Embolism spreading in dehydrating angiosperm xylem is driven by gas movement between embolised and sap-filled conduits. Here, we examine how proximity to pre-existing embolism and hydraulic segmentation affect embolism propagation. Based on the optical method, we compared xylem embolism resistance between detached leaves and leaves attached to branches, and between intact leaves and leaves with cut minor veins for six species. Moreover, we directly compared the optical and pneumatic method on detached leaves. Embolism resistance of detached leaves was significantly lower than leaves attached to stems, except for two species with all vessels ending in their petioles. Cutting of minor veins showed limited embolism spreading in minor veins near the cuts prior to major veins. Moreover, there was strong agreement in embolism resistance between the optical and pneumatic method, with minor differences occurring during early stages of embolism formation. We conclude that embolism resistance may represent a relative trait, depending on the proximity and connectivity to pre-existing embolism as a gas source. Since embolism formation may not rely on a certain pressure difference threshold between functional and embolised conduits, we suggest that embolism is facilitated by pressure-driven gas diffusion, while hydraulic segmentation can prevent embolism propagation by reducing gas diffusion.

Several species of soil free-living saprotrophs can sometimes establish biotrophic symbiosis with plants, but the basic biology of this association remains largely unknown. Here, we investigate the symbiotic interaction between a common soil saprotroph, Clitopilus hobsonii (Agaricomycetes), and the American sweetgum (Liquidambar styraciflua). Notably, the colonized root cortical cells contain numerous microsclerotia-like structures. Fungal colonization led to increased plant growth and facilitated potassium uptake, particularly under potassium limitation (0.05 mM K+). The expression of plant genes related to potassium uptake is not altered during symbiosis, whereas the transcripts of three fungal genes encoding ACU, HAK, and SKC involved in K+ nutrition is found in colonized roots. We confirmed the K+ influx activities by expressing the ChACU and ChSKC genes into a yeast K+-uptake-defective mutant. Upregulation of the ChACU under 0.05 mM K+ and no K+ conditions was demonstrated in planta and in vitro compared to normal condition (5 mM K+). In addition, colonized plants displayed a larger accumulation of soluble sugars under 0.05 mM K+. The present study highlights that potassium limitation promotes this novel tree-fungus symbiosis mainly through a reciprocal transfer of additional carbon and potassium to both partners, and the role of dual soil saprotroph/symbiotroph in tree nutrition.

CO2 responsive CCT protein (CRCT) is a positive regulator of starch synthesis related genes such as ADP-glucose pyrophosphorylase large subunit 1 and starch branching enzyme I particularly in the leaf sheath of rice (Oryza sativa L.). The promoter GUS analysis revealed that CRCT expressed exclusively in the vascular bundle, whereas starch synthesis related genes were expressed in different sites such as mesophyll cell and starch storage parenchyma cell. However, the chromatin immunoprecipitation (ChIP) using a FLAG-CRCT overexpression line and subsequent qPCR analyses showed that the 5’-flanking regions of these starch synthesis-related genes tended to be enriched by ChIP, suggesting that CRCT can bind to the promoter regions of these genes. The monomer of CRCT is 34.2 kDa, however CRCT was detected at 270 kDa via gel filtration chromatography, suggesting that CRCT forms a complex in vivo. Immunoprecipitation and subsequent MS analysis pulled down several 14-3-3-like proteins. A yeast two-hybrid analysis and bimolecular fluorescence complementation assays confirmed the interaction between CRCT and 14-3-3-like proteins. Although there is an inconsistency in the place of expression, this study provide important findings regarding the molecular function of CRCT to control the expression of key starch synthesis-related genes.

