In previous work no difference was found in leaf water potential or solute potential between young guttating leaves and older non-guttating leaves of the same plant. This suggested that the absence of guttation in older leaves was associated with a plant resistance component in the hydathodes. Hydathodes of young, folded leaves contained water pores with various apertures and no signs of occlusion.. In expanded, young leaves, production of epicuticular waxes and excretion of some substance through the pores was observed in the hydathode region. By the time leaves had fully expanded the hydathodes had become brownish. The combination of wax deposition and excreted substance had formed plates of solid material covering water pores. These observations suggest that deposition of substances on top of pores contribute to occlusion of water pores in old leaves.
Sap flow rates of three Cercis spp. exposed to supraoptimal root-zone temperatures were characterized in a controlled environment chamber using a water bath to control temperatures. Flow rates of sap in the xylem were measured every 15 sec. and averaged over 15 min. intervals. Sap flow measurements were correlated to root-zone temperatures recorded during the same time intervals. Whole plant transpiration was measured gravimetrically. Root-zone temperatures were maintained at 22C for three consecutive 24-hr cycles and then increased to 45C for an additional three 24-hr periods. All plants, regardless of species, had reduced sap flow patterns when exposed to high root-zone temperatures. Plants maintained at a constant temperature of 22C showed no extreme fluctuations in sap flow rate. Stomatal conductance rates and leaf water potentials showed similar trends to whole plant transpiration.
Uniform rooted cuttings of pyracantha (Pyracantha coccinea M.J. Roem. 'Lalandei') were potted into 3.8 liter containers in a pine bark:sand medium. Plants were treated with a medium drench at 0.5 mg ai per container, or a foliar spray at 150 mg ai per liter, or no uniconazole. Plants also were exposed to one of three irrigation regimes: nonstressed, stressed or acclimated. Uniconazole had little effect on leaf water potential, osmotic potential, transpiration or leaf conductance. The uniconazole drench treatments reduced plant growth and increased N, Ca, and Mn concentrations in the leaves. Foliar applications had less effect on plant growth and elemental content Acclimated and stressed plants had lower water and osmotic potentials, transpiration rates and leaf conductance than nonstressed plants on the final day of the stress cycle. Acclimated plants had higher levels of N and Mn with lower levels of Zn in the leaves than either stressed of nonstressed plants.
An experiment was conducted to determine the rate and frequency of irrigation needed for optimum yield in sweetpotato (Ipomoea batatas (L.)Lam). A line source irrigation system was used to provide continuously increasing amounts of water at each irrigation. The physiological responses of sweetpotato to water application were measured. There was an increase in leaf water potential with increasing rates of irrigation. Leaf diffusive resistance decreased as total water rate increased to 76% of pan evaporation (Epan) and then increased with higher rates of irrigation. Marketable yields increased as total water rate increased to 76% of Epan and then decreased rapidly with higher irrigation rates. Water relations measurements indicated that reduction in yield with higher amounts of water application was due to low soil oxygen content.
Typically, dormant seedlings are transplanted when revegetating disturbed lands to prevent transplant shock triggered by water stress. It may be possible to transplant nondormant seedlings by inducing drought-tolerant acclimation responses such as solute accumulation. Artemisia cana and Agropyron intermedium seedlings were subjected to three different water stress preconditioning treatments. After conditioning, seedlings were dried down in their containers until leaf senescence, or were transplanted to disturbed land sites. Leaf water potential components and relative water content were measured. Following treatments, water relations parameters of preconditioned seedlings were not markedly different from controls in either species. At the end of the final dry-down, water stress preconditioning had not induced active or passive solute accumulation, prolonged leaf survival during lethal drought conditions, or differences in transplant survival under the experimental conditions of this study.
