CsREV-CsTCP4-CsVND7 module shapes xylem patterns differentially between stem and leaf to enhance tea plant tolerance to drought.

Cultivating drought-tolerant tea varieties enhances both yield and quality of tea plants in northern China. However, the mechanisms underlying their drought tolerance remain largely unknown. Here we identified a key regulator called CsREV, which differentially regulates xylem patterns between leaves and stems, thereby conferring drought tolerance in tea plants. When drought occurs, upregulation of CsREV activates the CsVND7a-dependent xylem vessel differentiation. However, when drought persists, the vessel differentiation is hindered as CsVND7a is downregulated by CsTCP4a. This, combined with the CsREV-promoted secondary-cell-wall thickness of xylem vessel, leads to the enhanced curling of leaves, a characteristic closely associated with plant drought tolerance. Notably, this inhibitory effect of CsTCP4a on CsVND7a expression is absent in stems, allowing stem xylem vessels to continuously differentiate. Overall, the CsREV-CsTCP4-CsVND7 module is differentially utilized to shape the xylem patterns in leaves and stems, potentially balancing water transportation and utilization to improve tea plant drought tolerance.

Chloride, glutathiones, and insect-derived elicitors introduced into the xylem trigger electrical signaling.

Ricca assays allow the direct introduction of compounds extracted from plants or the organisms that attack them into the leaf vasculature. Using chromatographic fractionation of Arabidopsis (Arabidopsis thaliana) leaf extracts, we found glutamate was the most active low mass elicitor of membrane depolarization. However, other known elicitors of membrane depolarization are generated in the wound response. These include unstable aglycones generated by glucosinolate (GSL) breakdown. None of the aglycone-derived GSL-breakdown products, including nitriles and isothiocyanates, that we tested using Ricca assays triggered electrical activity. Instead, we found that glutathione and the GSL-derived compound sulforaphane glutathione triggered membrane depolarizations. These findings identify a potential link between GSL breakdown and glutathione in the generation of membrane depolarizing signals. Noting that the chromatographic fractionation of plant extracts can dilute or exchange ions, we found that Cl- caused glutamate receptor-like3.3-dependent membrane depolarizations. In summary, we show that, in addition to glutamate, glutathione derivatives as well as chloride ions will need to be considered as potential elicitors of wound-response membrane potential change. Finally, by introducing aphid (Brevicoryne brassicae) extracts or the flagellin-derived peptide flg22 into the leaf vasculature we extend the use of Ricca assays for the exploration of insect/plant and bacteria/plant interactions.

A Pectate Lyase Gene Plays a Critical Role in Xylem Vascular Development in Arabidopsis.

As a major component of the plant primary cell wall, structure changes in pectin may affect the formation of the secondary cell wall and lead to serious consequences on plant growth and development. Pectin-modifying enzymes including pectate lyase-like proteins (PLLs) participate in the remodeling of pectin during organogenesis, especially during fruit ripening. In this study, we used Arabidopsis as a model system to identify critical PLL genes that are of particular importance for vascular development. Four PLL genes, named AtPLL15, AtPLL16, AtPLL19, and AtPLL26, were identified for xylem-specific expression. A knock-out T-DNA mutant of AtPLL16 displayed an increased amount of pectin, soluble sugar, and acid-soluble lignin (ASL). Interestingly, the atpll16 mutant exhibited an irregular xylem phenotype, accompanied by disordered xylem ray cells and an absence of interfascicular phloem fibers. The xylem fiber cell walls in the atpll16 mutant were thicker than those of the wild type. On the contrary, AtPLL16 overexpression resulted in expansion of the phloem and a dramatic change in the xylem-to-phloem ratios. Altogether, our data suggest that AtPLL16 as a pectate lyase plays an important role during vascular development in Arabidopsis.

[Anatomical structure and physiological characteristics of Robinia pseudoacacia of different stand ages]. / 不同林龄刺槐解剖结构及生理特性.

