Biomedical subjects

P S Nobel

Publications and source records attributed to P S Nobel.

At least 19 recordsLinked to original sources

PubMed2001

Hydraulic conductance and mercury-sensitive water transport for roots of Opuntia acanthocarpa in relation to soil drying and rewetting.

Drought-induced changes in root hydraulic conductance (LP) and mercury-sensitive water transport were examined for distal (immature) and mid-root (mature) regions of Opuntia acanthocarpa. During 45 d of soil drying, LP decreased by about 67% for distal and mid-root regions. After 8 d in rewetted soil, LP recovered to 60% of its initial value for both regions. Axial xylem hydraulic conductivity was only a minor limiter of LP. Under wet conditions, HgCl2 (50 microM), which is known to block membrane water-transport channels (aquaporins), decreased LP and the radial hydraulic conductance for the stele (L(R, S)) of the distal root region by 32% and 41%, respectively; both LP and L(R, S) recovered fully after transfer to 2-mercaptoethanol (10 mM). In contrast, HgCl2 did not inhibit LP of the mid-root region under wet conditions, although it reduced L(R, S) by 41%. Under dry conditions, neither LP nor L(R, S) of the two root regions was inhibited by HgCl2. After 8 d of rewetting, HgCl2 decreased LP and L(R, S) of the distal region by 23% and 32%, respectively, but LP and L(R, S) of the mid-root region were unaltered. Changes in putative aquaporin activity accounted for about 38% of the reduction in LP in drying soil and for 61% of its recovery for the distal region 8 d after rewetting. In the stele, changes in aquaporin activity accounted for about 74% of the variable L(R, S) during drought and after rewetting. Thus, aquaporins are important for regulating water movement for roots of O. acanthocarpa.

Aquaporins↗

PubMed2001

Biomechanics and anatomy of cladode junctions for two Opuntia (Cactaceae) species and their hybrid.

Hybridization between the introduced arborescent Opuntia ficus-indica and the native shrubby O. littoralis has led to populations, referred to as O. "occidentalis," which form thickets that can dominate hillsides of chaparral and that can survive fires. Because the thickets apparently develop via vegetative reproduction, O. "occidentalis" was hypothesized to have a greater ability than its parent species to reproduce vegetatively due to weaker cladode junctions. Of the three taxa, the junctions for O. "occidentalis" had the least amount of wood, despite having cladode masses and junction cross-sectional areas similar to those of O. littoralis. The cladodes of O. "occidentalis" resisted deflection about their junctions the least and their junctions required the least amount of applied mass and the smallest bending moment to fail mechanically. The junction wood for all three taxa consisted mostly of parenchyma, with lesser amounts of cells with thickened secondary cell walls, indicating that some junction strength depended on hydrostatic pressure, especially for terminal junctions. Libriform fibers, which contribute to support and resist bending moments, were about 80% less frequent in the sub-subterminal junctions of O. "occidentalis" than in O. ficus-indica and O. littoralis. Vascular tracheids, which probably reduced shear among cells in the wood, were 90% less frequent in the terminal and sub-subterminal junction wood of O. "occidentalis" compared to O. littoralis. Thus wood characteristics can account for the weaker junctions of O. "occidentalis" compared to those of O. ficus-indica and O. littoralis, which apparently increases the ability of the hybrid to reproduce vegetatively.

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PubMed1999

Loss of water transport capacity due to xylem cavitation in roots of two CAM succulents.

Loss of axial hydraulic conductance as a result of xylem cavitation was examined for roots of the Crassulacean acid metabolism (CAM) succulents Agave deserti and Opuntia ficus-indica. Vulnerability to cavitation was not correlated with either root size or vessel diameter. Agave deserti had a mean cavitation pressure of -0.93 ± 0.08 MPa by both an air-injection and a centrifugal method compared to -0.70 ± 0.02 MPa by the centrifugal method for O. ficus-indica, reflecting the greater tolerance of the former species to low water potentials in its native habitat. Substantial xylem cavitation would occur at a soil water potential of -0.25 MPa, resulting in a predicted 22% loss of conductance for A. deserti and 32% for O. ficus-indica. For an extended drought of 3 mo, further cavitation could cause a 69% loss of conductance for A. deserti and 62% for O. ficus-indica. A model of axial hydraulic flow based upon the cavitation response of these species predicted that water uptake rates are far below the maximum possible, owing to the high root water potentials of these desert succulents. Despite various shoot adaptations to aridity, roots of A. deserti and O. ficus-indica are highly vulnerable to cavitation, which partially limits water uptake in a wet soil but helps reduce water loss to a drying soil.

