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G R Cramer

Publications and source records attributed to G R Cramer.

10 recordsLinked to original sources
PubMed2000

Water relations and leaf expansion: importance of time scale.

The role of leaf water relations in controlling cell expansion in leaves of water-stressed maize and barley depends on time scale. Sudden changes in leaf water status, induced by sudden changes in humidity, light and soil salinity, greatly affect leaf elongation rate, but often only transiently. With sufficiently large changes in salinity, leaf elongation rates are persistently reduced. When plants are kept fully turgid throughout such sudden environmental changes, by placing their roots in a pressure chamber and raising the pressure so that the leaf xylem sap is maintained at atmospheric pressure, both the transient and persistent changes in leaf elongation rate disappear. All these responses show that water relations are responsible for the sudden changes in leaf elongation rate resulting from sudden changes in water stress and putative root signals play no part. However, at a time scale of days, pressurization fails to maintain high rates of leaf elongation of plants in either saline or drying soil, indicating that root signals are overriding water relations effects. In both saline and drying soil, pressurization does raise the growth rate during the light period, but a subsequent decrease during the dark results in no net effect on leaf growth over a 24 h period. When transpirational demand is very high, however, growth-promoting effects of pressurization during the light period outweigh any reductions in the dark, resulting in a net increase in growth of pressurized plants over 24 h. Thus leaf water status can limit leaf expansion rates during periods of high transpiration despite the control exercised by hormonal effects on a 24 h basis.

Cell Division↗
PubMed1992

Kinetics of Maize Leaf Elongation : III. Silver Thiosulfate Increases the Yield Threshold of Salt-Stressed Plants, but Ethylene Is Not Involved.

The involvement of ethylene in the short-term responses of maize (Zea mays L.) leaf elongation to salinity was investigated. Leaf elongation rates (LER) were monitored with linear variable differential transformers. Salinity (80 mm NaCl) rapidly inhibited LER. Pretreatment with 4 mm silver thiosulfate (STS), an inhibitor of ethylene action, decreased LER of salt-stressed plants, but not that of controls. Investigation of the growth parameters affected by the interaction of STS and salinity indicated that the yield threshold was increased and the cell wall extensibility was decreased. All other growth parameters controlling cell elongation were unaffected. Further investigation indicated that ethylene production may not be involved in this reponse because treatments with 10 mum aminoethoxyvinylglycine, an ethylene biosynthesis inhibitor, did not affect the growth of salt-stressed plants, and no increase in ethylene production was detected in salt-stressed plants compared with controls. No changes in sensitivity to ethylene were evident because LER of both control and salt-stressed plants were inhibited to the same extent with exposure to 1.2 ppm ethylene. The above evidence indicated that ethylene was not involved in the short-term LER responses of salt-stressed maize.

Journal Article↗
PubMed1991

Short-term leaf elongation kinetics of maize in response to salinity are independent of the root.

The essentiality of roots to the short-term responses of leaf elongation to salinity was tested by removing the roots of maize (Zea mays L.) from the shoots and comparing the initial short-term response of leaf elongation to that with intact plants. Eightday-old seedlings growing in solution culture were treated with 80 millimolar NaCl and their leaf elongation rate (LER) was monitored with a linear variable differential transformer connected to a computerized data aquisition system. Initially, LER of intact plants was sharply reduced by salinity, then rose rapidly to reach a new steady-state rate about 1.5 hours after salinization. The new steady-state rate of salinized intact plants was about 80% of the control rate. When the roots of nonsalinized plants were excised under the surface of the nutrient solution, excision did not disturb the steady-state LER. When these shoots were salinized, they responded in a manner nearly identical to that of intact plants, indicating that roots are not essential for the modulation of short-term LER of salt-stressed plants.

Journal Article↗
PubMed1988

Transport Properties of the Tomato Fruit Tonoplast : III. Temperature Dependence of Calcium Transport.

