Induced Water Deficit Research Articles

The Water Relations of Heath Plants from Open and Shaded Habitats

Previous work with heath plants (Bannister 1964a, b, c, d) indicates that there is a good correlation between the distribution of species with regard to soil moisture and the water relations of the species concerned. A consideration of the water loss from cut shoots (Bannister 1964a; cf. Hygen 1953) shows that the water deficitt at the point of stomatal closure varies both between and within species. Plants of Calluna vulgarism from sites with different soil moisture status show different water deficits at the point of stomatal closure, those from the driest regimes showing the largest deficits at closure. This may be interpreted as an ability to maintain open stomata over a wide range of internal water tensions. Thus during a period of drought, other processes dependent on stomatal aperture (such as the gaseous exchanges of photosynthesis) would be less inhibited than in plants from wetter habitats (cf. Maximov 1929). The ability of plant parts to recover from induced water deficits (Rychnovska-Soudkova 1963; Bannister 1970) and the relationship between water deficit and water potential (Slatyer 1958, 1962) have also been found useful in characterizing plants of different ecological amplitudes. In the strongly oceanic climate of the west of Scotland, the marked local variation in soil moisture conditions is less common than in the east. However, the Glasgow region (particularly in the neighbourhood of Loch Lomond) supports many small areas of woodland with heath plants growing both under the shade of trees and away from its influence. Consequently, as in general plants from shaded environments tend to show morphological characteristics not dissimilar to those from moister soil, and those from open (sunny) habitats are comparatively xeromorphic (cf. Daubenmire 1959), it was considered that an investigation of the water relations of these plants might provide a useful comparison with previous work.

The Effects of Water Deficits on Slices of Beetroot and Potato Tissue:3

The effects of osmotically induced water deficits on the metabolism of aged beetroot and potato discs were investigated. In this paper the tissue-water relationships in two osmotica, mannitol, and Carbowax 1540, are described. Tissues in equilibrium with Carbowax solutions had lower fresh weights than those in isotonic mannitol solutions, particularly at water potentials below −0.7 J g−1 with potato and −2.0J g− with beetroot. Potato discs killed by freezing and thawing lost water to Carbowax but not to mannitol solutions. The extra effectiveness of Carbowax solutions in lowering fresh weight was attributed to an osmotic effect across the cell wall. Carbowax was found to penetrate plasmolysed potato tissue, however, at a rate of about 3.0 mg (g fresh weight)−1 h−. The extent to which water uptake occured on retransfer to water was unaffected by the nature of the soulte used, but depend on the degree of dehydration. The following phases were clearly defined: (1) recovery to the fresh weight at full turgor, when the water potential of potato tissue was not reduced below −0.5 J g− and of beetroot below −1.2 J g−1; (2) a declining degree of recovery with decreasing water potential over the ranges −0.5 to −1.0 J g−1 and −1.2 to −3.0 J g−1 for potato and beetroot, respectively, and (3)in potato, the absence of recovery of fresh weight following reduction of the water potential below −1.0 J g−1.

Potability of sea water with special reference to the cat.

Under certain conditions in which food provides an adequate caloric intake but too little water to sustain a cat or a rat in euhydration, these animals can be shown to depend for survival on their intake of sea water. They will generally drink enough sea water ad libitum to thrive, even overcoming thereby a previously induced water deficit; or, they will readily eat their food, mixed with sea water in amounts which can vary widely, with similar benefit. Without sea water they undergo progressive hydropenia and die. Along with experimental verification of the potability of sea water a theory of sea water drinking (mariposia) is presented, based upon the concept of urinary osmotic space.