Development and application of an inexpensive open-source dendrometer for detecting xylem water potential and radial stem growth at high spatial and temporal resolution.

There is currently a need for inexpensive, continuous, non-destructive water potential measurements at high temporal resolution (<1 min). We describe here the development and testing of an entirely open-source dendrometer that, when combined with periodic Scholander pressure chamber measurements, provides sub-minute resolution estimates of water potential when placed on tissues exhibiting little or no secondary growth (petioles, monocotyledon stems). The dendrometer can also be used to measure radial growth of stems and branches when placed on dicotyledon and gymnosperm species. The dendrometer can be interfaced directly with a computer in real time in the lab or greenhouse, or connected to a datalogger for long periods of use in the field on batteries. We tested this device on a herbaceous dicotyledon (Helianthus annuus) (petioles and stems) and a monocotyledon (Zea mays) species (stems) for 1 week during dehydration and re-watering treatments under laboratory conditions. We also demonstrated the ability of the device to record branch and trunk diameter variation of a woody dicotyledon (Rhus typhina) in the field. Under laboratory conditions, we compared our device (hereafter 'contact' dendrometer) with modified versions of another open-source dendrometer (the 'optical' dendrometer). Overall, contact and optical dendrometers were well aligned with one another, with Pearson correlation coefficients ranging from 0.77 to 0.97. Both dendrometer devices were well aligned with direct measurements of xylem water potential, with calibration curves exhibiting significant non-linearity, especially at water potentials near the point of incipient plasmolysis, with pseudo R2 values (Efron) ranging from 0.89 to 0.99. Overall, both dendrometers were comparable and provided sufficient resolution to detect subtle differences in stem water potential (ca. 50 kPa) resulting from light-induced changes in transpiration, vapour pressure deficit and drying/wetting soils. All hardware designs, alternative configurations, software and build instructions for the contact dendrometers are provided.

Foliar Phenotypic Plasticity Reflects Adaptation to Environmental Variability.

Arabidopsis thaliana ecotypes adapted to native habitats with different daylengths, temperatures, and precipitation were grown experimentally under seven combinations of light intensity and leaf temperature to assess their acclimatory phenotypic plasticity in foliar structure and function. There were no differences among ecotypes when plants developed under moderate conditions of 400 µmol photons m-2 s-1 and 25 °C. However, in response to more extreme light or temperature regimes, ecotypes that evolved in habitats with pronounced differences in either the magnitude of changes in daylength or temperature or in precipitation level exhibited pronounced adjustments in photosynthesis and transpiration, as well as anatomical traits supporting these functions. Specifically, when grown under extremes of light intensity (100 versus 1000 µmol photons m-2 s-1) or temperature (8 °C versus 35 °C), ecotypes from sites with the greatest range of daylengths and temperature over the growing season exhibited the greatest differences in functional and structural features related to photosynthesis (light- and CO2-saturated capacity of oxygen evolution, leaf dry mass per area or thickness, phloem cells per minor vein, and water-use efficiency of CO2 uptake). On the other hand, the ecotype from the habitat with the lowest precipitation showed the greatest plasticity in features related to water transport and loss (vein density, ratio of water to sugar conduits in foliar minor veins, and transpiration rate). Despite these differences, common structure-function relationships existed across all ecotypes and growth conditions, with significant positive, linear correlations (i) between photosynthetic capacity (ranging from 10 to 110 µmol O2 m-2 s-1) and leaf dry mass per area (from 10 to 75 g m-2), leaf thickness (from 170 to 500 µm), and carbohydrate-export infrastructure (from 6 to 14 sieve elements per minor vein, from 2.5 to 8 µm2 cross-sectional area per sieve element, and from 16 to 82 µm2 cross-sectional area of sieve elements per minor vein); (ii) between transpiration rate (from 1 to 17 mmol H2O m-2 s-1) and water-transport infrastructure (from 3.5 to 8 tracheary elements per minor vein, from 13.5 to 28 µm2 cross-sectional area per tracheary element, and from 55 to 200 µm2 cross-sectional area of tracheary elements per minor vein); (iii) between the ratio of transpirational water loss to CO2 fixation (from 0.2 to 0.7 mol H2O to mmol-1 CO2) and the ratio of water to sugar conduits in minor veins (from 0.4 to 1.1 tracheary to sieve elements, from 4 to 6 µm2 cross-sectional area of tracheary to sieve elements, and from 2 to 6 µm2 cross-sectional area of tracheary elements to sieve elements per minor vein); (iv) between sugar conduits and sugar-loading cells; and (v) between water conducting and sugar conducting cells. Additionally, the proportion of water conduits to sugar conduits was greater for all ecotypes grown experimentally under warm-to-hot versus cold temperature. Thus, developmental acclimation to the growth environment included ecotype-dependent foliar structural and functional adjustments resulting in multiple common structural and functional relationships.

