Radial distribution pattern of pectin methylesterases across the cambial region of hybrid aspen at activity and dormancy

Biochemical microanalysis combined with tangential cryosectioning was used to visualize the distribution of pectin methylesterases (PMEs) across the c ambial region in active and dormant hybrid aspen (Populus tremula L. x Popu lus tremuloides Michx). These novel techniques allowed us to relate activit y and isoforms of PMEs to specific tissues and developmental stages of the stem to get more information on the physiological function of PMEs in cambi al growth. Isoelectrofocusing analysis revealed numerous isoforms that were differentially distributed according to the tissue-type and to the cambial stage. A neutral isoform was found to be distributed ubiquitously across t he stem of both active and dormant trees, which suggests that it is a house keeping isoform involved in the maintenance of the cell wall integrity thro ughout the stem. In addition, two distinct isoforms having different isoele ctric points were found to be related to the differentiation of cambial der ivatives, A basic isoform arrears to be a physiological marker of the dorma nt stage involved in the cessation of meristematic radial growth, whereas a n acidic isoform is functionally related to the immediate expansion of the cambial daughter cells that occurs bilaterally on each side of the cambium at the active stage.