CHANGES IN LEAF ULTRASTRUCTURE AND CARBOHYDRATES IN ARABIDOPSIS-THALIANA L (HEYN) CV COLUMBIA DURING RAPID COLD-ACCLIMATION

We studied cell ultrastructure and carbohydrate levels in the leaf tissue of Arabidopsis thaliana L. (Heyn) cv. Columbia during rapid cold acclimation. Freezing tolerance of the leaves from 26 day old plants was determined after 48 h and 10 days at 4-degrees-C. Acclimation treatment of 48 h decreased the lethal freezing temperature from - 5.7-degrees-C to - 9.4-degrees-C. Freezing tolerance was not altered further by acclimation at 4-degrees-C for 10 days. Ultrastructural changes in the parenchyma cells were evident after 6 to 24 h of cold acclimation. The plasma membrane showed sips of extensive turnover. Evidence of membrane invaginations and sequestering of membrane material was observed. In addition, numerous microvesicles, paramural bodies, and fragments of endoplasmic reticulum were noticed in the vicinity of plasma membrane. Modifications in the structure of cell membranes were evident after 5 days of exposure to low temperature. Small, darkly stained globules were seen on the plasma membrane, tonoplast, chloroplast envelope membrane, mitochondrion outer membrane, dictyosome cisternae membrane, and microvesicle membrane. As far as we are aware, this type of membrane modification has not been described previously in plant cells exposed to low temperature. We propose to call these structures membraglobuli. Acclimation treatment also increased the concentrations of soluble sugars and starch. These observations suggest that cold acclimation in A. thaliana induces changes in both plasma membrane properties and carbohydrate composition.