Age Dependent Partitioning Patterns of Essential Nutrients Induced by Copper Feeding Status in Leaves and Stems of Poplar.

Copper (Cu) is an essential micronutrient, and its deficiency can cause plants to undergo metabolic changes at several levels of organization. It has been shown that leaf age can play a role in nutrient partitioning along the shoot axis of poplar. In this study, we investigated the effect of Cu deficiency on the altered partitioning of essential macro and micronutrients in leaves and stems of different age. Cu deficiency was associated with higher concentrations of calcium, magnesium, sulfur, iron, zinc, manganese, and molybdenum in leaves and relatively higher concentrations of calcium, phosphorus, iron, and zinc in stems. Leaf and stem age had significant effects on nutrient partitioning. Principal component analyses revealed patterns that point to inverse influences in leaves and stems on nutrient partitioning. Specifically, these analyses revealed that nutrient partitioning in leaves was influenced by Cu feeding status more than developmental stage, whereas nutrient partitioning in stems was influenced by developmental stage more than Cu feeding status. These results suggest that Cu deficiency and developmental stage can significantly influence the partitioning and homeostasis of macro and micronutrients in poplar organs.

Physiological trait networks enhance understanding of crop growth and water use in contrasting environments.

Plant function arises from a complex network of structural and physiological traits. Explicit representation of these traits, as well as their connections with other biophysical processes, is required to advance our understanding of plant-soil-climate interactions. We used the Terrestrial Regional Ecosystem Exchange Simulator (TREES) to evaluate physiological trait networks in maize. Net primary productivity (NPP) and grain yield were simulated across five contrasting climate scenarios. Simulations achieving high NPP and grain yield in high precipitation environments featured trait networks conferring high water use strategies: deep roots, high stomatal conductance at low water potential ("risky" stomatal regulation), high xylem hydraulic conductivity and high maximal leaf area index. In contrast, high NPP and grain yield was achieved in dry environments with low late-season precipitation via water conserving trait networks: deep roots, high embolism resistance and low stomatal conductance at low leaf water potential ("conservative" stomatal regulation). We suggest that our approach, which allows for the simultaneous evaluation of physiological traits, soil characteristics and their interactions (i.e., networks), has potential to improve our understanding of crop performance in different environments. In contrast, evaluating single traits in isolation of other coordinated traits does not appear to be an effective strategy for predicting plant performance.

Genome Sequences of 14 Siphophages That Infect Serratia marcescens.

We announce the complete genome sequences of 14 Serratia bacteriophages isolated from wastewater treatment plants. These phages define two previously undescribed types which we call the Carrot-like phage cluster (phages Carrot, BigDog, LittleDog, Niamh, Opt-148, Opt-169, PhooPhighters, Rovert, Serratianator, Stoker, Swain, and Ulliraptor) and Tlacuache-like phage cluster (Tlacuache and Opt-155).

Genome Sequences of 22 T1-like Bacteriophages That Infect Enterobacteriales.

Here, the full genome sequences of 22 T1-like bacteriophages isolated from wastewater are reported. Eight (BlueShadow, Brooksby, Devorator, ElisaCorrea, Reinasaurus, SorkZaugg, Supreme284, ZeroToHero) were isolated on Citrobacter, six on Klebsiella (Chell, FairDinkum, HazelMika, Opt-817, P528, PeteCarol), and eight on Escherichia (Fulano1, Mishu, Opt-719, PhleaSolo, Punny, Poky, Phunderstruck, Sadiya).

