Compounds In Xylem Sap Research Articles

Ralstonia solanacearum pandemic lineage strain UW551 overcomes inhibitory xylem chemistry to break tomato bacterial wilt resistance.

Plant-pathogenic Ralstonia strains cause bacterial wilt disease by colonizing xylem vessels of many crops, including tomato. Host resistance is the best control for bacterial wilt, but resistance mechanisms of the widely used Hawaii 7996 tomato breeding line (H7996) are unknown. Using growth in exvivo xylem sap as a proxy for host xylem, we found that Ralstonia strain GMI1000 grows in sap from both healthy plants and Ralstonia-infected susceptible plants. However, sap from Ralstonia-infected H7996 plants inhibited Ralstonia growth, suggesting that in response to Ralstonia infection, resistant plants increase inhibitors in their xylem sap. Consistent with this, reciprocal grafting and defence gene expression experiments indicated that H7996 wilt resistance acts in both above- and belowground plant parts. Concerningly, H7996 resistance is broken by Ralstonia strain UW551 of the pandemic lineage that threatens highland tropical agriculture. Unlike other Ralstonia, UW551 grew well in sap from Ralstonia-infected H7996 plants. Moreover, other Ralstonia strains could grow in sap from H7996 plants previously infected by UW551. Thus, UW551 overcomes H7996 resistance in part by detoxifying inhibitors in xylem sap. Testing a panel of xylem sap compounds identified by metabolomics revealed that no single chemical differentially inhibits Ralstonia strains that cannot infect H7996. However, sap from Ralstonia-infected H7996 contained more phenolic compounds, which are known to be involved in plant antimicrobial defence. Culturing UW551 in this sap reduced total phenolic levels, indicating that the resistance-breaking Ralstonia strain degrades these chemical defences. Together, these results suggest that H7996 tomato wilt resistance depends in part on inducible phenolic compounds in xylem sap.

Effects of Nitrogen Application on Post‐Silking Root Senescence and Yield of Maize

The size of roots and their physiological activity during the grain‐filling stage affect water and nutrient uptake, and grain yield (GY) in maize (Zea mays L.). The aim of this study was to determine the effects of different N levels on postanthesis root senescence in field‐grown maize. Three N levels (0, 120, 240 kg N ha−1) was applied to field‐grown maize, and the length and weight of roots in the 0‐ to 40‐cm soil layer, nitrogenous compounds in xylem sap, N uptake, dry matter (DM), N accumulation, and GY were analyzed. Shoot N accumulation, but not grain yield, was higher in the N240 treatment than in the N120 treatment. At the silking stage, the root length was longest in the N0 treatment and shortest in the N240 treatment. This was because of the high root/shoot (R/S) and root C/N ratios in N0. Total root length decreased throughout the grain‐filling period, mainly because of the reduced length of early developed nodal roots. The root length decreased by 27% in the N0 treatment, to a smaller extent compared to that in N120 (52%) and N240 (51%). The amounts of NO3−–N, NH4+–N and amino acid‐N in the xylem sap were highest in the N240 treatment during the entire grain‐filling stage, suggesting that a high N supply increased root N‐uptake activity. Based on these results, we conclude that high root N‐uptake activity, not delayed root senescence, resulted in the large accumulation of N in the shoot under excess N.

Grapevine Phenolic Compounds in Xylem Sap and Tissues Are Significantly Altered During Infection byXylella fastidiosa

Pierce's disease of grapevine (PD), caused by the bacterial pathogen Xylella fastidiosa, remains a serious problem for grape production in California and elsewhere. This research examined induction of phenolic compounds in grapevines ('Thompson Seedless') infected with X. fastidiosa over a 6-month period. Two months postinoculation with X. fastidiosa, catechin, digalloylquinic acid, and astringin were found at greater levels in xylem sap; multiple catechins, procyanidins, and stilbenoids were found at greater levels in xylem tissues; and precursors to lignin and condensed tannins were found at greater levels in xylem cell walls. However, such large-scale inductions of phenolic compounds were not observed 4 months after inoculation. Six months after inoculation, infected plants had significantly reduced phenolic levels in xylem sap and tissues when compared with control plants, including lowered levels of lignin and condensed tannins. At 6 months, PD symptoms were severe in infected plants and most photosynthetic tissue was abscised. These results suggest that, even though grapevine hosts may initially respond to X. fastidiosa infections with increased production of phenolic compounds, ultimately, PD causes grapevines to enter a state of decline whereby diseased hosts no longer have the resources to support secondary metabolite production, including defense-associated phenolic compounds.

