- © 1986 American Society of Plant Biologists
Abstract
Two naturally occurring species of the genus Alternanthera, namely A. ficoides and A. tenella, were identified as C3-C4 intermediates based on leaf anatomy, photosynthetic CO2 compensation point (Γ), O2 response of г, light intensity response of г, and the activities of key enzymes of photosynthesis. A. ficoides and A. tenella exhibited a less distinct Kranz-like leaf anatomy with substantial accumulation of starch both in mesophyll and bundle sheath cells. Photosynthetic CO2 compensation points of these two intermediate species at 29°C were much lower than in C3 plants and ranged from 18 to 22 microliters per liter. Although A. ficoides and A. tenella exhibited similar intermediacy in г, the apparent photorespiratory component of O2 inhibition in A. ficoides is lower than in A. tenella. The г progressively decreases from 35 microliters per liter at lowest light intensity to 18 microliters per liter at highest light intensity in A. tenella. It was, however, constant in A. ficoides at 20 to 25 microliters per liter between light intensities measured. The rates of net photosynthesis at 21% O2 and 29°C by A. ficoides and A. tenella were 25 to 28 milligrams CO2 per square decimeter per hour which are intermediate between values obtained for Tridax procumbens and A. pungens, C3 and C4 species, respectively. The activities of key enzymes of C4 photosynthesis, phosphoenolpyruvate carboxylase, pyruvate Pi dikinase, NAD malic enzyme, NADP malic enzyme and phosphoenolpyruvate carboxykinase in the two intermediates, A. ficoides and A. tenella are very low or insignificant. Results indicated that the relatively low apparent photorespiratory component in these two species is presumably the basis for the C3-C4 intermediate photosynthesis.
