A Freeze-Fracture Study of Membranes of Rapidly Drought-Stressed Leaf Bases of Wheat

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Abstract
Pearce, R. S. 1985. A frceze-fracture study of membranes of rapidly drought-stressed leaf bases of wheat.—J. exp. Bol. 36: 1209-1221. Bases of expanding leaves were taken from well-watered or drought-hardened wheat seedlings, and were progressively dehydrated (over ½−9 h or, more slowly, for 24 h or 36 h) to between 76% and 5% of the water content of the turgid tissue. Damage was assessed by an ion-leakage test. The dehydrated tissues were freeze-fixed without rehydration. Patches free from intramembraneous particles (IMP) occurred in the plasma membrane, tonoplast and chloroplast envelope of all the damaged leaf bases, and were mostly absent from undamaged tissues and controls. 15% of these patches appeared to have an ordered sub-structure. Lamellae with few or no IMP, were associated with some IMP-free patches of plasma membrane. Sometimes IMP-free patches and lamellae were associated with IMP-free folds. Groups of IMP-free lamellae occurred in the cytoplasm of the most severely stressed material. Vesicles and membraneous sacs accumulated just below the plasma membrane in some cells from stressed drought-hardened leaf bases. Depressions, ‘lesions’ (mainly unusual circular discontinuities), and associated IMP-free patches, occurred in some plasma membranes, mostly in the stressed hardened tissues, including in non-damaged tissue. The results are related to an hypothesis previously suggested to explain damage due to extracellular freezing in wheat tissues: the stress causes cell dehydration and this induces IM P-free patches leading to membrane reorganization (here expressed as IMP-free lamellae and folds) which results in leakage. The present results confirm the role of cytoplasmic dehydration in the formation of IMP-free patches and in other membrane changes.

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