Guttation Fluid Research Articles

Arabidopsis hydathodes are sites of auxin accumulation and nutrient scavenging.

Hydathodes are small organs found on the leaf margins of vascular plants which release excess xylem sap through a process called guttation. While previous studies have hinted at additional functions of hydathode in metabolite transport or auxin metabolism, experimental support is limited. We conducted comprehensive transcriptomic, metabolomic and physiological analyses of mature Arabidopsis hydathodes. This study identified 1460 genes differentially expressed in hydathodes compared to leaf blades, indicating higher expression of most genes associated with auxin metabolism, metabolite transport, stress response, DNA, RNA or microRNA processes, plant cell wall dynamics and wax metabolism. Notably, we observed differential expression of genes encoding auxin-related transcriptional regulators, biosynthetic processes, transport and vacuolar storage supported by the measured accumulation of free and conjugated auxin in hydathodes. We also showed that 78% of the total content of 52 xylem metabolites was removed from guttation fluid at hydathodes. We demonstrate that NRT2.1 and PHT1;4 transporters capture nitrate and inorganic phosphate in guttation fluid, respectively, thus limiting the loss of nutrients during this process. Our transcriptomic and metabolomic analyses unveil an organ with its specific physiological and biological identity.

A wearable electrochemical sensor for the monitoring of neonicotinoid insecticides, salicylic acid and the pH in plant guttation

Wearable plant sensors can continuously monitor the material absorption and health status of a plant, thereby providing data that can be used to provide precise crop management. Herein, we describe a noninvasive wearable electrochemical sensor designed for monitoring plant guttation that is capable of detecting trace levels of neonicotinoid insecticides, salicylic acid, and pH. The sensor electrodes are prepared using an improved laser-induced graphene (LIG) printing method, with which a single set (six sensors) can be fabricated in only 15.6 s. Leveraging the high surface area and conductivity of LIG, trace-level electrochemical testing for neonicotinoid insecticides, salicylic acid, and pH can be achieved without the need for electrode surface modification. When the sensors are combined with a guttation collection module, the repeated collection of the guttation fluid becomes possible. The sensor weighs only 0.1 g and can be connected to a portable electrochemical workstation and smartphone for real-time on-site data collection. The practical value of the sensor was validated by monitoring the guttation fluid produced by rice, placed under stress through the application of neonicotinoid insecticide, and real-time pH calibration. This noninvasive wearable sensor for monitoring plant guttation enables the real-time detection of target substances, avoids plant stress caused by sensor intrusion, and provides a new direction for the future development of wearable plant sensors.

Imidacloprid residues in cotton guttation fluid, pollen and soil when applied as seed dressings

Guttation fluid and pollen are possible pathways where pollinators may be exposed to systemic insecticides. During the investigation, Gossypium hirsutum v. H 1098i seeds were coated with Gaucho (Imidacloprid 600 FS at 2.4 g a.i. kg-1seeds) and planted in the field. Guttation fluid, pollen, and soil samples were collected during the season and the samples were analysed by HPLC (High-Performance Liquid Chromatography). The guttation fluid and pollen were collected at three times after 50 per cent flowering. Soil samples were collected before sowing and at harvest. Method validation was achieved by performing a recovery experiment at two fortification levels of 0.05 and 0.10 mg kg-1. The average recoveries obtained from guttation fluid, pollen and soil samples were above 85 per cent. The residues of imidacloprid in guttation fluid, pollen and soil in treated and untreated seed were below detectable levels.