Response pattern of amino compounds in phloem and xylem of trees to soil drought depends on drought intensity and root symbiosis

This study aimed to identify drought-mediated differences in amino nitrogen (N) composition and content of xylem and phloem in trees having different symbiotic N(2)-fixing bacteria. Under controlled water availability, 1-year-old seedlings of Robinia pseudoacacia (nodules with Rhizobium), Hippophae rhamnoides (symbiosis with Frankia) and Buddleja alternifolia (no such root symbiosis) were exposed to control, medium drought and severe drought, corresponding soil water content of 70-75%, 45-50% and 30-35% of field capacity, respectively. Composition and content of amino compounds in xylem sap and phloem exudates were analysed as a measure of N nutrition. Drought strongly reduced biomass accumulation in all species, but amino N content in xylem and phloem remained unaffected only in R. pseudoacacia. In H. rhamnoides and B. alternifolia, amino N in phloem remained constant, but increased in xylem of both species in response to drought. There were differences in composition of amino compounds in xylem and phloem of the three species in response to drought. Proline concentrations in long-distance transport pathways of all three species were very low, below the limit of detection in phloem of H. rhamnoides and in phloem and xylem of B. alternifolia. Apparently, drought-mediated changes in N composition were much more connected with species-specific changes in C:N ratios. Irrespective of soil water content, the two species with root symbioses did not show similar features for the different types of symbiosis, neither in N composition nor in N content. There was no immediate correlation between symbiotic N fixation and drought-mediated changes in amino N in the transport pathways.

Transport of Nitrogen Assimilation in Xylem Vessels of Green Tea Plants Fed with NH 4-N and NO 3-N

An experiment was carried out to study the transport process of nitrogen (N) assimilation from tea roots by monitoring the dynamic composition of N compounds in xylem sap after 15N-NO 3 and 15N-NH 4 were fed to the root of tea plants ( Camellia sinensis L.). Results showed that the main amino acids were glutamine, theanine, arginine, asparic acid and glutamic acid, which accounted for 49%, 17%, 8%, 7%, and 4%, respectively, of the total amino acids in the xylem sap. After the tea plants were fed with 15N-NO 3 and 15N-NH 4 for 48 h, the amount of total amino acids in xylem sap significantly increased and those fed with 15N-NH 4 had higher increment than those with 15N-NO 3. Two hours after 15N- NO 3 and 15N-NH 4 were fed, 15N abundance in glutamine, asparagine, glutamic acid, alanine, and arginine were detected and increased quickly over time. This indicated that it took less than 2 h for NO 3-N and NH 4-N to be absorbed by tea roots, incorporated into the above amino acids and transported to the xylem sap. Rapid increase in 15N-NO 3 in the xylem sap of tea plants fed with 15N-NO 3 indicated that nitrate could be directly transported to the xylem sap. Glutamine, theanine, and alanine were the main amino acids transported in xylem sap of tea plants fed with both 15N-NO 3 and 15N-NH 4.

Spatial and seasonal variation in amino compounds in the xylem sap of a mistletoe (Viscum album) and its hosts (Populus spp. and Abies alba).

