Rapid Effects on Ion and Water Uptake Induced by Changes of Water Potential in Young Wheat Plants

The effect of rapid changes in the water potential of the root medium or the atmosphere was investigated with particular respect to water and ion uptake in young wheat plants. Either PEG 400 or PEG 6000 were added to the nutrient solution, so that the water potential was decreased from about 0 to –5 bars and –13 bars, respectively. Both water and ion uptake immediately decreased when the water potential of the medium was reduced. By raising the humidity around the shoots from 1400 N m⁻² (60% RH) to about 2300 N m⁻² (100% RH) water uptake decreased, whereas ion uptake transiently increased. If sodium chloride was added to reduce the water potential of the mutrient solution, ion uptake was found to decrease to essentially the same level as when PEG was used. It is suggested that a change in the water potential of the plants has effects on the active-ion-transport mechanism.     

Effect of Changes of Temperature Around Roots in Relation to Water Uptake by Roots and Leaf Transpiration

Effects of changes in temperature around roots on water uptake by roots and leaf transpiration were studied in Leucaena leucocephala (Lam.) de Wit., a subtropical woody plant species, and in Zea mays L. When the temperature around roots was rapidly lowered from 25 ℃ to 15 ℃, the water uptake by the roots and leaf transpiration were stimulated significantly within a short period ( 14 min). However, this effect did not occur when the cooling time was prolonged neither did if occur when the temperature around the roots was resumed from 15 ℃ to 25 ℃. Both the hydraulic conductivity of roots and leaf transpiration were increased substantially at first (within 20 min)and then decreased steadily to a level lower than those of the control in which the roots were continuous exposed to a low temperature ( 15 ℃ ). Low temperature also promoted the biosynthesis of ABA in roots and enhanced the xylem ABA concentration, but such stimulation did not occur untill about 30 min after cooling treatment, leaf transpiration was reduced markedly, but the hydraulic conductivity of roots increased when the root system was treated with exogenous ABA. It was suggested that some mechanisms other than ABA may be involved in the short-time cryostimulation of water uptake by roots and leaf transpiration.     

Water Uptake during Rapid Changes of Transpiration Induced by the Presence of High Concentration of Growth Substances in Root Medium

Sériou potometrických meraní sa zi?tovala bezprostredná reakcia príjmu vody intaktnými rastlinamiPisum sativum L. na vnesenie vysokých koncentrácii α-naphthaleneacetic acid (NAA), β-indoleacetic acid (IAA), 2,4-dichlorphenoxyacetic acid (2,4-D), 2-methyl-4-chlorophenoxyacetic acid (MCPA), coumarin a ethylene diaminetetraacetic acid (EDTA) do koreňového prostredia. Rastové substancie boli v koreňovom prostredí prítomné v dvoch koncentráciach 10^-3 M a 10^-2 M; coumarin v koncentrácii 5. 10^-4 M a EDTA v koncentrácii 10^-3 M. Reakcia prijmu vody na aplikáciu rastových substancii a coumarínu bola v?dy negatívna. EDTA nevplývala bezprostredne na intenzitu príjmu vody. Za?iatok inhibície príjmu vody, vyvolanej rastovými substanciami, sa objevuje náhle. Coumarín vyvoláva pomalú, progresivne narastajúcu inhibiciu príjmu vody. Bola zistená zhoda ?asového priebehu zmien v intenzite príjmu vody za prítomnosti vysokých koncentrácii rastových látok a coumarínu v koreňovom prostredí, s ?asovým priebehom zmien v intenzite transpirácie, zistenými v analogických podmienkach Allerupom (1964). To sa pova?uje za dal?i argument pre opodstatnenost hypotézy, podla ktorej prí?inou rýchlych zmien intenzity transphácie za prítomnosti vysokýeh koncentrácii rastových látok v koreňovom médiu sú rýchle zmeny v intenzite príjmu vody.     