How variations in carbon supply affect wood formation remains poorly understood in particular in mature forest trees. To elucidate how carbon supply affects carbon allocation and wood formation, we attempted to manipulate carbon supply to the cambial region by phloem girdling and compression during the mid- and late-growing season and measured effects on structural development, CO2 efflux, and nonstructural carbon reserves in stems of mature white pines. Wood formation and stem CO2 efflux varied with location relative to treatment (i.e., above or below the restriction). We observed up to twice as many tracheids formed above versus below the treatment after the phloem transport manipulation, whereas cell-wall area decreased only slightly below the treatments, and cell size did not change relative to the control. Nonstructural carbon reserves in the xylem, needles, and roots were largely unaffected by the treatments. Our results suggest that low and high carbon supply affects wood formation, primarily through a strong effect on cell proliferation, and respiration, but local nonstructural carbon concentrations appear to be maintained homeostatically. This contrasts with reports of a decoupling of source activity and wood formation at the whole-tree or ecosystem level, highlighting the need to better understand organ-specific responses, within-tree feedbacks, as well as phenological and ontological effects on sink-source dynamics.

Since the first description of phloem sap composition nearly 60 years ago, it is generally assumed that phloem sap does not contain nitrate and that there is little or no backflow of nitrate from shoots to roots. While it is true that nitrate can occasionally be absent from phloem sap, there is now substantial evidence that phloem can carry nitrate and furthermore, transporters involved in nitrate redistribution to shoot sink organs and roots have been found. This raises the question of why nitrate may or may not be present in phloem sap, why its concentration is generally kept low, and whether plant shoot-root nutrient cycling also involves nitrate. We propose here that phloem sap nitrate is not only an essential component of plant nutritional signaling but also contributes to physical properties of phloem sap and as such, its concentration is controlled to ensure proper coordination of plant development and nutrient transport.

Little is known about the sources and age of C respired from tree roots. Previous research in tree stems has identified two functional pools of non-structural carbohydrates (NSC): an ‘active’ pool supplied directly from canopy photo-assimilates that supports metabolism and a ‘stored’ pool used when fresh C supplies are limited. We compared the C isotope composition of water soluble NSC and respired CO2 for aspen roots (Populus tremula hybrids) that were cut off fresh C supply via stem-girdling and prolonged incubation of excised roots. We used bomb radiocarbon to estimate the time elapsed since C fixation for respired CO2, water-soluble C, and structural α-cellulose. While freshly excised roots respired CO2 with mean age <1 yr, within a week the age increased to 1.6-2.9 yr. Freshly excised roots from trees girdled ~3 months previously had similar respiration rates and NSC stocks as un-girdled trees, but respired older C (~1.2 yr). We estimate the NSC in girdled roots must be replaced 5-7 times by reserves remobilized from root-external sources. Using a mixing model and observed correlations between Δ14C of water-soluble C and α-cellulose, we estimate ~30% of C is ‘active’ (~5 mg C g-1).

Plants transitioned from an aquatic to a terrestrial lifestyle during their evolution. On land, fluctuations on water availability in the environment became one of the major problems they encountered. The appearance of morpho-physiological adaptations to cope with and tolerate water loss from the cells was undeniably useful to survive on dry land. Some of these adaptations, such as carbon concentrating mechanisms (CCMs), desiccation tolerance (DT) and root impermeabilization, appeared in multiple plant lineages. Despite being crucial for evolution on land, it has been unclear how these adaptations convergently evolved in the various plant lineages. Recent advances on whole genome and transcriptome sequencing are revealing that co-option of genes and gene regulatory networks (GRNs) is a common feature underlying the convergent evolution of these adaptations. In this review we address how the study of CCMs and DT have provided insight into convergent evolution of GRNs underlying plant adaptation to dry environments, and how these insights could be applied to currently emerging understanding of evolution of root impermeabilization through different barrier cell types. We discuss examples of co-option, conservation, and innovation of genes and GRNs at the cell, tissue and organ levels revealed by recent phylogenomic (comparative genomic) and comparative transcriptomic studies.

