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ABSTRACT: The dynamics of stomatal resistance and osmotic adjustment in response to plant water deficits and stage of physiological development was studied in the leaves of spring wheat (Triticum aestivum L., GWO 1809). Plants were germinated and grown in pots in a growth chamber at the Duke University Phytotron to four physiological stages of development (4th leaf, 7th leaf, anthesis, and soft dough), during which time stomatal resistance, total water potential and osmotic potential were measured on the last fully developed leaf of water stressed and non-stressed plants. Pressure potential was obtained by difference. Stomatal closure of the abaxial and adaxial surfaces were independent of each other, each having a different critical total water potential. The total water potential required to close the stomata on the last fully developed leaf were different at different stages of physiological development, decreasing as the plants grew older. The development of osmoregulation in wheat allows the closure of stomata during the vegetative stage at a high total water potential, but insures that stomata remain open from anthesis through the ear filling period to a lower total water potential.
Physiologia Plantarum 04/2006; 55(3):296 - 300. · 3.11 Impact Factor
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ABSTRACT: Abstract Root fatty acid composition, photosynthesis, leaf water potentials, stomatal resistances, leaf specific weights, and root: shoot ratios of soybean were measured in two temperature regimes.Groups of soybean plants were grown in controlled chambers of the Duke University Phytotron under two thermoperiods. One group of the plants was grown from seed for 3 weeks in either 29/23°C or 17/11°C thermoperiods, and another group was grown for 2 weeks in 29/23°C and then transferred to the 17/11°C thermoperiod where it remained for 8 days. Broccoli was also grown in either 29/23°C or 17/11°C thermoperiods.Soybean roots contained more unsaturated fatty acids than broccoli roots, although broccoli roots showed a larger increase in unsaturation than soybean roots with decreased temperature. The fatty acid unsaturation in the roots of soybean began to increase rapidly after the temperature regime was changed. The increase was in the new roots produced in the cold regime rather than in the pre-existing roots.The soybean leaf water and osmotic potentials decreased about 0.4 MPa, beginning one day after the transfer from 29/23°C to 17/11°C, but recovered significantly after 8 d.Plants grown at 17/11 °C had lower rates of photosynthesis and adaxial stomatal resistances, but higher root: shoot ratios and specific leaf weights compared to plants grown at 29/23°C. Plants grown and maintained at 29/23°C showed a steady increase in photosynthetic rates over the 8-d experimental period, whether rates were measured in 1 mol m−3 or 9 mol m−3 oxygen. Plants transferred to 17/11°C however maintained constant rates of photosynthesis at 1 mol m−3 O2, whereas at 9 mol m−3 rates declined for 2 d then were constant for the remaining 6 d of the experimental period.These results suggest that changes in membrane fatty acid unsaturation is an important aspect of plant acclimation to chilling temperatures in terms of maintaining root permeability and water uptake. However, the degree of unsaturation is not a good indicator of differences in chilling tolerance among species. The apparent acclimation of photorespiration to a constant percentage of photosynthesis suggests a role of photorespiration in the plant.
Plant Cell and Environment 04/2006; 3(6):435 - 441. · 5.22 Impact Factor
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ABSTRACT: Magnetic resonance imaging (MRI) was used to nondestructively observe changes in water content in roots of Pelargonium hortorum x Bailey during a period of relatively rapid transpiration. Anatomical regions of the root could be differentiated with a spatial resolution of 0.1 x 0.1 mm. MRI shows great potential for study of plant-water relations.
Plant physiology 01/1987; 82(4):1158-60. · 6.53 Impact Factor
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ABSTRACT: The effects of SO(2) on stomatal aperture of attached sunflower leaves were observed with a remote-control light microscope system that permitted continuous observation of stomatal responses over periods of several hours. The relationship between actual stomatal aperture and stomatal conductance, measured with a porometer, also was examined on leaves before and after exposure to SO(2).A distinction between uninjured and injured regions was clearly visible on leaves after exposure to 1.5 microliters per liter SO(2) for less than an hour. During the exposure, the mean value of apertures for many stomata, which indicates stomatal conductance and transpiration rate, tended to decrease simultaneously in the uninjured and injured regions. However, the rate of decrease in the injured region was slower than that in the uninjured region because of a transient opening induced by water-soaking in the injured region. The transient opening was less common in stomata near veins and veinlets.There was a good correlation between pore width and stomatal conductance measured with a porometer before exposure to SO(2). This correlation continued in leaves exposed to SO(2) until visible, irreversible injury occurred, but then it disappeared.The results of these experiments indicate the necessity of continuous observation of individual stomata under the microscope to understand the effects of air pollutants such as SO(2) on stomatal behavior.
