D. W. Rains

Advances in salt tolerance

SummaryAdvances in and prospects for the development of salt tolerant crops are discussed. The genetic approach to the salinity problem is fairly new, but research has become quite active in a short span of time. Difficulties and opportunities are outlined. Salinity varies spatially, temporally, qualitatively, and quantitatively. In addition, the responses of plants to salt stress vary during their life cycle. Selection and breeding, including the use of wide crosses, are considered the best short-term approaches to the development of salt tolerant crops, but the new biotechnological and molecular biological techniques will make increasingly important contributions. Cooperation is called for among soil and water scientists, agronomists, plant physiologists and biochemists, cytologists, and plant geneticists, breeders, and biotechnologists. Given such cooperation and adequate support for these endeavors, the potential for increasing productivity in salt-affected areas can be realized.

Transport of Sodium in Plant Tissue

Two mechanisms are implicated in the absorption of alkali cations by barley roots. Mechanism 1 has a high affinity for potassium, but its affinity for sodium is so low that, in the presence of even a low concentration of potassium (1 mM), sodium absorption by this mechanism is all but abolished. Mechanism 2 has a much lower affinity for alkali cations and is not highly selective; it transports sodium as well as potassium.

The relationship between zinc, copper and the basophils of two crassostreid oyster, C. gigas and C. virginica☆

Abstract 1. 1. Histological estimates of the numbers of oyster granular basophilic blood cells, or basophils, per oyster were found to differ significantly for various populations of Pacific and American oysters. 2. 2. American oysters contained greater number of basophils than Pacific oysters. 3. 3. Various correlations established between number of basophils and zinc and copper levels in oyster indicated that oyster basophils contained both zinc and copper. It was estimated that oyster basophils might contain as muct as 6% zinc on a dry weight basis.

Evidence for Substrate Induction of a Nitrate Efflux System in Barley Roots.

Induction of an NO3- efflux system in intact barley (Hordeum vulgare L.) roots was demonstrated. Since the measurement of NO3- efflux is dependent on its accumulation, experiments were devised to facilitate accumulation under noninducing conditions. This was accomplished by incubating seedlings in 10 mM NO3- in the presence of RNA and protein synthesis inhibitors. Under these conditions NO3- uptake is mediated by constitutive high- and low-affinity transport systems. Control roots were incubated with 1.0 mM NO3-. This resulted in the accumulation of similar levels of NO3- in both treated and control roots; however, cytoplasmic NO3- efflux from inhibitor-treated roots was much lower than from control roots. Following a brief lag period, efflux rates increased rapidly in the presence of NO3- for 8 to 12 h. The NO3- efflux system was also induced by ambient NO2-. After induction the efflux system was relatively stable in the presence of RNA and protein synthesis inhibitors as long as NO3- or NO2- was present. These results suggest that NO3- efflux may be an inducible system requiring both RNA and protein synthesis, as does induction of the uptake system. The efflux system, however, has a much slower turnover rate than the uptake system.

Simultaneous determination of arsenite, arsenate, selenite and selenate in waters using suppressed ion chromatography with ultraviolet absorbance detection

Using Dionex AS4A anion-exchange column, with micromembrane supressor and UV detector at 195 nm, arsenite, arsenate, selenite and selenate can be determined simultaneously in water samples. The mole fraction of sodium carbonate in the eluent as well as eluent concentration affected the retention times especially for the divalent anions. An eluent of 2.5 mM Na2CO3 and 0.75 mM NaHCO3 was found to be the most suitable for sample analysis. The responses for all ions tested was linear in 0–5 mg 1−1 range. The system can tolerate up to 1600 mg 1−1 of SO2−4, before affecting arsenate peaks. Selenate peak area was not affected due to SO2−4 concentration up to 2000 mg 1−1. The detection limits using 100-μl loop were 0.1 mg 1−1 for AsO−2 and SeO2−3 and 0.25 mg 1t-1 AsO3−4 and SeO2−4.

Long-Term Reuse of Drainage Waters of Varying Salinities for Crop Irrigation in a Cotton-Safflower Rotation System in the San Joaquin Valley of California—A Nine Year Study: I. Cotton (Gossypium hirsutum L.)

