Salt-excreting function of vesiculated hairs of Atriplex nummularia.

Abstract

The morphological structure of the surface of leaves and stems of Atriplex nummularia, grown in a culture solution with or without 2% sodium chloride, was observed under optical as well as cryo-scanning electron microscopy. Both upper and lower surfaces of leaves were covered with 2-3 layers of densely grown vesiculated hairs (Figs. 1, 2, 3). The vesiculated hairs consisted of bladder cells (100 to 200μm in diameter) and stalk cells connected with the epidermis (Fig. 9). The bladder cells were covered with waxy bloom (Fig. 4). The stem surface was also covered with vesiculated hairs (Figs. 8, 10). The vesiculated hairs and the lamina were separated, and sodium and potassium contents of each fraction were analysed. When sodium chloride was added to the culture solution, the sodium content markedly increased in the vesiculated hairs unlike in the lamina (Table 1 ). Ion contents of the bladder cell and of various cells of the lamina were determined by using x-ray micro-probe under scanning electron microscope. The peaks corresponding to sodium and chlorine were observed on the surface, in the cytoplasm, and in the vacuole of the bladder cell. On the other hand, the small peaks correspondinng to potassium and chlorine were observed in the epidermal cell, mesophyll cell and bundle sheath cell (Figs. 11, 12). Crystals of sodium chloride could be seen in the internal part of collapsed bladder cells (Figs. 5, 6, 7, 11). Based on these observations it is suggested that A. nummularia, which was grown in a culture solution with 2% of sodium chloride, can remove the chloride from the lamina of plants which absorbed the ions through roots and conducting tissue, by the repetition of the following cycle ; (1) transport of sodium and chlorine from the lamina to the bladder cells and accumulation of sodium and chlorine in these cells, (2) collapse of the bladder cells containing crystals of sodium chloride and (3) liberation of the crystals from the collapsed bladder cells. It is postulated that sodium chloride can be excreted from the surface of the stem by the same mechanism since similar vesiculated hairs were observed on the surface of the stem.