Plant physiology 10/1985; 79(1):153-8. · 6.53 Impact Factor
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ABSTRACT: This paper describes a method for measuring the temperatures of all regions of an intact leaf by using an infrared scanning thermometer at wavelengths between 8 and 14 micrometers combined with a digital image processing system. Pictures obtained every 2 minutes from leaves of sunflower (Helianthus annuus L. cv Large Russian) plants subjected to increasing water stress showed that water deficit develops first at the margins of leaves, accompanied by stomatal closure and increase in temperature. Finally, the temperature of the entire leaf rises 3 to 5 degrees C above that of nonstressed leaves. When transpiration resumed, it did so first at the leaf margins and these proceeded nonuniformly inward.The results of these experiments indicate that there are significant differences in the temperature and water status of different parts of a leaf. This makes it important to determine causes of such behavior and decide in what part of a leaf the temperature and water status should be measured. The thermo-imaging method can be useful in monitoring short term temperature changes occurring in leaves undergoing water, chilling, and other stresses.
Plant physiology 10/1984; 76(1):266-9. · 6.53 Impact Factor
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ABSTRACT: The immediate short term effects on some physiological processes and the long term effects on morphology and reproductive development of root- and shoot-chilled soybeans (Glycine max L. cv Ransom) were studied. Roots or shoots of 16- or 17-day-old plants were chilled at 10 degrees C for one week, and then rewarmed to 25 degrees C. Leaf elongation rate, net CO(2) uptake rate, and stomatal conductance decreased during root or shoot chilling. Root chilling had only temporary effects on water relations, while shoot chilling caused large changes in potentials during chilling. Most processes measured returned to control levels after two days of rewarming. Root-chilled plants harvested 90 days after emergence were similar in morphology and seed weight to controls. Shoot-chilled plants showed a large increase over controls in axillary branch growth, but an early abortion of flowers and a delayed resumption of flowering caused a 78% reduction in seed weight. Root chilling in this study was found to have little or no long term effect on the plants, while shoot chilling caused significant changes in vegetative morphology, and a delay in flowering and subsequent pod filling.
Plant physiology 12/1983; 73(3):778-83. · 6.53 Impact Factor
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ABSTRACT: The effect of sink strength on photosynthetic rates under conditions of long-term exposure to high CO(2) has been investigated in soybean. Soybean plants (Merr. cv. Fiskeby V) were grown in growth chambers containing 350 microliters CO(2) per liter air until pod set. At that time, plants were trimmed to three trifoliolate leaves and either 21 pods (high sink treatment) or 6 pods (low sink treatment). Trimmed plants were either left in 350 microliters CO(2) per liter of air or placed in 1000 microliters CO(2) per liter of air (high CO(2) treatment) until pod maturity. Whole plant net photosynthetic rates of all plants were measured twice weekly, both at 350 microliters CO(2) per liter of air and 1000 microliters CO(2) per liter of air. Plants were also harvested at this time for dry weight measurements. Photosynthetic rates of high sink plants at both measurement CO(2) concentrations were consistently higher than those of low sink plants, and those of plants given the 350 microliter CO(2) per liter of air treatment were higher at both measurement CO(2) concentrations than those of plants given the 1000 microliters CO(2) per liter of air treatment. When plants were measured under treatment CO(2) levels, however, rates were higher in 1,000 microliter plants than 350 microliter CO(2) plants. Dry weights of all plant parts were higher in the 1,000 microliters CO(2) per liter air treatment than in the 350 microliters CO(2) per liter air treatment, and were higher in the low sink than in the high sink treatments.
