Photosynthesis in mesophyll protoplasts and bundle sheath cells of various type of C4 plants. III. Fluorescence emission spectra, delayed light emission, and P700 content

Abstract

Summary Mesophyll protoplasts from C 3 and C 4 plants and bundle sheath cells from C 4 plants were enzymatically isolated and purified from representative species of Gramineae. Chloroplast particles prepared by breaking protoplasts and cells with a French press were used for comparative photochemical studies. In C 4 grasses having high concentrations of NADP-malic enzyme, the ratio of fluorescence at 685 nm/730 nm, at liquid nitrogen temperature, and the delayed light emission was from 3 to 15 fold higher in mesophyll protoplast extracts than in bundle sheath cell extracts. This variation was species dependent. Based on delayed light emission and liquid nitrogen fluorescence emission spectra ratio 685 nm/730 nm, the relative level of photosystem II in bundle sheath chloroplast particles of NADP-malic enzyme species is Setaria lutescens, Setaria faberii > Digitaria sanguinalis > Zea mays > sugarcane, Sorghum bicolor , and Sorghum halepense . In Sorghum bicolor and Sorghum halepense at least 94 % of the photosystem II activity of the leaf is in mesophyll chloroplasts. The P700 content is 1.4 to 2.2 fold higher in bundle sheath extracts compared to mesophyll extracts of species having high NADP-malic enzyme. In C 4 grasses having high NAD-malic enzyme, such as Panicum capillare and Panicum miliaceum , the delayed light emission and liquid nitrogen fluorescence emission spectra at 685 nm/730 nm was higher in bundle sheath extracts than in mesophyll extracts. On the other hand, the P700 activity in these species was about 1.4 fold higher in mesophyll protoplasts extracts than in bundle sheath extracts. In C4 grasses having high phosphopyruvate carboxy-kinase, the liquid nitrogen fluorescence emission spectra were similar in mesophyll protoplast and bundle sheath extracts, the delayed light emission was higher in mesophyll extracts than in bundle sheath extracts, while the P700 activity was higher in bundle sheath than in mesophyll extracts. The results are discussed in relation to proposed energy requirements for carbon metabolism in mesophyll and bundle sheath cells of various C 4 species.