Developmental Studies on Photosynthetic Parameters in C 3, C 3 - C 4 and C 4 Plants of Panicum

Abstract

Summary Mature, half unfolded, and not unfolded leaves of Panicum bisulcatum, a C3 plant, P. milioides, a C3-C4 intermediate plant and P. maximum, a C4 plant, were examined in respect to leaf anatomy, photosynthetic rates, CO2 compensation points, phosphoenolpyruvate carboxylase (PEP-C, E.C. 4.1.1.31) and ribulose 1,5-bisphosphate carboxylase (RuBP-C, E.C. 4.1.1.39) activities. In cross sections of all leaf stages examined for the C3 and for the C3-C4 species no visible changes in the leaf anatomy were observed. In the C4 plant the characteristic centrifugal arrangement of the chloroplasts in the bundle sheath cell, found in mature leaves, was not found in all not unfolded leaves. In the C3 and the C3-C4species no significant changes in photosynthetic rates and CO2 compensation points during leaf development were found, while in the C4 plant an increase of the photosynthetic rates and a decrease of the CO2 compensation points were measured. This seems to be due to the increase of the PEP-C activity during leaf maturation in the C4 plant, while in the C3 and C3-C4 plants a decrease of PEP-C and an increase of RuBP-C activity was observed. The study of other photosynthetic tissues, e.g. stems and panicles, revealed an absence of distinctive morphological characteristics related to the type of photosynthesis. Nevertheless, physiological and enzymatic differences between the stems and the panicles of the different Panicum species were found.