Leaf Water Stress Research Articles

Effects of temperature and leaf water stress on growth and flowering of litchi(Litchi chinensisSonn.)

SummaryHigh day temperatures in the shoot (constant 20°C or 30°C day/10°C night or 30°C day/25°C night compared with 15°C day/10°C night) and high root temperatures (constant 27.5°C compared with constant 12.5°C or 15°C day/10°C night) promoted vegetative growth and reduced or eliminated flowering in ‘Tai So’ litchi. Higher temperatures also promoted the production of leafy rather than leafless panicles. Leaf water potential in most treatments during the day ranged from –0.3 to –1.5 MPa with warm days, cool nights and cool roots generally increasing tree water stress. A combination of warm shoots (30°C day/25°C night) and cool roots (constant 12.5°C) induced lower leaf water potentials (–1.0 to –2.0 MPa) and totally suppressed growth. Terminal buds grew out as vegetative shoots within two weeks when leaf water potential was increased (–0.3 to –1.5 MPa) by increasing the root temperature to 25–30°C. Starch levels were generally low (<5.0%) in mature leaves and roots, except for flowering plants at 15°C day/10°C night sampled at panicle emergence (6.2–9.8%). Starch levels were high in twigs, branches and trunks in non-flushing trees, especially in flowering trees at 15°C day/10°C night sampled at panicle emergence (10.6–12.6%), flowering trees at 20°C day and night and 12.5°C root harvested at anthesis (11.8–12.5%), and vegetatively dormant trees at 30°C day/25°C night and 12.5°C root (10.0–13.7%). The concentration of some nutrients in the shoots was increased by cool shoot temperatures and warm root temperatures. The levels of all nutrients, however, fell within the same range, in the standard nutrient table for litchi. A moderate or severe cyclical leaf water stress (irrigation when pre-dawn leaf water potential fell to –1.0 or –2.0 MPa compared to –0.6 MPa) and a constant moderate leaf water stress (–1.0 MPa) reduced vegetative growth in litchi (cv. Kwai May Pink) grown at 30°C day/25°C night. Flushing was completely prevented when plants were held at a severe constant leaf water stress (–2.0 MPa). Terminal buds grew out as leafy shoots when water stress (10°C root temperature and pre-dawn leaf water potential below – 1.5 MPa) was relieved after seven weeks and the plants maintained at 30°C day/25°C night, but were floral when transferred to 15°C day/10°C night. This experiment suggests that day shoot temperatures and root temperatures interact to control the level of flowering in litchi. Water stress appears to act by synchronizing vegetative dormancy in the branches before exposure to low temperatures. Flowering was very weak when day shoot temperatures and root temperatures exceeded 20°C. Poor flowering at high temperatures was associated with low starch reserves, especially in the twigs, branches and trunk.

Limitations of Gas Exchanges in Intact Leaves during Ontogeny of Field-grown Chickpeas

The ontogenic changes in several component processes of photosynthesis were measured in chickpeas. Gas exchange characteristics of intact leaves were studied to analyse the effects of ambient conditions under which chickpeas are usually grown. The C02 assimilation rate per unit leaf area remained fairly high during the vegetative stage, reaching a peak at early pod-fill and declining subsequently throughout pod development. The intercellular C02 partial pressure (Ci) remained more or less constant (~ 195 /?bar) during vegetative growth and the early stages of seed-filling. With falling RWC and PAR interception, the stomatal conductance declined more rapidly than the C02 assimilation rate resulting in a value of C, less than that normally existing under ambient conditions. From the ^/?i-analysis, C02 assimilation during pod-filling appears to be limited by the RuBP-regeneration capacity because the carboxylation efficiency and in vitro RuBPCase activity were initially unaffected. However, as leaves aged, the carboxylation efficiency and in vitro RuBPCase activity decreased abruptly with increasing leaf temperatures above 30 °C, and the Ci was greater than normally existing values (~ 195 /?bar), suggesting an increased mesophyll limitation of photosynthesis. It is suggested that a decline in the C02 assimilation rate of leaves during pod development and an accelerated senescence are induced by adverse ambient conditions, particularly plant water stress and high leaf temperature.

