Photosynthetic Characteristics of Cassava (<italic>Manihot esculenta</italic> Crantz), a C<sub>3</sub> Species with Chlorenchymatous Bundle Sheath Cells

Abstract

Cultivars of cassava, Manihot esculenta Crantz, were studied to determine the mechanism of photosynthetic carbon assimilation in this species. The results, contrary to recent reports, indicate that cassava is a C3 plant based on a number of physiological and biochemical photosynthetic characteristics. The CO2 compensation points among 10 cassava cultivars ranged from 55 to 62 μl liter−1, which was typical for C3 plants 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 C4 enzymes in cassava are low and similar to those of C3 plants. Data on the rates of photosynthesis per unit of leaf area and the photosynthetic response of cassava to CO2 is also consistent with C3 photosynthesis. Cassava has a distinctive chlorenchymatous vascular bundle sheath located below a single layer of palisade cells. Unlike C3-C4 intermediates and C4 species, 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 leaf.