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 f or two model systems. The first, treatment of suspension-cultured French be an (Phaseolus vulgaris L.) cells with an increase in the cytokinin/auxin ra tio and in the concentration of sucrose, models some aspects of differentia tion. Wall changes are characterised by up to a five-fold increase in thick ness due to the laying down of extra wall material. Sugar flux following la belling of cells with [C-14]-sucrose was examined during the period of maxi mum extractable catalytic activities of the enzymes of sugar nucleotide con version determined previously. Increased secretion was observed in all majo r groups of polysaccharides, particularly the cellulosic fraction. Analysis of the sugars in the hemicellulosic fraction indicated that the newly synt hesised polysaccharide was most probably xylan. It was confirmed by immunol ocalisation of xylan in these walls. This treatment thus increases incorpor ation 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. A gain, sugar flux was determined by labelling cells with [C-14]-sucrose and examined during the period determined previously of maximum extractable cat alytic activities of the enzymes of sugar nucleotide conversion. Increased secretion into unextractable polymers was the major change and was consiste nt with the occurrence of oxidative processes leading to immobilisation of some wall components. Callose, a polysaccharide characteristic of the defen ce response was immunolocalised in these walls but not in those of control cells. (C) Elsevier, Paris.