Drought intensity and frequency have been increased as a result of global warming. Exploring the drought resistance mechanism of Robinia pseudoacacia plantations of different stand ages on the Loess Plateau is crucial for understanding the stability of forest productivity in the region. We investigated anatomical traits, hydraulic function, and non-structural carbohydrate content of the xylem, as well as their association, in R. pseudoacacia plantations of different stand ages in a semi-arid region. The results showed that the vessel diameter, total pit membrane area, pit membrane area, vesture area, and vestured overlap of young and middle-aged stands were larger than those of mature stands, and the pit density was significantly lower in mature stands. Hydraulic conductivity was significantly related to vessel diameter, pit membrane area, and vesture area. Hydraulic conductivities of branches in young, middle-aged, and mature stands were 2.30, 2.12, and 0.76 kg·m-1·s-1·MPa-1, respectively, with embolism values of 54.5%, 53.8%, and 45.1%. Hydraulic conductivity was significantly related to soluble sugar and starch contents. The soluble sugar contents of branches in young, middle-aged and mature stands were 4.9%, 4.2%, and 3.8%, respectively. Xylem growth capacity of R. pseudoacacia in mature stand declined, resulting in the formation of small vessels with many small pits, which reduced hydraulic conductivity while maintaining hydraulic safety, resulting in a decrease of non-structural carbohydrates content. This study revealed the drought response mechanism of R. pseudoacacia plantations with different ages, providing a scientific foundation for the management and nurturing of R. pseudoacacia plantations on the Loess Plateau.

Structural variation and spatial polysaccharide profiling of intervessel pit membranes in grapevine.

BACKGROUND AND AIMS: Intervessel pit membranes (PMs) are important cell wall structures in the vessel system that may impact a plant's water transport and its susceptibility to vascular diseases. Functional roles of intervessel PMs largely depend on their structure and polysaccharide composition, which are the targets of this study. METHODS: With grapevine used as a model plant, this study applied an immunogold-scanning electron microscopy technique to simultaneously analyse at high resolution intervessel PM structures and major pectic and hemicellulosic polysaccharides that make up intervessel PMs. KEY RESULTS: Intervessel PMs in functional xylem showed significant structural variation, with about 90 % of them being structurally intact with smooth or relatively smooth surfaces and the remaining 10 % with progressively degraded structures. The results also elucidated details of the removal process of cell wall materials from the intervessel PM surface toward its depth during its natural degradation. Four groups of pectic and hemicellulosic polysaccharides were immunolocalized in intervessel PMs and differed in their spatial distribution and abundance. Weakly methyl-esterified homogalacturonans (WMe-HGs, detected by JIM5) were abundant in the surface layer, heavily methyl-esterified homogalacturonans (HMe-HGs, detected by JIM7) and xylans detected by CCRC-M140 were mostly found in deeper layers, and fucosylated xyloglucans (F-XyGs, detected by CCRC-M1) were more uniformly distributed at different depths of the intervessel PM. CONCLUSIONS: Intervessel PMs displayed diverse structural variations in grapevine. They contained certain major groups of pectic and hemicellulosic polysaccharides with different spatial distributions and abundance. This information is crucial to reveal the polysaccharide profiling of the primary cell wall and to understand the roles of intervessel PMs in the regulation of water transport as well as in a plant's susceptibility to vascular diseases.

Visualization of phosphorus re-translocation and phosphate transporter expression profiles in a shortened annual cycle system of poplar.

Phosphorus (P) is an essential macronutrient for plant growth. In deciduous trees, P is remobilized from senescing leaves and stored in perennial tissues during winter for further growth. Annual internal recycling and accumulation of P are considered an important strategy to support the vigorous growth of trees. However, the pathways of seasonal re-translocation of P and the molecular mechanisms of this transport have not been clarified. Here we show the seasonal P re-translocation route visualized using real-time radioisotope imaging and the macro- and micro-autoradiography. We analysed the seasonal re-translocation P in poplar (Populus alba. L) cultivated under 'a shortened annual cycle system', which mimicked seasonal phenology in a laboratory. From growing to senescing season, sink tissues of 32 P and/or 33 P shifted from young leaves and the apex to the lower stem and roots. The radioisotope P re-translocated from a leaf was stored in phloem and xylem parenchyma cells and redistributed to new shoots after dormancy. Seasonal expression profile of phosphate transporters (PHT1, PHT5 and PHO1 family) was obtained in the same system. Our results reveal the seasonal P re-translocation routes at the organ and tissue levels and provide a foothold for elucidating its molecular mechanisms.

Transfer of Metal(loid)s from Soil to Leaves and Trunk Xylem Sap of Medicinal Plants and Possible Health Risk Assessment.

