Inhibitors of proteinases in safflower (Carthamus L.) and other Compositae

Al.V.Konarev, I.N.Anisimova, T.E.Vachrusheva, G.Yu. Konechnaya, P.R.Shewry

 Abstract

Various proteinaceous inhibitors (I) of trypsin (T) and chymotrypsin (C), which are typical digestive enzymes of insects, mammals and microorganisms, and subtilisin (S), a proteinase of Sclerotinia sclerotiorum and many other phytopathogenic fungi, were found in seeds and vegetative organs of species representing the main taxa of the Compositae using simple and effective methods. Inhibitors with relative molecular mass (M_r) ranging from 7450 to 7800 and combining activity towards two or three proteinases (T/C/SI) appeared to be the most common inhibitor type in the Compositae and are presumably involved in plant defense mechanisms. They were found in the majority of representatives of the subfamilies Carduoideae (genera Carthamus, Centaurea, Cirsium), Cichorioideae (Lactuca, Taraxacum) and Asteroideae (Helianthus, Cosmos). Trypsin inhibitors with M_r ranging from 1500 to 14750 were found mainly in the Asteroideae. Seeds of Carthamus tinctorius var. Goldtuft contained single T/C/SI components with isoelectric point  (pI) about 7.0 and M_r 7555. All 25 studied cultivated accessions of C. tinctorius and representatives of species groups with 2n=24 (C. oxyacanthus and C. palaestinus), 2n=20 (C. glaucus) and 2n=44 (C. lanatus) contained the same inhibitor components. The N-terminal sequence of the peptide obtained by cleavage of the reactive site of the native inhibitor with subtilisin, DFR(C)DRVWVW, indicated that safflower T/C/SI belonged to the potato I inhibitor family. Species related to Carthamus in the genus Centaurea possessed T/C/SI with M_r near 7600 but differed in pI. Some other Carduoideae (Cynara, Arctium, Cousinia and Saussurea species) did not contain serine proteinase inhibitors in their seeds.

Key words: inhibitor, proteinase, subtilisin, safflower, pathogen, Compositae