Plant physiology 06/1981; 67(5):1007-10. · 6.53 Impact Factor
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ABSTRACT: The effects on water status and growth of controlled cycles of water stress applied at various stages of development were studied on a semi-dwarf spring wheat (Triticum aestivum L.). The plants were grown in controlled environment chambers of the Duke University Phytetron at 24/18°C with a 12-h photo-period at about 600 μE m−2 s−1. Groups of plants were subjected to severe water stress by withholding irrigation, beginning at the 7th leaf, early anthesis, or early dough stages of development. A second cycle started 9 to 13 days after termination of the first cycle and maintained until the flag leaf water potential reached –25 bars at each of the growth stages.The lower leaves showed sign of wilting as indicated by curling in the first drying cycle at –7 bars and in the second cycle at –9 bars of leaf water potential during all stages of growth. Although these leaves recovered completely upon rewatering, onset of senescence was accelerated by three days in stressed plants. A preliminary drying cycle did not increase the ability of the plants to withstand subsequent stress because of severity of stress. Water stress of –25 bars at all three stages of growth reduced seed yield. The reduction was greater when a second stress cycle was also applied. Stress applied during early anthesis stage produced the smallest and the least number of seeds. The lack of osmotic adjustment probably was due to very rapid and severe development of water stress.
Physiologia Plantarum 08/1980; 50(1):11 - 15. · 3.11 Impact Factor
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ABSTRACT: Reports of the effects of abscisic acid (ABA) on ion and water fluxes have been contradictory. Some of the confusion seems due to the interaction of ion and water transport across membranes. In these experiments root systems were subjected to hydrostatic pressures up to 5.0 bars to enable measurement of root conductance that was independent of measurement of osmotic potentials or ion fluxes.ABA between 5 x 10(-5) molar and 2 x 10(-4) molar resulted in a decrease in the conductance of the soybean root systems as compared with the controls. ABA treatment also eliminated the discontinuity in the Arrhenius plot of total flow versus reciprocal temperature at constant pressure. The results suggest that ABA acts at the membrane that is rate-limiting to water flow directly, or by altering metabolism that in turn affects the membrane.
Plant physiology 11/1979; 64(4):611-4. · 6.53 Impact Factor
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ABSTRACT: Steady-state flow rates and exudate osmotic potentials were measured from complete root systems from warm- (28/23 C) or cold-(17/11 C) grown soybean or broccoli (Brassica oleracea) plants at various pressures or different temperatures.In warm-grown soybean roots systems, a break occurred at 14.7 C in the Arrhenius plot of total flow at constant pressure. When plants were grown at lower temperatures, the break point shifted to 8 C. Broccoli, a chilling-resistant species, showed no break for the temperature range used, but cooler growth temperatures decreased the activation energy for water flow through the root system from 18 kilocalories per mole to 9 kilocalories per mole. In both broccoli and soybean, cold-grown plants had lower exudate potentials and greater flow rates at low hydrostatic pressures than the warm-grown plants.These observations indicate that the rate-limiting site for passive water transport is a membrane which may be modified as the plant acclimates to varying growth temperatures. An additional part of the acclimation process is an increase in activity of root ion pumps.
Plant physiology 08/1979; 64(1):83-7. · 6.53 Impact Factor
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ABSTRACT: Plants of two varieties of soybean (Glycine max (L.) Merr.) and two varieties of sunflower (Helianthus annuus L.) were grown in controlled environments and subjected to water stress at various stages of growth. Leaf resistances and leaf water potentials were measured as stress developed. In soybeans the upper leaf surface had a higher resistance than the lower surface at all leaf water potentials and growth stages. Resistance of the upper surface began to increase at a higher water potential and increased more than the resistance of the lower surface. Resistances returned to prestress values 4 days after rewatering. In sunflowers upper and lower leaf surfaces had similar resistances at all water potentials and growth stages. Leaf resistances were higher in sunflower plants stressed before flowering than in those stressed later. Sunflower plants stressed to -16 bars recovered their prestress leaf resistance and water potential a few days after rewatering, but leaves of sunflower plants stressed to -23 bars died. Leaves of soybean and sunflower plants stressed before flowering suffered less injury than those of older plants and sunflowers stressed after flowering suffered more injury than soybeans.
Plant physiology 11/1976; 58(4):537-40. · 6.53 Impact Factor
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ABSTRACT: This paper presents a general model to describe coupled solute and water flow through plant roots when they are subjected to osmotic or hydrostatic pressure gradients, or both simultaneously. The model is based on well-established membrane transport equations derived from irreversible thermodynamic considerations. A variety of experimentally observed phenomena such as changes in root resistance with flow rate, apparent negative resistance effects, xylem sap dilution, and apparent non-osmotic water transport can be adequately explained with this model. The model also predicts that an exuding excised root system will be very insensitive to changes in the hydraulic conductivity coefficient. Previous work with a flat membrane of unit surface area and uniform properties is confirmed for a cylindrical coordinate system of nonuniform characteristics.