The objective of the present study was to investigate metal(loid)s in soils, in the trunk xylem sap and in the leaves of the Dipteryx alata plant located near the highway with high vehicle traffic in agricultural regions and near landfills, and to assess the transfer of metal(loid)s from soil to plant and possible health risk assessment. Trunk xylem sap, leaves and soil samples were collected at three sites near the highway. The analysis of trace elements was carried out using inductively coupled plasma optical emission spectroscopy (ICP OES). In the three soil sampling sites far from the highway edge, 15 elements were quantified. The concentrations of elements in the soil presented in greater proportions in the distance of 5 m in relation to 20 and 35 m. The metal(loid)s content in the study soil was higher than in other countries. The concentrations of Al, Cu, Fe, Mg, Mn, P, Se and Zn in the xylem sap were much higher than the leaves. The values of transfer factor of P, Mg and Mn from soil to the xylem sap and transfer factor of P from soil to leaf were greater than 1, indicating that the specie have a significant phytoremediation and phytoextraction potential. This plant has a tendency to accumulate As, Cd and Cr in its leaf tissues. The chronic hazard index (HI) values recorded in this study were above 1 for adults and adolescents. It is concluded that the soil, the trunk xylem sap and leaves of this plant are contaminated by heavy metals. Ingestion of the trunk xylem sap of this plant can cause toxicity in humans if ingested in large quantities and in the long term; therefore, its consumption should be avoided.

Profiling of widely targeted metabolomics for the identification of chemical composition in epidermis, xylem and pith of Gleditsiae Spina.

Gleditsiae Spina, the thorn of Gleditsia sinensis Lam., has a long history of being used as a traditional medicine in East Asian countries. However, only a few biologically active substances have been identified from it. In this study, the epidermis, xylem and pith of Gleditsiae Spina, respectively Gs-E, Gs-X and Gs-P, were studied. We used a widely targeted metabolomics method to investigate the chemical composition of Gs-E, Gs-X and Gs-P. A total of 728 putative metabolites were identified from Gleditsiae Spina, including 211 primary metabolites and 517 secondary metabolites. These primary and secondary metabolites could be categorized into more than 10 different classes. Flavonoids, phenolic acids, lipids, amino acids and derivatives, and organic acids constituted the main metabolite groups. Multivariate statistical analysis showed that the Gs-E, Gs-X and Gs-P samples could be clearly separated. Differential accumulated metabolite (DAM) analysis revealed that more than half of the DAMs exhibited the highest relative concentrations in Gs-E, and most of the DAMs showed the lowest relative concentrations in Gs-X. Moreover, 11 common differential primary metabolites and 79 common differential secondary metabolites were detected in all comparison groups. These results further our understanding of chemical composition and metabolite accumulation of Gleditsiae Spina.

The plant axis as the command centre for (re)distribution of sucrose and amino acids.

Along with the increase in size required for optimal colonization of terrestrial niches, channels for bidirectional bulk transport of materials in land plants evolved during a period of about 100 million years. These transport systems are essentially still in operation - though perfected over the following 400 million years - and make use of hydrostatic differentials. Substances are accumulated or released at the loading and unloading ends, respectively, of the transport channels. The intermediate stretch between the channel termini is bifunctional and executes orchestrated release and retrieval of solutes. Analyses of anatomical and physiological data demonstrate that the release/retrieval zone extends deeper into sources and sinks than is commonly thought and covers usually much more than 99% of the translocation stretch. This review sketches the significance of events in the intermediate stretch for distribution of organic materials over the plant body. Net leakage from the channels does not only serve maintenance and growth of tissues along the pathway, but also diurnal, short-term or seasonal storage of reserve materials, and balanced distribution of organic C- and N-compounds over axial and terminal sinks. Release and retrieval are controlled by plasma-membrane transporters at the vessel/parenchyma interface in the contact pits along xylem vessels and by plasma-membrane transporters at the interface between companion cells and phloem parenchyma along sieve tubes. The xylem-to-phloem pathway vice versa is a bifacial, radially oriented system comprising a symplasmic pathway, of which entrance and exit are controlled at specific membrane checkpoints, and a parallel apoplasmic pathway. A broad range of specific sucrose and amino-acid transporters are deployed at the checkpoint plasma membranes. SUCs, SUTs, STPs, SWEETs, and AAPs, LTHs, CATs are localized to the plasma membranes in question, both in monocots and eudicots. Presence of Umamits in monocots is uncertain. There is some evidence for endo- and exocytosis at the vessel/parenchyma interface supplementary to the transporter-mediated uptake and release. Actions of transporters at the checkpoints are equally decisive for storage and distribution of amino acids and sucrose in monocots and eudicots, but storage and distribution patterns may differ between both taxa. While the majority of reserves is sequestered in vascular parenchyma cells in dicots, lack of space in monocot vasculature urges "outsourcing" of storage in ground parenchyma around the translocation path. In perennial dicots, specialized radial pathways (rays) include the sites for seasonal alternation of storage and mobilization. In dicots, apoplasmic phloem loading and a correlated low rate of release along the path would favour supply with photoassimilates of terminal sinks, while symplasmic phloem loading and a correlated higher rate of release along the path favours supply of axial sinks and transfer to the xylem. The balance between the resource acquisition by terminal and axial sinks is an important determinant of relative growth rate and, hence, for the fitness of plants in various habitats. Body enlargement as the evolutionary drive for emergence of vascular systems and mass transport propelled by hydrostatic differentials.