Leaf number, water stress and carbon nutrition effects on poplar leaf growth

Leaf number, water stress and carbon nutrition effects on poplar leaf growth

Water Relations of Grapefruit Trees in Response to Drip, Microsprinkler, and Overhead Sprinkler Irrigation

Abstract Water relations responses of 21-year-old grapefruit trees (Citrus paradisi Macf.) irrigated by three types of irrigation systems were compared. Drip, undertree microsprinkler, and overhead sprinkler with application levels of 150 and 450 mm of water per year were compared. Leaf water potential, stomatal conductance, and soil water status were measured under field conditions on a deep, well-drained sandy soil in central Florida. In the early part of a dry spring period, there were no differences in midday or early morning leaf water potential, but, by the end of this period, significant differences in leaf water potential were found among all three irrigation treatments. Highest leaf water potential and stomatal conductance values were maintained in the overhead sprinkler blocks. No midday stomatal closure was observed under the conditions of this study. Relationships among diurnal leaf water potentials, vapor pressure deficits, and stomatal conductance showed hysteresis; this affected the correlations among these factors. Greater water stress occurred in trees irrigated with drip than in trees irrigated with overhead sprinkler systems, but responses to microsprinklers were generally intermediate between the overhead sprinkler and the drip treatments. In an area with high rainfall and sandy soils, increased irrigation coverage can reduce leaf water stress.

Water-stress-induced changes in the abscisic acid content of guard cells and other cells of Vicia faba L. leaves as determined by enzyme-amplified immunoassay

A highly sensitive, solid-phase, enzyme-amplified immunoassay for the plant growth regulator (+)-abscisic acid (ABA) was developed. The assay sensitivity (0.2-10 fmol) was sufficient for analyzing free ABA in homogeneous tissue samples dissected from Vicia faba L. leaves. Eight hours after detached leaves had been desiccated to 10% loss of fresh weight, the bulk leaf ABA content increased from </=0.2 to 6.2 ng.(mg dry weight)(-1). Epidermal tissue, spongy parenchyma cells, and palisade parenchyma cells from this water-stressed leaf had the following ABA contents, respectively: 4.8, 9.4, and 9.0 ng.(mg dry weight)(-1). Guard cells, which respond to exogenous ABA by losing solutes and volume, were also assayed. When they were dissected from control (fully hydrated) leaves, their ABA content was approximately 0.7 fg.(cell pair)(-1) [[unk]0.2 ng.(mg dry weight)(-1)]. In contrast, the ABA content of guard cells of water-stressed leaves was approximately 17.7 fg.(cell pair)(-1). These results indicate that ABA accumulation in a highly stressed V. faba leaflet is generalized; guard cells contain only 0.15% of bulk leaf ABA. The time course for loss of ABA from guard cells of a floating epidermal peel was studied. There was little loss within 30 min, but after 4 hr, the ABA content was only 17% of the original value. These results indicate that the bulk of guard cell ABA is not readily diffusible (i.e., probably not apoplastic). The results also indicate that common laboratory procedures results in lowered guard cell ABA content.

Effects of temperature, tree water status and relative humidity on premature nut drop from macadamia

In macadamia ( Macadamia integrifolia, Maiden and Betche), premature nut drop increased at high temperature (30 compared with 15 and 25°C). Low relative humidity (RH 40 vs. 80%) had only a slight effect at 30°C. In contrast, leaf water stress ( ψ L of −1.5 to −3.0 MPa vs. −0.5 MPa) induced more nut drop at lower temperature and high RH. Only slight cultivar differences were noted. More nuts were retained under conditions of atmospheric stress where water was non-limiting. It may therefore be possible to alleviate the effects of these stresses by strategic irrigation or overhead misting.

