An immunohistochemical study of the compartmentation of metabolism during the development of grape (Vitis vinifera L.) berries

The compartmentation of key processes in sugar, organic acid and amino acid metabolism was studied during the development of the flesh and seeds of gr ape (Vitis vinifera L.) berries. Antibodies specific for enzymes involved i n sugar (cell wall and vacuolar invertases, pyrophosphate:fructose 6-phosph ate phosphotransferase, aldolase, NADP-glyceraldehyde-P dehydrogenase, cyto solic fructose 1,6-bisphosphatase), photosynthesis (Rubisco, fructose 1,6-b isphosphatase, sedoheptulose 1,7-bisphosphatase), amino acid metabolism (cy tosolic and mitochondrial aspartate aminotransferases, alanine aminotransfe rase, glutamate dehydrogenase, glutamine synthetase), organic acid metaboli sm (phosphoenolpyruvate carboxylase, NAD- and NADP-dependent malic enzyme, ascorbate peroxidase), and lipid metabolism (acetyl CoA carboxylase, isocit rate lyase) were used to determine how their abundance changed during devel opment. There were marked changes in the abundance of many of these enzymes in both the flesh and seeds, The intercellular location of some enzymes wa s investigated using immunohistochemistry. Several enzymes (e.g. phosphoeno lpyruvate carboxylase and those involved in amino acid metabolism) were ass ociated with tissues likely to function in the transport of imported assimi lates, such as the vasculature. Although other enzymes (e.g. NADP-malic enz yme and soluble acid invertase, involved in the metabolism of sugars and or ganic acids) were largely present in the parenchyma cells of the flesh, the ir distribution was extremely heterogeneous. This study shows that when con sidering the metabolism of complex structures such as fruit, it is essentia l to consider how metabolism is compartmentalized between and within differ ent tissues, even when they are apparently structurally homogeneous.