Translocation of metabolites between different plant species provides important hints in understanding the fate of bioactive root exudates. In the present study, targeted and untargeted mass spectrometry-based metabolomics was applied to elucidate the transfer of bioactive compounds between rye and several crops and weed species. Our results demonstrated that benzoxinoids (BXs) synthesized by rye were taken up by roots of neighboring plant species and translocated into their shoots. Furthermore, we showed roots of the rye plant took up compounds originating from neighboring plants. Among the compounds taken up by rye roots, wogonin was detected in the rye shoot, which indicates the root-to-shoot translocation of this compound. Elucidating the transfer of bioactive compounds between plants is essential for understanding plant-plant interactions, developing natural pesticides and understanding their modes of action.

Recent research has shown that plants can distinguish genetically-related individuals from strangers (kin recognition) and exhibit more cooperative behaviours towards these more related individuals (kin discrimination). The first evidence for this was found when Cakile edentula plants growing with half-sibs allocated relatively less biomass to roots than plants growing with unrelated individuals, indicating that kin recognition can reduce the intensity of competition (Dudley & File, 2007). Since then, kin discrimination has been shown to result in reduced competition for soil resources (Semchenko, Saar, & Lepik, 2014), light (Crepy & Casal, 2015) and pollinators (Torices, Gómez, & Pannell, 2018). On the other hand, allelopathy, plants producing chemical compounds that negatively affect performance of neighbour plants, has also been widely documented (Inderjit & Duke, 2003) and shown to profoundly affect local species coexistence and plant community structure (Meiners, Kong, Ladwig, Pisula, & Lang, 2012). In crops allelopathy can also be beneficial in suppressing weeds (Macías, Mejías, & Molinillo, 2019). In the current issue, Xu, Cheng, Kong, and Meiners (2021) published the first study to show that kin discrimination can also affect the balance between direct competition for resources and allelopathy, and this together may lead to improved weed suppression in rice.

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 seedling stage under different combinations of light level and temperature. Under high light and cool growth temperature (HLC), 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 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 maximization of productivity in environments with continuous low temperatures.

Recent results suggest that metabolism-mediated stomatal closure mechanisms are important to regulate differentially the stomatal speediness between ferns and angiosperms. However, evidence directly linking mesophyll metabolism and the slower stomatal conductance (gs) in ferns is missing. Here we investigated the effect of exogenous application of abscisic acid (ABA), sucrose and mannitol on gs kinetics and carried out a metabolic fingerprinting analysis of ferns and angiosperms leaves harvested throughout a diel course. Ferns stomata did not respond to ABA in the time period analysed. No differences in the relative decrease in gs was observed between ferns and the angiosperm following provision of sucrose or mannitol. However, ferns have slower gs responses to these compounds than angiosperms. Metabolomics analysis highlights that ferns have higher accumulation of secondary rather than primary metabolites throughout the diel course, with the opposite being observed in angiosperms. Our results indicate that metabolism-mediated stomatal closure mechanism is conserved among ferns and angiosperms and that the slower stomatal closure in ferns is associated to a reduced capacity to respond to mesophyll-derived sucrose and to a higher carbon allocation toward secondary metabolism, which likely modulates both photosynthesis-stomatal movements and growth-stress tolerance trade-offs.

Oxylipins are lipid-derived molecules that are ubiquitous in eukaryotes and whose functions in plant physiology have been widely reported. They appear to play a major role in plant immunity by orchestrating reactive oxygen species (ROS) and hormone-dependent signalling pathways. The present work focuses on the specific case of fatty acid hydroperoxides (HPOs). Although some studies report their potential use as exogenous biocontrol agents for plant protection, evaluation of their efficiency in planta is lacking and no information is available about their mechanism of action. In this work, the potential of 13(S)-hydroperoxyoctadeca-(9Z,11E)-dienoic acid (13-HPOD) and 13(S)-hydroperoxy-(9Z,11E,15Z)-octadecatrienoic acid (13-HPOT), as plant defence elicitors and the underlying mechanism of action are investigated. Arabidopsis thaliana leaf resistance to Botrytis cinerea was observed after root application with HPOs. They also activate early immunity-related defence responses, like ROS. As previous studies have demonstrated their ability to interact with plant plasma membranes (PPM), we have further investigated the effects of HPOs on biomimetic PPM structure using complementary biophysics tools. Results show that HPO insertion into PPM impacts its global structure without solubilizing it. Relationship between biological assays and biophysical analysis suggests that lipid amphiphilic elicitors that directly act on membrane lipids might trigger early plant defence events

