Influence of cadmium on water relations, stomatal resistance, and abscisic Acid content in expanding bean leaves

Ten day old bush bean plants (Phaseolus vulgaris L. cv Contender) were used to analyze the effects of 3 micromolar Cd on the time courses of expansion growth, dry weight, leaf water relations, stomatal resistance, and abscisic acid (ABA) levels in roots and leaves. Control and Cd-treated plants were grown for 144 hours in nutrient solution. Samples were taken at 24 hour intervals. At the 96 and 144 hour harvests, additional measurements were made on excised leaves which were allowed to dry for 2 hours. From the 48 hour harvest, Cd-treated plants showed lower leaf relative water contents and higher stomatal resistances than controls. At the same time, root and leaf expansion growth, but not dry weight, was significantly reduced. The turgor potentials of leaves from Cd-treated plants were nonsignificantly higher than those of control leaves. A significant increase (almost 400%) of the leaf ABA concentration was detected after 120 hours exposure to Cd. But Cd was found to inhibit ABA accumulation during drying of excised leaves. It is concluded that Cd-induced decrease of expansion growth is not due to turgor decrease. The possible mechanisms of Cd-induced stomatal closure are discussed.     

Photosystem II quantum yield as a measure of radical scavengers in chilling injury in cucumber fruits and bell peppers

Cucumber fruits (Cucumis sativus L. cv. Jessica) and green bell peppers (Capsicum annuum L. cvs. Lokas and Medeo) were stored at different temperatures ranging from 2 to 12°C. After three different storage periods, fruits from each temperature were transferred to 20°C for 7 d to allow for the development of visual symptoms of chilling injury (CI). During storage, the photochemical quantum yield of photosystem II (PSII) in peel tissue adapted to darkness, was calculated from measurements of pulse-amplitude-modulated chlorophyll fluorescence. The decrease in PSII quantum yield during storage at low temperatures in darkness can be described as a temperature-dependent inhibition of an enzyme according to Arrhenius, assuming a negative activation energy. By comparison with the radical-scavenger measurements of Hariyadi and Parkin (1991, Postharvest Biol. Techn.1, 33–45) it is postulated that the time and temperature dependence of the quantum yield parallels the diminution of radical-scavenging activity at lower temperatures in cucumber and capsicum fruits. This is combined with an equation for the process of radical scavenging itself and an equation for the auto-catalytic radical-producing lipid peroxidation reaction. These three basic processes lead to both a static and a dynamic model for the occurrence of chilling injury in low-temperature-sensitive plant tissue. A statistical fit of the measured data using the static model leads to the estimates of the different activation energies and reaction rates with a high degree of accuracy. The estimated values are in accord with what one would expect on the basis of knowledge of the processes leading to chilling injury, and directly point to meaningful physico-chemical parameters.Abbreviations C Symmetry point of logistic curve - CI intensity of chilling injury - e base of the natural logarithm system - E activation energy - Eff efficiency - F_v/F_m quantum yield of PSII - k reaction rate constant - R amount of free radicals - S amount of substrate for chilling injury (double bonds in fatty-acid chains) - t time - T temperature - Z amount of radical-scavenging enzyme Indices - CI chilling injury - d denaturation - i any index - max maximum value - min minimum value - r radical scavenging - ref reference (temperature) - s substrate - 0 initial amount This study was conducted in the framework of a research program on fruits and vegetables, partly financed by the Dutch Commodity Board for Vegetables and Fruits.     

蚜虫对设施辣椒产量和品质的影响

[目的]探讨不同蚜害等级危害对设施辣椒产量和品质的影响,为设施蔬菜的科学防控、按质定价及制定蚜虫经济阈值提供参考.[方法]通过田间蚜虫量调查,进行蚜害分级,并测定不同蚜害等级下辣椒叶片和果实的SPAD值,采收后记录单株果数,称重,计算座果率及单株果重等产量指标;同时测定不同蚜害等级下辣椒果实可溶性蛋白、可溶性糖、维生素...     

Effect of paclobutrazol on water stress-induced abscisic Acid in apple seedling leaves

Abscisic acid (ABA) was quantitated by enzyme-linked immunosorbent assay (ELISA) in water-stressed leaves from control apple seedlings, and also from apple seedlings treated for 28 days with paclobutrazol ([2RS, 3RS]-1-[4-chlorophenyl]-4,4-dimethyl-2-[1,2,4-triazol-1-yl] pentan-3-ol). The ELISA quantitative estimates were also validated by gas chromatography-electron capture detector and lettuce seed germination inhibition bioassay. Paclobutrazol treatment reduced endogenous ABA levels by about one-third, and prevented the marked accumulation of water-stress-induced ABA that occurred in untreated seedlings. The presence of ABA in the apple leaf extracts was confirmed by gas chromatography-mass spectrometry.     

