Search

Climate change threatens food security, and plant science researchers have investigated methods of sustaining crop yield under drought. One approach has been to overproduce abscisic acid (ABA) to enhance water use efficiency. However, the concomitant effects of ABA overproduction on plant vascular system functioning are critical as it influences vulnerability to xylem hydraulic failure. We investigated these effects by comparing physiological and hydraulic responses to water deficit between a tomato (Solanum lycopersicum) wild type control (WT) and a transgenic line overproducing ABA (sp12). Under well‐watered conditions, the sp12 line displayed similar growth rate and greater water use efficiency by operating at lower maximum stomatal conductance. X‐ray microtomography revealed that sp12 was significantly more vulnerable to xylem embolism, resulting in a reduced hydraulic safety margin. We also observed a significant ontogenic effect on vulnerability to xylem embolism for both WT and sp12. This study demonstrates that the greater water use efficiency in the tomato ABA overproducing line is associated with higher vulnerability of the vascular system to embolism and a higher risk of hydraulic failure. Integrating hydraulic traits into breeding programmes represents a critical step for effectively managing a crop's ability to maintain hydraulic conductivity and productivity under water deficit. We show that an ABA overproducing tomato line exhibits greater water use efficiency than its wild type counterpart but higher vulnerability to hydraulic failure through increased vulnerability to xylem embolism and a reduced hydraulic safety margin. This suggests that breeding programmes should integrate hydraulic traits for effectively managing a crop's ability to maintain hydraulic conductivity and productivity under drought. [ABSTRACT FROM AUTHOR]

Summary Chilling and freezing can reduce significantly vine survival and fruit set in Vitis vinifera wine grape. To overcome such production losses, a recently identified grapevine C-repeat binding factor (CBF) gene, VvCBF4, was overexpressed in grape vine cv. 'Freedom' and found to improve freezing survival and reduced freezing-induced electrolyte leakage by up to 2 °C in non-cold-acclimated vines. In addition, overexpression of this transgene caused a reduced growth phenotype similar to that observed for CBF overexpression in Arabidopsis and other species. Both freezing tolerance and reduced growth phenotypes were manifested in a transgene dose-dependent manner. To understand the mechanistic basis of VvCBF4 transgene action, one transgenic line (9-12) was genotyped using microarray-based mRNA expression profiling. Forty-seven and 12 genes were identified in unstressed transgenic shoots with either a >1.5-fold increase or decrease in mRNA abundance, respectively. Comparison of mRNA changes with characterized CBF regulons in woody and herbaceous species revealed partial overlaps, suggesting that CBF-mediated cold acclimation responses are widely conserved. Putative VvCBF4-regulon targets included genes with functions in cell wall structure, lipid metabolism, epicuticular wax formation and stress-responses suggesting that the observed cold tolerance and dwarf phenotypes are the result of a complex network of diverse functional determinants. [ABSTRACT FROM AUTHOR]

The CBF/DREB1 transcription factors control an important pathway for increased freezing and drought tolerance in plants. We report here the isolation of one CBF/DREB1-like gene, CBF4, from both freezing-tolerant wild grape ( Vitis riparia) and freezing-sensitive cultivated grape ( Vitis vinifera). The deduced protein in V. riparia is 99% identical to the corresponding protein in V. vinifera; 45–48% to three other Vitis CBF proteins reported earlier and 57% to AtCBF1, and contains CBF-specific amino acid motifs. Agroinfiltration experiments in tobacco leaves revealed that VrCBF4 activates expression from reporter genes driven by a CRT-containing promoter. Expression of the endogenous Vitis CBF4 genes was low at ambient temperature, but enhanced upon exposure to low temperature (4 °C). Uncommon for CBF genes, this expression was maintained for several days. No significant difference in expression pattern was observed between V. riparia and V. vinifera. Vitis CBF4 was expressed in both young and mature tissue, in contrast to the previously described Vitis CBF1, 2 and 3. Together, these results suggest that CBF4 represents a second type of CBF in grape that might be more important for the over-wintering of grape plants. [ABSTRACT FROM AUTHOR]

Trifluoroacetate (CH3COO-, TFA) is a breakdown product of hydrochlorofluorocarbons and hydrofluorocarbons and is released by the heating of Teflont products. Because of its chemical properties, concentrations in evaporative wetlands are predicted to increase with time. This study focused on assessing the impact of this haloacetic acid on vernal pool soil microbial communities as well as vernal pool and wetland plant species. Microbial respiration for three vernal pool soils and an agricultural soil was not affected by TFA exposures (0, 10, 100, 1,000, and 10,000 µg/L), and degradation of TFA by microbial communities was not observed in soils incubated for three months. Trifluoroacetate accumulated in foliar tissue of wetland plant species as a function of root exposure concentration (100 and 1,000 µg/L TFA), and accumulation was found to stabilize or decrease after the second or third month of exposure. Seeds accumulated TFA as a function of root exposure concentration; however, germination success was not affected. No adverse physiological responses, including general plant health and photosynthetic and conductance rates, were observed for root exposures at the TFA concentrations used in this study. Based on the soils and plant species used in this study, predicted TFA concentrations will not adversely affect the development of soil microbial communities and vernal pool plant species. [ABSTRACT FROM AUTHOR]

