Effect of co2 concentration on photorespiration, sucrose synthesis, and carbon transport in c3 and c4 plants

Abstract

The synthesis of sucrose from the glycolate pathway was investigated in relation to the carbon transportation at different COl concentrations in the air. Tomato and maize plants were fed with uCOI in the light in an assimilation chamber containing 90, 220, 840, and 2,290 ppm of CO. The distribution of uC in the leaf extract with 80% ethanol, the leaf residue, and the root and stem was determined at 30 and 60 min. L-U-14C-serine was supplied to tomato leaves through their cut bases in the light in the air containing 10, 340, and 1,700 ppm of CO and the radioactive compounds formed from serine were analyzed. The following results were obtained. 1) The proportion of uC transported from the leaves decreased in maize but not in tomato at lower CO2 concentration. 2) The proportion of uC in glycine, serine, and malic acid in the leaf extracts increased corresponding to the decrease of that in starch at lower COs concentration in tomato at 30 min. At 60 min, the proportion of uC in glycine and serine decreased and that in starch increased at lower COl concentration. On the other hand, the influence of CO. concentra. tion on the proportion of UC in the metabolites was small for maize. 3) The amounts of uC in the leaf extract and residue significantly increased in tomato with an increase in photosynthesis, but that in the leaf residue in maize was constant regardless of the photosynthesis and CO. concentration. 4) From LOU·HC-serine, the incorporation of uC into the COl evolved and the inter. mediates of glycolate pathway increased and that into starch decreased at lower COl concen. tration in tomato. From these results it was considered that sucrose is synthesized mainly from the inter. mediates of glycolate pathway at lower COl concentration and from the intermediates of Calvin cycle at higher CO. concentration in tomato and only from the latter in maize. One of the roles of photorespiration was thought to be the maintenance of the carbon transport in C. plants. © 1980 Taylor & Francis Group, LLC.