Stomatal Control of Photosynthesis ofEucalyptus globulusLabill. Trees under Field Conditions in Portugal

Pereira, J. S., Tenhunen, J. D. and Lange, O. L. 1987. Stomatal control of photosynthesis of Eucalyptus globulus Labill. trees under field conditions in Portugal.—J. exp. Bot. 38: 1678-1688. Stomatal behaviour of adult leaves of Eucalyptus globulus trees was studied under field conditions in Portugal. In the absence of severe plant water stress stomata were open when the summed total of photosynthetically active photon flux density incident on both leaf surfaces was above 100 pmol m ~ 2 s ~1 and leaf conductance to water vapour reached 245 mmol m ~ 2 s ~1 on a total (both epidermes) leaf area basis. The stomata of both leaf epidermes responded similarly to changes in solar radiation and water stress. Water stress resulted in decreasing daily maxima in leaf conductance as predawn leaf water potential decreased. Maximal leaf conductance decreased to less than 50 mmol m ~ 2 s 1 when predawn leaf water potential decreased below —10 MPa. At similar values of predawn leaf water potential stomata were more closed as the leaf to air water vapour partial pressure difference increased. The effect of increasing air dryness on stomata was greatest at high predawn leaf water potential. Daily maxima in photosynthetic rates and in leaf conductance were linearly related to one another in spring and summer. Both decreased with increase in leaf water stress. In autumn and winter, increases in leaf conductance occurring under natural conditions during the course of the day were not necessarily accompanied by increases in net photosynthesis. Stomata were more closed in the afternoon than in the morning at the same rates of net photosynthesis, temperature or leaf to air

Water Stress Response After Thinning Pinus contorta Stands in Montana

Abstract Seasonal development of leaf water stress in thinned stands of lodgepole pine (Pinus contorta var. latifolia Engelm.) was compared to adjacent controls at three sites in Montana. Each stand was thinned to varying densities in the fall of 1982 or spring of 1983. Pre-dawn leaf water potential measurements were taken monthly in the summers of 1983 and 1984 using the pressure chamber to determine plant water stress differences between thinned and unthinned stands. Late summer leaf water potential was significantly higher (0.17 to 0.35 MPa) in the thinned stands than in the controls. Computer simulation using the DAYTRANS/PSN ecosystem model suggested that 21 percent greater seasonal photosynthesis could occur in these trees as a result of the approximately 0.3 MPa higher plant water potential measured and additional radiation available to remaining trees. Based on estimated carbon budgets, this additional photosynthate could substantially increase the amount of carbon allocated to stem growth in these trees. Forest Sci. 32:614-625.

Photosynthetic Rate Control in Sorghum: Stomatal and Nonstomatal Factors1

The purpose of this series of experiments was to determine the cause of photosynthetic rate responses to environmental effectors in one grain sorghumh ybrid [Sorghum bicolor (L.) Moench cv. ATX623 ✕ TX430]. Field experiments were conducted over a 4‐year period (1980–1983) at two locations using a range irrigation levels, to provide different degrees of plant waters tress. One site had a fine loamy sand soil (fine loamy, mixed, thermic family of Aridic Paleustaifs) with the second site having a clay loam (fine mixed, thermic family of Torrertic Paleustolls). Gas exchange rates of individual leaves were monitored on both a diurnal and seasonal basis. The results indicated that the primary cause of the photosynthetic rate changes due to leaf age, water stress, and photon flux density effects was related to mesophyll problems rather than due to stomatal conductance limitations. Increasing leaf age and environmental stress affected the photosynthetic processes by reducing the CO2 saturated rate (Amax) and the assimilation rate at all intercellular CO2 concentrations evaluated. The assimilation rate per unit photon flux density was also reduced in water‐stressed plants. Stomatal conductance responded to photosynthetic rate changes to maintain a relatively constant intercellular CO2 concentration at ambient CO2 levels. The primary control of photosynthetic carbon fixation in sorghum appears to be related to chloroplast activity rather than to CO2 supply due to stomatal conductance.