Xylem, phloem and transpiration flows in developing European plums.

Neck shrivel is a quality disorder of European plum (Prunus × domestica L.). It has been suggested that backflow in the xylem (from fruit to tree) could contribute to the incidence of neck shrivel in plum. The objective was to quantify rates of xylem, phloem and of transpiration flow in developing plum fruit. Using linear variable displacement transducers, changes in fruit volume were recorded 1) in un-treated control fruit, 2) in fruit that had their pedicels steam-girdled (phloem interrupted, xylem still functional) and 3) in detached fruit, left in the canopy (xylem and phloem interrupted). Xylem flow rates were occasionally negative in the early hours after sunrise, indicating xylem sap backflow from fruit to tree. Later in the day, xylem flows were positive and generally higher in daytime and lower at night. Significant phloem flow occurred in daytime, but ceased after sunset. During stage II (but not during stage III), the rates of xylem flow and transpiration were variable and closely related to atmospheric vapor pressure deficit. The relative contribution of xylem inflow to total sap inflow averaged 79% during stage II, decreasing to 25% during stage III. In contrast, phloem sap inflow averaged 21% of total sap inflow during stage II, increasing to 75% in stage III. Our results indicate that xylem backflow occurs early in the day. However, xylem backflow rates are considered too low to significantly contribute to the incidence of neck shrivel.

Frozen in the dark: interplay of night-time activity of xanthophyll cycle, xylem attributes, and desiccation tolerance in fern resistance to winter.

While most ferns avoid freezing as they have a tropical distribution or shed their fronds, wintergreen species in temperate and boreoalpine ecosystems have to deal with sub-zero temperatures. Increasing evidence has revealed overlapping mechanisms of desiccation and freezing tolerance in angiosperms, but the physiological mechanisms behind freezing tolerance in ferns are far from clear. We evaluated photochemical and hydraulic parameters in five wintergreen fern species differing in their ability to tolerate desiccation. We assessed frond freezing tolerance, ice nucleation temperature and propagation pattern, and xylem anatomical traits. Dynamics of photochemical performance and xanthophyll cycle were evaluated during freeze-thaw events under controlled conditions and, in selected species, in the field. Only desiccation-tolerant species, which possessed a greater fraction of narrow tracheids (<18 µm) than sensitive species, tolerated freezing. Frond freezing occurred in the field at -3.4 ± 0.9 °C (SD) irrespective of freezing tolerance, freezable water content, or tracheid properties. Even in complete darkness, maximal photochemical efficiency of photosystem II was down-regulated concomitantly with zeaxanthin accumulation in response to freezing. This was reversible upon re-warming only in tolerant species. Our results suggest that adaptation for freezing tolerance is associated with desiccation tolerance through complementary xylem properties (which may prevent risk of irreversible cavitation) and effective photoprotection mechanisms. The latter includes de-epoxidation of xanthophylls in darkness, a process evidenced for the first time directly in the field.

Wood properties and transcriptional responses of poplar hybrids in mixed cropping with the nitrogen-fixing species Robinia pseudoacacia.

