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E V Maas

Publications and source records attributed to E V Maas.

10 recordsLinked to original sources
PubMed1993

Salinity and citriculture.

Soil salinity significantly limits citrus production in many areas worldwide. Although data on fruit yields in response to salinity are limited, they indicate that grapefruit, lemons, and oranges are among the most sensitive of all agricultural crops. Fruit yields decrease about 13% for each 1.0 dS m(-1) increase in electrical conductivity of the saturated-soil extract (EC(e)) once soil salinity exceeds a threshold EC(e) of 1.4 dS m(-1). Accumulation of excess Cl(-) and Na(+) can cause specific ion toxicities, but this problem can be minimized by selecting rootstocks that restrict the uptake of these ions. During the past two decades, numerous papers describing the agronomic and physiological responses of citrus to salinity have been published. This paper reviews these research reports and discusses differences in the response of citrus species to salt stress, the role of different rootstocks, the causes of salt injury, and the interactions of other environmental conditions or stresses with salinity.

Journal Article↗
PubMed1979

Salt-induced Inhibition of Phosphate Transport and Release of Membrane Proteins from Barley Roots.

Osmotic shock with sequential 30-minute treatments in ice-cold saline solutions and H(2)O released proteins from excised barley roots and inhibited the subsequent uptake of orthophosphate (Pi). The amount of protein released increased sharply at NaCl concentrations above 0.05 molar, approximately the threshold concentration above which Pi uptake was increasingly suppressed. About 60% of the nearly 100 micrograms of protein per gram fresh weight of roots that was eluted in 0.16 molar NaCl treatments apparently had no function in Pi transport, since it was eluted at NaCl concentrations (</=0.05 molar) that did not affect Pi uptake. Although 0.16 molar NaCl completely inhibited Pi uptake, active uptake resumed at about 60% of control rates within 1 to 2 hours. The presence of either puromycin or cycloheximide greatly reduced the recovery of Pi uptake activity after the NaCl treatment. Mannitol and various monovalent and divalent salts at concentrations isosmotic with NaCl also inhibited Pi uptake, but CaCl(2) was consistently the least inhibitory. The correlation between the concentration of the osmotic treatments and the simultaneous loss of protein and Pi uptake activity, together with the evidence that uptake recovery requires protein synthesis, support the hypothesis that the proteins eluted are required for active Pi transport.

Journal Article↗
PubMed1978

Growth, Phosphate Pools, and Phosphate Mobilization of Salt-stressed Sesame and Pepper.

The growth and phosphate mobilization of control and salt-stressed sesame (Sesamum indicum L.) and pepper (Capsicum annuum L.) plants were examined to ascertain whether or not translocation limits growth of salt-stressed plants. Plants were grown in a complete nutrient solution with and without excess salt. One-half of the control and salt-stressed plants were later transferred to phosphate-free culture solution ("-P" plants). Measurements of growth and phosphate pools in leaves indicated that with or without salinity "-P" plants utilized their phosphate reserves to support growth for a time at rates equaling those of plants supplied with phosphate. The results indicate that mobilization was not limiting for growth of salt-stressed plants.Defoliation experiments were performed at a developmental stage when the import of assimilates by the youngest expanding leaves could be changed by removing certain source or sink leaves. These experiments also indicated that phloem transport was not limiting for leaf growth on salt-stressed plants.

Journal Article↗
PubMed1972

Radial transport of sodium and chloride into tomato root xylem.