The effects of abscisic Acid on growth and nucleic Acid synthesis in excised embryonic bean axes

Abscisic acid (ABA) is an effective inhibitor of cell elongation in excised embryonic bean axes whether added prior to or after the initiation of cell elongation. Zeatin partially reverses this growth inhibition. ABA inhibits ³²P incorporation into ribosomal RNA, transfer RNA, and DNA but not into the tenaciously bound fraction of elongating axes in a manner resembling 5-fluorouracil, a compound which does not inhibit axis growth. The methylated albumin on kie-selguhr elution profiles of nucleic acids obtained from axes treated with either ABA, 5-fluorouracil, or a combination of the two are similar, and zeatin treatment has little apparent effect on these results. Our results suggest that the inhibition of growth in the axes by ABA is not due to its inhibition of DNA synthesis.     

A water potential threshold for the increase of abscisic Acid in leaves

A relationship between abscisic acid concentration and leaf water status is reported. Water potentials were measured in leaves of Ambrosia artemisiifolia L. and Ambrosia trifida L. throughout a period of dehydration of intact plants. Tissues from the same leaves were analyzed for abscisic acid. For both species, abscisic acid began to increase in a critical water potential range (−10 to −12 atmospheres). These data suggest a threshold water potential that stimulates abscisic acid synthesis. The data support the hypothesis that a small change in water potential could affect stomatal resistance to water loss by means of a very sensitive chemical feedback control mechanism.     

Influence of water deficits on the abscisic Acid and indole-3-acetic Acid contents of cotton flower buds and flowers

A field experiment was conducted during the summer of 1988 to test the hypothesis that water deficit affects the abscisic acid (ABA) and indole acetic acid (IAA) concentrations in cotton (Gossypium hirsutum L.) flower buds in ways that predispose young fruits (bolls) that subsequently develop from them to increased abscission rates. Water deficit had little effect on the ABA content of flower buds but increased the ABA content of flowers as much as 66%. Water deficit decreased the concentrations of free and conjugated IAA in flower buds during the first irrigation cycle but increased them during the second cycle. Flowers contained much less IAA than buds. Water deficit slightly increased the conjugated IAA content of flowers but had no effect on the concentration of free IAA in flowers. Because water deficit slightly increased the ABA content but did not decrease the IAA content of flowers, any carry-over effect of water deficit on young boll shedding might have been caused by changes in ABA but not from changes in IAA.     

The role of abscisic acid and water relations in drought responses of subterranean clover

The role of water relations and abscisic acid (ABA) in the responsesto drought were studied in a mediterranean forage crop, Trifoliumsubterraneum L. under field conditions. Soil and plant waterstatus, leaf gas exchange parameters, and xylem sap ABA contentwere determined at different times during a long-term soil dryingepisode in irrigated and droughted plants. The diurnal time-coursesof these parameters were also measured at the end of a droughtperiod. In response to soil drying stomatal conductance (g) was reducedearly to 50% that of irrigated plants before any substantialchange in water potential was detected. A close logarithmicregression between photosynthesis rate (A) and g was present.For the first weeks of drought the decline in A was less pronouncedthan in g, thus increasing water use efficiency. Stomatal conductanceduring diurnal time-courses showed no consistent relationshipswith respect to etther ABA or leaf water potential. Throughoutthe experimental period dependence of g on leaf water statuswas evident from the tight correlation (r²=0.88, P<0.01)achieved between stomatal conductance and midday water potential,but the correlation was also high when comparing g with respectto ABA content in xylem sap (r=0.83, P<0.001). However, thestomata from drought acclimated plants were apparently moresensitive to xylem ABA content. For similar xylem ABA concentrationsstomatal conductance was significantly higher in irrigated thanin waterstressed plants. Key words: Drought, stomatal conductance, water potential, abscisic acid     

Varietal influence of intercropped cowpea on the growth,yield and water relations of maize

The effects of three cowpea varieties namely, NewEra (a spreading type), Adzuki (an erect type) and Ife Brown (semi-erect) intercropped with maize on growth, yield and water relations of maize were investigated in the greenhouse and in the field. Cowpea varietal effects were significant on soil water extraction but insignificant on the performance of maize.     

