follows:
1). Photosynthetic rate of mulberry leaves varied greatly according to leaf order and growth stage, and they reached to a settled level of photosynthetic rate in 30 to 70 minutes after the beginning of illumination.
2). Time required to attain to a settled level of photosynthetic rate was determined with the season of measurement rather than with the leaf order.
The the time required was about 70 minutes in the middle of August where mulberry plants grew vigorously, about 50 minutes at the beginning of September, about 30 minutes in the middle of September, when the growth of plant was slowing down.
3). The proportion of photosynthetic rate measured in 10 minutes after the beginning of illumination to the maximum rate obtained was 30 to 60 percent in the middle of August, 30 to 70 percent early in September and 60 to 70 percent in the middle of September. The proportion was comparatively low in the leaves with high potential and was high with low potential.
4). It may be said that the ability of stomata to close decline at first and, afterward, the ability of stomata to open decline with the progress of the ageing of leaves and growth stage.
5). It was concluded that the change of photosnythetic rate after the beginning of illumination was intricately influenced with the ability of stomate to open and close, the seasen of measurement and the ageing of leaves.