Changes in photosynthesis and other chloroplast traits in lanceolate leaflet isoline of soybean

Lanceolate leaflet soybean (Glycine max L. Merrill) has been known to photosynthesize more CO₂ per unit leaf area than normal leaflet soybean. The exact reason for this increase in photosynthetic rate is still unclear. The present study was undertaken to investigate the leaf photosynthetic rate and other physiological traits in relation to chloroplast of lanceolate leaflet soybean. Ontogenic changes in apparent photosynthesis (AP) were related primarily to variations in the amount of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) per unit leaf area, and only secondarily to difference in specific activity of the said enzyme. Moreover, lanceolate leaflet consistently maintained a higher leaf AP, higher Rubisco activity, and more chloroplasts per unit leaf area basis than did normal leaflet soybean throughout leaf ontogeny. However, lanceolate soybean tended to have lower AP and Rubisco activity on a chloroplast basis. The superiority of leaf AP and other leaf physiological traits, expressed on a leaf area basis, in lanceolate leaflet soybean is associated with a corresponding increase in chloroplast number.