What role does bundle sheaths play in c4 plants

What role does bundle sheaths play in C4 Plants The plants use C3 and C4 photosynthesis for the production of energy. The C4 plants are very less innumber but they contribute to 25% of the photosynthesis that occurs on earth. C4 plants are classified into three groups based on the major decarboxylase enzyme involved in the decarboxylation of C4 acid cells. Bundle sheath cells are the major site of refixation of the CO2 and C4 acid decarboxylation. The mesophyll cells also concentrate the CO2 and send it to the bundle sheath cells. NADP-malic enzyme (NADP-ME) and phosphoenolpyruvate carboxykinase (PCK) are expressed in the bundle sheath cells of the C4 plants. They are the major enzymes responsible for the refixation of the CO2 from the C4 acid. (Nomura et al. 2005). In C4 leaves, each vein is surrounded by a ring of the bundle sheath cells surrounded again by the mesophyll cells. These bundle sheaths have the chloroplasts arranged centrifugally with the large starch granules and unstacked thylakoid membranes. In the bundle sheath cells ribulose-1, 5-bis-phosphate carboxylase/oxygenase (Rubisco) enzyme accumulates extensively. The specific enzyme activity can be easily determined by using the non aqueous fractionation techniques and pulse labeling techniques. (Majeran et al. 2005). The complete details about the C4 photosynthesis are not evolved. The maize is used extensively for the researches of C4 plants. In maize, the initial studies were done in 1981 and they found that mesophyll and the bundle sheath cells are distinct using the cell-specific gene expression. The studies have also found some interesting facts that some plants used C3 photosynthesis during the developing stage and C4 photosynthesis on maturation. This may be due to the changes in the enzyme synthesis pathways. The enzymes and proteins present in the bundle sheath cells and the mesophyll cells were studied and they have found distinct proteins in both the bundle sheath cells and the mesophyll cells. The chloroplast developmental dynamics was not performed so far. Similarly the end enzymes and their molecular mechanisms are not understood so far. (Bartsch et al. 2010). The chloroplast relocation movement is also not studied well in C4 plants. When the plants undergo a stress, the chloroplasts re- arrange according to the needs and this is studied in C3 plants. The chloroplasts present in the mesophyll change their position when they undergo a stress and the bundle sheath cells do not until maturation. The changes occurring between the developing stage and the maturation study can be performed. The transformation of the C3plants into c4 plants is the new area of research and many hypothesis and studies are showing promising results. The development of the C4 plants from C3 plants requires the understanding of the photosynthetic pathway. This provides a platform for the identification, regulation and biological consequences for the leaf vein pattern modification. The c4 plants have high vein density when compared with the C3 plants. (Sharpe et al. 2011). Hypothesis: The transformation of the C3 plants into C4 plants can be done by understanding the gene expression profile of the C3and C4 plants. Comparative transcriptomic and quantitative proteomic analysis of the C3 and C4 plants can be done by using the complete genome sequences of the chloroplasts. Methodology: Sequence similarity searching is the method for finding the similar sequences that are present in the C3 and C4 plants. Sequence similarity searching is done by using BLAST. BLAST ALL is the most commonly used sequence similarity search tool. It performs fast local alignment searches. Outcome: The expression level of the enzymes can be analysed and compared. All the enzymes and the metabolic precursors present in the C4 plants are also present in the C3 plants. But the level of expression of the enzymes varies. Either they may have very less activity or tissue specific expression may be the reason. Some of the enzymes like phosphenol pyruvate carboxylase (PEPC), NADP-malic enzyme ( NADP- ME), NAD – malic enzyme, ( NAD- ME), NADP-malate dehydrogenase ( NADP- MDH), Phosphoenolpyruvate carboxykinase ( PEPCK), pyruvate phosphate dikinase (PPDK) are some of the C4 cycle enzymes that have the potential for the variation in the level of expression. Individual over expression of the C4 cycle enzymes in C3 plants can be looked upon. Some studies have found that over expression of the enzyme phosphenol pyruvate carboxylase as the first step for the establishment of the C4 cycle in the C3 plants. So the sequence analysis and comparison will give us the details about the expression level of the enzymes and will provide the pathway for over expressing or suppressing the C4- enzymes in theC3 plants. (Hausler et al. 2002). References: Bartsch, O., Mikkat, S., Hagemann, M and Bauwe, H 2010, An Autoinhibitory Domain Confers Redox Regulation to Maize Glycerate Kinase, Plant physiology, 153: 832-840. Hausler, RE., Hirsch, HJ., Kreuzaler, F., and Peterhansel, C 2002, Over expression of C4 cycle enzymes in transgenic C3 plants : a biotechnological approach to improve C3- Photosynthesis, Journal of Experimental Botany, 53 (369): 591- 607. Nomura, M., Higuchi, T., Ishida, Y., Ohta, S., Komari, T., Imaizumi, N., Miyao- Tokutomi, M., Matsuoka., M and Tajima, S 2005, Differential Expression Pattern of C4 Bundle Sheath Expression Genes in Rice, a C3 Plant , Plant Cell Physiology, 46 (5): 754–761. Sharpe, RM., Mahajan, A., Takacs, EM., Stern, DB and Cahoon, AB 2011, Developmental and cell type characterization of bundle sheath and mesophyll chloroplast transcript abundance in maize, Current Genetics, 57: 89-102.