The temperature at which "clean" supercooled water freezes has been determined as a function of pressure up to 3 kilobars, using a differential thermal analysis technique on subdivided water samples. The supercooling limit of such samples, -38 degrees C at normal pressure, is lowered by initial increase of pressure, reaching a minimum value of -92 degrees C at 2.00 kilobars.
The root system architecture (RSA) of crops can affect their production, particularly in abiotic stress conditions, such as with drought, waterlogging, and salinity. Salinity is a growing problem worldwide that negatively impacts on crop productivity, and it is believed that yields could be improved if RSAs that enabled plants to avoid saline conditions were identified. Here, we have demonstrated, through the cloning and characterization of qSOR1 (quantitative trait locus for SOIL SURFACE ROOTING 1), that a shallower root growth angle (RGA) could enhance rice yields in saline paddies. qSOR1 is negatively regulated by auxin, predominantly expressed in root columella cells, and involved in the gravitropic responses of roots. qSOR1 was found to be a homolog of DRO1 (DEEPER ROOTING 1), which is known to control RGA. CRISPR-Cas9 assays revealed that other DRO1 homologs were also involved in RGA. Introgression lines with combinations of gain-of-function and loss-of-function alleles in qSOR1 and DRO1 demonstrated four different RSAs (ultra-shallow, shallow, intermediate, and deep rooting), suggesting that natural alleles of the DRO1 homologs could be utilized to control RSA variations in rice. In saline paddies, near-isogenic lines carrying the qSOR1 loss-of-function allele had soil-surface roots (SOR) that enabled rice to avoid the reducing stresses of saline soils, resulting in increased yields compared to the parental cultivars without SOR. Our findings suggest that DRO1 homologs are valuable targets for RSA breeding and could lead to improved rice production in environments characterized by abiotic stress.
A new high pressure volumetric technique, which employs a fine glass capillary as joint sample chamber and pressure vessel is described. Because of the small samples used, it is suitable for supercooled liquid studies. The compressibilities κT of water and of D2O have been determined over the applied pressure range 0.1–190 MPa (1–1900 bar) at temperatures in the range of 25–30°C. The anomalous low temperature increases in κT reported earlier for H2O at 1 bar are found at higher temperatures in D2O, as expected. In both liquids, increases in pressure cause the anomalous regions to be displaced to lower temperatures. The displacement per unit pressure change increases with increasing pressure. As found previously, the low temperature data conform to an empirical equation κT=A (Ts/T−1)−γ where Ts is a characteristic temperature now found strongly dependent on pressure. High pressure data are inadequate to yield both Ts and γ parameters reliably but, when γ is assigned a pressure-independent value, the best fit Ts values vary in each case with pressure in a manner strikingly similar to that of the homogeneous nucleation temperature, confirming a previously suspected relation between the two quantities. Preliminary attempts to separate the total compressibility into ’’normal’’ and ’’anomalous’’ parts suggest that the exponent γ is close to unity, as found previously for the anomalous component of the expansivity.
With glass capillary pressure vessels it has been possible to study the effect of pressure on the temperature of maximum density (TMD) and on the "sharpness" of the density maximum in liquid H(2)O and D(2)O in the important but little-studied supercooled regime. A pressure of 1200 bars produces a 33 degrees C depression of the TMD in these liquids and a considerable reduction in sharpness. Comparison with the rather flat density maximum for liquid SiO(2) supports the notion that the presence or absence of density anomalies in "tetrahèdral" liquids depends on the average bridge-bond angle, which is evidently unusually large in water at normal pressure.
Publication costs assisted by the National Science FoundationThe limit of supercooling determined by homogeneous nucleation has been investigated as a function of pressure for aqueous solutions of the common alkali halides LiC1, NaC1, KC1, CsC1, and KI for dilute solutions. The pressure dependence of the homogeneous nucleation temperature follows the pattern established earlier for HzO, TH decreasing curvilinearly until crystallization of ice I11 becomes favored at -2 kbar pressure and T C -90 "C. For 1 m solutions the TH vs. pressure plots are indistinguishable for these salts, implying that the TH depression, like the freezing point depression, is a colligative property. More concentrated solutions, containing 1 or more mol of salt per 20 mol of water (30 in the case of LiCl), fail to crystallize above -1.5 kbar and glassy phases may be obtained below -120 "C. The glass transition temperature shows a small positive pressure dependence. At constant alkali chloride concentration and pressure the glass transition temperature is a maximum for NaC1.
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