Drought resistance of hard wheat cultivars measured by a rapid chlorophyll fluorescence test

SummaryDisks of hard wheat (Triticum durum Desf.) leaves subjected to rapid desiccation over 4 h showed noticeable changes in the shape of the in vivo chlorophyll fluorescence induction curves. In drought-sensitive varieties (such as Claridoc), water stress resulted in a strong inhibition of the slow fluorescence induction transients. In particular, the fluorescence quenching rate was markedly decreased in water-stressed leaf disks. In contrast, leaves of drought-resistant varieties (such as Aouedj) showed only minor changes in chlorophyll fluorescence. The results of this investigation suggest that the slow transient of the in vivo chlorophyll fluorescence induction phenomenon may provide a simple method for selecting drought-tolerant wheats.

ROOT PENETRATION AND SHOOT ELONGATION OF TALL WHEATGRASS AND BASIN WILDRYE IN RELATION TO SALINITY

Tall wheatgrass [Elytrigia pontica (Podp.) Holub Syn: Agropyron elongatum (Host) Beauv. ’Jose’] and basin wildrye [Leymus cinereus (Scribn. &amp; Merr.) A. Love Syn: Elymus cinereus Scribn. and Merr. ’Magnar’] may have potential for increasing forage production once established on saline rangelands. The shoot and root elongation, osmotic adjustment, leaf water stress, and turgor at growth cessation of these grasses in response to drought and salinity were compared in a growth chamber experiment. Seedlings were grown in columns of soil initially saturated with solutions with an electrical conductivity of 1.0, 10, and 20 dS∙m−1 and allowed to grow until desiccated. The greater shoot elongation and root penetration of tall wheatgrass than basin wildrye at all soil salinities corresponds with the higher survival of tall wheatgrass than basin wildrye on a saline soil and on a nonsaline soil in central Nevada. As leaf water potential decreased, both species had similar or higher turgor maintenance in saline than nonsaline soil. But salinity decreased growth of both species, even when no water stress was apparent, and plant and soil water potentials in the saline and nonsaline columns were similar. This suggests that salt toxicity or nutritional imbalances due to accumulated ions, rather than water stress, depressed growth. Plant materials for revegetating saline, arid rangelands should be screened not only for seedling vigor and ability to tolerate or avoid water stress but also for tolerance to salinity.Key words: Drought, osmotic adjustment, turgor, ion toxicity, salt tolerance

Dinitrogen fixation in soybean in response to leaf water stress and seed growth rate.

Late season declines in N2 fixation by soybeans [Glycine max (L.) Merr.] frequently are observed under field conditions but do not always occur under glasshouse and growth chamber culture where water stress is avoided and photoperiod is manipulated to alter rate of seed growth. To evaluate the effects of water stress and photoperiod during reproductive growth declines in N2-fixation, nodulated 'Ransom' soybeans dependent entirely on N2-fixation and growing under controlled environment conditions were divided into two groups at the beginning seed (R5) stage. At R5, photoperiod was utilized to experimentally alter the rate of seed growth as a sink for photosynthate and N by imposing a short-day photoperiod (SD) on half of the plants and a long-day photoperiod (LD) on the other half. Within each photoperiod treatment, half of the plants were subjected to a single episode of leaf water stress between -1.2 and -1.8 MPa at the full seed (R6) stage, and half served as nonstressed controls. Plants were sampled at 1- to 5-day intervals between R5 and full maturity (R8) stages and analyzed for N and total nonstructural carbohydrates (TNC). The rate of N accumulation from N2-fixation declined during reproductive growth for the stressed plants but not for the nonstressed plants. Thus, a water stress can actuate a late season decline in N2-fixation. When rate of seed growth was slowed under LD, N composition in leaves remained higher following water stress than when a faster rate of seed growth was promoted under SD. Dinitrogen-fixation activity and dry matter production recovered after rewatering for stressed plants under LD but not under SD. Concentration of TNC in leaflets was greater under LD for both stressed and nonstressed plants. Thus, concentration of TNC in leaflets does not appear to be as important in recovery from water stress as concentration of N.