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PubMed1991

Diel Patterns of Water Potential Components for the Crassulacean Acid Metabolism Plant Opuntia ficus-indica when Well-Watered or Droughted.

Under well-watered conditions, chlorenchyma acidity in cladodes of Opuntia ficus-indica increased substantially at night, fully accounting for the 0.26-megapascal nocturnal increase in osmotic pressure in the outer 2 millimeters. Osmotic pressure in the inner part of the chlorenchyma and in the water-storage parenchyma did not change significantly over 24-hour periods. Three months of drought decreased nocturnal acid accumulation by 73% and essentially abolished transpiration; also, 27% of the chlorenchyma water and 61% of the parenchyma water was lost during such drought, but the average tissue osmotic pressure was little affected. Turgor pressure was maintained in the chlorenchyma after 3 months of drought, although it decreased sevenfold in the water-storage parenchyma compared with the well-watered condition. Moreover, the nocturnal increases in turgor pressure of about 0.08 megapascal in the outer part of the chlorenchyma was also unchanged by such drought. The water potential magnitudes favored water movement from the parenchyma to the chlorenchyma at the end of the night and in the reverse direction during the late afternoon. Experiments with tritiated water support this pattern of water movement, which is also in agreement with predictions based on electric-circuit analog models for Crassulacean acid metabolism plants.

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PubMed1991

Changes in Osmotic Pressure and Mucilage during Low-Temperature Acclimation of Opuntia ficus-indica.

Opuntia ficus-indica, a Crassulacean acid metabolism plant cultivated for its fruits and cladodes, was used to examine chemical and physiological events accompanying low-temperature acclimation. Changes in osmotic pressure, water content, low molecular weight solutes, and extracellular mucilage were monitored in the photosynthetic chlorenchyma and the water-storage parenchyma when plants maintained at day/night air temperatures of 30/20 degrees C were shifted to 10/0 degrees C. An increase in osmotic pressure of 0.13 megapascal occurred after 13 days at 10/0 degrees C. Synthesis of glucose, fructose, and glycerol accounted for most of the observed increase in osmotic pressure during the low-temperature acclimation. Extracellular mucilage and the relative apoplastic water content increased by 24 and 10%, respectively, during exposure to low temperatures. These increases apparently favor the extracellular nucleation of ice closer to the equilibrium freezing temperature for plants at 10/0 degrees C, which could make the cellular dehydration more gradual and less damaging. Nuclear magnetic resonance studies helped elucidate the cellular processes during ice formation, such as those revealed by changes in the relaxation times of two water fractions in the chlorenchyma. The latter results suggested a restricted mobility of intracellular water and an increased mobility of extracellular water for plants at 10/0 degrees C compared with those at 30/20 degrees C. Increased mobility of extracellular water could facilitate extracellular ice growth and thus delay the potentially lethal intracellular freezing during low-temperature acclimation.

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PubMed1988

Principles underlying the prediction of temperature in plants, with special reference to desert succulents.

The thermal motion of molecules responsible for the property we know as temperature influences essentially every aspect of plant biology. Emphasis in this review is on principles of wide biological applicability, with specific examples being chosen from research on agaves and cacti. Plant temperatures can be predicted using energy budgets incorporating shortwave and longwave radiation, heat conduction and convection, latent heat, and heat storage. Energy budgets are used here to show the effect of plant size and shortwave absorptance on tissue temperature. The importance of air temperature or transcription rate for tissue temperature is calculated quantitatively. The influences of surface appendages, such as apical pubescence and spines, on minimal temperatures near the apical meristem of cacti are predicted, such minimal temperatures influencing the geographical distribution of various species. The Boltzmann energy distribution and Arrhenius plots are presented and used to analyse thermal responses in terms of energy barriers and activation energies. The many ways that temperature can influence CO2 diffusion into a leaf are also considered. Tolerances to low and high temperatures, such as the ability of agaves and cacti to tolerate extremely high tissue temperatures of 70 degrees C, are discussed from both cellular and ecological perspectives. Although the influences of temperature on plants are multitudinous, many can be predicted, or at least analysed, based on well-established physical principles.

