Biomedical subjects

P J Kramer

Publications and source records attributed to P J Kramer.

At least 37 records · Page 2Linked to original sources

PubMed1971

Behavior of Corn and Sorghum under Water Stress and during Recovery.

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.

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PubMed1970

Radial movement of oxygen in plant roots.

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.

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PubMed1969

Water potential increase in sliced leaf tissue as a cause of error in vapor phase determinations of water potential.

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.

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PubMed1969

Radial transport of ions in roots.

Measurements were made of the relative amounts of (86)Rb, (36)Cl, and (32)P accumulated in the cortex and stele of intact roots of corn (Zea mays), either detached or attached to their shoots. Both 4- and 7-day-old roots accumulated as much or more (86)Rb in the stele as in the cortex. In experiments with (36)Cl, cortex and stele accumulated the same amount, except for 4-day-old and 7-day-old attached roots, in which the cortex contained more (36)Cl than the stele after 23 hr. An additional study of (32)P uptake showed greater accumulation in the cortex than the stele for a short period of time, but as much in the stele as in the cortex after 8 to 24 hr. Transport of (86)Rb, (36)Cl, and (32)P into the xylem exudate increased with increasing accumulation of these ions in stele and cortex of the root. These experiments show no consistent difference between cortex and stele of intact corn roots with respect to their ability to accumulate several kinds of ions.

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PubMed1967

Comparison of the dye method with the thermocouple psychrometer for measuring leaf water potentials.

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.

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PubMed1967

Phloem water relations and translocation.

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.

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PubMed1967

Radial salt transport in corn roots.

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.

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PubMed1966

Effects of decenylsuccinic Acid on the permeability and growth of bean roots.

Decenylsuccinic acid (DSA) at 10(-3)m has been reported to increase the permeability of bean root systems to water without seriously injuring the plants. We have confirmed the increase in permeability at 10(-3)m, but have found that 10(-4)m DSA reduces the permeability. Both concentrations cause leakage of salts from the roots and cessation of root pressure exudation. The roots of intact bean plants are killed by 1 hour's immersion in 10(-3)m DSA, but the plants may survive by producing new roots. Up to 4 hours in 10(-4)m DSA causes only temporary cessation of growth. Comparisons are made between the effects of DSA and some metabolic inhibitors. It is suggested that DSA is acting as a metabolic inhibitor, and that increase in water permeability is the result of injury to the roots. Experiments with 3 other species indicated variations in response to 10(-3)m DSA. These could be largely attributed to differences in susceptibility to injury.

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PubMed1956