| The partitioning of photosynthate between source and sink is the physiological basis for acquiring a high yield in wheat, and triose phosphate/ phosphate translocator (TPT) may be the first regulation point for this partitioning. Understanding the characteristics of TPT, its regulation on the distribution of assimilates and the expression of tpt gene may be critical for improving the utilization rate of photosynthetic assimilates. But up to now it is unknown about the transport characteristics, the physiological function of TPT, and the expression of tpt gene in wheat. In this paper, we described the localization and transport kinetics of TPT, analyzed its physiological role in the distribution of assimilates, explored the factors that effect the expression of tpt, and studied the role of hexokinase (HXK) in the expression of tpt gene regulated by glucose in wheat, which will provide clues for coordinating the partitioning of assimilates between source and sink, improving the utilization rate of photosynthate, and increasing crop yield.A peptide with a length of 13 amino acids (N'-KAK. IEE EKR AKA A-C') was synthesized according to the putative amino acid sequence by 3' end of wheat tpt cDNA (39 bp) cloned by us. The peptide coupled with bovine serum albumin (BSA) was used to inject rabbit to prepare antibody. The ratio of the prepared antibody against TPT was 1:500. Western blotting analysis showed that TPT only exists in the envelope membrane of wheat chloroplasts, but not in the membrane of vacuoles and mitochondrials. SDS-PAGE and labeling of TPT with [H3]2-DIDS (4, 4'-diisothiocyano-2, 2'-stilbenedisulfonate, DIDS), an irreversible specific inhibitor, indicated that TPT is a 35 kD chloroplast membrane protein and makes up about 15 % of the total membrane proteins of chloroplasts.Silicone-oil-layer centrifugation system was employed to study the kinetic properties of TPT, which catalyzes the counter exchange of dihydroxyacetone phosphate (DHAP)/phosphoenol -pyruvate (PEP)/glucose-6-phosphate (G6P) and inorganic phosphate (Pi). The maximal transport activity of TPT was the highest for DHAP/Pi, followed by PEP/Pi and G6P/Pi. The Km of TPT was the lowest for DHAP, followed by Pi, PEP and G6P, so the most preferred substrate of TPT is DHAP. The Vmas and Km of DHAP were 21.4 umol/mg chl-h and 0.019 mmol/L respectively in the dark. In the light, Vmax of DHAP increased by 54.67 %, and Km decreased by 10.5 %. Thus, the transport of TPT appears to be regulated by light, and it can increase Vmax, but illumination does not change the affinity of TPT to substrates, that is to say that light has few effects on the Km of substrates transported by TPT. The transport of the various substrates is strongly inhibited by DIDS whether in dark or in light.The transport activity of TPT being inhibited leads to an obvious increase of the content of many metabolites and an accumulation of starch in chloroplasts. A change of the enzyme acitvity in wheat chloroplasts also provide a support for the flux of photosynthate to starch. Wheat is a kind of sugar-leaf plants. TPT plays an important role in the regulation on the distribution of assimilates in wheat chloroplasts and in the transport of photosynthetic products from source to sink. Its function is to exportphotosynthetic assimilates out of chloroplasts efficiently and participate in all kinds of metabolism in cytosol.Northern blotting analysis demonstrated that the expression of tpt gene increased under osmotic stress treatments in seedlings of Jing 411, but decreased obviously under the treatments with glucose, sucrose and frucrose. The expression of tpt decreased clearly in wheat seedlings when the concentration of glucose was above 5 mmol/L for 4 days. Western blotting analysis showed that the expression of tpt of the cultivar Jing 411, with a middle photosynthetic rate, Zhongpin 97-37 and Zhong 924, with a low photosynthetic rate, is lower than No 6 Wenmai and No 16 Jinan, with a higher photosynthetic rate, so the abundance of expression of tpt may act as...
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