Leaf Water Stress Research Articles

THE INFLUENCE OF WATER STRESS AND TEMPERATURE ON LEAF PUBESCENCE DEVELOPMENT IN ENCELIA FARINOSA

The degree of leaf pubescence development in the arid land shrub Encelia farinosa Gray is affected by air temperature, leaf water potential, and previous history of the apical meristem during the current growing season. Changes in leaf pubescence levels change leaf spectral characteristics and affect both leaf temperature and photosynthesis. Decreasing leaf water potentials and increasing air temperatures both independently increase pubescence development as measured by decreased leaf absorptances. During any one growing season leaf absorptance may change reversibly coincident with air temperature changes, but with respect to water stress leaf absorptance only decreases as the season progresses. The ecological significance of regulation of the leaf spectral characteristics is discussed.

The Influence of Water Stress and Temperature on Leaf Pubescence Development in Encelia Farinosa

The degree of leaf pubescence development in the arid land shrub Encelia farinosa Gray is affected by air temperature, leaf water potential, and previous history of the apical meristem during the current growing season. Changes in leaf pubescence levels change leaf spectral characteristics and affect both leaf temperature and photosynthesis. Decreasing leaf water potentials and increasing air temperatures both independently increase pubescence development as measured by decreased leaf absorptances. During any one growing season leaf absorptance may change reversibly coincident with air temperature changes, but with respect to water stress leaf absorptance only decreases as the season progresses. The ecological significance of regulation of the leaf spectral characteristics is discussed.

The Effect of Wind and a Reduced Supply of Water on the Growth and Water Relations of Festuca arundinacea Schreb

Festuca arundinacea was grown at high and low wind-speeds at two levels of soil water. Transpiration was increased at high wind-speed and accompanied by leaf water stress. Growth of leaf area was progressively reduced according to the severity of the experimental treatments in the sequence: wet soil and low wind; dry soil and low wind; wet soil and high wind; dry soil and high wind. The leaf water potential was also reduced in this sequence.

Leaf Anatomy and Water Stress of Aseptically Cultured ‘Pixy’ Plum Grown under Different Environments1

Abstract This study examined the leaf anatomy and water stress of Prunus insititia L. cv. Pixy grown in aseptic culture before and after transfer to the greenhouse and grown in a layerage bed in the field. The depth of palisade cells was significantly less in aseptically cultured plantlets than in greenhouse transfererred plants, and less in greenhouse transferred than in field-grown plants. Percent mesophyll air space was greater in plantlet than in plant leaves. Upper or lower leaf epidermal cell length of plantlets of field grown plants was not significantly different. Stomatal frequency for plantlet leaves was significantly less about 150 stornata per mm2) than that of plant leaves (300 stornata per mm2). Excised plantlet leaves lost greater than 50% of total leaf water content within 30 min; excised greenhouse leaves lost 50% after 90 minutes.

Leaf Water Diffusion Resistance in Clonal Tea (Camellia sinensis L.): Effects of Water Stress, Leaf Age and Clones

Leaf diffusion resistance was influenced by leaf age in well-watered and water-stressed clonal tea plants. In well-watered plants and in two of the three clones studied, young leaves showed a significantly lower diffusion resistance than old leaves. In water- stressed plants young leaves always exhibited a higher diffusion resistance than old leaves. The highest diffusion resistance, irrespective of leaf age and water stress, occurred in clone DN which is known to be the most drought tolerant of the three clones studied, suggesting that drought tolerance in clone DN is caused, at least in part, by a stomatal regulation mechanism. Water release characteristic curves for the three clones indicated differences in the water content - water potential relationship between young and old leaves as well as between clones. The drought tolerant clones had a higher relative water content for a given water potential compared with the drought-susceptible clone.

