SIMS DETERMINATION OF THE DISTRIBUTION OF THE MAIN MINERAL CATIONS INTHE DEPTH OF THE CUTICLE AND THE PECTO-CELLULOSIC WALL OF EPIDERMAL-CELLS OF FLAX STEMS - PROBLEMS ENCOUNTERED WITH SIMS DEPTH PROFILING

Depth profiles of C, Na, Mg, Al, K and Ca were performed in the cuticl e and wall of epidermal cells of flax hypocotyls, with current densiti es ranging from 0.2 to 1 pA mu-m-2. The crater bottoms were never flat , but exhibited fairly complex, filiform or alveolar structures. The p rofiles of K, Ca and Mg were reasonably parallel to one another. The C a/Mg signal ratio was in the magnitude of 3.5 in the cuticle. The Na p rofile, except perhaps in the cuticle, did not parallel the K, Ca and Mg profiles, but rather paralleled the C profile. At the outset of the depth profiles, ie in the cuticle, the intensity of the Na signal, al though fairly variable, was usually above that of K; then there was an abrupt decrease of the Na signal, possibly at the border of the cutic le and of the wall. The Al signal usually began to increase, thus reve aling the occurrence of perforations through the epidermis sample, aft er 80 min sputtering at a current density of 1 pA mu-m-2; the mean spu ttering rate was thus estimated to be in the order of 1-mu-m h-1.