Red light-induced appearance of phosphotyrosine-like epitopes on nuclear proteins from pea (Pisum sativum L.) plumules.

As assayed by western blot analysis, red light induces the appearance of epitopes recognized by anti-phosphotyrosine antibodies in several pea nuclear proteins. The immunostaining is blocked by preadsorbing the antibodies with phosphotyrosine but not by preadsorbing them with phosphoserine or phosphothreonine. This light response is observed whether the red light irradiation is given to pea plumules or nuclei isolated from the plumules. The red-light-induced response seen in plumules is reversible by a subsequent far-red-light irradiation, indicating that the likely photoreceptor for this response may be phytochrome. By immunoblot analysis pea phytochrome A, but not phytochrome B, can be detected in proteins extracted from pea nuclear chromatin-matrix preparations. Phytochrome A and the protein bands immunostained by anti-phosphotyrosine antibodies can be solubilized from unirradiated pea chromatin by 0.3 M NaCl, but irradiating this preparation with red light does not induce the appearance of phosphotyrosine-like epitopes in any nuclear proteins. These results suggest that the association of phytochrome with purified pea nuclei is such that its conversion to the far-red light-absorbing form can induce a post-translational epitope change in nuclear proteins in vivo.