Photosynthesis in maize (Zea mays L.) and Cecropia peltata L. (C. asperrima Pittier)

Abstract

Several small pieces of leaves (2 x 4 cm) of corn (Zea mays L.) and Cecropia peltata L. (C. asperrima Pittier) were exposed to a CO2 atmosphere for 10 and 30 seconds, respectively. In addition, whole leaves of each of these species were exposed for 30 seconds, 5 and 30 minutes, respectively, to the same treatment. After the treatments, the material was immediately fixed by quenching in isopentane for subsequent microscopic and radiographic observation or in boiling 80 percent ethyl alcohol to obtain extracts produced from the leaf pieces. Approximately 2-3 seconds elapsed between removal of the leaf pieces from the CO2 source until the tissue was frozen. Microscopic examination revealed that the photosynthetic products were equally distributed in the mesophyll cells of corn. Therefore, it can be concluded that CO fixation occurred uniformly in the chloroplasts that were distributed throughout the leaf tissue and was not necessarily located in the vascular pavenchyma as reported by Moss and Rasmussen in their article (7). Qualitative and quantitative changes were observed in the early products of photosynthesis. Such changes probably depended on the type of leaf tissue. In the case of maize, the changes were primarily qualitative in nature, but in Cecropia, they were predominantly quantitative. In both plants, virtually all of the radioactivity was detected in the sucrose 5 to 30 minutes after exposure of the material to the radioactive source.