Photosynthesis in cells around veins of the C₃ plant Arabidopsis thaliana is important for both the shikimate pathway and leaf senescence as well as contributing to plant fitness

• Published in: The Plant journal : for cell and molecular biology 2009-07, Vol.59 (2), p.329-343
• Main Authors: Janacek, Sophie H, Trenkamp, Sandra, Palmer, Ben, Brown, Naomi J, Parsley, Kate, Stanley, Susan, Astley, Holly M, Rolfe, Stephen A, Paul Quick, W, Fernie, Alisdair R, Hibberd, Julian M
• Format: Article
• Language: English
• Subjects: Arabidopsis; Biological and medical sciences; Botany; C4 photosynthesis; Carbon; Carbon dioxide; Cellular biology; C₄ photosynthesis; Fundamental and applied biological sciences. Psychology; Metabolism; Photosynthesis; Photosynthesis, respiration. Anabolism, catabolism; Plant physiology and development; senescence; shikimate pathway; veins
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313X.2009.03873.x

Cells associated with veins of C₃ species often contain significant amounts of chlorophyll, and radiotracer analysis shows that carbon present in the transpiration stream may be used for photosynthesis in these cells. It is not clear whether CO₂ is also supplied to these cells close to veins via stomata, nor whether this veinal photosynthesis supplies carbon skeletons to particular metabolic pathways. In addition, it has not been possible to determine whether photosynthesis in cells close to veins of C₃ plants is quantitatively important for growth or fitness. To investigate the role of photosynthesis in cells in and around the veins of C₃ plants, we have trans-activated a hairpin construct to the chlorophyll synthase gene (CS) using an Arabidopsis thaliana enhancer trap line specific to veins. CS is responsible for addition of the phytol chain to the tetrapyrolle head group of chlorophyll, and, as a result of cell-specific trans-activation of the hairpin to CS, chlorophyll accumulation is reduced around veins. We use these plants to show that, under steady-state conditions, the extent to which CO₂ is supplied to cells close to veins via stomata is limited. Fixation by minor veins of CO₂ supplied to the xylem stream and the amount of specific metabolites associated with carbohydrate metabolism and the shikimate pathway were all reduced. In addition, an abundance of transcripts encoding components of pathways that generate phosphoenolpyruvate were altered. Leaf senescence, growth rate and seed size were all reduced in the lines with lower photosynthetic ability in veins and in cells close to veins.