Rates of Photosynthesis Relative to Activity of Photosynthetic Enzymes, Chlorophyll and Soluble Protein Content Among Ten C₄ Species

Abstract

Among 10 C₄ species having a wide range in photosynthetic activity, the rates of photosynthesis/leaf area under high light were examined and compared with the chlorophyll and soluble protein content and the activities of several photosynthetic enzymes. The species examined were Digitaria sanguinalis, Echinochloa crus-galli, Microstegium vimineum, Panicum capillare, Panicum miliaceum, Paspalum dilatatum, Paspalum notatum, Pennisetum purpureum, Setaria lutescens, and Zea mays. The photosynthetic rates per unit leaf area ranged from 10 to 38 µmol CO₂ fixed m^-2 s^-1.

Among the 10 species there was a high degree of correlation of rate of photosynthesis/leaf area with soluble protein (r = 0.88), ribulose 1,5-bisphosphate carboxylase (r = 0.88) and pyruvate,P_I dikinase (r = 0.94), but a lower correlation of photosynthetic rate/leaf area with phosphoenolpyruvate carboxylase (r = 0.74) and no significant correlation of photosynthetic rate/leaf area with chlorophyll content (r = 0.56). Among eight species of the NADP-malic enzyme C₄ subgroup, there was a good correlation of photosynthetic ratelleaf area with NADP-malate dehydrogenase (r = 0.88) and NADP- malic enzyme (r = 0.92). Extractable activities of both the ribulose 1,5-bisphosphate carboxylase and the dikinase were generally close to the rate of photosynthesis. When comparing the activity per unit leaf area of one enzyme with another, generally a high degree of correlation was found among the species. The results suggest that a given C₄ species tends to maintain a balance in the activities of several photosynthetic enzymes and that there is potential to estimate capacity for C₄ photosynthesis under high light through determining activity of certain photosynthetic enzymes.