Metabolism and Export of 14C-Labelled Photosynthate From Water-Stressed Leaves

The effect of water stress on the translocation of 14C-labelled photosynthate from leaves was examined in four contrasting plant species, Sorghum sudanense (Piper) Stapf. (C4, monocot), Triticum aestivum L. (C3, monocot), Amaranthus caudatus L. (C4, dicot) and Helianthus annuus L. (C3, dicot). Water stress reduced the rate of loss of 14C from the leaves of all species following a pulse application of 14CO2, but the effects of stress were most apparent in sorghum and sunflower, the species with the highest control rates of export. Slower labelling of sucrose, following the application of 14CO2, could explain the reduced rate of export of 14C from stressed wheat leaves, but this would not explain the response in sorghum. An examination of the products of 14CO2 fixation in wheat leaves suggests that the changes in metabolism of 14C under stress may be due to reduced CO2 levels, resulting from stomatal closure. In contrast the change in metabolism of 14C-labelled photosynthate due to water stress in sorghum was very different from that expected in response to reduced CO2 levels. Prevention of translocation of photosynthate out of a leaf of either wheat or sorghum, by steam killing the tissue at the base of the blade, altered the pattern of labelling of metabolites with 14C following a pulse of 14CO2. However changes in translocation due to reduced export associated with a reduction in growth under water stress did not appear to play a part in the responses observed in these experiments.

Phenology, productivity, and nutrient accumulation in the post-fire chaparral shrub Lotus scoparius.

Lotus scoparius is a drought-deciduous shrub which is an early and abundant colonizer of sites following fire in southern California chaparral. Productivity, seasonal nutrient concentrations, nutrient accumulations and phenology were studied in a 4-year-old burn site in Adenostoma chaparral in which L. scoparius had established 49% cover. Net aboveground primary production for L. scoparius was 105 g m-2 y-1; leaves accounted for 40% of the annual production. The true increment to biomass was only 17 g m-2 y-1; 83% of the net production entered the litter layer or standing dead components. In response to the Mediterranean climatic regime, most of the annual net production and plant activity occurred from May through June when photoperiod and temperatures were favorable and moisture was available. In July leaf abscission occurred in response to the summer drought conditions. Correlation and principal component analysis suggested consistent seasonal behavior in the foliar concentrations of N, P, Zn, and Mn. Nitrogen, P, K, and Zn were strongly reabsorbed from leaf tissues before abscission. Calcium, Mg, and Fe formed a second functional group of elements which increased in concentration throughout leaf maturation and which were not reabsorbed from senescing foliage. The seasonal pattern of nitrogen-containing organic compounds (chlorophylls and proteins) was most associated with the leaf phenology and water stress. The rapid growth of Lotus scoparius plays a role in conserving nutrients that might be lost through runoff and erosion after fire in the chaparral.

EFFECTS OF CYCOCEL AND NITROGEN FORM ON TOMATO WATER RELATIONS, ION COMPOSITION, AND YIELD

Fertilizing tomatoes (Lycopersicon esculentum Mill.) Missouri breeding line 76-1-60-8 with NH4-N, as compared to NO3-N sources, in pot culture with unequal anion species and concentration and constant substrate moisture supply increased leaf diffusive resistance and water stress; reduced total transpiration and transpiration rate, leaf area, and mean fruit weight; and increased fruit and leaf Ca concentration and fruit Mg, K, and P concentration. Cycocel applied both foliarly and as a substrate drench to plants under NH4 nutrition increased leaf diffusive resistance; and reduced water stress, total transpiration, plant height, and total and mean fruit weights. Cycocel treatment under both N forms, with the exception of reduced leaf Ca concentration, either had no effect or increased leaf and fruit ion concentration. Under NH4-N nutrition, Cycocel treatment gave a 54% increase in fruit Ca concentration.

Seasonal Changes in Stomatal Response to Leaf Water Potential in Apple1

Abstract The relationship between stomatal conductance and leaf water potential in field-grown apple trees (Malus domestica Borkh.) was determined throughout one growing season. Between May and September the leaf water potential required to close stomates decreased (became more negative) by about 25 bars, indicating decreasing sensitivity of the stomates to leaf water stress. A good linear correlation was found between stomatal conductance and net photosynthesis in trees grown under a wide range of water stress conditions. In September net photosynthesis of excised leaves of field trees was not reduced to zero until leaf water potentials reached −50 to −60 bars. The results emphasize the importance of pre-conditioning and time of season in plant water relations studies.

