Pectin methylesterase pattern in flax seedlings during their development

We have investigated pectin methylesterase (PME) activity in flax seedlings (Linum usitatissimum L.) grown either in the dark or in the light. The activity was maximal in hypocotyls at the end of the growth, especially in the dark (2 to 3 nkatal per organ), and about 5500 nkatal per g of dry cell walls of 3-day-old hypocotyls. When calculated relative to the mass of fresh organ, the activity was the largest in cotyledons of dark-developed plantlets (200 nkatal g(-1)), but strongly decreased during the growth in the light. The largest specific activity (600 nkatal mg(-1)) was measured in roots at the end of the culture. In these organs, the activity was independent of the light conditions. Over the culture duration, we observed (a) an activity increase in the basal part of the hypocotyl (from 0.4 to 1 nkatal, in average) whatever the culture conditions and (b) a new pool of activity in the apical part that was larger in the dark (about 1 nkatal) than in the light (about 0.5 nkatal) conditions. After isofocusing electrophoresis of PME extracts and incubation with pectins, ruthenium red most strongly reacted (a) in the pH range 8-9 (at least 2 isoforms were visualized and named bla and bib) and also (b) in very basic zones (pH 9.5-10 : isoform b2). The b1(b) and b2 forms mainly originated from the epidermis and accounted for 65% of the total activity, while b1(a) seemed more specific for the inner tissues.