Effects of Osmotic Potential in Nutrient Solution on Diurnal Growth of Tomato Fruit

Tomato fruit on plants grown in circulating nutrient solutionexhibited a diurnal cycle in growth rate, measured as a changein diameter, with a maximum during thc day. The diurnal growthcycle was less evident in those fruit grown at high electricalconductivity (17 mS), or on days of reduced irradiance. Girdledfruit of low conductivity plants grew at a much reduced ratewith a diurnal cycle in reverse to that of ungirdled fruit,while girdled fruit of high conductivity plants showed no diurnalgrowth. The evidence suggests that phloem and xylem water transportinto fruit operate on opposite diurnal cycles. Partitioning of available xylem water in detached fruit betweenthe calyx and berry, as well as within the berry, was determinedby berry size and relative humidity in the air. Although berrytranspiration rate was unaffected by conductivity treatmentduring plant growth, water uptake capacity was greatly reducedin the berry from high conductivity plants, suggesting an increasedresistance in the xylem transport system within the fruit. Key words: Salinity, electrical conductivity, tomato fruit, xylem transport, transpiration     

The Relationship between Transpiration, Root Water Uptake, and Leaf Water Potential

The effect of changing the transpiration rate on leaf waterpotential and water balance has been examined to show if permeabilityof the plant (predominantly the roots) is constant or varieswith the transpiration rate. Measurements of leaf effectivethickness, water potential, transpiration, and uptake of waterby roots were made on sunflower, barley, and maize plants grownin solution culture and subjected to a range of atmosphericconditions and root treatments: cooling, low osmotic potential,and removal of part of the root system. Leaf water potential changed little under a wide range of atmosphericconditions and rates of water flux in the three species, sothat the root permeability to water increases as the rate oftranspiration, and therefore flow across the root surface, increases.Equality between uptake and loss of water and thereby maintenanceof constant leaf water potential is assisted by stomatal changes,which appear to be in response to conditions at or in the rootrather than a direct response to changes in bulk leaf waterpotential.     

The Effect of Low Osmotic Potential on Phosphate Uptake and Metabolism by Beetroot Discs

The uptake of phosphate by aged beetroot discs was examinedunder a range of water deficits which were induced osmoticallywith mannitol or polyethylene glycol At low water potentialsthe absorption of labelled phosphate was enhanced when the ambientconcentration of phosphate was high (10^–3 M) and the timefor absorption was short (30 mm): this occurred even when themetabolism was inhibited (by the water deficit), as indicatedby lowered oxygen consumption and incorporation of ³³P intohexose-phosphate, phosphoglycenc acid, a liquid fraction, anda precipitate consisting mainly of cell walls. The Q₁₀ of theuptake process approached unity at these low water potentials.Accompanying the enhanced uptake there was an increase in leakageof previously absorbed phosphate. It is postulated that thestimulation in uptake of phosphate in low osmotic potentialswas due to an increase in permeability Over long periods (6 h) uptake was inhibited by treatment atlow osmotic potentials. This is interpreted in terms of inhibitionof a metabolic component of phosphate uptake.     

Water Uptake and Germination of Leguniinous Seeds Under Changing External Water Potential in Osmotic Solutions

Water uptake patterns and germination rates of chickpea (Cicerarietinum L.) and veteh (Vicia faba L.), as affected by constantand changing external water potential, were studied experimentally.The initial water uptake rate was found to decrease as the externalwater poten tial decreased, due te reduced diffusivity to waterof the seed coats, but the final water gained by imbibitionwas sufficient to ensure full germination. Germination ratedecreased with a decrease in the external water potential. Thedata presented suggest that more work should be directed towarda better understanding of the effects of external water potentialchanges on the enzymatic activity during and after the imbibitionstage.     

Water Uptake and Germination of Leguminous Seeds in Soils of Changing Matric and Osmotic Water Potential

Water uptake and germination rate of chickpea and pea seedswere compared under changing water potentials in sand and soilaggregate columns and osmotic solutions. The final water uptake and germination were the same in allcases for a given water potential, but the rates were lowerfor seeds planted in sand columns, probably due to mechanicalconstraints imposed on the swelling seed by the dense sand,since the capillary conductivity, and the diffusivity to waterof the sand were very high. The area of the seed in contact with soil is not of importanceif soil aggregates are small as compared to the seeds but increasesin importance when the seeds and the soil aggregates are ofthe same size and at low water potentials.     

