Photosynthetic Response of Soybeans with Genetically Altered Chlorophyll

Abstract

The photosynthetic response of soybean plants (Glycine max (L.) Merr. Strain T219) at the start of a photoperiod showed that both normally pigmented plants (dark green) and chlorophyll-deficient plants (light green) had an induction period averaging 6 min, before a net CO2 uptake could be measured. The induction period was followed by a rapid increase in photosynthesis until a maximum rate was reached after 15 min and then gradually declined. Both chlorophyll content and ribulose diphosphate carboxylase activity were greatest in dark green plants. Plants tested at mid-day exhibited the highest carboxylase activity and plants assayed at mid-night the lowest activity. During the first 5 min of illumination (following a 12 hr dark period) the carboxylase activity increased 1.5 times in dark green and 1.9 times in light green plants. This indicated that initiation of the photoperiod enhanced ribulose diphosphate carboxylase activity.