Effects of light quality on photosynthetic carbon metabolism in C₄ and C₃ plants: rapid movements of photosynthetic intermediates between mesophyll and bundle sheath cells

Abstract

The influence of varying light intensity and quality on the carbon labelling patterns in Rumex vesicarius (a C₃ plant), Setaria italica (a malate-forming C₄ plant), and Amaranthus paniculatus (an aspartate-forming C₄ plant) was studied. In A. paniculatus and B. vesicarius blue light decreased the transfer of radioactivity to sugars and starch but in S. italica only slightly decreased radioactivity in sugar phosphates, sucrose, and insolubles. Negligible transfer was observed from the C₄ acids to sugar phosphates, sucrose, and starch under dim blue-green and blue-yellow lights in S. italica and A. paniculatus. Blue light favoured the formation of malate, aspartate, and alanine in all three plants. The differential effect of blue and red light suggested a variation in the mechanisms of C₄-photosynthesis in Setaria and Amaranthus. Leaves of S. italica and A. paniculatus were allowed to photosynthesize in ¹⁴CO₂ for 5 s and then the distribution of the labelled products between the mesophyll and the bundle sheath cells was determined during subsequent photosynthesis in ¹²CO₂. Malate and aspartate which appeared initially in the mesophyll layer moved rapidly into the bundle sheath cells. Phosphoglyceric acid originating in the bundle sheath moved swiftly to the mesophyll layer. Sugar phosphates were recovered from both the mesophyll and the bundle sheath cells. Most of the starch was found in the bundle sheath cells while sucrose and alanine were localized in the mesophyll cells.