Impact of guttation fluid from perennial ryegrass infected with different strains of Epichloe festucae var. lolii endophyte on Microctonus aethiopoides adult longevity

Perennial ryegrass (Lolium perenne L.) grows in association with a fungal endophyte Epichloe festucae var. lolii (Latch, Christensen & Samuels) Bacon & Schardl, which produces alkaloids that protect the grass against grazing by mammals and insects. These alkaloids are found in guttation fluid (xylem sap exuded from leaves through special structures known as hydathodes) and have the potential to impact on beneficial invertebrates in pastoral ecosystems. Newly emerged adults of the parasitoid Microctonus aethiopoides Loan (Hymenoptera: Braconidae) were supplied with guttation fluid from pot-grown ryegrasses infected with three different strains of endophyte (standard, AR37, AR1) or no endophyte collected at different times of the year, or water, sucrose solution or no liquid. Longevity was compared when individuals were held in separate vials in controlled environment room at 20oC with 16:8 h light:dark photoperiod. An enzymatic method was used to measure sugars in guttation fluid samples collected on three dates. Guttation fluid from endophyte-infected grasses was found to have no detrimental effect on M. aethiopoides longevity and to contain glucose and fructose. Guttation fluid from AR37-infected ryegrass collected in autumn increased insect longevity compared to water and fluid from standard-type infected ryegrass by 26% and 24% respectively. The lack of available food sources in New Zealand ryegrass-dominant pastures means that guttation fluid from AR37-infected ryegrass in autumn may contribute to M. aethiopoides efficacy as a biocontrol agent through enhanced longevity.

Hydathodes in ferns: their phylogenetic distribution, structure and function.

Ferns are the second largest group of vascular plants and are distributed nearly worldwide. Although ferns have been integrated into some comparative ecological studies focusing on hydathodes, there is a considerable gap in our understanding of the functional anatomy of these secretory tissues that are found on the vein endings of many fern leaves. In this study, we aimed to investigate the phylogenetic distribution, structure and function of fern hydathodes. We performed a global review on fern hydathodes and their phylogenetic distribution, carried out an ancestral character state reconstruction, and studied the structure, guttation and elemental composition of salt residues of eight species, and the diurnal patterns of xylem pressure of two species. Hydathodes are known from 1189 fern species, 92 genera and 19 families of 2 orders, Equisetales and Polypodiales. Stochastic character mapping indicated multiple gains and losses of hydathodes at the genus level, occurring especially during the last 50 million years of fern evolution. Hydathodes were located on the adaxial leaf surface and characterized by a cytoplasm-rich, pore-free epidermis, and became functional for several weeks after nearly complete leaf expansion. In two species, positive xylem pressure built up at night, potentially facilitating guttation. Guttation fluid was rich in Ca and often Si, but also contained P, Mg, Na and Al. Stochastic character mapping and the structural and functional diversity of hydathodes indicate multiple origins, and their presence/absence in closely related taxa implies secondary losses during fern evolution. Positive xylem pressure and high air humidity play an important role as drivers of guttation. Hydathodes may contribute to the regulation of leaf nutrient stoichiometry by the release of excessive compounds and minerals other than waste products, but the presence of essential chemical elements in salt residues also indicates possible leakage.

GC - MS analysis of guttation fluids from selected crop plants

ABSTRACT Guttation is the mechanism by which liquid exudes from hydathodes located on the tip, along the margins, and on the adaxial and abaxial surfaces of leaves. In contrast to stomata, hydathodes, also known as water stomata or water pores, are often open, representing the path of least resistance to liquid outflow from them. Guttation fluids are made up of several organic compounds. This paper focuses on the defensive properties of the chemical compositions of the guttation extracts of Oryza sativa, Momordica charantia, Luffa acutnugula, and Ricinus communis extracted using five different solvents, which were analyzed using Gas Chromatography–Mass Spectrometry (GC-MS). The mass spectra of the compounds present in the guttation fluids were matched by the National Institute of Standards and Technology (NIST) library. GC-MS analysis of guttation fluid extracts of crop plants revealed the existence of compounds with antifungal and antimicrobial properties which may act as barriers to pathogens. The numerous compounds found in plant extracts, such as fatty acids, organic acids, and terpenoids, have a wide range of protective activities and mechanisms that can serve as the first line of defense against pests and diseases.

