CELL-WALL POLYSACCHARIDE BIOSYNTHESIS AND RELATED METABOLISM IN ELICITOR-STRESSED CELLS OF FRENCH BEAN (PHASEOLUS-VULGARIS L)

Enzyme activities involved in quantitative and qualitative flux of sug ars into cell wall polysaccharides were determined following elicitor treatment of suspension cultured cells of French bean (Phaseolus vulga ris L.). Two subsets of activities were examined: the first were invol ved in synthesis and metabolism of UDP-glucose and the provision of th e pool of UDP-sugars, and the second a selection of membrane-bound gly cosyltransferases involved in the synthesis of pectins, hemicelluloses and glucans of the primary cell wall. Of the first group, only UDP-gl ucose dehydrogenase (EC 1.1.1.22) showed any significant induction in response to elicitor treatment, sucrose synthase (EC 2.4.1.13), UDP-gl ucuronate decarboxylase (EC 4.1.1.35), UDP-glucose and UDP-xylose 4-ep imerases (EC 5.1.3.2 and EC 5.1.3.5 respectively) did not change in ac tivity significantly over the time course. In contrast, enzymes of the second group showed a more complex response. Callose synthase (glucan synthase II, EC 2.4.1.12) increased in activity, as has been shown in other systems, while arabinan synthase (EC 2.4.1.-), xylan synthase ( EC 2.4.1.72), xyloglucan synthase (EC 2.4.1.72) and glucan synthase I (EC 2.4.1.12) activities were rapidly depleted from membranes within 3 h following elicitor action. This rapid turnover of activity was stri king, indicating that the half-life of such enzymes can be short and t hat elicitor action causes substantial perturbation of some membrane a ctivities. Glucan synthase I activity appears to increase in the later stages over the time period measured, indicating some recovery of thi s metabolism.