Phosphoenolpyruvate carboxykinase plays a role in interactions of carbon and nitrogen metabolism during grape seed development

Phosphoenolpyruvate carboxykinase (PEPCK) was shown to be present in a rang e of developing seeds by measurement of its activity and by immunoblotting. Its function was investigated during grape (Vitis vinifera L.) seed develo pment. The maximum abundance of PEPCK coincided with the deposition of stor age reserves. At this stage of development, immunohistochemistry showed tha t PEPCK was very abundant in a layer of cells located at the boundary of de veloping storage tissues and in the chalaza (close to the termination of th e vascular supply to the seed) and was also present in the palisade layer o f the seed coat (the inner layer of the outer integument). Earlier in devel opment PEPCK was also present in the developing palisade layer and in the i nner region of the nucellus which surrounds the developing endosperm. At la ter stages of development, PEPCK was located in the outer region of the end osperm. However, PEPCK was present in the phloem of the seed at all stages of development. Feeding of asparagine to developing grape seeds led to a st rong induction of PEPCK. We suggest that, in developing grape seeds, both t he chalaza and palisade tissue may distribute imported assimilates from the vasculature to the developing storage tissues and that PEPCK may play a ro le in the metabolism of nitrogenous assimilates during their delivery from the vasculature to the storage tissues.