Complete Genome Sequences of Five SO-1-Like Siphoviridae Bacteriophages That Infect Enterobacteriales.

The Enterobacteriales order is composed of Gram-negative bacteria that range from harmless symbionts to well-studied pathogens. We announce complete genome sequences of five related SO-1-like Enterobacteriales bacteriophages (also known as the Dhillonvirus genus) isolated from wastewater that infect Escherichia coli (Opt-212, Over9000, Pubbukkers, and Teewinot) or Shigella boydii (StarDew).

Distinct Cold Acclimation of Productivity Traits in Arabidopsis thaliana Ecotypes.

Improvement of crop climate resilience will require an understanding of whole-plant adaptation to specific local environments. This review places features of plant form and function related to photosynthetic productivity, as well as associated gene-expression patterns, into the context of the adaptation of Arabidopsis thaliana ecotypes to local environments with different climates in Sweden and Italy. The growth of plants under common cool conditions resulted in a proportionally greater emphasis on the maintenance of photosynthetic activity in the Swedish ecotype. This is compared to a greater emphasis on downregulation of light-harvesting antenna size and upregulation of a host of antioxidant enzymes in the Italian ecotype under these conditions. This differential response is discussed in the context of the climatic patterns of the ecotypes' native habitats with substantial opportunity for photosynthetic productivity under mild temperatures in Italy but not in Sweden. The Swedish ecotype's response is likened to pushing forward at full speed with productivity under low temperature versus the Italian ecotype's response of staying safe from harm (maintaining redox homeostasis) while letting productivity decline when temperatures are transiently cold. It is concluded that either strategy can offer directions for the development of climate-resilient crops for specific locations of cultivation.

Growth and Nutritional Quality of Lemnaceae Viewed Comparatively in an Ecological and Evolutionary Context.

This review focuses on recently characterized traits of the aquatic floating plant Lemna with an emphasis on its capacity to combine rapid growth with the accumulation of high levels of the essential human micronutrient zeaxanthin due to an unusual pigment composition not seen in other fast-growing plants. In addition, Lemna's response to elevated CO2 was evaluated in the context of the source-sink balance between plant sugar production and consumption. These and other traits of Lemnaceae are compared with those of other floating aquatic plants as well as terrestrial plants adapted to different environments. It was concluded that the unique features of aquatic plants reflect adaptations to the freshwater environment, including rapid growth, high productivity, and exceptionally strong accumulation of high-quality vegetative storage protein and human antioxidant micronutrients. It was further concluded that the insensitivity of growth rate to environmental conditions and plant source-sink imbalance may allow duckweeds to take advantage of elevated atmospheric CO2 levels via particularly strong stimulation of biomass production and only minor declines in the growth of new tissue. It is proposed that declines in nutritional quality under elevated CO2 (due to regulatory adjustments in photosynthetic metabolism) may be mitigated by plant-microbe interaction, for which duckweeds have a high propensity.

Genotype-dependent contribution of CBF transcription factors to long-term acclimation to high light and cool temperature.

When grown under cool temperature, winter annuals upregulate photosynthetic capacity as well as freezing tolerance. Here, the role of three cold-induced C-repeat-binding factor (CBF1-3) transcription factors in photosynthetic upregulation and freezing tolerance was examined in two Arabidopsis thaliana ecotypes originating from Italy (IT) or Sweden (SW), and their corresponding CBF1-3-deficient mutant lines it:cbf123 and sw:cbf123. Photosynthetic, morphological and freezing-tolerance phenotypes, as well as gene expression profiles, were characterized in plants grown from the seedling stage under different combinations of light level and temperature. Under high light and cool (HLC) growth temperature, a greater role of CBF1-3 in IT versus SW was evident from both phenotypic and transcriptomic data, especially with respect to photosynthetic upregulation and freezing tolerance of whole plants. Overall, features of SW were consistent with a different approach to HLC acclimation than seen in IT, and an ability of SW to reach the new homeostasis through the involvement of transcriptional controls other than CBF1-3. These results provide tools and direction for further mechanistic analysis of the transcriptional control of approaches to cold acclimation suitable for either persistence through brief cold spells or for maximisation of productivity in environments with continuous low temperatures.