Betaine Accumulation and [14C]Formate Metabolism in Water-stressed Barley Leaves

Barley (Hordeum vulgare L.) plants at the three-leaf stage were water-stressed by flooding the rooting medium with polyethylene glycol 6000 with an osmotic potential of -19 bars, or by withholding water. While leaf water potential fell and leaf kill progressed, the betaine (trimethylglycine) content of the second leaf blade rose from about 0.4 micromole to about 1.5 micromoles in 4 days. The time course of betaine accumulation resembled that of proline accumulation. Choline levels in unstressed second leaf blades were low (<0.1 micromole per blade) and remained low during water stress. Upon relief of stress, betaine-like proline-remained at a high concentration in drought-killed leaf zones, but betaine did not disappear as rapidly as proline from viable leaf tissue during recovery.When [methyl-(14)C]choline was applied to second leaf blades of intact plants in the growth chamber, water-stressed plants metabolized 5 to 10 times more (14)C label to betaine than control plants during 22 hours. When infiltrated with tracer quantities of [(14)C]formate and incubated for various times in darkness or light, segments cut from water-stressed leaf blades incorporated about 2- to 10-fold more (14)C into betaine than did segments from unstressed leaves. In segments from stressed leaves incubated with [(14)C]formate for about 18 hours in darkness, betaine was always the principal (14)C-labeled soluble metabolite. This (14)C label was located exclusively in the N-methyl groups of betaine, demonstrating that reducing equivalents were available in stressed leaves for the reductive steps of methyl group biosynthesis from formate. Incorporation of (14)C from formate into choline was also increased in stressed leaf tissue, but choline was not a major product formed from [(14)C]formate.These results are consistent with a net de novo synthesis of betaine from 1- and 2-carbon precursors during water stress, and indicate that the betaine so accumulated may be a metabolically inert end product.

The effects of water-stress on leaf H2(18O) enrichment.

Water-stress experiments with Phaseolus vulgaris L. were undertaken to determine the transpiration rate dependency of the naturally occuring leaf H2(18O) fractionation process. Water-stress leaf H2(18O) levels were observed to be unexpectedly higher than controls. Speculations on the cause of this phenomenon are discussed. Since transpiration rate variations should theoretically affect only the rate and not the extent of leaf H2(18O) fractionation, the respective time courses for water-stressed and control leaf H2(18O) accumulations were compared. Water-stressed leaves displayed a slower rate of isotopic enrichment relative to controls, as was predicted from their reduced transpiration rate. In an absolute sense, however, both control and water-stress leaf H2(18O) fractionation rates were markedly greater than projected values from the existing model. Consequently, transpiration rates cannot be derived accurately at present from the observed rates of leaf H2(18O) discrimination. Several modifications of the theory are also considered.

LEAF RESPIRATION AND ATP LEVELS AT CHILLING TEMPERATURES

SUMMARYIn the extremely chill‐sensitive species Episcia reptans the dark respiration rate of leaves after 80 min chilling at 5°C was three times greater than in leaves maintained at 25°C. The rate and size of the respiratory increase depended on the chilling temperature and the growth conditions prior to chilling and was at a maximum at the same time as the onset of visible injury. The addition of 2,4‐dinitrophenol and potassium cyanide to the leaves of E. reptans accelerated the rate of oxygen uptake at 5°C. In contrast, there was no increase in the respiration rate of the leaves of the less chill‐sensitive species Phaseolus vulgaris after prolonged chilling at 5°C.A reduction in ATP supply below that necessary to maintain the metabolic integrity of the cytoplasm is not considered to be important in the development of chilling‐injury to Episcia reptans or Phaseolus vulgaris as the ATP level decreased only after the onset of visible leaf injury. Furthermore, the increase in ATP level on chilling P. vulgaris leaves which had been either chill‐hardened or maintained in a saturated atmosphere on transfer from 25 to 5°C (Wilson, 1976) demonstrated that leaf injury and water stress are the primary cause of the decline in ATP level during chilling and not low temperature per se.