Proceedings of the National Academy of Sciences 09/1975; 72(8):3114-8. · 9.68 Impact Factor
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P J Kramer
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ABSTRACT: Many of the basic concepts dealing with soil and plant water relationships were in existence 50 years ago, but were inadequately presented in the textbooks of that time. There has been a marked increase in the amount of work done in this field during recent decades, but much of it involves advances in understanding the concepts already in existence. Three of the most important advances in the field of water relations are: (a) acceptance of the term, water potential, to describe the free energy status of water in soil and plants; (b) marked improvement in methods of measuring water potential and stomatal resistance; and (c) use of the concept of water flow in the soil-plant system as analogous to flow of electricity in a conducting system.A number of interesting and important problems remain to be studied. Of these, probably the most important is to learn why mild water stress of less than - 10 bars can affect various enzyme-mediated metabolic processes. Plant scientists in applied fields also need to learn more about the causes of differences in ability to tolerate drought among plants of various kinds. There is uncertainty concerning the relative magnitude of the resistances to water flow in various parts of the soil-plant system and concerning the causes of the apparent changes in resistance to water flow with increase in rate and with time of day. More information also is needed concerning the role of growth regulators synthesized in roots and the importance of the older, suberized roots in the absorption of water and mineral nutrients.
Plant physiology 11/1974; 54(4):463-71. · 6.53 Impact Factor
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ABSTRACT: Corn (Zea mays L.) and sorghum (Sorghum vulgare, Pers.) plants were grown in a vermiculite-gravel mixture in controlled environment chambers until they were 40 days old. Water was withheld until they were severely wilted, and they were then rewatered. During drying and after rewatering stomatal resistance was measured with a diffusion porometer each morning, and water saturation deficit and water potential were measured on leaf samples. The average resistance of the lower epidermis of well watered plants was lower for corn than for sorghum. When water stress developed, the stomata began to close at a higher water potential in corn than in sorghum. The stomata of both species began to reopen normally soon after the wilted plants were rewatered, and on the 2nd day the leaf resistances were nearly as low as those of the controls. The average leaf water potential of well watered corn was -4.5 bars; that of sorghum, -6.4 bars. The lowest leaf water potential in stressed corn was -12.8 bars at a water saturation deficit of 45%. The lowest leaf water potential in stressed sorghum was -15.7 bars, but the water saturation deficit was only 29%. At these values the leaves of both species were tightly rolled or folded and some injury was apparent. Thus, although the average leaf resistance of corn is little lower than that of sorghum, corn loses much more of its water before the stomata are fully closed than does sorghum. The smaller reduction in water content of sorghum for a given reduction in leaf water potential is characteristic of drought-resistant species.
Plant physiology 12/1971; 48(5):613-6. · 6.53 Impact Factor
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ABSTRACT: The radial movement of oxygen in excised corn and jack bean roots was measured with a platinum wire electrode embedded in the root tissue. Measurements were made with the roots exposed to air and with the roots immersed in nutrient solution in the presence and absence of millimolar sodium azide. Effective rates of oxygen diffusion in the root tissue were also measured from 5 to 30 C and compared to the respiration rates of similar root segments over the same temperature range. Under conditions which allow the roots to exude freely, the interior of the root operates under an oxygen deficit. Inhibition of respiratory oxygen uptake by low temperature or azide treatment increased the flux of oxygen to the root interior.
Plant physiology 07/1970; 45(6):667-9. · 6.53 Impact Factor
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ABSTRACT: Earlier reports that the water potential of sliced leaf tissue is higher than that of unsliced control tissue are confirmed. The effect is shown to increase as damage to the tissue due to slicing is increased. However, there is some evidence that increase in damage beyond a certain point causes water potentials to fall again towards the control value. The electrical resistance of washings from sliced leaf tissue increases with increase in the time interval between slicing and washing. Both the rise in water potential of sliced tissue and the rise in electrical resistance of washings are partially and reversibly inhibited by low temperature. These results suggest that the remaining intact cells actively accumulate solutes released from the cells cut open on slicing. The sap from the sliced cells is thereby diluted and flows passively into the intact cells. Since pressure potential changes more rapidly with cell volume than does osmotic potential, the net result is a rise in the total water potential of sliced tissue. It is concluded that this effect may cause spuriously high water potential values to be measured if excessively small pieces of leaf tissue are used. This is demonstrated with stacks of annuli cut from leaves.
