ISHS Acta Horticulturae 526: V International Symposium on Grapevine Physiology
ROLE OF PHOSPHOENOLPYRUVATE CARBOXYLASE IN THE ACIDIFICATION OF GRAPE BERRIES |
| Authors: | P. Diakou, A. Moing, N. Ollat, C. Rothan, J. Gaudillère |
| Keywords: | Vitis vinifera, acidity, malate, metabolism |
| Abstract:
Grape berries were produced under controlled conditions on fruiting cuttings of cv. Cabernet Sauvignon. Their maximum concentration of malate in skin and mesocarp (about 490 mM) was observed at veraison. The key enzyme for malate synthesis is phosphoenolpyruvate carboxylase (PEPC). We studied the amount and regulatory properties of PEPC during the berry development. Immunodetection of denaturated PEPC was performed with antibodies raised against sorghum PEPC. Immunodetection of berry PEPC on Western blots resolved two bands separated by about 8 kDa. Small differences were observed between stages of development on a fresh weight basis. We estimated in vivo PEPC activity using incorporation of 14CO2. The total incorporated radioactivity was about 17 times higher before veraison than after. Therefore, PEPC activity seems to be highly regulated during berry development. We studied its regulation by some effectors. The maximum overall concentration of glucose-6-phosphate, an activator of PEPC, was observed at maturity and reached about 0.17 mM. The maximum global concentration of oxaloacetate, an inhibitor of PEPC, was observed at veraison and reached 0.44 mM. These concentrations could not be correlated with the net accumulation or degradation of malate. PEPC regulation by phosphorylation also needs to be studied. Moreover, PEPC can be regulated by malate concentration in cytosol which depends on the efficiency of malate vacuolar storage. | |
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