Oscillatory Transpiration and Water Uptake of Avena Plants

The action of D₂O on oscillatory transpiration of Avena plants was investigated. D₂O affects the amplitude and the period of the oscillations when given as a root medium to intact plants. The period is then dependent on the amplitude. From such experiments it is not possible to conclude whether the period change is simply due to the changed amplitude or to a change in the stomatal parameters. When given to xylem compressed, excised plants without roots, the D₂O hardly affects the amplitude of the oscillations but the period is increased. Thus, the period of the self-sustained transpiratory oscillations is lengthened by D₂O action on the stomatal parameters. Phase and amplitude changes of the oscillatory transpiration caused by short D₂O pulses given both to intact and excised plants, are discussed. The following conclusion is emphasized: a substance which affects the root system can also cause profound changes in the stomatal water regulation.     

Oscillatory Transpiration and Water Uptake of Avena Plants

Xylem vessels in the lower part of the leaf of young Avena plants have been exposed to deformation by application of an external pressure. In this way a resistance to the water flow at the deformation site has been achieved, inducing undamped oscillations in transpiration and water uptake, even after removal of the root system.     

Oscillatory Transpiration and Water Uptake of Avena Plants

The transpiration rate of oat plants, 6 days old, has been investigated. Dependent on the irradiance level of the white light used in the experiments, the transpiration rate oscillated with different period times. In darkness or at low irradiances the period was about 100–110 min. At higher irradiances the period was about 40 min. At intermediate irradiances autocorrelation analysis was used to find the period content of the transpiration rate. It was concluded that two oscillatory systems were present in the plants, characterized by their different periods. When plants cultivated in a light/dark cycle were used, the transpiration oscillations were influenced by a circadian rhythm. Oscillations in darkness were then most pronounced in the mornings. Plants cultivated in continuous light did not show such a circadian rhythm, but the oscillations died out after about 20 h. Kinetin induced transpiration oscillations in darkness and made them sustain for a longer time.     

Oscillatory Transpiration and Water Uptake of Avena Plants

The oscillatory transpiration of 6 days old Avena plants was investigated with respect to the water potential of the root medium. The desired water potential was obtained by means of mannitol solutions. When the water potential was lowered (“mannitol step”), the amplitude of the oscillations decreased. Below –3.0 bars no oscillations persisted. A detailed study was made of the phase changes of the oscillations caused by a short time decrease of the water potential of the root medium (“mannitol pulse”). The duration of these short term treatments was either 9.0, 3.0 or J.5 min. The experimental results are discussed on the basis of an electric analogue previously presented in the literature. Published simulations based on the model were in clear contrast to the present experimental results as well as to earlier results in the literature. However, simulations in the present paper showed that the model could explain the experimental results if suitable parameter values were chosen.     

Leaf Water Potential Response to Transpiration by Citrus

This paper reports on further studies of a model for interpreting leaf water potential data for Citrus. Experimental data confirmed the assumption that the ratio of vapor pressure deficit to leaf diffusion resistance adequately estimates transpiration when leaf-to-air temperature differences are small. Data collected diurnally indicated that the relationship between leaf water potential and transpiration followed a sequence of steady states without hysteresis. No difference in water transport characteristics was found for Valencia orange on three rootstocks in well-watered soil, but the two rootstocks Cleopatra mandarin and Rangpur gave slightly greater leaf water stress in Valencia orange leaves than‘Troyer’ citrange rootstock at high transpiration rates under mild soil water deficits. In laboratory studies, previously unstressed seedlings had higher leaf water potentials than field trees at equivalent transpiration rates. After several drying cycles, however, leaf water potentials were similar to those observed in the field.     

Transpiration and Water Uptake in the Fruit Bodies of Some Hymenomycetes

The relationship between relative humidity and transpiration was studied in the basidiocarps of Coprinus, Amanita, Agaricus, Tricholoma, Collybia and Polyporus. Transpiration decreases with an increase in the humidity and there is virtually no transpiration in nearly saturated air. To determine the relationship between uptake and transpiration, stipes were immersed in solutions of various osmotic ally active substances and inhibitors. Results showed that uptake has no influence on the transpiration. Additional data suggested that uptake in a detached basi-diocarp proceeds as long as the fruit body is young and healthy. Studies with fluorescein dye and mannitol showed that most transpiration occurs at the surface and edges of the hymenium.     