Translocation of clothianidin to guttation fluid and its potential impact on honey bee, Apis mellifera anatoliaca Maa, 1953 (Hymenoptera: Apidae)

Honey bees, Apis mellifera anatoliaca Maa, 1953 (Hymenoptera: Apidae) forage water from guttation fluid so transported neonicotinoid insecticides in guttation fluid poses a risk to the bees. The first aim of this study was to determine the toxicity and risk of clothianidin to honey bees. In addition, the changes of clothianidin residue in the guttation fluid of maize plants in Turkey were determined in 2018 and 2019. Also, the toxicity of guttation fluid collected from the maize plants to bees was determined in ecotoxicological tests. The acute oral LD50 of clothianidin to honey bees in the first 24 h was 1.80 ng bee-1 and residue analysis demonstrated that honey bees were exposed to clothianidin concentration in guttation fluid ranging from 0.02 to 6.0 mg L-1 with mortality ranging between 80 and 100%. As the measured concentration of clothianidin in guttation fluid can lead to the mortality of honey bees, present study indicates that clothianidin, and possibly related pesticides in treated maize seed poses a risk to honey bees. Future studies are needed to determine the scale and distribution of this risk in Turkey.

Is there a risk to honeybees from use of thiamethoxam as a sugar beet seed treatment?

The ban imposed by the European Union on the use of neonicotinoids as sugar beet seed treatments was based on the exposure of bees to residues of neonicotinoids in pollen and nectar of succeeding crops. To address this concern, residues of thiamethoxam (TMX) and clothianidin (CTD) were analyzed in soil collected from fields planted in at least the previous year with thiamethoxam‐treated sugar beet seed. This soil monitoring program was conducted at 94 sites across Germany in two separate years. In addition, a succeeding crop study assessed residues in soil, guttation fluid, pollen, and nectar sampled from untreated succeeding crops planted in the season after thiamethoxam seed‐treated sugar beet at eight field sites across five countries. The overall mean residues observed in soil monitoring were 8.0 ± 0.5 µg TMX + CTD/kg in the season after the use of treated sugar beet seed. Residue values decreased with increasing time interval between the latest thiamethoxam or clothianidin application before sugar beet drilling and with lower application frequency. Residues were detected in guttation fluid (2.0–37.7 µg TMX/L); however, the risk to pollinators from this route of exposure is likely to be low, based on the reported levels of consumption. Residues of thiamethoxam and clothianidin in pollen and nectar sampled from the succeeding crops were detected at or below the limit of quantification (0.5–1 µg a.i./kg) in 86.7% of pollen and 98.6% of nectar samples and, unlike guttation fluid residues, were not correlated with measured soil residues. Residues in pollen and nectar are lower than reported sublethal adverse effect concentrations in studies with honeybee and bumble bee individuals and colonies fed only thiamethoxam‐treated sucrose, and are lower than those reported to result in no effects in honeybees, bumble bees, and solitary bees foraging on seed‐treated crops. Integr Environ Assess Manag 2022;18:709–721. © 2021 SYNGENTA. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Guttation droplets of sugarcane red rot pathogen Colletotrichum falcatum: Formation, toxigenic properties, and composition

ABSTRACT Production of guttation droplets in the cultures of Colletotrichum falcatum was often noticed. Hence, formation of guttation droplets, exudation of toxin in guttation, and guttation droplet chemical composition were assessed to find the ecological importance of guttation. Among the tested culture media, more guttation was noticed in oat meal agar medium and host extracts broth medium. Assessing the effect of five different carbon sources on guttation of C. falcatum showed that among solid media, sparse guttation droplets were noticed in glucose-, fructose-, and starch-amended media, whereas in broth cultures except fructose-amended media no other carbon sources induced guttation in mycelium. The guttation phenomenon was noticed only in sporulating mycelia, and it also followed a specific pattern in connection with sporulation. Bioassay of guttation exudates on sugarcane leaves produced pronounced necrotic lesions with large, yellow halo similar to positive control, thus confirming the presence of toxin. The guttation fluid initiated browning symptom on sugarcane leaves at a concentration of 1000 ppm and produced pronounced necrotic lesions of 3.7 cm at 10 000 ppm. The toxicity of crude fraction was thermostable up to 60 C. The gas chromatography–mass spectrometry (GC-MS) analysis of crude guttation droplets identified the presence of 24 compounds belonging to fatty acids, derivatives of fatty acids, flavonoids, flavonoid glycosides, sterols, quinone derivatives, amides, and glycol ethers, and among them fatty acids were dominant. The two compounds, viz., hexadecanoic acid methyl ester and 9-octadecenoic acid (Z) methyl ester, were abundant (18.14% and 17.98%, respectively) and identified as probable toxic compounds.

