PECTIN IMMUNOLOCALIZATION AND CALCIUM VISUALIZATION IN DIFFERENTIATING DERIVATIVES FROM POPLAR CAMBIUM

Calcium distribution and pectin esterification patterns in the cambial zone of poplar branches were studied with ionic microscopy and immuno logical tools respectively. Dynamic changes cor relating with cell gro wth and cell differentiation were observed both on the xylem and on th e phloem sides. In expanding cell walls of xylem derivatives, unesteri fied pectins were restricted to cell junctions and middle lamellae, oc casionally accompanied by calcium ions. In contrast, in differentiatin g and mature phloem cells, acidic pectins and Ca2+ were present all ov er the walls leading to early stiffening of the polysaccharide network . Significant labelling was detected with JIM5 antibodies in some dict yosomes suggesting exocytosis of low methylated polymers towards the c ell walls. At cell junctions, unesterified pectins might originate fro m the activity of pectinmethylesterases localized in these areas. Thus un-and deesterified pectins might be located in different cell wall d omains whose distribution, varying with cell type, will confer specifi c extensibility to the wall matrix.