PECTIN METHYLESTERASE PATTERN IN FLAX SEEDLINGS DURING THEIR DEVELOPMENT

We have investigated pectin methylesterase (PME) activity in flax seed lings (Linum usitatissimum L.) grown either in the dark or in the ligh t. The activity was maximal in hypocotyls at the end of the growth, es pecially 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 relat ive to the mass of fresh organ, the activity was the largest in cotyle dons of dark-developed plantlets (200 nkatal g(-1)), but strongly decr eased during the growth in the light. The largest specific activity (6 00 nkatal mg(-1)) was measured in roots at the end of the culture. In these organs, the activity was independent of the light conditions. Ov er the culture duration, we observed (a) an activity increase in the b asal 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 p art that was larger in the dark (about 1 nkatal) than in the light (ab out 0.5 nkatal) conditions. After isofocusing electrophoresis of PME e xtracts and incubation with pectins, ruthenium red most strongly react ed (a) in the pH range 8-9 (at least 2 isoforms were visualized and na med 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 speci fic for the inner tissues.