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After the imposition of soil drying treatments, an elevation of xylem sap pH is one of the earliest observable responses in many herbaceous model plant species. It is theorized that alkalization of sap results in a concurrent elevation in abscisic acid (ABA) concentration delivered to transpiring tissues by preventing Henderson–Hasselbalch-regulated partitioning between the apoplast and symplast. However, here it is demonstrated that the sap alkalzation response to soil drying is far from universal in higher plant species. Tests were conducted to determine how universal the pH response to drying soil was in a range of perennial species from a diverse range of plant families. The response was not found in the majority of the 22 species tested. Four species exhibited significant increases in pH, but the majority showed no significant change in xylem sap pH. There was no evolutionary relationship between the species that showed alkalization under drought stress. However, the species that alkalized sap also exhibited good control over internal water status and were the most isohydric species of those tested. None of the species exhibiting anisohydric responses alkalized xylem sap under drought stress. Regardless of alkalization response, plants still retain the ability to respond to changes in xylem sap pH when manipulated by alkaline buffer foliar sprays. This finding indicates that plants have conserved the ability to respond to changes in xylem pH and redistribute ABA, even if they do not currently utilize the mechanism when exposed to drought stress. It was found in Buddleja davidii, Euonymus fortunei, and Hydrangea serrata that the xylem sap pH response to water deficits mirrored the natural pH changes that occur as sap is transported to the leaves, indicating that plants need to be able to have naturally occurring alkalization processes in place for them to be up-regulated under drought stress. [ABSTRACT FROM PUBLISHER]

Several mechanisms enable leaf stomata to optimize water loss with respect to carbon gain. Stomatal responses to environmental variation constitute a plant's first and second lines of defense against damaging water deficits. Changes in the concentrations of endogenous growth regulators and their influence on stomata may well be important to both defense strategies. [ABSTRACT FROM AUTHOR]

In two experiments, the effect has been investigated of a mild and more prolonged drought on the spatial distribution of growth, epidermal cell lengths and cell wall peroxidase activities in the leaf elongation zone of the grass species Lolium temulentum L. In both experiments drought reduced the size of the elongation zone and local rates of elongation within it. Abrupt increases in cell wall-associated peroxidase activity occurred at or close to the position where elongation ceased in the leaf elongation zones of well-watered and mildly drought-stressed plants. More prolonged drought caused a 200-300% increase in the cell wall-associated peroxidase activity in the elongation zone only. The significant increase in the elongation zone cell wall peroxidase activity and it spatial variation provides evidence of a potentially causal role for cell wall-associated peroxidase in restricting cell expansion during drought. [ABSTRACT FROM PUBLISHER]

Background and Aims Bioenergy crops are central to climate mitigation strategies that utilize biogenic carbon, such as BECCS (bioenergy with carbon capture and storage), alongside the use of biomass for heat, power, liquid fuels and, in the future, biorefining to chemicals. Several promising lignocellulosic crops are emerging that have no food role – fast-growing trees and grasses – but are well suited as bioenergy feedstocks, including Populus , Salix , Arundo , Miscanthus , Panicum and Sorghum. Scope These promising crops remain largely undomesticated and, until recently, have had limited germplasm resources. In order to avoid competition with food crops for land and nature conservation, it is likely that future bioenergy crops will be grown on marginal land that is not needed for food production and is of poor quality and subject to drought stress. Thus, here we define an ideotype for drought tolerance that will enable biomass production to be maintained in the face of moderate drought stress. This includes traits that can readily be measured in wide populations of several hundred unique genotypes for genome-wide association studies, alongside traits that are informative but can only easily be assessed in limited numbers or training populations that may be more suitable for genomic selection. Phenotyping, not genotyping, is now the major bottleneck for progress, since in all lignocellulosic crops studied extensive use has been made of next-generation sequencing such that several thousand markers are now available and populations are emerging that will enable rapid progress for drought-tolerance breeding. The emergence of novel technologies for targeted genotyping by sequencing are particularly welcome. Genome editing has already been demonstrated for Populus and offers significant potential for rapid deployment of drought-tolerant crops through manipulation of ABA receptors, as demonstrated in Arabidopsis , with other gene targets yet to be tested. Conclusions Bioenergy is predicted to be the fastest-developing renewable energy over the coming decade and significant investment over the past decade has been made in developing genomic resources and in collecting wild germplasm from within the natural ranges of several tree and grass crops. Harnessing these resources for climate-resilient crops for the future remains a challenge but one that is likely to be successful. [ABSTRACT FROM AUTHOR]

The role of bacterial 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity in the interaction between tomato (Lycopersicon esculentum=Solanum lycopersicum) and Pseudomonas brassicacearum was studied in different strains. The phytopathogenic strain 520-1 possesses ACC deaminase activity, an important trait of plant growth-promoting rhizobacteria (PGPR) that stimulates root growth. The ACC-utilizing PGPR strain Am3 increased in vitro root elongation and root biomass of soil-grown tomato cv. Ailsa Craig at low bacterial concentrations (106 cells ml−1 in vitro and 106 cells g−1 soil) but had negative effects on in vitro root elongation at higher bacterial concentrations. A mutant strain of Am3 (designated T8-1) that was engineered to be ACC deaminase deficient failed to promote tomato root growth in vitro and in soil. Although strains T8-1 and 520-1 inhibited root growth in vitro at higher bacterial concentrations (>106 cells ml−1), they did not cause disease symptoms in vitro after seed inoculation, or in soil supplemented with bacteria. All the P. brassicacearum strains studied caused pith necrosis when stems or fruits were inoculated with a bacterial suspension, as did the causal organism of this disease (P. corrugata 176), but the non-pathogenic strain Pseudomonas sp. Dp2 did not. Strains Am3 and T8-1 were marked with antibiotic resistance and fluorescence to show that bacteria introduced to the nutrient solution or on seeds in vitro, or in soil were capable of colonizing the root surface, but were not detected inside root tissues. Both strains showed similar colonization ability either on root surfaces or in wounded stems. The results suggest that bacterial ACC deaminase of P. brassicacearum Am3 can promote growth in tomato by masking the phytopathogenic properties of this bacterium. [ABSTRACT FROM PUBLISHER]