Abstract
Greenhouse experiments were conducted to investigate the relationships between ribulose-1, 5-bisphosphate carboxylase (RuBPCase) and phosphoenolpyruvate carboxylase (PEPCase) activities per unit leaf area of warm-season grasses and N, P, K contents of leaves. Sorghum (Sorghum vulgare PERS, CV. Sweet Sioux IV) and African millet (Eleusine coracana, GAERTN, CV. Snow Brand) were cultivated in cultural solution with 4 levels of N, P, K concentration. RuBPCase and PEPCase activities per unit leaf area and the contents of N, P, K and soluble protein in leaves were measured at selected time after planting. In order to analyze the activity of enzyme per unit leaf area, it was expressed as the product of soluble protein content per unit leaf area and the enzyme activities per unit soluble protein. 1) RuBPCase and PEPCase activities of Sorghum and African millet increased with increasing N contents of leaves. This increase was not due to the increase of enzyme activity per unit soluble protein which was rather decreased with increasing N content, but to the increase of soluble protein per unit leaf area. 2) The activities of these enzyme per unit leaf area increased with increasing P contents of leaves at the range of 0-2.0mgP/dm^2 in PEPCase of African millet, and at the range of 0-1.0 mgP/dm^2 in RuBPCase of both grasses. Activities of these enzyme per unit leaf area increased with increasing K contents of leaves at the range of 0-11 mgK/dm^2 in PEPCase of African millet, and at the range of 0-6mgK/dm^2 in RuBPCase of both grasses. And these increase of activity were mainly due to the increase of activity of enzyme per unit soluble protein. The protein contents per unit leaf area were kept almost stable. 3) Significant negative correlations were found between the activity of enzyme per unit protein and protein contents per unit leaf area. These results indicate that RuBPCase and PEPCase activities per unit leaf area of Sorghum and African millet are limited by the decrease of soluble protein contents in case of low N contents, and by the decrease of activity per unit soluble protein in both cases of low P (below 2.0mg/dm^2) and low K (below 10mg/dm^2) contents in leaves.
