UVB/UVA radiation activates a 48 kDa myelin basic protein kinase and potentiates wound signaling in tomato leaves

We investigated the effect of UV radiation on early signaling events in the response of young tomato plants (Lycopersicorn esculentum) to wounding. Ul traviolet-C (<280 nm) and UVB/UVA (280-390 nm) radiation both induced 48 kD a myelin basic protein kinase activity in leaves. The activation was associ ated with phosphorylation of tyrosine residues on the kinase, which is indi cative of protein kinases of the mitogen-activated protein kinase family. U ltraviolet-C irradiation resulted in a strong proteinase inhibitor synthesi s, as reported previously (Conconi et al., Nature 383, 826-829, 1996), Unde r the conditions used, UVB/UVA radiation did not induce proteinase inhibito r synthesis but resulted in a strong potentiation of systemic proteinase in hibitor synthesis in response to wounding. The UVB/UVA-irradiated plants th at were subsequently wounded accumulated 2.5-4-fold higher levels of protei nase inhibitor I when compared to wounded non-irradiated plants. The potent iating effect was most prominent in the systemic unwounded leaf of a wounde d plant. Levels of 12-oxo-phytodienoic acid and jasmonic acid that have bee n well documented to increase in response to wounding were not detected in response to UVB/UVA irradiation alone. The effect of UVB/UVA radiation in p otentiating plant defense signaling should be further considered as a facto r that may influence the ecological balance between plants and their predat ors.