Development of precise micro analytical tool to identify potential insecticide hazards to bees in guttation fluid using LC–ESI–MS/MS

This paper illustrates the development of a miniaturized and precise analytical tool for biomonitoring of honey bee exposure to insecticides. This is the first work describing an analytical method for determination of very low concentrations of a wide range of insecticides in maize guttation fluid. Seed treatment with systemic insecticides or their foliar application causes the accumulation of compounds in the guttation liquid, which consists of excess water and compounds removed by plants and is a source of water for bees. A micro-QuEChERS protocol using 1 g of sample was used for analysis of over 140 insecticides belonging to 30 different chemical classes by LC–ESI–MS/MS. The determination of insecticides in guttation fluid is a difficult analytical task due to 1) the complexity of the sample matrix, 2) small amounts of test samples and 3) trace levels of analytes (often equal sublethal dose of insecticide for bees). An efficient sample treatment is proposed, involving 1 g of sample, extraction with 1% formic acid in acetonitrile, frozen, ultrasound-assisted, centrifugation and dispersive solid phase extraction with nano graphene oxide. Other tested sorbents: Fe3O4MNPs and two mixtures PSA/C18/GCB and Z-Sep did not give satisfactory parameters during sample purification. The graphene oxide proved to be the best, ensuring negligible matrix effects and analyte recoveries between 70% and 120% with relative standard deviations <20% for most of the compounds studied. The proposed method enables assessment of risk to honey bees resulting from exposure to guttation fluids containing toxic insecticides at very low concentrations.

Investigations on neonicotinoids in guttation fluid of seed treated sugar beet: Frequency, residue levels and discussion of the potential risk to honey bees

Little is known about the likelihood of occurrence of guttation fluids in sugar beet, and the extent to which its occurrence is related to weather conditions. There is also uncertainty regarding the extent to which the concentration of neonicotinoid residues in guttation fluid of seed treated sugar beet represents an environmentally relevant route of exposure for honey bees. In our study in 2009 and 2010, guttation monitoring, sampling and analysis of neonicotinoid residues in guttation fluids were conducted on 31 field sites consisting of differing landscapes with frequent cultivation of sugar beet. High concentrations of neonicotinoids in the guttation fluid up to 9 mg clothianidin L−1 were recorded, levels that would result in lethal effects to honey bees consuming such droplets. However, we demonstrated that the occurrence of guttation in sugar beet was very rare especially compared to the occurrence of guttation in the vegetation adjacent to sugar beet fields or the occurrence of dew. Therefore, we concluded that guttation fluids from seed treated sugar beet might not be a preferred water source for water foraging bees. Thus, an exposure of honey bee colonies to neonicotinoids dissolved in guttation fluids of seed treated sugar beet is very unlikely.

Quantitative weight of evidence assessment of higher tier studies on the toxicity and risks of neonicotinoids in honeybees. 4. Thiamethoxam