Summary Use of saline drainage water for crop irrigation was evaluated as a means of decreasing its volume. Results of a nine-year crop rotation (cotton-cotton-safflower, × 3) in which only the cotton was irrigated with drainage water of 400, 1,500, 3,000, 4,500, 6,000, and 9,000 ppm total dissolved salts are presented. The different salinity levels of irrigation waters were achieved by mixing nonsaline canal water (400 ppm) and saline drainage water. Cotton lint yields were not affected by increased salinity level of the irrigation water for the first two years. Detrimental effects became evident in the third cotton crop with increasing severity in later years. In the fifth year of cotton (seventh year of the study), lint yields were adversely affected by waters of salinity greater than 3,000 ppm. However, fiber quality remained unaffected at all levels of irrigation water salinity. The reductions in lint yield appeared to be a function of time and the salinity level of applied water. Shoot height and biomass were reduced by the irrigation water salinity before lint yields. Stand establishment appeared to be the most sensitive to salinity and was perhaps the main reason for yield reduction. Increase in irrigation water salinity increased Na+ content of leaf blades and petioles and decreased K+/Na+ ratio of leaf blades and petioles. The study showed that irrigation waters of up to 3,000 ppm salinity may be used for four years without any yield reductions, as long as some leaching occurs through preplant irrigations with low salinity water. Data on crop growth and development and ionic content collected over the nine year period are presented.

Light-Enhanced Potassium Absorption by Corn Leaf Tissue

The rate of absorption of potassium by slices of corn leaf in the light was about twice the rate in the dark. When the light was turned on or off, changes in the rate of absorption took place some minutes after the change in illumination. Experiments with the antimetabolites, 2,4-dinitrophenol and cyanide, indicated that the source of energy for active accumulation of potassium by green tissue in the light was different from that in the dark. In the light, energy was closely linked to photosynthetic reactions; in the dark, it was linked to respiratory processes.

Interactive effects of exogenous combined nitrogen and phosphorus on growth and nitrogen fixation by azolla

Effects of N source and media-N and P levels were examined on growth, N uptake, and N2 fixation ofAzolla pinnata withAnabaena azollae association (azolla) at two inoculum-P concentrations. Each expeiment was conducted for 7 days in a growth chamber using azolla at a predetermined inoculum-P concentration and the growth media containing a combination of four levels of P (0, 15, 75, and 200 μM) and three levels (0, 1, and 5 mM) of either15N-enriched NH4+ as ammonium sulfate or15N-enriched NO3− as potassium nitrate. Nitrogen uptake and N2 fixation were measured by15N isotopic dilution method. Tissue P and N, N uptake, and N2-fixation increased with increasing P concentration in the media regardless of the inoculum-P level of azolla. Increasing P concentration in the media increased growth of azolla at low inoculum P, but the effect on high inoculum-P azolla was either small or absen. High inoculum-P concentration resulted in increased growth, tissue-N and P concentrations, N uptake, and N2 fixation by azolla. Ammonium in the growth media caused larger increase in tissue-N and greater repression of N2 fixation than equimolar concentration of NO3−. In the presence of NH4+ or NO3−, in the growth media, N uptake by azolla exceeded the corresponding decrease in N2 fixation, resulting in an overall increase in tissue-N concentration. Phosphorus in the media tended to negate the inhibitory effect of NH4+ or NO3− on N2 fixation. A multiple regression model showed that the effect of tissue-N on N2 fixation was negative while that of tissue-P was positive. Therefore, a relative change in tissue-N and P appeared to regulate N2 fixation. Tissue-N and P had similar effects on relative growth rate of azolla also. Inoculum-P level of azolla was important in determining the response to media-P.

Long-term reuse of drainage waters of varying salinities for crop irrigation in a cotton-safflower rotation system in the San Joaquin Valley of California : a nine year study : II. safflower (Carthamus tinctorius L.)

Summary This paper reports the results on safflower crops grown in a nine-year study, conducted on a 8 ha site, to determine the feasibility of using drainage water for irrigation in a 2-year cotton/1-year safflow-er rotation system. The cotton crops were irrigated with waters of 400, 1,500, 3,000, 4,500, 6,000, and 9,000 ppm total dissolved salts, and safflower was grown only with a preplant irrigation with nonsaline water. The use of drainage water for crop irrigation may be a means of decreasing its volume. Even though safflower was never irrigated with saline drainage water directly, the residual effect of using saline water for cotton irrigation adversely impacted safflower growth and development. Safflower seed yields were reduced in plots previously irrigated with waters of 4,500 ppm or higher salinity and even more severe effects on crop growth were seen as the numbers of years of irrigation with the saline water increased. After irrigating six cotton crops, the safflower seed yield in plots irrigated with 9,000 ppm waters was reduced to only 14% of the control. The safflower oil content and quality were not affected. Impacts on plant density, shoot height, shoot biomass, and leaf ionic content also are discussed.