| Abstract: | Pearce, R. S. 1985. A frceze-fracture study of membranes ofrapidly drought-stressed leaf bases of wheat.—J. exp.Bol. 36: 1209-1221. Bases of expanding leaves were taken from well-watered or drought-hardenedwheat seedlings, and were progressively dehydrated (over ?–9h or, more slowly, for 24 h or 36 h) to between 76% and 5% ofthe water content of the turgid tissue. Damage was assessedby an ion-leakage test. The dehydrated tissues were freeze-fixedwithout rehydration. Patches free from intramembraneous particles(IMP) occurred in the plasma membrane, tonoplast and chloroplastenvelope of all the damaged leaf bases, and were mostly absentfrom undamaged tissues and controls. 15% of these patches appearedto 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 withIMP-free folds. Groups of IMP-free lamellae occurred in thecytoplasm of the most severely stressed material. Vesicles andmembraneous sacs accumulated just below the plasma membranein 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-damagedtissue. The results are related to an hypothesis previouslysuggested to explain damage due to extracellular freezing inwheat tissues: the stress causes cell dehydration and this inducesIM P-free patches leading to membrane reorganization (here expressedas IMP-free lamellae and folds) which results in leakage. Thepresent results confirm the role of cytoplasmic dehydrationin the formation of IMP-free patches and in other membrane changes. Key words: Drought stress, freezing stress, plasma membrane |
