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Blueberry reducers in Texas must often irrigate with sodic water. Excess Na+ leads to reduced growth, necrosis, and plant mortality. Ca2+ is known to ameliorate such detrimental effects in many crops, but little is known about the response of rabbiteye blueberry. To elucidate the influence of Ca2+ on the uptake and translocation of Na+, plants were subjected to NaCl in hydroponics solutions (10, 25, 50 and 100 mM NaCl) and the uptake of Na+ was traced over a 24h period using 22Na+ Additionally, for each treatment, half the plants were supplied with 10 mM Ca2+. Plants were then transferred to identical, but unlabeled, solution, then harvested at intervals up to 28 days following cessation of labelling.
Preliminary results indicate that plants subjected to 25 mM Na+ and 0 mM Ca2+ showed less ability to exclude Na+ from the roots, and accumulated more Na+ in roots, stems, an leaves than did plants supplied with 25 mM Na+ and 10 mM Ca2+. Leaf tissue accumulated more Na per gram fresh weight than did any other part of the plant, regardless of Ca2+ treatment.
Results from the remaining treatments, root 22Na+ efflux data, and total tissue Na+ and Ca2+ concentrations will also be reported.
The water potential gradient through the plant and the resistance to the viscous flow of water are two properties that may be affected by salinity stress within a plant. In this study, sunflowers in sand culture were irrigated with various concentrations of NaCl up to 75 mM. The concentration of NaCl was gradually raised to avoid osmotic shock and the Ca2+ concentration was maintained at 4.0 mM. Non-destructive techniques such as stem-flow gauges, psychrometers, porometry and weighing were used to determine changes in the resistance to flow and the pattern of water movement. Estimates of water potential were obtained for the rooting medium, the xylem at the shoot-root junction, and the upper leaves. From measurements of transpiration values, resistance to water flow across the roots, and between roots and leaves could be calculated. At 5 and 6 days of salinization, there were increases in the resistance to water flow across roots at the 75 mM salt level. This was accompanied by an increase in stomatal resistance to water vapor. These results suggest that moderate increases in salt level markedly affect the water relations of sunflower.
Rooted cuttings of Hibiscus rosa sinensis L. cv. Leprechaun were grown in fine sand and irrigated with full strength Hoaglands solution containing 0, 2.5, or 10 mM K+. Half of the plants at each K+ level were subjected to a 21-day slowly developing drought stress cycle (DS) and the other half were non-drought stressed (NDS), which yielded a midday leaf water potential (Ψleaf) at day 21 of -1.5 to -1.6 MPa and -0.5 MPa, respectively. Drought stress reduced leaf area (LA), leaf area ratio (LAR), shoot, root, leaf and total dry weights of 2.5 and 10 mM plants and increased the root:shoot ratio of all K+ treatments. Increasing K+, increased all growth parameters measured in both DS and NDS plants, except for LAR, which was greatest at 0 mM K+. At 0 mM K+, drought stress did not affect LA, LAR, shoot, root and total dry weights. Neither drought nor K+ treatments affected specific leaf area (SLA). In NDS plants, K+ had no effect on percent live root ratio (PLR) as indicated by translocation of 86Rb+ from leaves into living roots, determined by autoradiography. Although drought stress reduced PLR at all K+ levels, PLR was greatest at the higher K+ levels.
We have been examining the response of maize seedling roots to oxygen stress. Previously, we have shown that maize seedlings with primary root lengths of 10cm or greater require a pretreatment with low oxygen (hypoxia) for survival of greater than 12 hours of anoxia. During the pretreatment there is induction of mRNA and increase in enzymatic activity of alcohol dehydrogenase (ADH) and other enzymes that are necessary for alcoholic fermentation. However, we have found that younger seedlings do not need a pretreatment to survive anoxia. They appear to have high levels of ADH and other enzymes that are needed for anaerobic survival at levels equivalent to those that are induced in older seedlings. These results suggest that, at the time of seedling emergence, seedlings may be more adapted to oxygen stress than during later stages of growth.