ABSTRACTA quantitative weight of evidence (QWoE) methodology was used to assess several higher-tier studies on the effects of thiamethoxam (TMX) on honeybees. Assessment endpoints were population size and viability of commercially managed honeybee colonies and quantity of hive products. A higher-tier field toxicology study indicated a no-observed-adverse effect concentration (NOAEC) of 29.5 µg TMX/kg syrup, equivalent to an oral no-observed-adverse-effect-dose (NOAED) of 8.6 ng/bee/day for all responses measured. For exposures via deposition of dust, a conservative no-observed-adverse-effect-rate at the level of the colony was 0.1 g TMX/ha. There was minimal risk to honeybees from exposure to TMX via nectar and pollen from its use as a seed-treatment. For exposures via dust and dust/seed applications, there were no concentrations above the risk values for TMX in nectar and pollen. Although some risks were identified for potential exposures via guttation fluid, this route of exposure is incomplete; no apparent adverse effects were observed in field studies. For exposures via dust/seed and dust/foliar applications, few adverse effects were observed. Considering all lines of evidence, the quality of the studies included in this analysis was variable. However, the results of the studies were consistent and point to the same conclusion. The overall weight of evidence based on many studies indicates that TMX has no adverse effects on viability or survival of the colony. Thus, the overall conclusion is that the treatment of seeds with thiamethoxam, as currently used in good agricultural practices, does not present a significant risk to honeybees at the level of the colony.

Hydathode function and changes in contents of elements in eddo exposed to zinc in hydroponic solution

To explore the zinc stress response in eddo, plants were grown for 15 d in hydroponic solutions containing 1 (control), 200, and 1000 μM zinc, and the hydathode function and changes in the contents of various elements in these plants were investigated. Under 1000 μM zinc, the dry weights of leaf blades and roots are decreased by 17 and 42%, respectively. The zinc contents in leaf blades, petioles, corms, and roots increased with increasing zinc levels in the solution. The zinc content in roots was 6.57 mg g−1 dry weight, which was 2.8–4.3 times higher than in other plant parts under 1000 μM zinc. These results demonstrate that the severe root damage occurring under 1000 μM zinc is due to higher zinc content in the roots. Under zinc stress, the contents of iron and copper in roots increased, but the contents of magnesium and calcium in petioles, corms, and roots, iron in leaf blades and corms, and manganese in petioles and corms decreased. In the guttation fluid, the concentrations of zinc, magnesium, and potassium increased, while the iron concentration decreased under 1000 μM zinc. Thus, elemental changes occurred in the guttation fluid as well as in different plant parts in eddo. In the 200 and 1000 μM zinc treatments, the amount of zinc eliminated via guttation was 2.8 and 8.5 times higher, respectively, than in the control. The results indicate that guttation partly contributes to the excretion of excess zinc under zinc stress conditions.

Dew from Warm‐Season Turfgrasses as a Possible Route for Pollinator Exposure to Lawn‐Applied Imidacloprid

Core Ideas This is the first study to report warm‐season turfgrass dew as a potential source for pollinator contact with imidacloprid. Observed imidacloprid concentrations were similar to those reported in creeping bentgrass guttation droplets but less than those typically found in agronomic crops grown from treated seed. Foliar‐treated bermudagrass contained more than 10 times the imidacloprid residue of the isolated soil‐only treatment. Imidacloprid is a neonicotinoid insecticide used for the control of turfgrass insect pests. It can be translocated into guttation fluid, thus potentially creating an exposure avenue for beneficial insects. Our research objectives were to investigate the fate of soil‐ and foliar‐applied imidacloprid in dew forming on bermudagrass (Cynodon spp.) and St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze] turf. Imidacloprid was applied at standard use rates (443 g a.i. ha−1; 6.32 oz a.i. acre−1) to soil only via sub‐irrigation (Years 1 and 2) or by foliar treatment (Year 2), which is representative of standard home lawn application. Dew fluid, which includes guttation, was collected 48 h after treatment and was analyzed for imidacloprid. During Year 1, dew collected from the soil‐only treatment of bermudagrass and St. Augustinegrass contained 15.8 and 9.2 ng imidacloprid mL−1, respectively. During Year 2, foliar treated bermudagrass contained more than 10 times the amount of imidacloprid as found in the soil‐only treatment (59.8 versus 5.2 ng mL−1, respectively). Observed imidacloprid concentrations were similar to those reported in creeping bentgrass guttation droplets but were less than those typically found in agronomic crops grown from treated seed. Levels were less than those reported to be acutely lethal to the European honeybee. However, depending on the amount of contaminated dew or guttation transported into hives, similarly low concentrations could be associated with sublethal effects (reportedly &gt;10 ng mL−1). This is the first study to report warm‐season turfgrass dew as a potential source for pollinator contact with imidacloprid and suggests that post‐application irrigation is perhaps the best way to avoid pollinator exposure.