Foliar sieve elements: Nexus of the leaf.

In this review, a central position of foliar sieve elements in linking leaf structure and function is explored. Results from studies involving plants grown under, and acclimated to, different growth regimes are used to identify significant, linear relationships between features of minor vein sieve elements and those of 1) leaf photosynthetic capacity that drives sugar synthesis, 2) overall leaf structure that serves as the platform for sugar production, 3) phloem components that facilitate the loading of sugars (companion & phloem parenchyma cells), and 4) the tracheary elements that import water to support photosynthesis (and stomatal opening) as well as mass flow of sugars out of the leaf. Despite comprising only a small fraction of physical space within the leaf, sieve elements represent a hub through which multiple functions of the leaf intersect. As the conduits for export of energy-rich carbohydrates, essential mineral nutrients, and information carriers, sieve elements play a central role in fueling and orchestrating development and function of the plant as well as, by extension, of natural and human communities that depend on plants as producers and partners in the global carbon cycle.

Photosynthesis and foliar vascular adjustments to growth light intensity in summer annual species with symplastic and apoplastic phloem loading.

Concomitant adjustments in photosynthetic capacity and size, composition, and/or density of minor foliar veins in response to growth environment were previously described primarily for winter annuals that load sugars into foliar phloem apoplastically. Here, common trends, differences associated with phloem-loading mechanism, and species-dependent differences are identified for summer annuals (loading sugars either symplastically [cucumber, pumpkin, and basil] or apoplastically [tomato and sunflower]) that were grown in low and high light. Photosynthetic capacity per leaf area was significantly positively correlated with leaf-level volume of phloem-loading cells (LCs), sugar-export conduits (sieve elements), and water conduits (tracheary elements) irrespective of phloem-loading mechanism. The relative contribution to leaf-level volume of LC numbers versus individual LC size was greater in apoplastic loaders than in symplastic loaders. Species-dependent differences included different vein density within each loading group and either greater or lower numbers of cells per minor vein (especially of tracheary elements in the symplastic loaders basil versus cucumber, respectively), which may be due to genetic adaptation to different environmental conditions. These results indicate considerable plasticity in foliar vascular features in summer annuals as well as some loading-mechanism-dependent trends.

Features of the Duckweed Lemna That Support Rapid Growth under Extremes of Light Intensity.

This study addresses the unique functional features of duckweed via comparison of Lemna gibba grown under controlled conditions of 50 versus 1000 µmol photons m-2 s-1 and of a L. minor population in a local pond with a nearby population of the biennial weed Malva neglecta. Principal component analysis of foliar pigment composition revealed that Malva was similar to fast-growing annuals, while Lemna was similar to slow-growing evergreens. Overall, Lemna exhibited traits reminiscent of those of its close relatives in the family Araceae, with a remarkable ability to acclimate to both deep shade and full sunlight. Specific features contributing to duckweed's shade tolerance included a foliar pigment composition indicative of large peripheral light-harvesting complexes. Conversely, features contributing to duckweed's tolerance of high light included the ability to convert a large fraction of the xanthophyll cycle pool to zeaxanthin and dissipate a large fraction of absorbed light non-photochemically. Overall, duckweed exhibited a combination of traits of fast-growing annuals and slow-growing evergreens with foliar pigment features that represented an exaggerated version of that of terrestrial perennials combined with an unusually high growth rate. Duckweed's ability to thrive under a wide range of light intensities can support success in a dynamic light environment with periodic cycles of rapid expansion.

Zeaxanthin, a Molecule for Photoprotection in Many Different Environments.

Conversion of sunlight into photochemistry depends on photoprotective processes that allow safe use of sunlight over a broad range of environmental conditions. This review focuses on the ubiquity of photoprotection associated with a group of interconvertible leaf carotenoids, the xanthophyll cycle. We survey the striking plasticity of this process observed in nature with respect to (1) xanthophyll cycle pool size, (2) degree and speed of interconversion of its components, and (3) flexibility in the association between xanthophyll cycle conversion state and photoprotective dissipation of excess excitation energy. It is concluded that the components of this system can be independently tuned with a high degree of flexibility to produce a fit for different environments with various combinations of light, temperature, and other factors. In addition, the role of genetic variation is apparent from variation in the response of different species growing side-by-side in the same environment. These findings illustrate how field studies can generate insight into the adjustable levers that allow xanthophyll cycle-associated photoprotection to support plant photosynthetic productivity and survival in environments with unique combinations of environmental factors.

