EFFECTS OF NITROGEN NUTRITION ON STORAGE PROTEIN POLYPEPTIDES OF YELLOW LUPIN COTYLEDONS CULTURED IN-VITRO

Cotyledons of yellow lupin (Lupinus luteus I,.) isolated from seeds at the mid-maturation stage of development were cultured for 4 days in v itro in,the presence of various nitrogen sources: sodium nitrate and a sparagine both supplied either alone at 35 mM or supplemented with 7 m M methionine. Total globulins extracted from in vivo labelled cotyledo ns of either variant as well as polypeptides immunologically related t o conglutins alpha, beta and gamma were analysed by SDS polyacrylamide gel electrophoresis (SDS-PAGE) followed by fluorography. SDS-PAGE of the in vivo labelled globulins, extracted from in vitro cultured cotyl edons in the presence of asparagine, showed increased synthesis and ac cumulation of high molecular weight polypeptides. They were greatly de pressed when sodium nitrate was the only source of nitrogen. In cotyle dons grown on nitrate supplemented with methionine the labelling of po lypeptides was enhanced, although their accumulation was still at low level. Analysis of polypeptides immunologicaly related to lupin globul ins revealed that the precursor polypeptides of both conglutin alpha a nd conglutin beta were preferentially synthesised and accumulated in c otyledons cultured on media with asparagine either alone or supplement ed with methionine. On medium with sodium nitrate the labelling of 56 and 69 kDa polypeptides was strongly inhibited and addition of methion ine improved the synthesis of both components. Moreover, only at this combination a polypeptide of 63 kDa was observed on stained gel. In co ntrast to other seed globulins, the synthesis of polypeptides related to conglutin gamma remained at the same level in all experimental vari ants. These results seem to indicate that the kind of nitrogen supply influences both the synthesis and accumulation of main storage globuli ns and changes the ratio of synthesised polipeptides in cultured cotyl edons of developing lupin seeds. The possibility of improving the nutr itional quality of storage proteins in lupin seeds by increasing the l evel of conglutin a is discussed.