Cellular responses of two rapid-cycling Brassica species, B. napus and B. carinara, to seawater salinity were characterized to determine whether callus showed a tolerance similar to that of whole plants. Callus was initiated from the leaves of 7-day-old seedlings of B. napus and B. carinata and then subcultured with two different levels of seawater salinity (2.3 and 5.2 g l-1 Instant Ocean. Aquatlum Systems, Inc.. Mentor. OH. USA) for 14 days. Callus growth of both species was reduced by seawater salinity- Based on the percentage of the reduction in the relative fresh weight gain. B. napus was more salt-tolerant than B. carinata, consistent with the response of whole plants of the same species to seawater salinity. Seawater salinity caused changes in the concentrations of Na, K. Ca, Mg and Cl- in both B. napus and B. carinata. The growth expressed as the percentage of control was significantly (P = 0.05) positively correlated with the concentration of Ca, and K/Na and Ca/Na ratios. It was also negatively correlated (P = 0.01) with the concentrations of Na. Cl-and Mg. In comparison with B. carinata. the salt-tolerant species. B. napus. showed a small reduction in the concentrations of Ca and K in the salt-stressed plants relative to the control. [ABSTRACT FROM AUTHOR]

Previous results in our laboratory indicated that a reduced Mn concentration in the leaves of barley was highly correlated with the reduced relative growth and net assimilation rates of salt-stressed plants. If Mn deficiency limits the growth of salt-stressed barley, then increasing leaf Mn concentrations should increase growth. In the present study, the effect of supplemental Mn on the growth of salt-stressed barley (Hordeum vulgare L. cv. CM 72) was tested to determine if a salinity-induced Mn deficiency was limiting growth. Plants were salinized with 125 mol m-3 NaCl and 9.6 mol m-3 CaCl2. Supplemental Mn was applied in 2 ways: 1) by increasing the Mn concentration in the solution culture and 2) by spraying Mn solutions directly onto the leaves. Growth was markedly inhibited at this salinity level. Dry matter production was increased 100% in salt-stressed plants treated with supplemental Mn to about 32% of the level of nonsalinized controls. The optimum solution culture concentration was 2.0 mmol m-3, and the optimum concentration applied to the leaves was 5.0 mol m-3. Supplemental Mn did not affect the growth of control plants. Further experiments showed that supplemental Mn increased Mn concentrations and uptake to the shoot. Supplemental Mn increased the relative growth rate of salt-stressed plants and this increase was attributed to an increase in the net assimilation rate; there were no significant effects on the leaf area ratio. Supplemental Mn also increased the net photosynthetic rate of salt-stressed plants. The data support the hypothesis that salinity induced a Mn deficiency in the shoot, which partially reduced photosynthetic rates and growth. [ABSTRACT FROM AUTHOR]

We grew barley (Hordeum vulgare L. CM 72) for a 28-day period and sequentially harvested plants every 3 or 4 days. Plants were salt-stressed with either NaCl or KCl (125 mM) with or without supplemental Ca (10 or 0.4 mM final concentration, respectively). We determined tissue concentrations of Na, Ca, Mg, K, S, P, Fe, Mn, Cu and Zn for each harvest date by inductively coupled plasma spectrometry. Uptake (specific absorption rate) was calculated from the element content and growth rates. Salinity had significant effects on the uptake and concentrations of most elements. Mg and Mn concentrations declined with time. The concentrations of all other elements determined increased over time. Element uptake on a root dry weight basis declined with time. Three variables were significantly affected by salinity and correlated with growth; 1) the Ca concentration, 2) the total sum of the cation concentration (TC), and 3) the Mn concentration of the shoot. Salinity reduced Ca uptake and concentrations. Supplemental Ca increased Ca concentrations and was positively correlated with growth during salt stress. Salinity doubled TC, which was negatively correlated with relative growth rate (RGR). Relative growth rate declined at TC values above 150 mM. Salinity reduced the uptake and concentration of Mn. Manganese concentrations in the shoot were highly correlated with RGR. Relative growth rate declined at Mn concentrations below 50 nmol (g fresh weight)-1. [ABSTRACT FROM AUTHOR]

Barley (Hordeum vulgare L. cv. CM 72) was grown for a 28-day period and stressed with treatments of 125 mol m-3 NaCI or KCI with low Ca2+ (0.4 mol m-3 Ca2+) or high Ca2+ (10 mol m-3 Ca2+). Plants were harvested periodically so that relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR) could be calculated using the functional approach to plant growth analysis. Relative growth rate declined with time for all treatments, including controls. Salinity inhibited RGR relative to control values by day 10. High Ca2+ improved the growth of salts-tressed plants in both NaCl-salinity and KCl-salinity. KCl proved more toxic than NaCl, especially for KCl-salinity plants with low Ca2+, which died by day 28. Net assimilation rate, but not LAR, was highly correlated with RGR for all treatments. This indicates that the photosynthetic-assimilatory machinery was limiting RGR and not the leaf area of the plant. [ABSTRACT FROM AUTHOR]