Influence of nitrogen on guttation fluid and development of bacterial blight of rice

Bacterial blight disease of rice is major constraint in rice cultivation. This disease is influenced by prevailing weather conditions, rice physiology and nutrition. The experiment was carried out to assess the role of nitrogenous fertilizer on development of bacterial blight disease of rice and Xanthomonas oryzae pv. oryzae density in guttation fluid. Disease development increased with increase in nitrogen fertilizer, among four doses of nitrogen tested (control, 36, 54,72 kg urea/acre), disease severity was maximum in the plot supplied with highest dose of nitrogen i.e. 72 kg urea/acre at both seedling (19.3%) and tillering stage (32.4%) at 30 days after inoculation. The highest population density of X. oryzae pv. oryzae (6.02 log cfu/ml) was also recovered in guttation fluid collected from X.oryzaepv. oryzae inoculated plants at tillering stage, from the plots supplied with highest dose (72 kg urea/acre) of nitrogen.Scanning electron microscopic studies also revealed intense colonization by X. oryzae pv. oryzae in rice leaves supplied with high nitrogen dose.

Hydathode morphology and role of guttation in excreting sodium at different concentrations of sodium chloride in eddo

Mature leaves of field-grown eddo plants were used for observing hydathode morphology by light and scanning electron microscopies. There were approximately five hydathode pores on the adaxial surface of each leaf tip. A ring structure with two borders around the pore was detected in this study. Further observations revealed a large cavity underneath the pores. The cavity was directly connected to vascular bundles that lacked a bundle sheath, via intercellular spaces among loosely organized parenchyma cells. Many crystal cells were present around the cavity and vascular bundles. To evaluate the role of guttation in sodium excretion under salinity stress, eddo plants were grown in hydroponic solutions containing 0, 1, 4, 8, and 12 mM sodium chloride (NaCl) for 7 d. As the NaCl concentration in the hydroponic solution increased, the sodium contents increased in leaf blades, petioles, and roots but remained unchanged in corms. The sodium concentration in the guttation fluid increased; however, the volume of guttation fluid decreased with increasing NaCl concentrations. Therefore, sodium elimination via guttation decreased with increasing NaCl concentrations. The ratios of the sodium content in guttation fluid to that of leaf blades, leaves, and whole plants decreased with increasing NaCl concentrations. The ratios of potassium to sodium contents in leaves, roots, and guttation fluid also decreased as the NaCl concentration increased. These results indicate that guttation did not eliminate sufficient sodium to play a role in adjusting sodium homeostasis and the ratios of potassium to sodium contents in eddo plants under saline conditions.

The entry of cucumber mosaic virus into cucumber xylem is facilitated by co-infection with zucchini yellow mosaic virus.

We investigated the synergistic effects of co-infection by zucchini yellow mosaic virus (ZYMV) and cucumber mosaic virus (CMV) on viral distribution in the vascular tissues of cucumber. Immunohistochemical observations indicated that ZYMV was present in both the phloem and xylem tissues. ZYMV-RNA was detected in both the xylem wash and guttation fluid of ZYMV-inoculated cucumber. Steam treatment at a stem internode indicated that ZYMV enters the xylem vessels and moves through them but does not cause systemic infection in the plant. CMV distribution in singly infected cucumbers was restricted to phloem tissue. By contrast, CMV was detected in the xylem tissue of cotyledons in plants co-infected with CMV and ZYMV. Although both ZYMV-RNA and CMV-RNA were detected in the xylem wash and upper internodes of steam-treated, co-infected cucumbers grown at 24°C, neither virus was detected in the upper leaves using an ELISA assay. Genetically modified CMV harboring the ZYMV HC-Pro gene was distributed in the xylem and phloem tissues of singly inoculated cucumber cotyledons. These results indicate that the ZYMV HC-Pro gene facilitates CMV entry into the xylem vessels of co-infected cucumbers.