Calcium transport into tomato (Lycopersicon esculentum Mill, cv Castlemart) fruit tonoplast vesicles was studied. Calcium uptake was stimulated approximately 10-fold by MgATP. Two ATP-dependent Ca(2+) transport activities could be resolved on the basis of sensitivity to nitrate and affinity for Ca(2+). A low affinity Ca(2+) uptake system (K(m) > 200 micromolar) was inhibited by nitrate and ionophores and is thought to represent a tonoplast localized H(+)/Ca(2+) antiport. A high affinity Ca(2+) uptake system (K(m) = 6 micromolar) was not inhibited by nitrate, had reduced sensitivity to ionophores, and appeared to be associated with a population of low density endoplasmic reticulum vesicles that contaminated the tonoplast-enriched membrane fraction. Arrhenius plots of the temperature dependence of Ca(2+) transport in tomato membrane vesicles showed a sharp increase in activation energy at temperatures below 10 to 12 degrees C that was not observed in red beet membrane vesicles. This low temperature effect on tonoplast Ca(2+)/H(+) antiport activity could only by partially ascribed to an effect of low temperature on H(+)-ATPase activity, ATP-dependent H(+) transport, passive H(+) fluxes, or passive Ca(2+) fluxes. These results suggest that low temperature directly affects Ca(2+)/H(+) exchange across the tomato fruit tonoplast, resulting in an apparent change in activation energy for the transport reaction. This could result from a direct effect of temperature on the Ca(2+)/H(+) exchange protein or by an indirect effect of temperature on lipid interactions with the Ca(2+)/H(+) exchange protein.

Journal Article↗
PubMed1987

Salinity reduces membrane-associated calcium in corn root protoplasts.

Calcium is an important factor in the ability of plants to resist salt stress, possibly because of its role in maintaining membrane integrity. We studied the effects of NaCl stress on membrane-associated Ca in corn root protoplasts (Zea mays L. cv Pioneer 3377) using the fluorescent Ca probe chlorotetracycline (CTC). Protoplasts were isolated from the cortex of primary roots of corn seedlings (Gronwald and Leonard, Plant Physiol 1982 70: 1391-1395). After a 30 minute incubation in 50 micromolar CTC, the protoplasts were exposed to isosmotic treatment solutions containing various concentrations of NaCl just before fluorimetric analysis. Increasing NaCl concentrations caused a progressive reduction in net CTC fluorescence, to 50% of control values at 150 mm NaCl. NaCl did not displace CTC from the cells, nor did it directly interfere with Ca-CTC binding. Tests with CsCl, RbCl, KCl, LiCl, Na(2)SO(4), NaNO(3), and NaBr indicated that the reduction in CTC fluorescence was not specific to either Na or Cl, but may have been due to increased ionic strength of the treatment solutions. Like CTC fluorescence, root growth of intact corn seedlings was not specifically sensitive to Na, but was inhibited by several monovalent cations in the order Li > Cs >> Rb > Na > K. CTC fluorescence at 100 mm NaCl was restored to unstressed levels by increasing Ca concentrations. Since our salt treatments were isosmotic, we conclude that the ionic component of salt stress displaces Ca from membranes of corn root cells.

Journal Article↗
PubMed1987

Influx of na, k, and ca into roots of salt-stressed cotton seedlings : effects of supplemental ca.

High Na(+) concentrations may disrupt K(+) and Ca(2+) transport and interfere with growth of many plant species, cotton (Gossypium hirsutum L.) included. Elevated Ca(2+) levels often counteract these consequences of salinity. The effect of supplemental Ca(2+) on influx of Ca(2+), K(+), and Na(+) in roots of intact, salt-stressed cotton seedlings was therefore investigated. Eight-day-old seedlings were exposed to treatments ranging from 0 to 250 millimolar NaCl in the presence of nutrient solutions containing 0.4 or 10 millimolar Ca(2+). Sodium influx increased proportionally to increasing salinity. At high external Ca(2+), Na(+) influx was less than at low Ca(2+). Calcium influx was complex and exhibited two different responses to salinity. At low salt concentrations, influx decreased curvilinearly with increasing salt concentration. At 150 to 250 millimolar NaCl, (45)Ca(2+) influx increased in proportion to salt concentrations, especially with high Ca(2+). Potassium influx declined significantly with increasing salinity, but was unaffected by external Ca(2+). The rate of K(+) uptake was dependent upon root weight, although influx was normalized for root weight. We conclude that the protection of root growth from salt stress by supplemental Ca(2+) is related to improved Ca-status and maintenance of K(+)/Na(+) selectivity.