Variations among Woody Angiosperms in Response to Flooding

AbstractEffects of flooding on young Populus deltoides, Salix nigra, Eucalyptus camaldulensis, E. globulus, Ulmus americana, Quercus rubra and Fraxinus pennsylvanica plants were studied. Flooding variously induced several sequential physiological disturbances, with stomatal closure among the earliest responses. Subsequent responses included inhibition of root growth, alterations in root and stem morphology, formation of adventitious roots, and leaf senescence. In amphistomatous species (Populus deltoides, Salix nigra, Eucalyptus camaldulensis) flooding rapidly induced stomatal closure on the adaxial leaf surface. It also significantly induced stomatal closure on the abaxial epidermis of Populus deltoides but not that of Salix nigra or Eucalyptus camaldulensis. In hypostomatous species (Eucalyptus globulus, Ulmus americana) flooding significantly induced stomatal closure on the abaxial surface within 3 days. Stomatal responses to flooding were not correlated with leaf water stress. In both long‐ and short‐term experiments, flooding did not significantly increase plant water stress. These results deemphasized the importance of plant water stress in inducing plant responses to flooding. The importance of various hormones in inducing flooding symptoms is discussed.

A new technique for measuring oscillatory and diurnal changes in leaf thickness

A new technique is described for measuring oscillatory and diurnal changes in leaf thickness. Mature leaves of Populusdeltoides × nigra undergo diurnal or oscillatory changes in thickness of up to 20 μm in amplitude; thickness changes were measured to ±0.2 μm and appear to correlate with expected levels of leaf water stress.

The response of diffusive conductance in wilted and unwilted Atriplex hastata L. leaves to humidity

Summary Diffusive conductance increased in a very similar way in wilted and unwilted leaves of A. hastata as external humidity was increased. It was concluded that the humidity response is probably a hydroactive one to water stress within the epidermis, which can be different from bulk leaf water stress.

果樹の葉内水分不足に関する研究

果樹の葉内水分不足に関する研究

果樹の葉内水分不足に関する研究 (第6報)

果樹の葉内水分不足に関する研究 (第6報)

Studies on Leaf Water Stress in Fruit Trees

The purpose of this paper is to investigate the feasibility of predicting leaf water potential before sunrise (ψmax) from the potential during 13:00-14:00 (ψmin) and of obtaining an index accounting for fluctuations of ψmin in Satsuma mandarin (Citrus unshiu MARC.) trees. We were unable to find an indicator accounting for the fluctuations of c min under various environmental conditions. However, our data suggested a possibility of estimating ψmax from the leaf water potential at about 19:00. ψmax for trees on the soil of similar properties could also be estimated from ψmin/VPD where VPD is vapor pressure deficit.

Effects of NH4 and NO3 Nutrition with and without pH Adjustment on Tomato Growth, Ion Composition, and Water Relations1

Abstract Fertilization of tomato (Lycopersicon esculentum Mill.) in solution culture with NH4-N resulted in reduced shoot and root concentration of Ca, Mg, K, P, and NO3, increased leaf and root resistances to water flux, and decreased water use efficiency as compared to plants cultured with NO3-N. Solution adjustment to pH 6.5 decreased shoot/root fresh weight ratio with both N forms; decreased leaf diffusive resistance and water stress but increased root resistance to water flux and shoot NH4 concentration under NH4-N nutrition. Solution pH had little effect on tissue ion concentration.

Rapid Ultrastructural Recovery of Water Stressed Leaf Tissue

Summary When buffered glutaraldehyde was used as a fixative for water stressed leaf tissue, ultrastructural recovery occurred during the 90 minute fixation period. The addition of formaldehyde to the fixation mixture prevented this subcellular recovery and revealed extensive vacuolation of the mesophyll cells but no apparent changes in ultrastructure of the bundle sheath cells.