Expression of auxin and light-regulated arrestin-like proteins, G proteins and nucleoside diphosphate kinase during induction and development of wheat somatic embryos

The modulation of three signal transduction elements: arrestin-like proteins, G proteins and NDPK was assessed during the induction of wheat (Triticum aestivum L.) somatic embryogenesis under different auxin (2,4-D) and light conditions. Immunological approaches using specific antibodies, kinase activity measurement and [α-32P]-GTP-binding assay were performed. The induction of embryogenic capacity by 2,4-D was characterised both by the increased expression of the classical 40-kDa arrestin-like form and by the appearance of an additional arrestin-like protein of 29 kDa. The 40-kDa arrestin-like soluble form was unaffected by light stimuli. On the other hand, the 29-kDa arrestin-like form, specific of the embryogenic tissue culture, was found to be light regulated. From embryogenic cultures grown under light or dark, different soluble G proteins from 22 to 48 kDa were detected by probing polyvinylidene fluoride (PVDF) blots with [α-32P]-GTP. In addition, in the microsomal fraction from light-grown cultures, a polypeptide of 20 kDa was heavily labelled. Under light conditions, cell proliferation induced by 2,4-D stimulated the appearance of a 32-kDa nucleoside diphosphate kinase (NDPK) form in addition to the classical 16–18-kDa protein, without a significant change in the NDPK activity. The modulated expression of plant arrestin-like proteins, G proteins and NDPK molecules in response to auxin and light support the view that they play key roles in signalling cascades participating in plant development.