Journal Article↗
PubMed1986

Effects of NaCl and CaCl(2) on Ion Activities in Complex Nutrient Solutions and Root Growth of Cotton.

Sodium displaces Ca(2+) from membranes (GR Cramer, A Läuchli, VS Polito Plant Physiol 1985 79: 207-211) and this can be related to the (Ca(2+))/(Na(+))(2) activity ratio in the external solution (GR Cramer, A Läuchli 1986 J Exp Bot 37: 321-330). Supplemental Ca(2+) is known to mitigate the adverse effects of salinity on plant growth. In this report we investigated the effects of NaCl (0-250 millimolar) and Ca(2+) (0.4 and 10 millimolar) on the ion activities in solution and on root growth of cotton (Gossypium hirsutum L.). Ion activities were analyzed using the computer program, GEOCHEM. Most ion activities in a 0.1 modified Hoagland solution were significantly reduced by both NaCl and supplemental Ca(2+). Ion-pair formation and precipitation were significant for some ions, especially phosphate. Root growth of 6-day-old seedlings was stimulated by low NaCl concentrations (25 millimolar). At higher NaCl concentrations, root growth was inhibited; the concentration at which this occurred depended on the Ca(2+) concentration and the growth index used. Supplemental Ca(2+) mitigated the inhibition of root growth caused by NaCl. There was a curvilinear relationship between root growth and the (Ca(2+))/(Na(+))(2) ratio in the nutrient solution. The mechanisms by which Na(+) and Ca(2+) may affect root growth are discussed.

Journal Article↗
PubMed1986

Effects of NaCl and CaCl(2) on Cell Enlargement and Cell Production in Cotton Roots.

In many crop species, supplemental Ca(2+) alleviates the inhibition of growth typical of exposure to salt stress. In hydroponically grown cotton seedlings (Gossypium hirsutum L. cv Acala SJ-2), both length and weight of the primary root were enhanced by moderate salinities (25 to 100 millimolar NaCl) in the presence of 10 millimolar Ca(2+), but the roots became thinner. Anatomical analysis showed that the cortical cells of these roots were longer and narrower than those of the control plants, while cortical cells of roots grown at the same salinities but in the presence of only 0.4 millimolar Ca(2+) became shorter and more nearly isodiametrical. Cell volume, however, was not affected by salinities up to 200 millimolar NaCl at either 0.4 or 10 millimolar Ca(2+). Our observations suggest Ca(2+)-dependent effects of salinity on the cytoskeleton. The rate of cell production declined with increasing salinity at 0.4 millimolar Ca(2+) but at 10 millimolar Ca(2+) was not affected by salinities up to 150 millimolar NaCl.

Journal Article↗
PubMed1985

Displacement of ca by na from the plasmalemma of root cells : a primary response to salt stress?

A microfluorometric assay using chlorotetracycline (CTC) as a probe for membrane-associated Ca(2+) in intact cotton (Gossypium hirsutum L. cv Acala SJ-2) root hairs indicated displacement of Ca(2+) by Na(+) from membrane sites with increasing levels of NaCl (0 to 250 millimolar). K(+)((86)Rb) efflux increased dramatically at high salinity. An increase in external Ca(2+) concentration (10 millimolar) mitigated both responses. Other cations and mannitol, which did not affect Ca(2+)-CTC chelation properties, were found to have no effect on Ca(2+)-CTC fluorescence, indicating a Na(+)-specific effect. Reduction of Ca(2+)-CTC fluorescence by ethyleneglycol-bis-(beta-aminoethyl ether) N,N'-tetraacetic acid, which does not cross membranes, provided an indication that reduction by Na(+) of Ca(2+)-CTC fluorescence may be occurring primarily at the plasmalemma. The findings support prior proposals that Ca(2+) protects membranes from adverse effects of Na(+) thereby maintaining membrane integrity and minimizing leakage of cytosolic K(+).

Journal Article↗