Adaptation of Grasses to Water Stress-Leaf Rolling and Stomate Distribution

Leaf dimension, degree of leaf rolling or folding, and stomatal densities on adaxial and abaxial leaf surfaces were measured on herbarium specimens of 39 grass species from a range of dry to wet habitats in western Canada. Stomata were counted on vinyl leaf impressions taken from the herbarium specimens. Representative surfaces also were examined using scanning electron microscopy. All species from dry habitats had narrow rolled or folded leaves (4 mm or less). The proportion of stomata on the abaxial surface of species from dry habitats ranged from 0 to 65%, but 56% of the species were strongly amphistomatous. The results were compatible with a conceptual model predicting that rolling, amphistomatous leaves would be selected for habitats in which water supply and demand fluctuate widely on seasonal or diurnal time scales. The evolutionary adaptation of grasses involves a syndrome of physiological, anatomical, and morphological characteristics. Grass leaf structure is closely coupled with major physiological processes such as photosynthesis, water relations, and energy balance. For example, vascular bundle and mesophyll cell arrangement are related to the type of photosynthetic pathway (Black et al., 1973; Hattersley & Watson, 1975), which, in turn, can influence niche separation in grasses (Monson et al., 1983). Specialized leaf tissue structure in some grasses results in leaf rolling, which strongly influences water and energy balances by changing the characteristic leaf dimension and the conductance of heat, water vapor, and carbon dioxide (Ripley & Redmann, 1976). This paper concentrates on the relationship between leaf rolling and stomatal distribution and conductance. The anatomy and mechanism of leaf rolling in grasses have been studied for over a century (Tschirch, 1882; Shields, 1951). Loss of turgor in the bulliform cells on the adaxial (upper) surface generally is considered to induce rolling. Shrinkage of the adaxial subepidermal sclerenchyma and mesophyll, due to water loss, also contributes to involution; rolling can occur in leaves that lack bulliform cells (Shields, 1951). Some grasses have permanently rolled or folded leaves. Leaves of native grasses from semi-arid grassland roll in response to increased plant water stress during dry periods (Ripley & Redmann, 1976). More mesic grasses such as cereal crops also exhibit leaf rolling when exposed to water stress (Hurd, 1976; O'Toole et al., 1979). Leaves of Sorghum bicolor roll and unroll in response to diurnal changes in plant water status, provided stress is not too severe (Begg, 1980). The early textbooks on plant ecology generally explained rolling as a xeromorphic adaptation for reducing transpiration by protecting the stomata, which were considered to be concentrated on the upper surface (Warming, 1909; Weaver & Clements, 1929; McDougall, 1949). Unfortunately, references to data supporting this explanation were not given, but the idea probably originated with early work on ecological plant anatomy. Tschirch (1882) classified grasses as meadow type, with flat leaves, or steppe type, with rolling leaves. Lewton-Brain (1904) grouped British grasses into four categories representing progressively more drought resistant types: (1) leaves with flat upper surfaces, amphistomatous, (2) leaves with ribbed upper surfaces, amphistomatous, (3) leaves with ridged upper surfaces, rolled with drying, epistomatous, and (4) leaves permanently rolled or folded, epistomatous. I was unable to find published comparative data on relative stomatal distributions on grass leaves in relation to rolling or drought resistance that would verify the generalizations described above. Parkhurst (1978) pointed out that the limited data in the literature show no clear trends 1 This research was supported by a Natural Science and Engineering Research Council of Canada grant. Thanks go to G. Shaw who did the electron microscopy work using facilities in the Department of Biology, University of Saskatchewan. V. L. Harms contributed valuable discussion regarding drought resistance classification. 2 Department of Crop Science and Plant Ecology, University of Saskatchewan, Saskatoon S7N OWO, Canada. ANN. MISSOURI BOT. GARD. 72: 833-842. 1985. This content downloaded from 207.46.13.153 on Fri, 05 Aug 2016 06:11:51 UTC All use subject to http://about.jstor.org/terms

The Heritability of Abscisic Acid Accumulation in Water-stressed Leaves of Pearl Millet [Pennisetum americanum (L.) Leeke