Long non-coding RNAs (lncRNAs) have been considered to be important regulators of gene expression in a range of biological processes in plants. A large number of lncRNAs have been identified in plants. However, most of their biological functions still remain to be determined. Here, we identified total 3 004 lncRNAs in cassava under normal or cold-treated conditions from Iso-seq data. We further characterized a lincRNA, CRIR1, as a novel positive regulator of the plant response to cold stress. CRIR1 can be significantly induced by cold treatment. Overexpression of CRIR1 in cassava enhanced the cold tolerance of transgenic plants. Transcriptome analysis demonstrated that CRIR1 regulates a range of cold stress-related genes in a CBF-independent pathway. We further found that CRIR1 RNA can interact with MeCSP5, a homolog of the cold shock protein that acts as RNA chaperones, indicating that CRIR1 may recruit MeCSP5 to improve the translation efficiency of mRNA. In summary, our study greatly extends the repertoire of lncRNAs in plants as well as its responding to cold stress. Moreover, it reveals a sophisticated mechanism by which CRIR1 regulates plant cold stress response by modulating the expression of stress-responsive genes and increasing the translational yield.

To explore diversity in cold hardiness mechanisms, high resolution magnetic resonance imaging (MRI) was used to visualize freezing behaviors in wintering flower buds of Daphne kamtschatica var. jezoensis, which have no bud scales surrounding well-developed florets. MRI images showed that anthers remained stably supercooled to -14 ∼ -21°C or lower whilst most other tissues froze by -7°C. Freezing of some anthers detected in MRI images at ∼ -21°C corresponded with numerous low temperature exotherms and also with the “all-or-nothing” type of anther injuries. In ovules/pistils, only embryo sacs remained supercooled at -7°C or lower, but slowly dehydrated during further cooling. Cryomicroscopic observation revealed ice formation in the cavities of calyx tubes and pistils but detected no ice in embryo sacs or in anthers. The distribution of ice nucleation activity in floral tissues corroborated the tissue freezing behaviors. Filaments likely work as the ice blocking barrier that prevents ice intrusion from extracellularly frozen calyx tubes to connecting unfrozen anthers. Unique freezing behaviors were demonstrated in Daphne flower buds: preferential freezing avoidance in male and female gametophytes and their surrounding tissues (by stable supercooling in anthers and by supercooling with slow dehydration in embryo sacs) whilst the remaining tissues tolerate extracellular freezing.

The counteractive influence of atmospheric CO2 enrichment and drought stress on tree growth results in great uncertainty in growth patterns of planted forests in cold semi-arid regions. We used tree-ring chronology and carbon isotope analysis to track ecophysiological processes in reaction to environmental factors over the past four decades of Populus simonii plantations in cold semi-arid areas in northern China. Our results showed that the boosting effect of the rising atmospheric CO2 concentration (Ca) on iWUE and stem growth was more significant in declined stands. However, the increased iWUE did not negate tree dieback when water stress was present. Therefore, the BAI and iWUE deviation of different health status trees started from a very early age. Climatic factors showed limited influences on the stem growth of the poplar plantations. The inaccessibility of deep soil water due to site-specific soil conditions rendered the trees exposed to chronic soil water stress and constrained stomatal conductance and reduced the CO2 fertilization effect. Consequently, these stands experienced a lower stem growth rate. In summary, we suggest that soil moisture conditions the iWUE and growth sensitivity to global warming and thus portrays site-specific decline episodes of different degrees in drought-prone areas.

