Changes In Tissue Hydration Research Articles

Thermonastic leaf movements: a synthesis of research with Rhododendron

Thermonastic leaf movements in Rhododendron L. occur in response to freezing temperatures. These movements are composed of leaf curling and leaf angle changes that are distinct leaf movements with different responses to climatic factors. Leaf angle is controlled by the hydration of the petiole, as affected by soil water content, atmospheric vapour pressure, and air temperature. In contrast, leaf curling is a specific response to leaf temperature, and bulk leaf hydration has little effect. The physiological cause of leaf curling is not well understood, but the mechanism must lie in the physiology of the cell wall and/or regional changes in tissue hydration. Available evidence suggests that intercellular freezing is not a cause of leaf curling. Manipulation experiments demonstrate that changes in leaf orientation in Rhododendron most likely serve to protect the leaves from membrane damage due to high irradiance and cold temperatures. In particular, the pendent leaves protect the chloroplast from photoinhibition. Leaf curling may serve to slow the rate of thaw following freezing, a common phenomenon in the Appalachian mountains of the U.S. The thermonastic leaf movements have a greater importance to plants in a dim environment because the potential impact to canopy carbon gain is greater than in high light environments. These leaf movements have several implications for horticultural management. There seems to be a trade-off between water stress tolerance and freezing stress tolerance by leaf movements. Thermonastic leaf movements may be a major mechanism of cold stress tolerance in Rhododendron species. The actual physiological cause of leaf movement has not been elucidated and many more species need to be evaluated to verify the general importance of leaf movements to Rhododendron ecology and evolution.

Hypoosmotic volume regulation in the sea anemone metridium senile

1. The anemone Metridium senile survives salinities from seawater (950 mOsm) to 55% SW (520 mOsm) for at least two weeks. Animals exposed to 40% SW (380 mOsm) die within three days. 2. The tissue amino acid content of M. senile acclimated to 950 mOsm, 807 mOsm, 665 mOsm and 520 mOsm for two weeks is respectively, 444, 382, 331 and 251 μmol/g dry wt. A decrease in the concentration of taurine accounts for nearly all of the decrease in the free amino acid pool. 3. Tissue hydration increases in M. senile acclimated to dilute seawater, but the increase was not proportional to the change in ambient salinity, indicating that the anemones partially regulate volume in dilute media. 4. Mathematical analyses of changes in tissue hydration as a function of ambient salinity in M. senile , Haliplanella lineata , and Diadumene leucolena suggest that the effectiveness of volume regulation increases in individuals of these species acclimated to progressively more dilute media. The volume regulatory capability of Bunodosoma cavernata does not change in dilute media.

Responses of the euryhaline sea anemone bunodosoma cavernata (bosc) (anthozoa, actinaria, actiniidae) to osmotic stress

1. 1. The sea anemone Bunodosoma cavernata tolerated exposure for two weeks to salinities ranging from 11 to 49‰ at 25°C. 2. 2. Acute exposure to hypo- and hyper-osmotic stress resulted in rapid equilibration of the coelenteron fluid with the external medium, indicating that this species is an osmoconformer. 3. 3. Acclimation produced compensatory changes in tissue hydration in B. cavernata. 4. 4. This cell volume regulation was mediated by compensatory changes in ninhydrin positive substances (NPS), as there was a direct relationship between NPS and acclimation salinity.

Water Relations, Stomatal Behavior, and Root Conductivity of Red Osier Dogwood during Acclimation to Freezing Temperatures

Red osier dogwood (Cornus stolonifera Michx.) was artificially acclimated by exposing plants to 8-hour short days (SD) and low (15/5 C) temperatures for 54 to 63 days. Several factors including transpiration rate, stomatal resistance, and root conductivity were correlated so that the rate of water loss in acclimating plants was higher during the first 30 to 40 days of the acclimation sequence. Six days after transferring plants to SD conditions, the stomatal resistance (r(8)) decreased significantly below the r(8) of the 16-hour long day (LD) control plants at the same temperature. Transpiration rate increased by approximately 20 to 30% in the plants transferred to SD. After the initially higher transpiration rate and greater stomatal opening, the stomates closed tightly during the last 2 weeks of acclimation and the transpiration rate of the SD plants dropped to well below the LD control plants. By the end of the acclimation sequence, root conductivity to water uptake was two to three times lower in the SD plants. Leaf xylem water potentials were similar or slightly lower in the plants kept under SD conditions during the first 5 to 7 weeks of the acclimation sequence. During the last 10 to 15 days of acclimation when the stomates closed, SD leaf water potential rose significantly above the plants in the LD conditions. During acclimation, stem water content decreased by 40 to 50%. Changes in tissue hydration can be indirectly related to plant hardiness and may be affected by alteration of stomatal resistance, transpiration rate, and root conductivity during acclimation.

An analysis of water‐content regulation in osmoconforming limpets (Mollusca: Patellacea)

AbstractThe capacity to regulate body volume is important in the ability of soft‐bodied osmoconforming marine animals to withstand osmotic stress. In the present study two intertidal limpets, Collisella digitalis and Notoacmea scutum, which differ in their tolerance of osmotic stress, are compared in their ability to regulate water content. Two direct measurements and two mathematical approaches developed by Oglesby ('75) and Machin ('75), respectively, have been used. Both species are osmoconformers over the range 500–1,500 mOs/1 but showed a slight tendency to hyporegulate Cl− and Na+ in the hemolymph. In weight and tissue hydration changes following a change in osmotic pressure of the medium, C. digitalis did not vary as widely as did N. scutum and so appears to have better control of body volume. This correlates well with the previous finding that C. digitalis tolerates a wider range of salinity than does N. scutum.

Water balance of a euryhaline sea anemone, Diadumene leucolena

1. 1. Diadumene leucolena is an osmoconformer in salinities ranging from 6 to 33‰. 2. 2.Over the entire non-lethal salinity range, tissue hydration varied by only 3.5 per cent. 3. 3.Intracellular concentrations of taurine, glutamic acid, glycine and alanine increased by an amount far in excess of that predicted by tissue hydration changes. 4. 4.Volume regulation in D. leucolena is accomplished by the regulation of an intracellular, osmotically active solute: the free amino acid pool.