Seasonal changes in mesophyll ultrastructure of needles of Norway spruce (Picea abies)

Abstract

Seasonal changes in the ultrastructure of the mesophyll of needles of Norway spruce are described. During the growing season, the tannin is in the form of a ribbon along the margin of the vacuole or in the form of small, more or less scattered particles. The cytoplasm is dark and its organelles are along the cell wall; only the chloroplasts with large starch grains and the nucleus can be clearly resolved. During and after Sept., the cytoplasm is very netlike, all of the cytoplasmic organelles clump together, the amount of lipid droplets increases and ribosomes are clearly visible. The tannin is in the form of rather large granules and it increases over its growing-season amount. The shape of chloroplasts changes. Chloroplasts lose their starch and the stroma becomes sparsely granular and rich in ribosomes. This structure is maintained throughout the winter. During spring activation, the cell structure is reorganized and reassumes the condition typical of the growing season. At this time, the needles have some collapsed cells and cells in which some chloroplasts are not quite intact. The injuries were probably caused by weather conditions (a warm period in March followed by a frost).