Endogenous levels of abscisic Acid and decanoic Acid in dutch iris bulbs and the influence of abscisic Acid and decanoic Acid on iris meristems cultured in vitro

Abscisic acid (ABA) and decanoic acid inhibited shoot elongation and floral development of Dutch iris (Iris hollandica Hoog. cv Ideal) meristems cultured in vitro. No synergism with respect to inhibition of leaf growth between ABA and decanoic acid was observed. With monthly harvest dates, from July 10, 1981 to October 10, 1981, there was a progressive decrease in endogenous level of free ABA in `Ideal' iris bulbs. Bulbs subjected to a full set of the usual preplanting storage conditions flowered, on average, 46 days after planting versus 194 days after planting for bulbs planted directly after harvest. ABA levels at harvest were 4- to 5-fold those after the preplanting storage treatment. In general, ABA levels did not correlate well with the length of time from planting until flowering of iris bulbs. Endogenous decanoic acid levels did not follow any pattern with respect to harvest date or postharvest treatment. After the postharvest high temperature treatment, there was about a 3-fold increase in nonscale decanoic acid concentration. Decanoic acid levels, in nonscale tissue, remained high after each of the other postharvest treatments. It is concluded that there is no good evidence to support the contention that either ABA or decanoic acid is directly involved in iris bulb dormancy.     

Interdependence of growth, water relations and abscisic acid level in Phaseolus vulgaris during waterlogging

The interdependence between changes in growth and water relations after waterlogging was investigated by recording simultaneously growth, transpiration, water potential, turgor, leaf diffusion resistance and abscisic acid content in Phaseolus vulgaris L. cv. bruine Noord-Hollandse. Growth was inhibited immediately after flooding, whereas transpiration decreased gradually to a low level in about three days. The first two days after flooding a small increase in abscisic acid content in the leaves was observed which was accompanied by an increase in diffusion resistance. The increase in abscisic acid content could result from an inhibited export from the leaves. After the first two days a decrease in water potential and turgor was accompanied by a drastic increase in both abscisic acid content and diffusion resistance. This large increase in abscisic acid content occurred before the turgor had reached its minimum value. The change in diffusion resistance kept showing a lag of about one day with the change in abscisic acid content. The possibility is discussed that besides abscisic acid also its metabolite phaseic acid is involved in stomatal closure. After the formation of adventitious roots on the hypocotyl, abscisic acid level, diffusion resistance, water potential and turgor returned to the control values. Transpiration showed a slow recovery from the sixth day after flooding, whereas growth was inhibited for at least nine days. A remarkable similarity exists between our observations on the responses of bean plants to flooding and the well known responses to drought.     

Effect of obstructed translocation on leaf abscisic Acid, and associated stomatal closure and photosynthesis decline

Pod removal or petiole girdling, which causes obstruction of translocation, was found in our previous study to cause reduced rates of photosynthesis in soybean leaves due to stomatal closure. The purpose of this research was to determine the involvement of photoassimilate accumulation and leaf abscisic acid (ABA) levels in the mechanism of stomatal closure induced by such treatments.     

Stomatal response of cotton to water stress and abscisic Acid as affected by water stress history

The threshold leaf water potential required to initiate stomatal closure in cotton (Stoneville 213) became progressively more negative when plants were subjected to a series of water stress cycles. The shift in the threshold water potential required for induction of stomatal closure was dependent on the number of previous stress cycles and leaf age. The basal level of endogenous abscisic acid (ABA) in fully turgid leaves increased in response to the stress treatments, whereas the amount accumulated in response to a subsequent stress did not differ greatly among plants that had experienced different degrees of stress conditioning.     

Effect of ethylene perception inhibitor on growth, water relations, and abscisic acid content in wheat plants under water deficit

The effects of treatment with 1-methylcyclopropene (1-MCP, the inhibitor of ethylene receptors) of 7-day-old wheat (Triticum durum Desf., cv. Bezenchukskaya 139) seedlings on growth characteristics, water relations, and the content of phytohormones during three days after watering cessation were studied. In treated seedlings, a decrease in the water content in the substrate resulted in a decrease in stomatal conductance in the leaves by one day earlier than in untreated seedlings. This could be related to the more rapid and substantial accumulation of ABA in treated plants. There was no clear relationship between changes in the content of cytokinins and water relations under the influence of 1-MCP under drought conditions. The role of ethylene and ABA in the regulation of growth and water relations in plants suffering from water deficit is discussed.     