Transport of Na and Cl across exuding tomato (Lycopersicon esculentum Mill.) roots was determined as a function of ambient NaCl concentrations in the ranges of both systems 1 and 2. Kinetics of radial transport under steady-state conditions and the effect of dinitrophenol indicate that Na and Cl were transported by two different mechanisms. Sodium was neither accumulated against a concentration gradient nor directly inhibited by dinitrophenol from diffusing into the xylem. Chloride was accumulated in the xylem and its transport was nearly completely blocked by dinitrophenol. A comparison of the radial transport isotherms for Na and Cl for intact and decapitated plants indicates that the separate mechanisms were not unique to excised roots. It is concluded that radial Na transport in tomatoes was facilitated by a passive convective type process with the rate-limiting barrier located at the outer cortical plasmalemma. Chloride transport in both concentration ranges involved, either directly or indirectly, a metabolic mechanism. Absorption and retention of Na in the root tissue was negligible. Chloride was accumulated by the tissue but was unaffected by dinitrophenol.

Journal Article↗
PubMed1971

Absorption of magnesium and chloride by excised corn root.

Absorption characteristics of Mg(2+) and Cl(-) were investigated with 5-day-old excised corn (Zea mays) roots. Uptake from both 0.5 and 10 milliequivalents per liter MgCl(2) solutions occurred at steady state rates for the first 6 hours. Inhibition by dinitrophenol and low temperatures established that absorption during this period was metabolically mediated in the absence and presence of Ca(2+). Absorption isotherms indicated dual mechanisms of Mg(2+) and Cl(-) absorption from solutions above 1 milliequivalent per liter. The effect of H(+) on absorption of Mg(2+) and Cl(-) was typical of that generally reported for other plant roots and other ions. In the physiological pH range, Ca(2+) greatly suppressed the rate of Mg(2+) absorption but had little effect on Cl(-). The influence of Ca(2+) on Mg(2+) appeared to be noncompetitive and independent of its effect on membrane permeability.

Journal Article↗
PubMed1969

Influence of calcium and magnesium on manganese absorption.

Mutual effects between Mn, Ca, and Mg were studied during steady-state absorption experiments with excised barley roots. Calcium appeared to enhance the rate of Mn absorption; whereas, Mg had a highly depressive effect. The combination of both Ca and Mg was even more inhibitory to Mn absorption than Mg alone. Manganese had no effect on the usual negligible Ca absorption by this tissue, but effectively inhibited the absorption of Mg. Although divalent cation absorption from the Ca-Mg-Mn system was essentially nil, K absorption was greatly stimulated in the presence of these cations. These mutual effects and others reported in the literature are explained by the hypothesis that selectivity in ion absorption results from cation-induced conformational changes in the structure of the carrier molecule.

Calcium↗
PubMed1969

Calcium uptake by excised maize roots and interactions with alkali cations.

Ca(2+) uptake was studied in short-term experiments using 5-day-old excised maize roots. This tissue readily absorbs Ca(2+), and inhibition by dinitrophenol and low temperature shows that the process is metabolically mediated. The uptake of Ca(2+), like that of other cations, is influenced by the counter ion, the pH and concentration of the ambient solution, and the presence of other cations. The rate of uptake from various salts decreases in the following order: NO(3) (-) > Cl(-) = Br(-) > SO(4) (2-). K(+) and H(+) greatly interfere with Ca(2+) absorption, while Li(+) and Na(+) have only slight effects.

Journal Article↗
PubMed1968

Manganese absorption by excised barley roots.

Short-term absorption studies with 5-day-old excised barley roots revealed that the basic aspects of Mn absorption were similar to those of other metabolically absorbed cations. Following an initial non-metabolic equilibration with the root, Mn was absorbed for several hours at a slower steady-state rate comparable to that of other inorganic cations. Complete or nearly complete inhibition of the steady-state phase by low temperature, dinitrophenol, and azide provides strong evidence that Mn transport into this tissue was metabolically mediated. Within limits, the rate of transport was strongly dependent upon the concentrations of Mn and the hydrogen ions in the ambient solution. Absorption increased rapidly with increasing concentrations of Mn up to 1 meq per liter. Above this concentration, the rate leveled off, apparently due to a saturation of the transport mechanism. Within the physiological pH range in which Mn is soluble (below pH 7), absorption increased greatly with decreasing hydrogen-ion concentration.

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