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W R Jordan

Publications and source records attributed to W R Jordan.

26 records · Page 2Linked to original sources
PubMed1975

Leaf Age as a Determinant in Stomatal Control of Water Loss from Cotton during Water Stress.

The stomatal resistance of individual leaves of young cotton plants (Gossypium hirsutum L. var. Stoneville 213) was measured during a period of soil moisture stress under conditions of constant evaporative demand. When plants were subjected to increasing soil water stress, increases in stomatal resistance occurred first on the lower leaves and the stomata on the upper surfaces were the most sensitive to decreasing leaf-water potential. Stomatal closure proceeded from the oldest leaves to the youngest as the stress became more severe. This apparent effect of leaf age was not due to radiation differences during the stress period. Radiation adjustments on individual leaves during their development altered the stomatal closure potential for all leaves, but did not change the within-plant pattern. Our data indicate that no single value of leaf water potential will adequately represent a threshold for stomatal closure in cotton. Rather, the stomatal resistance of each leaf is uniquely related to its own water potential as modified by age and radiation regime during development. The effect of age on stress-induced stomatal closure was not associated with a loss of potassium from older leaves. Increases in both the free and bound forms of abscisic acid were observed in water-stressed plants, but the largest accumulations occurred in the youngest leaves. Thus, the pattern of abscisic acid accumulation in response to water stress did not parallel the pattern of stomatal closure induced by water stress.

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PubMed1972

Water Stress Enhances Ethylene-mediated Leaf Abscission in Cotton.

Abscission of cotyledonary leaves from cotton (Gossypium hirsutum L. cv. Stoneville 213) seedlings occurred following relief from water stress. The amount of abscission was related to the magnitude of the plant water deficit. Leaf abscission promoted by exogenous ethylene was enhanced in seedlings subjected to water stress. Treatment with ethylene (2.0 to 3.2 microliters of ethylene per liter of air for 24 hours) raised the threshold plant water potential required to induce abscission from -17 to -7 bar, indicating that the stress caused the tissue to become predisposed to ethylene action. Based on the abscission response curve for seedlings treated with ethylene while under water stress, this apparent predisposition was developed as the plant water potentials reached the -7 to -10 bar range. The abscission-promoting effects of ethylene in combination with water stress were reversed with 15% CO(2) at plant water potentials above -12 bar, but the CO(2) reversal was lost at lower water potentials. These results are compatible with the concept that ethylene plays a regulatory role in leaf abscission induced by water stress.

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PubMed1971

Influence of soil water stress on evaporation, root absorption, and internal water status of cotton.

Diurnal variations in leaf water potential, diffusion resistance, relative water content, stem diameter, leaf temperature, and energy balance components were measured in cotton (Gossypium hirsutum L. var. Lankart 57) during drought stress under field conditions. A plot of leaf water potential against either relative water content or stem diameter during the 24-hour period yielded a closed hysteresis loop. The relation between cell hydration and evaporation is discussed.Despite low soil water potential in the main root zone, significant plant evaporation rates were maintained. Root absorption rates as a function of soil depth were calculated from water content profiles measured with a neutron probe. The maximal root absorption rate of 3.5 x 10(-3) day(-1) occurred at the 75-centimeter depth, well below the main root zone.Stomatal resistance of individual leaves during the daylight hours remained nearly constant at 2.5 seconds centimeter(-1) even though leaf water potentials approached -30 bars. A growth chamber study indicated stomatal closure occurred at potentials near -16 bars. Possible implications of high soil water stress in relation to stomatal function and growth are discussed. Based on an energy balance method, the actual to potential plant evapotranspiration ratio was 0.43 for the 24-hour period, indicating partial stomatal closure. A surface resistance, r(s), of 4.0 seconds centimeter(-1) was calculated for the incomplete canopy with the use of the energy balance data. Alternatively, a canopy resistance of 1.3 seconds centimeter(-1) was attained from a relationship between leaf area and stomatal resistance of individual leaves. If the soil resistance was assumed to be very large and the canopy resistance was weighted for the fractional ground cover of the crop, the calculated surface resistance was 4.3 seconds centimeter(-1). Under these conditions, the two independent estimates of r(s) were in essential agreement.

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PubMed1969

Evidence for an Inactivating System of Nitrate Reductase in Hordeum vulgare L. during Darkness That Requires Protein Synthesis.

The disappearance of nitrate reductase activity in leaves of Hordeum vulgare L. during darkness was inhibited by cycloheximide, actinomycin D, and low temperature. Thus, protein synthesis was probably required for the disappearance of nitrate reductase in the dark. Since chloramphenicol did not affect the rate of loss of activity, the degradation or inactivation apparently required protein synthesis by the cytoplasmic ribosomal system. Consistent with this observation, nitrate reductase is also reportedly located in the cytoplasm. Thus, the amount of nitrate reductase activity present in leaves of barley may be controlled by a balance between activating and inactivating systems.

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