Adaptation, Physiological↗

PubMed1987

High-temperature sensitivity and its acclimation for photosynthetic electron transport reactions of desert succulents.

Photosynthetic electron transport reactions of succulent plants from hot deserts are able to tolerate extremely high temperatures and to acclimate to seasonal increases in temperature. In this study, we report the influence of relatively long, in vivo, high-temperature treatments on electron transport reactions for two desert succulents, Agave deserti and Opuntia ficus-indica, species which can tolerate 60 degrees C. Whole chain electron transport averaged 3 degrees C more sensitive to a 1-hour high-temperature treatment than did PSII (Photosystem II) which in turn averaged 3 degrees C more sensitive than did PSI. For plants maintained at day/night air temperatures of 30 degrees C/20 degrees C, treatment at 50 degrees C caused these reactions to be inhibited an average of 39% during the first hour, an additional 31% during the next 4 hours, and 100% by 12 hours. Upon shifting the plants from 30 degrees C/20 degrees C to 45 degrees C/35 degrees C, the high temperatures where activity was inhibited 50% increased 3 degrees C to 8 degrees C for the three electron transport reactions, the half-times for acclimation averaging 5 days for A. deserti and 4 days for O. ficus-indica. For the 45 degrees C/35 degrees C plants treated at 60 degrees C for 1 hour, PSI activity was reduced by 54% for A. deserti and 36% for O. ficus-indica. Acclimation leads to a toleration of very high temperatures without substantial disruption of electron transport for these desert succulents, facilitating their survival in hot deserts. Indeed, the electron transport reactions of these species tolerate longer periods at higher temperatures than any other vascular plant so far reported.

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PubMed1986

Concomitant changes in high temperature tolerance and heat-shock proteins in desert succulents.

Raising the day/night air temperatures from 30 degrees C/20 degrees C to 50 degrees C/40 degrees C increases the high temperature tolerated by Agave deserti, Carnegiea gigantea, and Ferocactus acanthodes by 6 degrees C to 8 degrees C; the increase is about half completed in 3 days and fully completed in 10 days. A 25 to 27 kilodalton protein concomitantly accumulates for all three desert succulents upon transfer to 50 degrees C/40 degrees C, while accumulation of other heat "heat-shock" proteins is species specific. Some of the induced proteins are more abundant at 3 days, while others (including the 25-27 kilodalton protein) remain after completion of high temperature acclimation.

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PubMed1986

Leaf and Stem CO(2) Uptake in the Three Subfamilies of the Cactaceae.

Net CO(2) uptake over 24-hour periods was examined for the leaves and for the stems of 11 species of cacti representing all three subfamilies. For Pereskia aculeata, Pereskia grandifolia, and Maihuenia poeppigii (subfamily Pereskioideae), all the net shoot CO(2) uptake was by the leaves and during the daytime. In contrast, for the leafless species Carnegiea gigantea, Ferocactus acanthodes, Coryphantha vivipara, and Mammillaria dioica (subfamily Cactoideae), all the shoot net CO(2) uptake was by the stems and at night. Similarly, for leafless Opuntia ficus-indica (subfamily Opuntioideae), all net CO(2) uptake occurred at night. For leafy members of the Opuntioideae (Pereskiopsis porteri, Quiabentia chacoensis, Austrocylindropuntia subulata), at least 88% of the shoot CO(2) uptake over 24 hours was by the leaves and some CO(2) uptake occurred at night. Leaves responded to the instantaneous level of photosynthetically active radiation (PAR) during the daytime, as occurs for C(3) plants, whereas nocturnal CO(2) uptake by stems of O. ficus-indica and F. acanthodes responded to the total daily PAR, as occurs for Crassulacean acid metabolism (CAM) plants. Thus, under the well-watered conditions employed, the Pereskioideae behaved as C(3) plants, the Cactoideae behaved as CAM plants, and the Opuntioideae exhibited characteristics of both pathways.