Plant physiology 08/1969; 44(7):959-64. · 6.53 Impact Factor
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ABSTRACT: The dye method for measuring water potential was examined and compared with the thermocouple psychrometer method in order to evaluate its usefulness for measuring leaf water potentials of forest trees and common laboratory plants. Psychrometer measurements are assumed to represent the true leaf water potentials. Because of the contamination of test solutions by cell sap and leaf surface residues, dye method values of most species varied about 1 to 5 bars from psychrometer values over the leaf water potential range of 0 to -30 bars. The dye method is useful for measuring changes and relative values in leaf potential. Because of species differences in the relationships of dye method values to true leaf water potentials, dye method values should be interpreted with caution when comparing different species or the same species growing in widely different environments. Despite its limitations the dye method has a usefulness to many workers because it is simple, requires no elaborate equipment, and can be used in both the laboratory and field.
Plant physiology 11/1967; 42(10):1315-20. · 6.53 Impact Factor
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ABSTRACT: Primary roots of solution-grown, 5-day-old or 6-day-old seedlings of corn (Zea mays L.) 10 to 14 cm in length were used to study radial salt transport. Measurements were made of the volume of root pressure exudation, salt concentration of the exudate, and rate of salt movement into the xylem exudate. The (32)P uptake, O(2) consumption, and dehydrogenase activity of the root cortex and stele also were studied.These roots produced copious root pressure exudate containing 4 to 10 times the concentration of (32)P in the external solution. Freshly separated stele from 5-day-old roots accumulated (32)P as rapidly as the cortex from which it was separated and the stele of intact roots also accumulated (32)P. Separated stele has a higher oxygen uptake than cortex. It also shows strong dehydrogenase activity with the tetrazolium test. The high oxygen consumption, (32)P uptake and strong dehydrogenase activity indicate that the cells of the stele probably play a direct role in salt transport.These data raise doubts concerning theories of radial salt transport into the xylem based on the assumption that the stele is unable to accumulate salt vigorously.
Plant physiology 08/1967; 42(7):985-90. · 6.53 Impact Factor
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ABSTRACT: Satisfactory measurements of phloem water potential of trees can be obtained with the Richards and Ogata psychrometer and the vapor equilibration techniques, although corrections for loss of dry weight and for heating by respiration are required for the vapor equilibrium values. The psychrometer technique is the more satisfactory of the 2 because it requires less time for equilibration, less tissue, and less handling of tissue. Phloem water potential of a yellow-poplar tree followed a diurnal pattern quite similar to that of leaves, except that the values were higher (less negative) and changed less than in the leaves.The psychrometer technique permits a different approach to the study of translocation in trees. Measurements of water potential of phloem discs followed by freezing of samples and determination of osmotic potential allows estimation of turgor pressure in various parts of trees as the difference between osmotic potential and total water potential. This technique was used in evaluating gradients in water potential, osmotic potential, and turgor pressure in red maple trees. The expected gradients in osmotic potential were observed in the phloem, osmotic potential of the cell sap increasing (sap becoming more dilute) down the trunk. However, values of water potential were such that a gradient in turgor pressure apparently did not exist at a time when rate of translocation was expected to be high. These results do not support the mass flow theory of translocation favored by many workers.
Plant physiology 03/1967; 42(2):191-4. · 6.53 Impact Factor
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ABSTRACT: Use of the term "water potential" in place of "diffusion pressure deficit" would improve communication between botanists and scientists in other fields because the concept of potential is familiar to most scientists. Water potential, expressed as PsiW, is the difference in free energy or chemical potential per unit molal volume between pure water and water in cells at the same temperature. The potential of pure water is set at zero; hence the potential of water in cells and solutions is less than zero, or negative. The water potential of a cell is numerically equal to its diffusion pressure deficit, but has a negative sign.
Science 09/1966; 153(3738):889-90. · 31.20 Impact Factor
