Somatic Embryogenesis in Vitis vinifera: a Proteomic Approach

In this study, we have identified a number of proteins involved in different pathways during early embryo induction. Proteins were extracted from embryogenic and non-embryogenic calli of Vitis vinifera grown on a 2,4-D containing media. The protein extracts were separated by two dimensional gel electrophoresis and identified by mass spectrometry. Some of the differentially expressed proteins identified may be involved in detoxification or in the maintenance of redox state. This suggests that an oxidative burst occurs during the development of somatic embryos and might lead to programmed cell death (PCD) of certain cells. Glutathione-S-transferase (GST) and cytosolic ascorbate peroxidase during acquisition of embryogenic potential are likely to be involved in protecting cells against the harmful effects of reactive oxygen species (ROS); however, the redox status of cells and the glutathione content may have important roles in developmental processes, especially in triggering cell division. In fact, it has recently been proposed that GST may serve as carrier for plant hormones, including auxin. A proteasome subunit was also identified. It is known that proteasome activity is closely aligned with cell proliferation processes; moreover, knockout mutants of Physcomitrella patens show developmental defects partially reversed by auxin and cytokinin, suggesting that the responses to these hormones may require degradation of short-lived regulators by the proteasome. An intriguing possibility is that this regulator acts as a repressor, preventing development in the absence of appropriate hormonal signals. When a sufficient concentration of hormone is reached, these repressors are removed by degradation. NDPK was differentially expressed; its role remains to be elucidated in somatic embryogenesis but the literature suggests a possible function in the regulation of cell morphogenesis. These proteins are candidates for further investigation in term of functional relevance for somatic embryogenesis.