In a field study, the composition and concentrations of amino compounds in the xylem sap of the mistletoe, Viscum album L., and in the xylem sap of two host species, an evergreen conifer (Abies alba Mill.) and a deciduous broad-leaved tree (Populus x euramericana), were analyzed. The xylem sap of both hosts and mistletoe contained large, but similar amounts of total organic nitrogen in low molecular weight amino compounds (TONLW). Nevertheless, individual amino compounds accumulated in the xylem sap of mistletoe relative to the host xylem sap, indicating selective uptake. In the xylem sap of Populus, major amino compounds (asparagine (Asn) and glutamine (Gln)) and the bulk parameters, TONLW and proteinogenic amino acids, showed significant seasonal variation. In Abies and in mistletoe on either host, variation of amino compounds in xylem sap was largely explained by inter-annual differences, not by seasonal variation. In both hosts, TONLW in the xylem sap was dominated by Gln. There was a steady decrease in relative abundance of Gln from the host xylem sap to the mistletoe xylem sap and to the stems and leaves of mistletoe. Simultaneously, the abundance of arginine (Arg) increased. Arginine was the predominant amino compound in the stems and leaves of mistletoe, occurring at concentrations previously observed only in leaves of trees exposed to excess nitrogen. We conclude that Gln (2 mol N mol(-1)) delivered by the host xylem sap is converted, in mistletoe, to Arg (4 mol N mol(-1)) and that the organic carbon liberated from Gln contributes significantly to the parasite's heterotrophic carbon gain. Statistical analyses of the data support this conclusion. Accumulation of Arg in mistletoe is an indication of excess N supply as a result of the uptake of amino compounds from the host xylem sap and a lack of phloem uploading.

Possible involvement of leaf gibberellins in the clock-controlled expression of XSP30, a gene encoding a xylem sap lectin, in cucumber roots.

Root-produced organic compounds in xylem sap, such as hormones and amino acids, are known to be important in plant development. Recently, biochemical approaches have revealed the identities of several xylem sap proteins, but the biological functions and the regulation of the production of these proteins are not fully understood. XYLEM SAP PROTEIN 30 kD (XSP30), which is specifically expressed in the roots of cucumber (Cucumis sativus), encodes a lectin and is hypothesized as affecting the development of above-ground organs. In this report, we demonstrate that XSP30 gene expression and the level of XSP30 protein fluctuate in a diurnal rhythm in cucumber roots. The rhythmic gene expression continues for at least two or three cycles, even under continuous light or dark conditions, demonstrating that the expression of this gene is controlled by a circadian clock. Removal of mature leaves or treatment of shoots with uniconazole-P, an inhibitor of gibberellic acid (GA) biosynthesis, dampens the amplitude of the rhythmic expression; the application of GA negates these effects. These results suggest that light signals perceived by above-ground organs, as well as GA that is produced, possibly, in mature leaves, are important for the rhythmic expression of XSP30 in roots. This is the first demonstration of the regulation of the expression of a clock-controlled gene by GA.

Nitrogen and phosphorus availability limit N2 fixation in bean

Availability of nitrogen (N) and phosphorus (P) might significantly affect N2 fixation in legumes. The interaction of N and P was studied in common bean (Phaseolus vulgaris), considering their effects on nodulation and N2 fixation, nitrate reductase activity, and the composition of N compounds in xylem sap. The effect of N on the uptake of P by plants was estimated by analysing rhizospheric pH and P concentration in xylem sap and in plant shoots. Inoculated bean plants were grown in pots containing perlite/vermiculite in two experiments with different amounts of P and N. In a third experiment, bean plants were grown on two soil types or on river sand supplied with different concentrations of N. At harvest, shoot growth, number of nodules and mass, and nitrogenase activity were determined. Xylem sap was collected for the determination of ureides, amino acids, nitrate and phosphate concentration. At low nitrate concentration (1 mM), increasing amounts of P promoted both nodule formation and N2 fixation, measured as ureide content in the xylem sap. However, at high nitrate concentration (10 mM), nodulation and N2 fixation did not improve with increased P supply. Glutamine and aspartate were the main organic N compounds transported in the xylem sap of plants grown in low nitrate, whereas asparagine was the dominant N compound in xylem sap from plants grown in high nitrate. Nitrate reductase activity in roots was higher than in shoots of plants grown with low P and high N. In both soils and in the sand experiment, increased application of N decreased nodule mass and number, nitrogenase activity and xylem ureides but increased the concentration of asparagine in xylem sap. Increasing P nutrition improved symbiotic N2 fixation in bean only at low N concentrations. It did not alleviate the inhibitory effect of high nitrate concentration on N2 fixation. A decrease in plant P uptake was observed, as indicated by a lower concentration of P in the xylem sap and shoots, correlating with the amount of N supplied. Simultaneously with the specific inhibition of N2 fixation, high nitrate concentrations might decrease P availability, thus inhibiting even further the symbiotic association because of the high P requirement for nodulation and N2 fixation.