Salt stress is a major limiting factor that severely affects the survival and growth of crops. It is important to understand the salt tolerance ability of Brassica napus and explore the underlying related genetic resources. We used a high-throughput phenotyping platform to quantify 2,111 image-based traits (i-traits) of a natural population under 3 different salt stress conditions and an intervarietal substitution line (ISL) population under 9 different stress conditions to monitor and evaluate the salt stress tolerance of B. napus over time. We finally identified 928 high-quality i-traits associated with the salt stress tolerance of B. napus. Moreover, we mapped the salt stress-related loci in the natural population via a genome-wide association study (GWAS) and performed a linkage analysis associated with the ISL population, respectively. The results revealed 234 candidate genes associated with salt stress response, and two novel candidate genes, BnCKX5 and BnERF3, were experimentally verified to regulate the salt stress tolerance of B. napus. This study demonstrates the feasibility of using high-throughput phenotyping-based QTL mapping to accurately and comprehensively quantify i-traits associated with B. napus. The mapped loci could be used for genomics-assisted breeding to genetically improve the salt stress tolerance of B. napus.

Similar to other cropping systems, few walnut cultivars are used as scion in commercial production. Germplasm collections can be used to diversify cultivar options and hold potential for improving crop productivity, disease resistance and stress tolerance. In this study we explored the anatomical and biochemical bases of photosynthetic capacity in 11 J. regia accessions in the USDA-ARS National Clonal Germplasm Repository. Net assimilation rate (An) differed significantly among accessions and was greater in those from lower latitudes coincident with increases in stomatal and mesophyll conductance, leaf thickness, mesophyll porosity and gas-phase diffusion, and leaf nitrogen, and lower leaf mass and stomatal density. High CO2-saturated assimilation rates led to increases in An under limiting conditions. Greater An was found in lower latitude accessions native to climates with more frost-free days, greater precipitation seasonality, and lower temperature seasonality. As expected, water stress consistently impaired photosynthesis with the highest % reductions in three lower latitude accessions (A3, A5, and A9), which had the highest An under well-watered conditions. However, An for A3 and A5 remained amongst the highest under dehydration. J. regia accessions, which have leaf structural traits and biochemistry that enhance photosynthesis, could be used as commercial scions or breeding parents to enhance productivity.

Plant vacuoles serve as the primary intracellular compartments for phosphorus (P) storage and play a central role to maintain P homeostasis. The Oryza sativa (rice) genome contains three genes that encode SPX (SYG1/PHO81/XPR1)-MFS (Major Facility Superfamily) proteins (OsSPX-MFS1, 2, 3). OsSPX-MFS1 and OsSPX-MFS3 were shown previously to have vacuolar phosphate (Pi) transporter activities, but the physiological role of the three transporters under varying P conditions and under field grown conditions for a crop plant is not known. To address this knowledge gap, we generated single, double, and triple mutants (7 mutants with at least two lines of each) for the three rice Os SPX-MFS genes. All the mutants except osspx-mfs2 display lower vacuolar Pi concentrations and all Os SPX-MFSs overexpression plant lines display higher Pi accumulation, demonstrating that all three OsSPX-MFSs are vacuolar Pi influx transporters. OsSPX-MFS3 plays the dominant role based on the phenotypes of three single mutants in terms of growth, vacuolar and tissue Pi concentrations. OsSPX-MFS2 is the weakest and only functions as vacuole Pi sequestration under osspx-mfs1/3 background. The vacuolar Pi sequestration was severely impaired in osspx-mfs1/ 3 and osspx-mfs1/2/ 3, which led to Pi toxicity and subsequently increased Pi allocation to aerial organs. High Pi in the panicle result in necrotic symptoms on husks and impaired panicle and grain development in osspx-mfs1/ 3 and osspx-mfs1/2/ 3 mutant lines. The mutation in the weak vacuolar Pi transporter OsSPX-MFS2 resulted more stable yield compared to the wildtype under low P field conditions. The results suggest that alteration of vacuolar Pi sequestration may be a novel effective strategy to improve rice (crop) tolerance to low phosphorus field conditions and maintain yield.