Photosynthetic and Respiratory Studies During Pod and Seed Development in Pisum sativum L.

The photosynthetic and respiratory potential of Pisum sativum fruit depends on a combination of factors such as fruit age, light intensity and the atmospheric CO2 concentration. Fruit were capable of a net CO2 uptake from the atmosphere only during the period of pod extension growth and at light intensities greater than 12 klx. During subsequent development the respiratory CO2 evolution attributable to seed growth exceeded the photosynthetic capacity of the pod. Despite this the extent of fruit CO2 loss was consistently less in the light than in the dark. An increase in the CO2 concentration beyond 300 p.p.m. markedly reduced fruit CO2 loss and in some instances effected a transition from a net CO2 output to a net CO2 uptake. Conversely, a decrease in the CO2 concentration substantially increased the extent of fruit CO2 loss. The CO2 compensation point concentration increased with fruit age from 150 p.p.m. to possibly more than 550 p.p.m., whereas the corresponding value for the pod (minus seed) remained between 120 and 175 p.p.m. throughout fruit development. A proportion of the CO2 respired by the seed and pod accumulated within the pod cavity. The CO2 concentration attained depended on fruit age and nodal location. In the course of fruit development concentrations within the range 0⋅1 to 4˙3 per cent CO2 occurred during mid-photoperiod. The CO2 concentration was highest when the enclosed seed had attained approximately 50 per cent of their final dry weight.