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PubMed1986

Short-Term and Long-Term Responses of Crassulacean Acid Metabolism Plants to Elevated CO(2).

For the leaf succulent Agave deserti and the stem succulent Ferocactus acanthodes, increasing the ambient CO(2) level from 350 microliters per liter to 650 microliters per liter immediately increased daytime net CO(2) uptake about 30% while leaving nighttime net CO(2) uptake of these Crassulacean acid metabolism (CAM) plants approximately unchanged. A similar enhancement of about 30% was found in dry weight gain over 1 year when the plants were grown at 650 microliters CO(2) per liter compared with 350 microliters per liter. Based on these results plus those at 500 microliters per liter, net CO(2) uptake over 24-hour periods and dry weight productivity of these two CAM succulents is predicted to increase an average of about 1% for each 10 microliters per liter rise in ambient CO(2) level up to 650 microliters per liter.

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PubMed1984

Influence of Applied NaCl on Crassulacean Acid Metabolism and Ionic Levels in a Cactus, Cereus validus.

To determine possible physiological responses to salinity, seedlings of Cereus validus Haworth, a cactus from Salinas Grandes, Argentina, were treated with up to 600 millimolar NaCl for up to 16 days when they were about 9 months old and 100 millimeters tall. Salt stress decreased stem biomass, e.g. it was 19.7 grams for controls and 11.4 grams for plants treated with 400 millimolar NaCl for 14 days. Nocturnal CO(2) uptake in these obligate Crassulacean acid metabolism (CAM) plants was inhibited 67% upon treatment with 400 millimolar NaCl for 14 days (controls, 181 millimoles CO(2) per square meter), while nocturnal accumulation of malate was inhibited 49% (controls, 230 millimoles malate per square meter). The larger accumulation of malate as compared to uptake of atmospheric CO(2) suggests that internal CO(2) recycling occurred during the dark period. Such recycling was lower in the controls ( approximately 20%) than in the NaCl-treated plants ( approximately 50%). The nocturnal increase in malate and titratable acidity depended on the total daily photosynthetically active radiation available; measurements suggest a quantum requirment of 26 photons per malate. As NaCl in the medium was increased to 600 millimolar in daily increments of 50 millimolar, Na and Cl concentrations in the roots increased from about 7 to 100 millimolar, but K concentration in the cell sap remained near 26 millimolar. Concomitantly, concentrations of Na and Cl in the shoots increased from 8 to 17 millimolar and from 1 to 7 millimolar, respectively, while the K concentration increased about 16 to 60 millimolar. In plants maintained for 14 days at 500 millimolar NaCl, the root levels of Na and Cl increased to 260 millimolar, the shoot levels were about 60 millimolar, and the stem bases began to become necrotic. Such Na retention in the roots together with the special possibilities of carbon reutilization given by CAM are apparently survival mechanisms for the temporarily saline conditions experienced in its natural habitat.

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PubMed1984

Day-Night Variations in Malate Concentration, Osmotic Pressure, and Hydrostatic Pressure in Cereus validus.

Malate concentration and stem osmotic pressure concomitantly increase during nighttime CO(2) fixation and then decrease during the daytime in the obligate Crassulacean acid metabolism (CAM) plant, Cereus validus (Cactaceae). Changes in malate osmotic pressure calculated using the Van't Hoff relation match the changes in stem osmotic pressure, indicating that changes in malate level affected the water relations of the succulent stems. In contrast to stem osmotic pressure, stem water potential showed little day-night changes, suggesting that changes in cellular hydrostatic pressure occurred. This was corroborated by direct measurements of hydrostatic pressure using the Jülich pressure probe where a small oil-filled micropipette is inserted directly into chlorenchyma cells, which indicated a 4-fold increase in hydrostatic pressure from dusk to dawn. A transient increase of hydrostatic pressure at the beginning of the dark period was correlated with a short period of stomatal closing between afternoon and nighttime CO(2) fixation, suggesting that the rather complex hydrostatic pressure patterns could be explained by an interplay between the effects of transpiration and malate levels. A second CAM plant, Agave deserti, showed similar day-night changes in hydrostatic pressure in its succulent leaves. It is concluded that, in addition to the inverted stomatal rhythm, the oscillations of malate markedly affect osmotic pressures and hence water relations of CAM plants.