Cultivation of fast-growing tree species is often confined to marginal land. Mixed cropping with Robinia pseudoacacia, a legume tree species that forms a symbiosis with N2-fixing bacteria, has been proposed to be a measure to improve soil fertility and to achieve beneficial effects on the cocultivated tree species. The goal of our study was to examine the influence of a Robinia mixture on wood chemistry, anatomy and gene expression in poplar. We hypothesized that annual wood growth is stimulated in species mixtures due to the positive effects of Robinia on nitrogen availability and complementary resource use. Alternatively, we hypothesized that competition, especially for water, has negative effects on the wood growth of poplar. We used two commercial biomass clones, Hybride 275 (H275, Populus trichocarpa × Populus maximowiczii) and Max1 (Populus nigra × P. maximowiczii), which were planted at two locations with contrasting soil fertility in monoculture or mixed plots with Robinia to investigate the annual wood increment, wood nitrogen and δ13C, wood anatomy (length, cell wall thickness, lumina and frequencies of fibers and vessels) and transcriptional profiles in the developing xylem of 4-year-old stems. In a mixture with Robinia, the annual stem increment was reduced, nitrogen in wood was enhanced, δ13C in wood was decreased, vessel and fiber frequencies were increased and fiber lengths and fiber lumina were decreased. Transcriptional profiles showed stronger differences between the genotypes and sites than between mono and mixed cultivation. The transcriptional abundances of only one gene (the putative nitrate transporter, NRT1.2) and one gene ontology term ('immune system process') were significantly enriched in wood-forming tissues in response to the mixture, irrespective of the poplar genotype and growth location. Weighted gene coexpression network analyses extracted gene modules that linked wood nitrogen mainly to vessel traits and wood δ13C with fiber traits. Collectively, molecular and anatomical changes in poplar wood suggest beneficial effects on the water and N supply in response to the mixture with Robinia. These alterations may render poplars less drought-susceptible. However, these benefits are accompanied by a reduced wood increment, emphasizing that other critical factors, presumably light competition or allelopathic effects, overrule a potential growth stimulation.

Effects of shading on lignin biosynthesis in the leaf of tea plant (Camellia sinensis (L.) O. Kuntze).

Shading can effectively reduce photoinhibition and improve the quality of tea. Lignin is one of the most important secondary metabolites that play vital functions in plant growth and development. However, little is known about the relationship between shading and xylogenesis in tea plant. To investigate the effects of shading on lignin accumulation in tea plants, 'Longjing 43' was treated with no shading (S0), 40% (S1) and 80% (S2) shading treatments, respectively. The leaf area and lignin content of tea plant leaves decreased under shading treatments (especially S2). The anatomical characteristics showed that lignin is mainly distributed in the xylem of tea leaves. Promoter analysis indicated that the genes involved in lignin pathway contain several light recognition elements. The transcript abundances of 12 lignin-associated genes were altered under shading treatments. Correlation analysis indicated that most genes showed strong positive correlation with lignin content, and CsPAL, Cs4CL, CsF5H, and CsLAC exhibited significant positively correlation under 40% and 80% shading treatments. The results showed that shading may have an important effect on lignin accumulation in tea leaves. This work will potentially helpful to understand the regulation mechanism of lignin pathway under shading treatment, and provide reference for reducing lignin content and improving tea quality through shading treatment in field operation.

Transcription-mediated tissue-specific lignification of vascular bundle causes trade-offs between growth and defence capacity during invasion of Solidago canadensis.

Allocation of more resources to growth but less to defense causing growth vigor of invasive alien plant populations contributes to successful invasion. However, few studies has addressed to relationship between vascular development variation and this mechanism. In this study, a common garden experimentwas established to compare the growth and vascular bundle development between native and introduced populations of Solidago canadensis, which is a wide-distributed invasive species in China. Our results suggested that the rapid growth of introduced populations could be explained by the well-developed and highly lignified xylem; while native populations present more developed and highly lignified phloem, which contributed more resistance to the infection of Sclerotiun rofsii compared with introduced populations. This difference was resulted from tissue-specific tradeoff distribution of lignification related gene expression between xylem and phloem, which is regulated by upstream MYB transcription factors. Our study gives a novel insight of mechanism that explain invasion success: lignin-related gene transcription-mediated tissue-specific lignification of vascular bundle contributes tradeoffs in resource allocation between growth and defence capacity during successful invasion of S. canadensis.

Characterization of a new natural cellulosic fiber extracted from Derris scandens stem.

