Respiration of soybean plants in relation to their physiological conditions. II. Effects of preceding light conditions on the time course change of respiration in the following dark period.

Abstract

The time course of respiration in the continuous dark was examined with soybean plants having experienced various preceding light conditions, aiming to elucidate the determination mechanism of changes with time in respiration rate. The initial value of respiration rate per unit dry weight (RPW) observed immediately after the onset of dark period was dependent on the light intensity in the preceding light period, and it was not affected by the length of light period. However, the bottom level of RPW observed after the initial decrease was affected by the length, with the lower levels in the plants exposed to the shorter light period. Furthermore, the magnitude of midnight rise of respiration, the temporal rise in the dark period, was affected by both light intensity and length of light period. It showed the linear relationship against cumulative light intensity which was obtained from light intensity multiplied by length of light period. RPW in nitrogen-depleted plants did not respond to length of light period. In this experiment, it was found that the time course of respiration consisted of two different phases. One was in the initial part of the dark period and dependent on light intensity. The other was in the following part and dependent on cumulative light intensity in the preceding light period. From this observation, it was considered that respiration in the dark period was regulated by two different physiological processes.