Is coordination of leaf and root growth mediated by abscisic acid? Opinion

Leaf growth is more inhibited than root growth when the soil is nitrogen-deficient, dry, saline, compacted, or of restricted volume. Similar differential responses in leaf and root growth occur when ABA is applied to plants in well-watered and well-fertilised conditions, and opposite responses are often found in ABA-deficient mutants. ABA levels increase in plants in dry or saline soils, suggesting a regulating role in leaf and root growth in soils of low water potential. In nitrogen-deficient or compacted soils, or soils of restricted volume, ABA only sometimes increases, and in these situations its accumulation may be of secondary importance. Use of ABA-deficient mutants has so far indicated that ABA influences leaf and root growth in unstressed plants, and plants in dry soils, but not in soils that are compacted, of restricted volume, or are nitrogen-deficient. For ABA to determine the relationship between the rate of leaf growth and the rate of root growth, there must be long-distance transport of either ABA itself or a compound that controls ABA synthesis in the growing cells of leaves and roots. ABA invariably increases in xylem sap as the soil becomes dry or saline, and sometimes when it becomes nitrogen-deficient or compacted, however the ABA is of too low a concentration to affect leaf growth. There may be a compound in xylem sap that controls the synthesis of ABA in the leaf, but no such compound has been identified. ABA accumulates in phloem sap of plants in dry or saline soil, but its function in controlling root or leaf growth is unknown. We conclude that ABA affects the ratio of root growth to leaf growth via its independent effects on root and leaf growth, and may regulate the ratio of root to leaf growth via feedforward signals in xylem or phloem, but there is no satisfactory explanation of its mechanism of control.

Evaluation of the xylem ureide method for measuring N 2 fixation in six tree legume species

The xylem ureide method, based on analysis of xylem sap for N solutes associated with N 2 fixation (ureides) and soil-N use (NO 3 −, α amino-N), is used for estimating Pfix (proportion of plant N derived from N 2 fixation) of herbaceous species of the leguminous tribes Phaseoleae and Desmodieae and may have application for tree legumes. We report experiments, involving Calliandra calothyrsus, Leucaena leucocephala, Gliricidia sepium, Sesania grandiflora, Desmodium rensonii and Codariocalyx gyroides, to: (i) determine for each species the composition of N solutes of xylem sap and to calibrate, where possible, the xylem ureide method using 15N isotope dilution as an independent measure of Pfix; and (ii) establish appropriate procedures for sampling xylem sap in field studies. In the first experiment, the tree legumes were grown for 55–77 weeks and sampled repeatedly (6–9 times) for vacuum-extracted xylem sap, shoot dry matter, total N and 15N. Asparagine was the predominant amino compound in xylem sap of all species. The relative abundance of ureide-N in xylem sap (ureide-N as a proportion of ureide-N + α amino-N + NO 3 −N) was compared with Pfix for five of the six tree legumes. Sap of S. grandiflora could not be analysed for ureides and NO 3 − using the standard colorimetric methods because of high levels of non-specific, background colour. For D. rensonii and C. gyroides, relative ureide-N ranged from less than 20% (Pfix of zero) to around 65 and 40%, respectively (Pfix of 100%). Functions describing the relationships between relative ureide-N ( y) and Pfix ( x) were: y = 18.3 + 0.446 x ( r = 0.91) for D. rensonii; and y = 8.49 + 0.279 x ( r = 0.92) for C. gyroides. With the other three species, relative ureide-N was not related to Pfix. We concluded that the xylem ureide technique is suitable for estimating Pfix for D. rensonii and C. gyroides only. In the second experiment, established trees of G. sepium, D. rensonii, C. calothyrsus and C. gyroides were used to assess sampling protcols. Results indicated that vacuum extraction of sap should proceed immediately the branch is cut, that plants need to be sampled around noon to eliminate diurnal effects and that branch-to-branch variation in relative ureide-N values within a single tree was minor.