The present study aims to identify a potential substitute for the harmful synthetic fibers in the field of polymer composites. With this objective, a comprehensive characterization of Derris scandens stem fibers (DSSFs) was carried out. The presence of high strength gelatinous fibers with a traditional hierarchical cell structure was found in the anatomical study. The chemical compositional analysis estimated the cellulose, hemicellulose, and lignin contents of 63.3 wt%, 11.6 wt%, and 15.3 wt%, respectively. Further analysis with XRD confirmed the presence of crystalline cellulose having a size of 11.92 nm with a crystallinity index of 58.15%. SEM and AFM studies show that these fibers are porous, and the average roughness is 105.95 nm. Single fiber tensile tests revealed that the DSSFs exhibited the mean Young's modulus and tensile strength of 13.54 GPa and 633.87 MPa respectively. Furthermore, the extracted fibers were found to be thermally stable up to 230 °C, as confirmed by thermogravimetric analysis. The fibers extracted from the stem of medicinal plant Derris scandens have the properties comparable to that of existing natural fibers, thus, suggesting it to use as a highly promising reinforcing agent alternative to synthetic fibers in polymer matrix composites.

Comparative effectiveness of Se translocation between low-Se and high-Se rice cultivars under Se fertilization.

The production of natural selenium (Se)-rich food by using a high-Se crop cultivar is beneficial to human health and environmental safety; however, the underlying mechanism of different Se-accumulation ability between high- and low-Se rice cultivars remains unclear. A low-grain-Se cultivar and high-grain-Se cultivar of rice were used as test materials, and two levels of Se (0 and 0.5 mg kg-1) were arranged in a randomized design containing twelve replicates. The dynamic changes of shoot Se concentration and accumulation, xylem sap Se concentration, shoot and grain Se distribution, Se transporters genes (OsPT2, Sultr1;2, NRT1.1B) expression of the high- and low-Se rice cultivars were determined. The shoot Se concentration and accumulation of the high-Se rice showed a greater degree of reduction than those of the low-Se rice during grain filling stage, indicating that leaves of high-Se rice served as a Se source and supplied more Se for the growth centre grain. The expression levels of OsPT2, NRT1.1B and Sultr1;2 in the high-Se rice cultivar were significantly higher than those in the low-Se rice cultivar, which indicated that the high-Se rice cultivar possessed better transport carriers. The distribution of Se in grain of the high-Se rice cultivar was more uniform, whereas the low-Se cultivar tended to accumulate Se in embryo end. The stronger reutilization of Se from shoots to grains promoted by increased transporters genes expression and optimized grain storage space may explain how the high-Se rice cultivar is able to accumulate more Se in grain.

Phosphorus deficiency induces root proliferation and Cd absorption but inhibits Cd tolerance and Cd translocation in roots of Populus × euramericana.

To disclose how phosphorus deficiency influence phytoremediation of Cd contamination using poplars, root architecture, Cd absorption, Cd translocation and antioxidant defense in poplar roots were investigated using a clone of Populus × euramericana. Root growth was unaltered by Cd exposure regardless of P conditions, while the degree of root proliferation upon P deficiency was changed by high level of Cd exposure. The concentration and content of Cd accumulation in roots were increased by P deficiency. This can be partially explained by the increased expression of genes encoding PM H + -ATPase under the combined conditions of P deficiency and high Cd exposure, which enhanced Cd2+-H+ exchanges and led to an increment of Cd uptake under P deficiency. Despite of the increasing Cd accumulation in roots, the translocation of Cd from roots to aerial tissues sharply decreased upon P deficiency. The relative expression of genes responsible for Cd translocation (HMA4) decreased upon P deficiency and thus inhibited Cd translocation via xylem. GR activity was decreased by P deficiency, which can inhibit the form of GSH and GSH-Cd complexes and decrease Cd translocation via GSH-Cd complexes. The transportation of PC-Cd complexes into vacuole decreased under P deficiency as a result of the low expression of PCS and ABCC1, and thus suppressed Cd tolerance and Cd detoxification in roots. Moreover, P deficiency decreased the levels of antioxidase (GR and CAT) and phytohormones including JA, ABA and GA3, which synchronously reduced antioxidant capacity in roots.

Xylem sap phosphorus sampling using microdialysis-a non-destructive high sampling frequency method tested under laboratory and field conditions.

