Photosynthetic Characteristics of Cassava (Manihot esculentaCrantz), a C3Species with Chlorenchymatous Bundle Sheath Cells

摘要

Cultivars of cassava,Manihot esculentaCrantz, were studied to determine the mechanism of photosynthetic carbon assimilation in this species. The results, contrary to recent reports, indicate that cassava is a C3plant based on a number of physiological and biochemical photosynthetic characteristics. The CO2compensation points among 10 cassava cultivars ranged from 55 to 62μl liter−1, which was typical for C3plants including castor bean, a member of the same family (Euphorbiaceae). The initial products of photosynthesis in cassava are C3-like; the activities of several key C4enzymes in cassava are low and similar to those of C3plants. Data on the rates of photosynthesis per unit of leaf area and the photosynthetic response of cassava to CO2is also consistent with C3photosynthesis. Cassava has a distinctive chlorenchymatous vascular bundle sheath located below a single layer of palisade cells. Unlike C3-C4intermediates and C4species, the bundle sheaths of cassava are not surrounded by mesophyll cells. The bundle sheath cells which occur at high frequency in cassava may function in both photosynthesis and transport of photosynthates in the le