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PubMed1983

Relationships between Photosynthetically Active Radiation, Nocturnal Acid Accumulation, and CO(2) Uptake for a Crassulacean Acid Metabolism Plant, Opuntia ficus-indica.

The influences of photosynthetically active radiation (PAR) and water status on nocturnal Crassulacean acid metabolism (CAM) were quantitatively examined for a widely cultivated cactus, Opuntia ficus-indica (L.) Miller. When the total daily PAR was maintained at 10 moles photons per square meter per day but the instantaneous PAR level varied, the rate of nocturnal H(+) accumulation (tissue acidification) became 90% saturated near 700 micromoles per square meter per second, a PAR level typical for similar light saturation of C(3) photosynthesis. The total nocturnal H(+) accumulation and CO(2) uptake reached 90% of maximum for a total daily PAR of about 22 moles per square meter per day. Light compensation occurred near 0 moles per square meter per day for nocturnal H(+) accumulation and 4 moles per square meter per day for CO(2) uptake. Above a total daily PAR of 36 moles per square meter per day or for an instantaneous PAR of 1150 micromoles per square meter per second for more than 6 hours, the nocturnal H(+) accumulation actually decreased. This inhibition, which occurred at PAR levels just above those occurring in the field, was accompanied by a substantial decrease in chlorophyll content over a 1-week period.A minimum ratio of H(+) accumulated to CO(2) taken up of 2.5 averaged over the night occurred for a total daily PAR of 31 moles per square meter per day under wet conditions. About 2 to 6 hours into the night under such conditions, a minimum H(+)-to-CO(2) ratio of 2.0 was observed. Under progressively drier conditions, both nocturnal H(+) accumulation and CO(2) uptake decreased, but the H(+)-to-CO(2) ratio increased. A ratio of two H(+) per CO(2) is consistent with the H(+) production accompanying the conversion of starch to malic acid, and it apparently occurs for O. ficus-indica when CAM CO(2) uptake is strongly favored over respiratory activity.

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PubMed1983

Water Relations, Diurnal Acidity Changes, and Productivity of a Cultivated Cactus, Opuntia ficus-indica.

Physiological responses of the Crassulacean acid metabolism (CAM) plant Opuntia ficus-indica (Cactaceae) were studied on a commercial plantation in central Chile. Young cladodes (flattened stems) and flower buds exhibited daytime stomatal opening, whereas mature cladodes and fruit exhibited the nocturnal stomatal opening characteristic of CAM plants. Severe water stress suppressed the nocturnal stomatal opening by mature cladodes, but their high water vapor conductance occurring near dawn was not affected. Nocturnal acidity increases were not as sensitive to water stress as was the nocturnal stomatal opening. The magnitude of the nocturnal acidity increases depended on the total daily photosynthetically active radiation (PAR), being 90% PAR-saturated at 27 moles per square meter per day for a mean nighttime air temperature of 5 degrees C and at 20 moles per square meter per day for 18 degrees C. Inasmuch as the PAR received on unshaded vertical surfaces averaged about 21 moles per square meter per day, nocturnal acidity increases by the cladodes were on the verge of being PAR-limited in the field. The net assimilation rate, which was positive throughout the year, annually averaged 3.4 grams per square meter per day for 1.0- and 2.0-year-old plants. Plants that were 5.4 years old had 7.2 square meters of cladode surface area (both sides) and an annual dry weight productivity of 13 megagrams (metric tons) per hectare per year when their ground cover was 32%. This substantial productivity for a CAM plant was accompanied by the highest nocturnal acidity increase so far observed in the field, 0.78 mole H(+) per square meter.

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PubMed1980

Nutrient Influences on Leaf Photosynthesis: EFFECTS OF NITROGEN, PHOSPHORUS, AND POTASSIUM FOR GOSSYPIUM HIRSUTUM L.