Gibberellin-Induced Changes in the Water Absorption, Osmotic Potential and Starch Content of Cucumber Hypocotyls

The effects of GA₃ on the water absorption, osmotic potentialand starch content of light-grown cucumber (cv. Aonagajibai)hypocotyl sections were examined. GA₃ (100µM.) stimulatedfresh weight increase as well as elongation. It had no effecton the dry weight change in the presence, or absence, of 50mM sucrose although dry weight increased significantly in thepresence of sucrose. In the absence of sucrose the weight wasunchanged. The osmotic potential of the epidermal cells of sectionsincubated with GA₃ was lower than that of the control, and thedifference between the two values was larger in young seedlings.When sections were incubated with sucrose, the osmotic potentialgreatly decreased. This decrease was more marked in the presenceof GA₃. GA₃ reduced the starch content of the sections bothin the presence and absence of sucrose. The total amount ofstarch, however, was markedly increased in its presence. Thedegradation of starch formed in advance from exogenous sucrosein light was not accelerated by GA₃. We discuss a possible rolefor gibberellin in cell elongation, based on our results, interms of cell water relations. (Received January 18, 1983; Accepted July 19, 1983)     

Environmental Effects on Transpiration and Leaf Water Potential in Avocado

A field study was conducted to determine how atmospheric and edaphic conditions influenced the water relations of avocado trees (Persea americana Mill. cv. Bacon). With high and low levels of incident photosynthetically active radiation (PAR, 400–700 nm wave length), and either wet or dry soil, leaf conductance decreased as the absolute humidity difference from leaf to air increased. For any water stress treatment, conductance was higher at high PAR than at low PAR. Both conductance and transpiration were higher in well-watered trees than in stressed trees, and in prestressed trees levels were intermediate to unstressed and stressed trees. A model for water flux through the soil-plant-atmosphere continuum was used to examine the relationship of leaf xylem pressure potential to transpiration in well-watered trees and in trees stressed by dry soil. There was a close linkage between leaf xylem pressure potential and transpiration in unstressed and previously stressed trees with high or low PAR, i.e. similar potentials occurred with equivalent transpiration regardless of previous treatment or time of day. In stressed trees, xylem pressure potential was lower than in unstressed trees both during the day and night, and at a given transpiration rate the potential was lower after 1400 h than before that time. The model indicated that in stressed trees xylem pressure potential was uncoupled from transpiration, presumably because of altered resistance in the soil-root portion of the transport system.     

营养液照光引起的化学变化及其对植物生长的影响

水稻(Oryza sativa)根系照光实验表明, 光的效应随循环水影响到不照光的植株, 暗示营养液中发生了化学变化。在Si (K₂SiO₃)和Fe (FeEDTA)组成的溶液模拟系统中, 分别照射LED-紫光或阳光, 观察到反应液的OD₄₀₀值随光照时间的延长而增加。光照引起的化学变化发生在FeEDTA和K₂SiO₃之间。化学变化只与光能量有关, 与溶液温度无关, 这是一种光化学反应。光化反应溶液的光吸收从OD₃₆₀到OD₅₆₀都有明显增高。LED-蓝光和阳光诱导产生的并含FeEDTA-SiO₃成分并能吸收光的二元螯合铁硅酸盐复合物附着在衬底膜上, 形成三元复合物。衬底膜上可见大量的颗粒, 其中有些是反光的微晶颗粒。除LED-蓝光和阳光外, LED-紫光、LED-红光和LED-红外光也能诱导产生光谱性质相同的螯合铁硅酸盐复合物。制备含螯合铁硅酸盐复合分子的溶液并进行植物生长实验, 结果显示小球藻生长好, 死亡的藻体分解褪色后留下的是褐色的蓬松团状铁-硅化物。经螯合铁硅酸盐复合物处理的水稻干重增加明显。