Zeaxanthin and Lutein: Photoprotectors, Anti-Inflammatories, and Brain Food.

This review compares and contrasts the role of carotenoids across the taxa of life-with a focus on the xanthophyll zeaxanthin (and its structural isomer lutein) in plants and humans. Xanthophylls' multiple protective roles are summarized, with attention to the similarities and differences in the roles of zeaxanthin and lutein in plants versus animals, as well as the role of meso-zeaxanthin in humans. Detail is provided on the unique control of zeaxanthin function in photosynthesis, that results in its limited availability in leafy vegetables and the human diet. The question of an optimal dietary antioxidant supply is evaluated in the context of the dual roles of both oxidants and antioxidants, in all vital functions of living organisms, and the profound impact of individual and environmental context.

Growth and Essential Carotenoid Micronutrients in Lemna gibba as a Function of Growth Light Intensity.

Duckweed is a promising food crop with multiple benefits for space applications. Fresh duckweed could deliver synergistically acting essential antioxidant nutrients to a crew - but only if growth conditions provide the plant with the right cues to trigger antioxidant formation. We grew Lemna gibba under continuous growth light ranging from low to very high intensities (photosynthetic photon flux densities = PPFDs) in order to investigate the effect on plant growth, photosynthesis, and level of carotenoid antioxidants that are essential human micronutrients. Lemna gibba achieved remarkably high growth rates under modest growth PPFD by virtue of superior light absorption resulting from minimal self-shading and high chlorophyll levels. Conversely, L. gibba's growth rate remained high even under very high growth PPFDs. This notable ability of L. gibba to avoid inactivation of photosynthesis and diminished growth under very high growth PPFDs resulted from a combination of downregulation of chlorophyll synthesis and increased biochemical photoprotection that limited a build-up of excessive excitation energy. This biochemical photoprotection included accumulation of zeaxanthin (an essential human micronutrient) and high levels of zeaxanthin-catalyzed thermal energy dissipation of excess excitation. Compared to the light levels needed to saturate L. gibba photosynthesis and growth, higher light levels were thus required for strong induction of the essential antioxidant zeaxanthin. These results indicate a need for design of light protocols that achieve simultaneous optimization of plant yield, nutritional quality, and light-use efficiency to circumvent the fact that the light requirement to saturate plant growth is lower than that for production of high zeaxanthin levels. How this trade-off between light-use efficiency of growth and nutritional quality might be minimized or circumvented to co-optimize all desired features is discussed.

Less photoprotection can be good in some genetic and environmental contexts.

Antioxidant systems modulate oxidant-based signaling networks and excessive removal of oxidants can prevent beneficial acclimation responses. Evidence from mutant, transgenic, and locally adapted natural plant systems is used to interpret differences in the capacity for antioxidation and formulate hypotheses for future inquiry. We focus on the first line of chloroplast antioxidant defense, pre-emptive thermal dissipation of excess absorbed light (monitored as nonphotochemical fluorescence quenching, NPQ) as well as on tocopherol-based antioxidation. Findings from NPQ-deficient and tocopherol-deficient mutants that exhibited enhanced biomass production and/or enhanced foliar water-transport capacity are reviewed and discussed in the context of the impact of lower levels of antioxidation on plant performance in hot/dry conditions, under cool temperature, and in the presence of biotic stress. The complexity of cellular redox-signaling networks is related to the complexity of environmental and endogenous inputs as well as to the need for intensified training and collaboration in the study of plant-environment interactions across biological sub-disciplines.

Quantification of Leaf Phloem Anatomical Features with Microscopy.

