No abstract

The effects of salinity on corn plants (Zea mays L.) are influenced by the concentration of nutrient orthophosphate. Salinity (-2 bars each of NaCI and CaCI2) was more injurious in combination with a high concentration of orthophosphate (2 mM) (that gave optimum yields in the absence of salinity) than it was with a lower concentration (0.1 mM). With 2 mm orthophosphate, salinity seemed to damage the plant mechanisms that normally regulate the internal concentration of orthophosphate resulting in excessive accumulation and P toxicity. On the other hand, with 0.1 mM orthophosphate, salinity decreased orthophosphate concentration in mature leaves. This effect was paralleled by decreases in the concentration of adenosine 5'-triphosphate and in the energy charge of the adenylate system, indicating an orthophosphate deficit. Even so, plants survived salinity better under these conditions than in the presence of 2 mM orthophosphate. The data indicated that salinity affected the phosphorylated state of the adenine nucleotides only indirectly through its effect on the concentration of orthophosphate in the cells. Salinity, especially in the presence of 2 mM orthophosphate, resulted in an increase in the concentrations of sugar phosphates in mature photosynthesizing leaves, suggesting that translocation rather than photosynthesis was a limiting process. Decreased translocation could be a secondary effect of decreased growth. However, a decreased translocation rate could cause decreased growth by limiting the supply of essential metabolites reaching growing tissues.The recent salinity-fertility studies of Bernstein et al. (7) showed a marked interactive effect of salinity and nutrient Pi on corn plants. Salinity was more deleterious in combination with a high concentration of Pi (2 mM) than with a low concentration (0.05 mM). There occurred a greater reduction in yield and a characteristic leaf injury. The injury seemed to be a result of excessive accumulation of P; other ions did not accumulate sufficiently to account for it. Also, the injury signs were similar to those caused by P toxicity in wheat (8) and barley ( 15). These observations suggested that salinity affected the uptake and utilization of Pi by the plants. Considering the central role of P in cell metabolism, evidence of salt-induced changes in P metabolism might also provide insight regarding the mechanism of salt injury to plants. The work reported here was concerned with the effects of salinity in combination with low and high concentrations of nutrient Pi on the concentrations of Pi and of Pesters2 in mature photosynthesizing corn leaves. Preliminary ' This paper is dedicated to a fellow plant physiologist and friend.Leon Bernstein.2 Abbreviations: F6P: fructose 6-phosphate; FDP: fructose 1 6-diwork showed that salinity, like extremes in P nutrition (9), affected the concentrations of these compounds much more than it did the concentrations of lipid P and nucleic acid P. MATERIALS AND METHODS Plant Culture. Corn plants (Zea mays L. T-strain Golden...

No abstract

Measurements of transpiration, cell division, and cell enlargement show that no single lower limit of available water can be defined for these three plant processes. The soil-water content at which permanent wilting is exhibited does not represent a true lower limit for any of these.

The effects of external salt and inorganic phosphate (Pi) on the concentrations of vacuolar Pi, and cytoplasmic Pi, ATP, glucoe-6-phosphate and UDP-glucose in maize root tips were examined using 31P nuclear magnetic resonance spectroscopy. We observed a more than twofold stimulation of Pi uptake from 10 millimoar KH2PO4 solutions when root tips were exposed to 100 millimolar NaC + CaCI2. This stimulation of Pi uptake was associated with an increase in the concentration of cytoplasmic Pi in root tip cells. Thus, the molar ratio of cytoplasmic Pi to Pi + ATP + glucose-aphosphate + UDP-glncose increased greatly in root tips exposed to salt and Pi. We speculate that it is this disturbance in relative concentrations of cytoplasmic phosphates (which we show are normally tightly regulated) that is responsible for both the greater rte of uptake of Pi by vacuoles of excised maize root tips, and the previously documented stimulation of Pi translocation from root to shoot in whole maize plants exposed to salt and Pi.A significant interactive effect of salinity and nutrient Pi on yield in maize has been described by Bemstein et al. (1). High concentrations of Pi (2 mM) caused lower yields in salt-treated plants than low concentrations of Pi (0.05 mM). This lower yield appears to result from excessive uptake of Pi, with translocation to the leaves, leading to symptoms of phosphorus toxicity (1, 9). Thus, some aspect of uptake and/or translocation is disturbed by the combination of salt and high Pi. An inability to regulate Pi transport has also been observed in phosphorus-deficient barley plants when they were supplied with Pi (4, 6).The study of Pi transport and metabolism in plants is complicated by the existence of metabolically distinct pools of Pi, in the vacuolar and cytoplasmic intracellular compartments (2), and by the rapid exchange of P between Pi and organic phosphates in the cytoplasm (8). 3"P-NMR2 spectroscopy permits observation of both these aspects of Pi metabolism. The method permits simultaneous monitoring of the cytoplasmic and vacuolar Pi pools in plant tissues (11,15) and also can be used to estimate rates of exchanges between cytoplasmic Pi and ATP in maize root tips (14). Recently, 3'P-NMR has been used to 'Supported by grants from the-National Institutes of Health (RROO7 11), the National Science Foundation (PCM 82-04877 and GP 23633), and a United States Department of Agriculture cooperative agreement (AGRIC 58 9AZ-2-665).2Abbreviation: NMR, nuclear magnetic resonance. measure cytoplasmic and vacuolar Pi pool sizes in cell suspension cultures (10) and pea root tips (7) exposed to Pi. In both studies uptake of Pi resulted in large increases in the concentration of vacuolar Pi, while the concentration of cytoplasmic Pi was essentially unchanged; this result was observed over external concentrations of Pi ranging from 0.2 to 45 mm. In this paper we describe the time course for changes in cytoplasmic and vacuolar Pi pool sizes in maize root tips exposed to solutions of salt and Pi. We show that s...

Treating carrot (Daucus carota L.) discs with ice-cold NaCl solutions for 30 minutes caused three effects that appear to be functionally related: the exchange of tissue Ca+ and Mg' for Na+, the release of protein, and the suppression of active uptake of glucose and orthophosphate. Cyclosis continued apparently unabated after treatment with NaCl at concentrations of up to 0.25 M, so the cells remained viable and energetically competent. The correlation between the release of Ca'+ and Mg+ and release of protein, and between these effects and the suppression of glucose and orthophosphate uptake, supports the hypothesis that divalent cations maintain, and monovalent cations disrupt, linkages between the outer cell surface and proteins required for active solute uptake. Calcium preserved uptake activity only when it was added in time to prevent the release of protein. Cells gradually recovered some glucose uptake activity after it had been completely inactivated by treatment with 0.25 M NaCl. This recovery occurred in the absence of added Ca+. It was inhibited by puromycin and so appears to require some protein synthesis. Beet (Beta vulgaris L.) discs were more resistant than carrot discs to treatment with NaCl solutions, thus reflecting the difference in tolerance of the two species to sodicity.

Salinity has the curious faculty to

No abstract