A kinetic analysis of the effects of gibberellic Acid, zeatin, and abscisic Acid on leaf tissue senescence in rumex

Hormones which inhibit senescence in Rumex leaf tissue in the dark include gibberellic acid and the cytokinin zeatin. Abscisic acid accelerates senescence in this tissue. Other workers have proposed that cytokinins, but not gibberellins, interact with abscisic acid in senescing Rumex leaf tissue. The present study reinvestigates the question of interaction using measurements of chlorophyll degradation kinetics as parameters of senescence rate and draws the conclusion that neither zeatin nor gibberellic acid interact with abscisic acid in this system. In support of this conclusion are these results. Zeatin clearly cannot overcome the effects of abscisic acid when hormone solutions are replaced every other day. The kinetics of chlorophyll breakdown for tissue treated with unreplaced saturating zeatin solutions is different from that of tissue exposed to saturating zeatin plus abscisic acid. The observed rates of chlorophyll breakdown for tissue treated with abscisic acid and zeatin agree closely with predicted rates using a multiplicative model for independent action of the two hormones.     

Initiation and regulation of water deficit-induced abscisic acid accumulation in maize leaves and roots: cellular volume and water relations

Water deficit-induced ABA accumulation in relation to cellular water relations was investigated in maize root and leaf tissues. While polyethylene glycol (PEG) treatment led to a significant increase of ABA content in both root and leaf tissues, ethylene glycol (EG), a permeable monomer of PEG, had no effect on ABA accumulation at similar or much lower osmotic potentials. A rapid and massive accumulation of ABA in leaf tissues occurred at a specific threshold of PEG 6000 concentration, about 20% (w/v), and closely coincided with the start of the tissue weight loss and the obvious decrease of cellular osmotic potential. Pretreatment with EG lowered the cell sap osmotic potential and also lowered the capability of both root and leaf tissues to accumulate ABA in response to further air-drying or PEG treatment. When samples were dehydrated and incubated under pressure, a method to maintain high water potential and pressure potential during dehydration, ABA accumulation was similar to those dehydrated and incubated under atmospheric pressure. Such results suggest that both the absolute water potential and pressure potential per se had no direct effects on the dehydration-induced ABA accumulation. The results have provided evidence that the initiation of ABA accumulation is related to the weight loss of tissues or changes in cellular volume rather than the cell water relation parameters, and the capability of ABA accumulation can be regulated by cellular osmotic potential.     

Stomatal responses to water stress and to abscisic Acid in phosphorus-deficient cotton plants

Cotton (Gossypium hirsutum L.) plants were grown in sand culture on nutrient solution containing adequate or growth-limiting levels of P. When water was withheld from the pots, stomata of the most recently expanded leaf closed at leaf water potentials of approximately −16 and −12 bars in the normal and P-deficient plants, respectively. Pressure-volume curves showed that the stomata of P-deficient plants closed when there was still significant turgor in the leaf mesophyll. Leaves of P-deficient plants accumulated more abscisic acid (ABA) in response to water stress, but the difference was evident only at low water potentials, after initiation of stomatal closure. In leaves excised from unstressed plants, P deficiency greatly increased stomatal response to ABA applied through the transpiration stream. Kinetin blocked most of this increase in apparent sensitivity to ABA. The effect of P nutrition on stomatal behavior may be related to alterations of the balance between ABA and cytokinins.     

High temperature effects on photosynthesis and water relations of grain legumes

Effects of high temperature on photosynthesis, and its interaction with water relations in common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), faba bean (Vicia faba), and five cultivars of field pea (Pisum sativum) were investigated. Responses of all species were compared at 20/15, 30/15, or 30/25 °C day/night, and cowpea and pea were compared at 20/15 and 30/25 °C under well-watered and limited-water conditions. Response of pea to 20/15 and 30/25 °C during flowering was ascertained, and sensitivity of the photosystem of pea and faba bean to 40 °C was determined.High temperature decreased chlorophyll variable fluorescence (F_v), a measure of injury to photosynthesis, in all species except cowpea, which was highly tolerant. Leaf chlorophyll and most measures of growth were favored by high day temperature but not by high night temperature, and photosynthetic rates were enhanced by high temperatures that increased leaf chlorophyll and nitrogen (N) contents. High temperature diminished growth less than water deficiency and increased water use of all three species but only lowered the water potential in faba bean. Water deficiency generally decreased growth, water use, and water potential more at 30/25 °C than at 20/15 °C. Stress from high temperature during flowering of pea decreased all components of yield at maturity, particularly at nodes that flowered latest. Whole-chain photosynthetic activity in thylakoids of pea, faba bean, and wheat (Triticum aestivum) were equally sensitive to high temperature, suggesting that Photosystem Il was the most labile component. The results show that high temperature affects photosynthesis, growth, and water relations of grain legumes, and sensitivity to the stress differs among species and genotypes.