For a better understanding of plant nutrition processes, it is important to study the flux of nutrients within plants. However, existing xylem sap sampling methods are typically destructive and do not allow for repeated, highly frequent measurements of nutrient concentration. In this paper, we present a novel use of microdialysis (MD) for characterizing xylem sap phosphate (PO43-) concentration as a possible alternative to destructive sampling. First, MD probes were tested under laboratory conditions in vitro, in a stirred solution test, and in vivo, using beech tree stem segments. Exponential decline in the relative recovery (RR) with an increasing MD pumping rate allows for determining an optimal sampling interval (i.e., the maximum amount of sample volume with the minimum required concentration). The RR changed only minimally, with a change in the simulated sap flow velocity during the in vivo stem segment test. This suggests that MD can be applied over a range of naturally occurring sap flow velocities. Differences in the ionic strength between the xylem sap and the perfusate pumped through the MD did not influence the RR. Then, MD was successfully applied in a 24 h field campaign in two beech trees of different ages and allowed for in situ assessments of the diurnal variation of PO43- concentration and (together with xylem flow measurements) flux variability in living trees. Both beech trees exhibited the same diurnal pattern in PO43- concentrations with higher concentrations in the younger tree. The xylem PO43- concentration measured with MD was in the same order of magnitude as that received through destructive sampling in the younger tree. The MD probes did not show a decline in RR after the field application. We showed that MD can be applied to capture the PO43- concentration dynamics in the xylem sap with bihourly resolution under field conditions.

MYB43 in Oilseed Rape (Brassica napus) Positively Regulates Vascular Lignification, Plant Morphology and Yield Potential but Negatively Affects Resistance to Sclerotinia sclerotiorum.

Arabidopsis thaliana MYB43 (AtMYB43) is suggested to be involved in cell wall lignification. PtrMYB152, the Populus orthologue of AtMYB43, is a transcriptional activator of lignin biosynthesis and vessel wall deposition. In this research, MYB43 genes from Brassica napus (rapeseed) and its parental species B. rapa and B. oleracea were molecularly characterized, which were dominantly expressed in stem and other vascular organs and showed responsiveness to Sclerotinia sclerotiorum infection. The BnMYB43 family was silenced by RNAi, and the transgenic rapeseed lines showed retardation in growth and development with smaller organs, reduced lodging resistance, fewer silique number and lower yield potential. The thickness of the xylem layer decreased by 28%; the numbers of sclerenchymatous cells, vessels, interfascicular fibers, sieve tubes and pith cells in the whole cross section of the stem decreased by 28%, 59%, 48%, 34% and 21% in these lines, respectively. The contents of cellulose and lignin decreased by 17.49% and 16.21% respectively, while the pectin content increased by 71.92% in stems of RNAi lines. When inoculated with S. sclerotiorum, the lesion length was drastically decreased by 52.10% in the stems of transgenic plants compared with WT, implying great increase in disease resistance. Correspondingly, changes in the gene expression patterns of lignin biosynthesis, cellulose biosynthesis, pectin biosynthesis, cell cycle, SA- and JA-signals, and defensive pathways were in accordance with above phenotypic modifications. These results show that BnMYB43, being a growth-defense trade-off participant, positively regulates vascular lignification, plant morphology and yield potential, but negatively affects resistance to S. sclerotiorum. Moreover, this lignification activator influences cell biogenesis of both lignified and non-lignified tissues of the whole vascular organ.

LaALMT1 mediates malate release from phosphorus-deficient white lupin root tips and metal root to shoot translocation.

Under phosphorus (P) deficiency, Lupinus albus (white lupin) releases large amounts of organic acid anions from specialized root structures, so-called cluster or proteoid roots, to mobilize and acquire sparingly soluble phosphates from a restricted soil volume. The molecular mechanisms underlying this release and its regulation are, however, poorly understood. Here, we identified a gene belonging to the aluminium (Al)-activated malate transporter (ALMT) family that specifically contributes to malate, but not citrate release. This gene, LaALMT1, was most prominently expressed in the root apices under P deficiency, including those of cluster roots and was also detected in the root stele. Contrary to several ALMT homologs in other species, the expression was not stimulated, but moderately repressed by Al. Aluminium-independent malate currents were recorded from the plasma membrane localized LaALMT1 expressed in Xenopus oocytes. In composite lupins with transgenic roots, LaALMT1 was efficiently mutated by CRISPR-Cas9, leading to diminished malate efflux and lower xylem sap malate concentrations. When grown in an alkaline P-deficient soil, mutant shoot phosphate concentrations were similar, but iron and potassium concentrations were diminished in old leaves, suggesting a role for ALMT1 in metal root to shoot translocation, a function that was also supported by growth in hydroponics.