X‐Ray Microanalytical Studies on Mineral Concentrations in Vacuoles of Needle Tissues from Larix decidua (L.) Mill.

Elemental concentrations in the vacuoles of mesophyll, endodermis and transfusion parenchyma cells were determined by means of electron probe microanalysis on bulk frozen hydrated needles of an outdoor‐grown larch tree. The investigations were done routinely throughout a life cycle of the deciduous larch needle, starting with bud burst in March and ending with leaf abscission in November. It could be shown that the endodermal vacuoles preferentially accumulate S, CI and Ca while the transfusion parenchyma vacuoles transiently store Mg, K and S. Between May and September the inorganic ion level of mesophyll cells is constantly lower than in the endodermal and transfusion parenchyma vacuoles. In autumn, when the degradation of chlorophylls becomes detectable, the elements Mg, S, CI and Ca are found increasingly in the vacuoles of the mesophyll cells. It is concluded that, in mature and intact larch needles, the vacuoles of the endodermis in cooperation with the transfusion parenchyma vacuoles act as efficient ion storage buffers which maintain a constant low ion level in the vacuoles of mesophyll cells.