Stimulation of cell wall biosynthesis and structural changes in response to cytokinin- and elicitor-treatments of suspension-cultured Phaseolus vulgaris cells

Qualitative sugar flux into cell wall polysaccharides has been determined for two model systems. The first, treatment of suspension-cultured French bean (Phaseolus vulgaris L.) cells with an increase in the cytokinin/auxin ratio and in the concentration of sucrose, models some aspects of differentiation. Wall changes are characterised by up to a five-fold increase in thickness due to the laying down of extra wall material. Sugar flux following labelling of cells with [14C]-sucrose was examined during the period of maximum extractable catalytic activities of the enzymes of sugar nucleotide conversion determined previously. Increased secretion was observed in all major groups of polysaccharides, particularly the cellulosic fraction. Analysis of the sugars in the hemicellulosic fraction indicated that the newly synthesised polysaccharide was most probably xylan. It was confirmed by immunolocalisation of xylan in these walls. This treatment thus increases incorporation into the wall of components characteristic of secondary wall. In the second system, which models the defence response, suspension cultures were treated with an elicitor from the walls of Colletotrichum lindemuthianum. Again, sugar flux was determined by labelling cells with [14C]-sucrose and examined during the period determined previously of maximum extractable catalytic activities of the enzymes of sugar nucleotide conversion. Increased secretion into unextractable polymers was the major change and was consistent with the occurrence of oxidative processes leading to immobilisation of some wall components. Callose, a polysaccharide characteristic of the defence response was immunolocalised in these walls but not in those of control cells.