`Delicious' apple (Malus domestica Borkh.) trees received regulated deficit irrigation (RDI) early in the growing season to determine if fruit quality and storage life would he altered compared to well-watered trees. Soil moisture and leaf water potential were lower in RDI trees than in those that did not receive RDI most of the season. Internal ethylene concentration increased logarithmically earlier in RDI apples. At harvest, RDI fruit were smaller and had a higher soluble solids concentration (SSC) and lower titratable acidity. Starch degradation was delayed in RDI fruit, and their color was not affected. Firmness was not affected when the effect of size on firmness was removed. The SSC of RDI apples remained higher during storage, but starch content, titratable acidity, firmness, and color were similar.
We determined the effect of moderate water stress on the growth of american ginseng (Panax quinquefolium), and on concentrations of six major ginsenosides (Rg1, Re, Rb1, Rc, Rb2, and Rd). Two-year-old “rootlets” (dormant rhizome and storage root) were cultivated in pots, in a cool greenhouse (18.3 ± 2 °C). Pots were watered either every 5 days (control) or every 10 days (stress), repeatedly for 8 days. Soil volumetric water content was measured during the last 10 days of the experiment for both treatments. Leaf water potential, measured on the last day of the experiment, was -0.43 MPa for the control and -0.83 MPa for the stress treatment. Drought stress did not affect above-ground shoot or root dry weight. Initial rootlet fresh weight (covariate) had a significant effect on the concentration of ginsenosides Re, Rb1, Rc, and Rb2. Drought stress increased the concentration of ginsenosides Re, Rb1, and total ginsenoside concentration.
Fruiting spurs (`Red Prince Delicious') (RD) and shoots (`Sundale Spur Golden Delicious') (CD) with three leaf:fruit ratios and comparable nonfruiting spurs and shoots were girdled on 7 September 1988. An interaction between fruiting status and time existed for most parameters measured on both cultivars while there was no effect of leaf:fruit ratio. At 1 day after treatment (DAT) few differences existed due to fruiting status on either cultivar. At 8 DAT with RD and at 4 and 8 DAT with GD, Pn, transpiration (Tr), leaf water potential (ψ L), and nonreducing sugars were greater on fruiting than nonfruiting spurs and shoots while leaf resistance (RL), SLW, and starch were lower on fruiting spurs. In nonfruiting spurs and shoots Pn, Tr, and ψL tended to decrease while RL and SLW increased with time whereas m fruiting spurs and shoots most parameters remained constant. Total nonstructural carbohydrates, reducing sugars, and starch were greater in nonfruiting than fruiting spurs and shoots.
Abstract
Mature potted rose bushes and cut rose blooms (Rosa hybrida ‘Samantha’) were used to assess the reliability of in situ stem psychrometers for measuring the water potential of these plant systems. Concurrent measurements of adjacent leaf water potential using a pressure bomb were correlated with the psychrometer measurements. The plants were subjected to a series of drought and rehydration cycles in order to exhibit a wide range of water potential (— 0.1 to —1.8 MPa). The results closely followed a 1:1 correlation. The psychrometer installations on intact rose bush stems produced reliable measurements of stem water potential for up to 6 weeks. The technique described is a nondestructive means to monitor the water status of intact plants or cut flowers continuously in response to management practices, storage and shipping techniques, or methods to enhance keeping quality.
Abstract
Paclobutrozol PP333 = (2R,3R + 2S,3S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl) pentan-3-ol at concentrations of 11.6, 58.0, and 116.0 mg of active ingredient per liter caused significant reductions in water use of sunflowers (Helianthus annuus L.) but there was no significant influence on leaf diffusive resistance. The primary mechanism for reduced water use is by a reduction in leaf expansion. PP333 inhibited internode elongation which causes increased leaf shading. Under nonstress conditions there was no effect on leaf water potential or its components. At the highest concentration, photosynthetic rate was reduced. Fresh and dry weight of shoots was reduced proportional to leaf area. Gibberellic acid reversed the effect of PP333 of shoot height, leaf area, evapotranspiration, and shoot fresh and dry weight.