Using detached leaves, two cultivars of pearl millet [Pennisetum americanum (L.) Leeke], B282 and Serere 39, were assessed for variation in the capacity to accumulate ABA in response to water stress. Significant differences in ABA accumulation were detected between cultivars and between different inbred lines within a cultivar, but within lines there was much less variation in this character. In crosses between individual lines of B282 (low ABA) and Serere 39 (high ABA), ABA accumulation in the F1 was mid-way between parental values, indicating additive genetic control and lack of dominance. Selfed progeny of a B282 × Serere 39 cross were selected for contrasting ABA accumulation in the F2 to F4 generations. A sixfold range in ABA accumulation was found amongst 207 F2 progeny. This increased to nearly ninefold at F3 and F4. Regression analysis indicated high heritability of ABA accumulation and rapid approach to homozygosity. As the cross studied involved a dwarf (B282) and a tall (Serere 39) parent, segregation occurred for height as well as for ABA, though not entirely independently. Tall F3 progeny had significantly higher ABA contents than dwarf progeny and high ABA was therefore associated with other traits (e.g. large leaves, high leaf per cent d. wt) characteristic of tall plants. Nevertheless, there was a substantial range of ABA content within both groups which was uncorrelated with height and other characters. The potential use of the selections in studies on drought response is briefly discussed.

Evidence for Spider Mite (Acari: Tetranychidae) Injury-Induced Leaf Water Deficits and Osmotic Adjustment in Peppermint1

Studies were conducted to examine the physiological response of peppermint, Mentha piperita L., to leaf water stress induced by feeding of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Levels of mite injury were estimated by a leaf injury index developed for these studies. Symptoms of water stress in mite-injured leaves were: a significant reduction in leaf fresh weight; reduced leaf specific weight (mg of fresh weight per cm2 of leaf area); and accumulation of soluble leaf carbohydrates. Soluble leaf carbohydrates of peppermint are sucrose (ca. 50%) and the galactosyl oligosaccharides raffinose and stachyose. Leaf starch content was unaffected by injury at all injury levels. Accumulation of soluble leaf carbohydrate in water-stressed leaves may help mite-injured leaves maintain cell turgor pressure through an osmotic adjustment (osmoregulation) mechanism. A new method for in situ starch hydrolysis for quantitative analysis of leaf starch also is presented.

Effects of Spider Mite (Acari: Tetranychidae) Injury on Essential Oil Metabolism in Peppermint1

Studies were conducted to examine the effects of injury by the twospotted spider mite, Tetranychus urticae Koch, on metabolism of essential oil components (monoterpenes) in peppermint, Mentha piperita L. Mite injury increased the relative amounts of menthol and neomenthol and decreased the amount of pulegone in oil extracted from single leaves, thereby effecting more rapid oil “maturation.” We believe this resulted from accelerated enzymatic reduction of pulegone to the menthol isomers brought about by increased availability of soluble carbohydrate to oil-producing epidermal gland cells. Osmotic adjustment, utilizing soluble carbohydrate, in response to mite-induced leaf water stress, is the probable mechanism operating to increase carbohydrate levels. Reduction of pulegone to menthol and neomenthol requires reducing power in the form of NADPH and thus is dependent on the energy status of the gland cells in which monoterpene metabolism occurs. Increased supply of carbohydrate from surrounding water-stressed mesophyll cells may provide the additional energy needed for the acceleration of pulegone reduction to menthol isomers in mite-injured peppermint leaves.

&amp;lsquo;バートレット&amp;rsquo;果実の &lt;b&gt;Hard end&lt;/b&gt; 発生初期における水ポテンシャル及び果実への水移動率

In order to clarify the water relationships of the occurrence of hard end disorder in ‘Bartlett’ pear, the water potentials of leaves, fruits and stems and water influx into the fruit at the initial time of development of the disorder were investigated.1. The stem water potentials were almost constant during the fruit growing season. The leaf water potentials fell after the end of July, but it showed large fluctuations before mid-July. The fruit water potentials fell gradually after the end of July, but it seldom fell greatly at the initial time of development of the disorder. In addition, there was no difference in water potentials between the normal trees and the tree affected by hard end.2. The ratios of the water influx into the fruit per day to the fruit weight or the daily increase of fruit weight were evidently low at the initial time of development of the disorder (from mid-June to the beginning of July). However, there was no difference in the ratios between the normal trees and the affected tree, and the stronger the leaf water stress, the greater the drop in the ratios.3. From these results, it seemed that the low ratios of the water influx into the fruit to the daily increase of fruit weight during the period from mid-June to the beginning of July tend to result in Ca deficiency of the fruit and the hard end disorder develop at this period in some trees grown in poor conditions which permit only insufficient Ca absorption.

