Change in the predominance from C₄ to C₃ pathway following anthesis in Sorghum

Abstract

Sorghum and Pennisetum species are known to have predominantly C₄ pathway. This pathway is associated with several other characteristics. These conclusions are based on studies confined largely to seedlings. A developmental study of PEP carboxylase and RuDP carboxylase in Sorghum bicolor and Pennisetum typhoides confirmed in seedlings the predominance of PEP carboxylase, high malate: 3-phorophoglycerate ratio and 'Krantz' anatomy. However, after flowering, RuDP carboxylase was predominant in the leaves of both Sorghum and Pennisetum. This observation was associated with higher 3-phosphoglycerate:malate ratio following ¹⁴CO₂ fixation. The anatomy of the leaf remained unchanged and so was the chlorophyll a:b ratio. This change in system coincided with a slight fall in mean daily temperature. But in wheat RuDP carboxylase remained the predominant enzyme in spite of the rising mean daily temperature. Therefore, the change from C₄ to C₃ appears to be related more to the developmental stages.