The net rate of CO(2) uptake for leaves of Gossypium hirsutum L. was reduced when the plants were grown at low concentrations of NO(3) (-), PO(4) (2-), or K(+). The water vapor conductance was relatively constant for all nutrient levels, indicating little effect on stomatal response. Although leaves under nutrient stress tended to be lower in chlorophyll and thinner, the ratio of mesophyll surface area to leaf area did not change appreciably. Thus, the reduction in CO(2) uptake rate at low nutrient levels was due to a decrease in the CO(2) conductance expressed per unit mesophyll cell wall area (g(cell) (CO(2) )). The use of g(cell) (CO(2) ) and nutrient levels expressed per unit of mesophyll cell wall provides a new means of assessing nutrient effects on CO(2) uptake of leaves.

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PubMed1979

Environmental Influences on Open Stomates of a Crassulacean Acid Metabolism Plant, Agave deserti.

The major short term stomatal response of Agave deserti was to temperature; increases in leaf temperature led to decreases in water vapor conductance for stomatal opening during the daytime (C(3) mode) as well as at night (Crassulacean acid metabolism or CAM mode). Hourly changes in the water vapor concentration drop from leaf to air had no significant stomatal effect in either mode. Stomatal responses to external CO(2) levels up to 800 microliters per liter were not significant after 15 minutes and only moderate after a few hours, suggesting that CO(2) effects on open stomates of this succulent were indirect in both CAM and C(3) modes.

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PubMed1979

Salinity effects on leaf anatomy: consequences for photosynthesis.

Increasing salinity led to substantially higher ratios of mesophyll surface area to leaf area (A(mes)/A) for Phaseolus vulgaris and Gossypium hirsutum and a smaller increase for Atriplex patula, a salt-tolerant species. The increase in internal surface for CO(2) absorption did not lead to higher CO(2) uptake rates, since the CO(2) resistance expressed on the basis of mesophyll cell wall area (r(cell)) increased even more with salinity. The differences among species in the sensitivity of photosynthesis to salinity in part reflect the different A(mes)/A and r(cell) responses.

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PubMed1978

Resistance Analysis of Nocturnal Carbon Dioxide Uptake by a Crassulacean Acid Metabolism Succulent, Agave deserti.

Nocturnal CO(2) uptake by a Crassulacean acid metabolism succulent, Agave deserti Engelm. (Agavaceae), was measured so that the resistance properties of the mesophyll chlorenchyma cells and their CO(2) concentrations could be determined. Two equivalents of acidity were produced at night per mole of CO(2) taken up. The nocturnal CO(2) uptake became light-saturated at 3.5 mEinsteins cm(-2) of photosynthetically active radiation (400-700 nm) incident during the preceding day; at least 46 Einsteins were required per mole of CO(2) fixed. Variations in the daytime leaf temperature between 20 and 37 C had little effect on nocturnal CO(2) uptake. After the first few hours in the dark, the leaf liquid phase CO(2) resistance (r(liq) (CO(2) )) and the CO(2) concentration in the chlorenchyma cells (c(i) (CO(2) )) both increased, the latter usually reaching the ambient external CO(2) level at the end of the dark period. Increasing the leaf surface temperature above 15 C at night markedly increased the stomatal resistance, r(liq) (CO(2) ), and c(i) (CO(2) ).The minimum r(liq) (CO(2) ) at night was about 1.6 seconds cm(-1). Based on the ratio of chlorenchyma surface area to total leaf surface area of 82, this r(liq) (CO(2) ) corresponded to a minimum cellular resistance of approximately 130 seconds cm(-1), comparable to values for mesophyll cells of C(3) plants. The contribution of the carboxylation reaction and/or other biochemical steps to r(liq) (CO(2) ) may increase appreciably as the nighttime temperature shifts a few degrees from the optimum or after a few hours in the dark, both of which caused large increases in r(liq) (CO(2) ). This necessitates a large internal leaf area for CO(2) diffusion into the chlorenchyma to support moderate nocturnal CO(2) uptake rates by these succulent leaves.

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