Studies on the Photosynthesis of the Gramineae. : I. Differences in photosynthesis anlong subfamilies and their relationd with the systematics of the Gramireae

Abstract

Downton et al. have recently reported that differences of photosynthetic rate among species in higher plants have close relations wlith the differences of compensation point of carbon dioxide dnd the presence of chloroplasts in bundle sheath cells (BSC). The authors made further physiological and morphological investigations on the Gramineae, and the following were obtained : 1. As reported by Downton et al., it was ascertained by us that the low CO2 compensation point and the presence of chlorplasts in BSC were closely related to the high photosynthetic rate without any exception in about the 60 species tested. 2. It was found out that the distance between two adjacent vascular bundles(Da), and that between two adjacent bundle sheathes (Db) were c1ose1y related to the photosynthetic rate. Species with smaller values in Da and Db had high photosynthetic rate, and vise versa. 3. Differences of photosjnthetic rate which were classifted by the above four properties coincided almost completely at subfamily level with the Gramineae systematics proposed by Tateoka. 4. It should be noted that there were some exceptions in the subfamily Panicoideae. At species level Panicum bisulcatum and Panicum lindheimeri were exceptions, at genus level the genus Sacciopis was an exception, and at tribe level the tribe Isachneae was an exception. Panicum bisulcatum, without BSC and with high carbon dioxide compensation point and having comparatively large values in Da and Db, showed low photosynthetic rate. 5. Judging from the phylogenetic schemes of the Gramineae proposed by Tateoka, and those by Stebbins, it can be considered that the members of the high photosynthesis subfamily have supposedly evolved from the low photosynthesis one.