IN TRANSFORMED TOBACCO CELLS THE APOPLASMIC INVERTASE INHIBITOR OPERATES AS A REGULATORY SWITCH OF CELL-WALL INVERTASE

Agrobacterium tumefaciens-transformed pension-cultured cells (TSCC) ex hibit no significant quantitative changes of cell wall invertase prote in (CWI) during a culture period of 40 days, whereas CWI activity decr eases strongly between 10 and 30 days after cell transfer to fresh med ium. Western blot analysis revealed that the apoplasmic invertase inhi bitor (INH) is equally expressed throughout the entire culture period. When apoplasmic protein fractions from 4 and 28 days old cell culture s are chromatographed on Concanavalin A(ConA)-Sepharose, the non-glyco sylated INH always coelutes with the ConA-bound fraction, suggesting t hat (i) INH and the glycosylated CWI form a complex in the apoplasmic space, and (ii) INH binding is not sufficient for CWI inhibition. The high specificity of INH binding to CWI was confirmed by native cathodi c polyacrylamide gel electrophoresis. Expression analysis of CWI and I NH indicates that, at least during certain stages of plant development (seedlings, roots of adult plants), CWI activity may be modulated by INH, the latter operating as a regulatory switch.