Nitrogen recycling from the xylem in rice leaves: dependence upon metabolism and associated changes in xylem hydraulics.

Measurements of amino acids in the guttation fluid and in the xylem exudates of cut leaves from intact plants provide evidence of the remarkable efficiency with which these nitrogenous compounds are reabsorbed from the xylem sap. This could be achieved by mechanisms involving intercellular transport and/or metabolism. Developmental changes in transcripts and protein showed that transcripts for phosphoenolpyruvate carboxykinase (PEPCK) increased from the base to the leaf tip, and were markedly increased by supplying asparagine. Supplying amino acids also increased the amounts of protein of PEPCK and, to a lesser extent, of pyruvate, Pi dikinase. PEPCK is present in the hydathodes, stomata and vascular parenchyma of rice leaves. Evidence for the role of PEPCK was obtained by using 3-mercaptopicolinic acid (MPA), a specific inhibitor of PEPCK, and by using an activation-tagged rice line that had an increase in PEPCK activity, to show that activation of PEPCK resulted in a decrease in N in the guttation fluid and that treatment by MPA resulted in an increase in amino acids in the guttation fluid and xylem sap towards the leaf tip. Furthermore, increasing PEPCK activity decreased the amount of guttation fluid, whereas decreasing PEPCK activity increased the amount of xylem sap or guttation fluid towards the leaf tip. The findings suggest the following hypotheses: (i) both metabolism and transport are involved in xylem recycling and (ii) excess N is the signal involved in modulating xylem hydraulics, perhaps via nutrient regulation of water-transporting aquaporins. Water relations and vascular metabolism and transport are thus intimately linked.

A Glycosyltransferase from Nicotiana alata Pollen Mediates Synthesis of a Linear (1,5)-α-L-Arabinan When Expressed in Arabidopsis.

The walls of Nicotiana alata pollen tubes contain a linear arabinan composed of (1,5)-α-linked arabinofuranose residues. Although generally found as a side chain on the backbone of the pectic polysaccharide rhamnogalacturonan I, the arabinan in N. alata pollen tubes is considered free, as there is no detectable rhamnogalacturonan I in these walls. Carbohydrate-specific antibodies detected arabinan epitopes at the tip and along the shank of N. alata pollen tubes that are predominantly part of the primary layer of the bilayered wall. A sequence related to ARABINAN DEFICIENT1 (AtARAD1), a presumed arabinan arabinosyltransferase from Arabidopsis (Arabidopsis thaliana), was identified by searching an N alata pollen transcriptome. Transcripts for this ARAD1-like sequence, which we have named N. alata ARABINAN DEFICIENT-LIKE1 (NaARADL1), accumulate in various tissues, most abundantly in the pollen grain and tube, and encode a protein that is a type II membrane protein with its catalytic carboxyl terminus located in the Golgi lumen. The NaARADL1 protein can form homodimers when transiently expressed in Nicotiana benthamiana leaves and heterodimers when coexpressed with AtARAD1 The expression of NaARADL1 in Arabidopsis led to plants with more arabinan in their walls and that also exuded a guttation fluid rich in arabinan. Chemical and enzymatic characterization of the guttation fluid showed that a soluble, linear α-(1,5)-arabinan was the most abundant polymer present. These results are consistent with NaARADL1 having an arabinan (1,5)-α-arabinosyltransferase activity.

Collection of Apoplastic Fluids from Arabidopsis thaliana Leaves.

The leaf apoplast comprises the extracellular continuum outside cell membranes. A broad range of processes take place in the apoplast, including intercellular signaling, metabolite transport, and plant-microbe interactions. To study these processes, it is essential to analyze the metabolite content in apoplastic fluids. Due to the fragile nature of leaf tissues, it is a challenge to obtain apoplastic fluids from leaves. Here, methods to collect apoplastic washing fluid and guttation fluid from Arabidopsis thaliana leaves are described.