Chemical composition of xylem sap of tomato grown on bicarbonate containing medium

Abstract Incorporation of bicarbonate (HCO3 ‐) by the roots of tomato seedlings resulted in an increase in biomass production and changed the chemical composition of xylem sap. In the xylem sap of seedlings grown on a medium enriched with HCO3 ‐ (5.68 mM dm‐3, series II) compared with the control (series I) the element content increased by about 27% and 33% for cations and anions, respectively. Potassium was the major cation in the xylem sap and constituted 69% of the total concentration of all the inorganic cations determined. Calcium attained 19% of this amount. The anionic load in the xylem sap was chiefly nitrate, constituting about 90% of the content of all the inorganic anions. The exudate was analysed for seven organic acids. In general, malic (MA), maleic, and citric (CA) occurred in xylem exudate at greater concentrations, constituting about 95% of the total content of organic acids. Cultivation of seedlings on the medium enriched with HCOJ brought about an increased content of organic acids, exceeding the control by about 60%. The concentration of MA increased by about 104% and that of CA and maleic acid exceeded the control by about 40% and 14%, respectively. Twenty amino acids were identified in tomato xylem sap. Glutamic, aspartic and y‐arninobutyric acid, and particularly the amides aspargine and glutamine occurred in greater amounts. Their total concentration was about 60% and 70% of the total amino acid content in series I and II, respectively. The remaining amino acids occurred at concentrations ≥ 90 μM. The cultivation of plants on the medium containing HCO3 ‐ resulted in an increase in amino acid content in xylem sap by about 28% as compared with the control. The ratio of amino acid to organic acid content was 2: 2.5 and 2: 3 for series I and II, respectively. The similar value of the ratio in the two series suggests that the synthesis of both groups of compounds be equally favoured by the carbon source (endogenous in the control and from the medium enriched with HCO3 ‐ in series II). The increased level of elements and organic compounds in xylem sap in the case of plants supplied with HCO3 ‐ is discussed in the work in respect of metabolic processes of roots.

Involvement of Abscisic Acid in Controlling Plant Growth in Soil of Low Water Potential

Hormones appear to be important in controlling plant growth in soils of low water potential, particularly in changing the root:shoot ratio as the soil dries or becomes saline, and in communicating soil conditions to the leaves. This review has necessarily focused on abscisic acid (ABA), as there is little information about the role of other hormones in controlling growth in dry or saline soils. ABA is partly responsible for the differential response of root and shoot growth to dry soils. In dry soil it maintains root growth and inhibits shoot growth. However, when applied to well-watered plants, it usually inhibits root and shoot growth, showing that plants in dry soil respond quite differently from well-watered plants. ABA affects the rate of cell expansion in plants in dry soils: it maintains cell expansion in roots and inhibits that in leaves. It may also affect the rate of cell production, but little is known about this. The role of ABA as a long-distance signal in controlling growth by root-to-shoot communication is unclear: the concentrations found in xylem sap can affect stomatal conductance, but seem too low to affect leaf expansion. Yet drought and salinity generally affect leaf expansion before they affect leaf conductance. A possible solution to this puzzle is that ABA is transported in xylem sap in a complexed form, or that another compound in xylem sap stimulates the synthesis or activity of ABA in leaves, or affects leaf expansion independently of ABA.

Changes in the Nitrogen Compounds of Xylem Sap of Mulberry (Morus alba L.) during Regrowth after Pruning

Changes in fresh and dry weights and total nitrogen in stem sections of mulberry ( Morus alba L.) and seasonal fluctuation in the amounts of exudate, pH and nitrogen compounds in xylem sap from cut stems of the plant after pruning have been studied. The amount and concentrations of nitrogen compounds in the sap changed during the experimental period, but nitrate-nitrogen and ammonia-nitrogen were constant constituents, and asparagine was quantitatively the major organic nitrogen compound. Smaller amounts of glutamine, aspartic acid and glutamic acid were also found, but no ureides or alkaloids were detected. Relationships between growth and nitrogen in xylem sap of mulberry and the role and importance of asparagine in nitrogen metabolism are discussed.

Spring Shoot Growth in Douglas-Fir May Be Initiated by Gibberellins Exported from the Roots

Trials conducted under controlled environments demonstrated that the delay of bud activity of Douglas-fir (Pseudotsuga menziesii) seedlings occasioned by low temperature of the soil could be eliminated by application of gibberellic acid. Analyses of field-grown plants showed a parallel increase in bud activity, level of gibberellin-like compounds in xylem sap, and soil temperature during February and March.