Measurements of vein density and foliar minor vein phloem cell numbers, minor vein phloem cell sizes, and transfer cell wall ingrowths provide quantitative proxies for the leaf's capacities to load and export photosynthates. While overall infrastructural capacity for sugar loading and sugar export correlated positively and closely with photosynthetic capacity, the specific targets of the adjustment of minor vein organization varied with phloem-loading mechanism, plant life-cycle characteristics, and environmental growth conditions. Among apoplastic loaders, for which sugar loading into the phloem depends on cell membrane-spanning transport proteins, variation in minor vein density, phloem cell number, and level of cell wall ingrowth (when present) were consistently associated with photosynthetic capacity. Among active symplastic loaders, for which sugar loading into the phloem depends on cytosolic enzymes, variation in vein density and phloem cell size were consistently associated with photosynthetic capacity. All of these anatomical features were also subject to acclimatory adjustment depending on species and environmental conditions, with increased levels of these features supporting higher rates of photosynthesis. We present a procedure for the preparation of leaf tissue for minor vein analysis, using both light and transmission electron microscopy, that facilitates quantification of not only phloem features but also xylem features that provide proxies for foliar water import capacity.

Effects of Foliar Redox Status on Leaf Vascular Organization Suggest Avenues for Cooptimization of Photosynthesis and Heat Tolerance.

The interaction of heat stress with internal signaling networks was investigated through Arabidopsisthaliana mutants that were deficient in either tocopherols (vte1 mutant) or non-photochemical fluorescence quenching (NPQ; npq1, npq4, and npq1 npq4 mutants). Leaves of both vte1 and npq1 npq4 mutants that developed at a high temperature exhibited a significantly different leaf vascular organization compared to wild-type Col-0. Both mutants had significantly smaller water conduits (tracheary elements) of the xylem, but the total apparent foliar water-transport capacity and intrinsic photosynthetic capacity were similarly high in mutants and wild-type Col-0. This was accomplished through a combination of more numerous (albeit narrower) water conduits per vein, and a significantly greater vein density in both mutants relative to wild-type Col-0. The similarity of the phenotypes of tocopherol-deficient and NPQ-deficient mutants suggests that leaf vasculature organization is modulated by the foliar redox state. These results are evaluated in the context of interactions between redox-signaling pathways and other key regulators of plant acclimation to growth temperature, such as the C-repeat binding factor (CBF) transcription factors, several of which were upregulated in the antioxidant-deficient mutants. Possibilities for the future manipulation of the interaction between CBF and redox-signaling networks for the purpose of cooptimizing plant productivity and plant tolerance to extreme temperatures are discussed.

Arabidopsis thaliana Ei-5: Minor Vein Architecture Adjustment Compensates for Low Vein Density in Support of Photosynthesis.

An Arabidopsis thaliana accession with naturally low vein density, Eifel-5 (Ei-5), was compared to Columbia-0 (Col-0) with respect to rosette growth, foliar vein architecture, photosynthesis, and transpiration. In addition to having to a lower vein density, Ei-5 grew more slowly, with significantly lower rates of rosette expansion, but had similar capacities for photosynthetic oxygen evolution on a leaf area basis compared to Col-0. The individual foliar minor veins were larger in Ei-5, with a greater number of vascular cells per vein, compared to Col-0. This compensation for low vein density resulted in similar values for the product of vein density × phloem cell number per minor vein in Ei-5 and Col-0, which suggests a similar capacity for foliar sugar export to support similar photosynthetic capacities per unit leaf area. In contrast, the product of vein density × xylem cell number per minor vein was significantly greater in Ei-5 compared to Col-0, and was associated not only with a higher ratio of water-transporting tracheary elements versus sugar-transporting sieve elements but also significantly higher foliar transpiration rates per leaf area in Ei-5. In contrast, previous studies in other systems had reported higher ratios of tracheary to sieve elements and higher transpiration rate to be associated with higher - rather than lower - vein densities. The Ei-5 accession thus further underscores the plasticity of the foliar vasculature by illustrating an example where a higher ratio of tracheary to sieve elements is associated with a lower vein density. Establishment of the Ei-5 accession, with a low vein density but an apparent overcapacity for water flux through the foliar xylem network, may have been facilitated by a higher level of precipitation in its habitat of origin compared to that of the Col-0 accession.