Leaf water stress detection utilizing thematic mapper bands 3, 4 and 5 in soybean plants

Abstract Foliar water stress in a mature soybean canopy, manifested as wilt rather than as a reflectance shift, was studied using reflectance measurements for Thematic Mapper bands 3 (0.63-0.69 μm), 4 (0.76-0.90 μm) and 5 (1.55-1.75μm). Diffuse and total reflectances were determined using polarization measurements and compared statistically at a variety of look angles at 15min intervals from about 09.00 until 14.00 hours EST. Plots of the data from unstressed canopy show that the behaviour of both the diffuse and total reflectances mimics that of the solar radiance curve with time of day, whereas the stressed canopy reflectance data revealed a nearly linear behaviour with a small negative slope. For both the diffuse and total reflectances measured in the nadir position, TM4 was found to be the most responsive spectral band for foliar water stress detection when the water deficit was sufficient to cause wilting, implying that substantial changes in canopy leaf geometry can best be monitored by TM4. TM3 was not found as responsive to the level of foliar water stress which occurred during this investigation. TM5 showed a response intermediate between TM4 and TM3. The results of polarization calculations for TM4 indicated that during the process of wilting, the level of canopy polarization gradually decreased.

Time Trends of Solute Accumulation and the Influence of Potassium Fertilizer on Osmotic Adjustment of Water-Stressed Leaves of Three Tropical Grasses

Osmotic adjustment, calculated from the difference in concentrations of ions and sugars between stressed and unstressed leaves of green panic, buffel grass and speargrass given normal or high potassium supply in the field, was determined during a 37-day drying cycle and following rewatering. Pressure/volume (P/V) curves were used to characterize the water relations of buffel grass with normal K supply on eight occasions during the experiment, and of the remaining treatments only at the end of the drying cycle. The maximum osmotic adjustment for the three grasses was 0.84-1.0 MPa calculated from chemical analyses of solutes and 0.5-0.7 MPa derived from the P/V analyses. High K supply did not enhance osmotic adjustment of water-stressed leaves. Osmotic adjustment reached a plateau 22 days after watering ceased, and its relationship with leaf water potential (Ψ) was the same for all species. When midafternoon Ψ was c. -4.8 MPa and leaves were permanently wilted, osmotic adjustment was 90% of maximum, suggesting that osmotic adjustment ceased when growth and most physiological activity were curtailed by loss of turgor. Osmotic adjustment delayed the onset of permanent wilting in water-stressed leaves by c. 4 days. Therefore, its contribution to the maintenance of leaf growth during water stress in these three grasses was small.

Effects of Spider Mite 1 Injury on Transpiration and Leaf Water Status in Peppermint 2

Studies were conducted to examine effects of feeding injury by the spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), on diurnal transpiration and daytime leaf water status in peppermint, Mentha piperita L. A new approach to investigate mite injury of the leaf epidermis and cuticle is presented. Feeding injury significantly affected daytime stomatal transpiration and nighttime cuticular transpiration. High rates of nighttime transpiration that resulted from mite injury to leaf epidermal cells and overlying cuticle caused leaf water stress during the day. Differences in rates of transpiration during the day and night, between uninjured and injured leaves. were correlated with a leaf injury index developed for this study. Water stress (more negative leaf osmotic potential) developed in injured leaves during the day and the magnitude of stress was correlated with our leaf injury index. Continued water loss at night from mite-injured leaves is discussed in terms of the underlying cause of water stress during the day.