Root Metabolism Research Articles

Measurements of 18 O-Pi uptake indicate fast metabolism of phosphate in tree roots.

Phosphorus (P) nutrition of beech ecosystems depends on soil processes, plant internal P cycling and P acquisition. P uptake of trees in the field is currently not validated due to the lack of an experimental approach applicable in natural forests. Application of radiolabelled tracers such as 33 P and 32 P is limited to special research sites and not allowed in natural environments. Moreover, only one stable isotope of P, namely 31 P, exists. One alternative tool to measure P acquisition in the field could be the use of 18 O-labelled 31 P-phosphate (31 P18 O4 3- ). Phosphate (Pi ) uptake rates calculated from the 18 O enrichment of dried root material after application of 31 Pi 18 O4 3- via nutrient solution was always lower compared to 33 P incorporation, did not show increasing rates of Pi uptake at P deficiency under controlled conditions, and did not reveal seasonal fluctuations in the field. Consequently, a clear correlation between 33 P-based and 18 O-based Pi uptake by roots could not be established. Comparison of Pi uptakerates achieved from 33 P-Pi and 18 O-Pi application led to the conclusion of high Pi metabolism in roots after Pi uptake. The replacement of 18 O by 16 O from water in 18 O-Pi during root influx, but most probably after Pi uptake into roots, due to metabolic activities, indicates high and fast turnover of Pi . Hence, the use of 18 O-Pi as an alternative tool to estimate Pi acquisition of trees in the field must consider the increase of 18 O abundance in root water that was disregarded in dried root material.

Physiological and biochemical responses of Eucalyptus seedlings to hypoxia

Hypoxia promoted distinct changes in the levels of hormones, amino acids and organic acids in the roots and shoots of a seedling from 2 Eucalyptus clones. These results indicate that modulation of hormone production, as well as specific chemical constituents associated with primary metabolism, contributes to the regulation of growth of Eucalyptus seedlings under hypoxic conditions. Although floods in areas under Eucalyptus cultivation in Brazil negatively affect plant growth, chemical markers and/or indicators of hypoxia contributes to the regulation.s This study aimed to evaluate the hormonal and metabolic alterations induced by hypoxia on seedling growth. Seedlings of Eucalyptus urograndis clones VCC 975 and 1004 were grown in liquid solution and submitted to bubbling with air or with nitrogen. Levels of indol-3-acetic acid (IAA), abscisic acid (ABA), ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC), primary metabolite profile and photosynthetic parameters were evaluated after fourteen days. Hypoxia did not affect shoot dry mass of the seedlings. However, it decreased stomatal conductance and photosynthetic CO2 assimilation rate, and increased levels of ABA in the shoot. Hypoxia greatly reduced the dry mass and volume of roots, concomitantly with higher ACC and ethylene production. Moreover, hypoxia promoted distinct changes in IAA levels, and in amino acid and organic acid metabolism in roots and shoots. The biosynthesis of ABA, ethylene and IAA and its quantity in root tissues indicates the regulation of metabolism in response to hypoxia in Eucalyptus clones.

The relative importance of influence factors to field soil respiration is shifted by straw incorporations: comprehensive analysis of the seasonal variability

Understanding the effects of agricultural managements (e.g., straw incorporation) on soil respiration (Rs) and its temperature sensitivity (Q10) is crucial for accurate estimation of the soil carbon sequestration potential under an increasing-temperature scenario in the future. However, how the influence drivers regulate Rs and whether their relative roles are changed under different agricultural practices remain unexplored. Static chambers were used to monitor field CO2 flux in one growing season for a straw return experiment, which had been amended with different amounts of straw (CK, no straw return; S4, straw amendment at 4000 kg ha−1; and S8, straw amendment at 8000 kg ha−1) for five consecutive years. Our monitoring showed that Rs was elevated with intensified use of straw and confirmed soil temperature, soil moisture, and rainfall were important seasonal drivers of Rs. Moreover, the lower coefficient of variations (CV) for each series of treatments of Rs was detected at the vigorous growth stage of the crop, implying the biotic factor of crop roots might also exert a role simultaneously. Straw addition tended to reduce Q10, probably due to the fact that the microbial degradation of SOC in S4 and S8 was less sensitive to temperature change. Interestingly, the Q10 of S4 but not S8 was significantly smaller (P < 0.05) than that of CK as the reduced magnitude of Q10 for S4 was more profound. This result corresponded with more proportional growth of crop root of S8 than S4. By comprehensively analyzing the seasonal variability of our data set, we inferred that for S8, the negative impact of straw incorporation on Q10 would be more offset by upregulated root metabolism. Although additional works were needed to corroborate and specify this explanation, present research highlighted the abiotic and biotic factors should both be incorporated to analyze the underlying mechanisms responsible for the seasonal dynamics of soil C emissions under agricultural managements.

Supplementation of Nitrogen and its Influence on Free Sugars, Amino Acid and Protein Metabolism in Roots and Internodes of Wheat

Effect of different doses of nitrogen (N) (90, 120, 150 and 180 kg Nha–1) on the activities of aminotransferases and alkaline inorganic pyrophosphatase (AIP) in relation to the accumulation of proteins, amino acids and sugars in roots and internodes at 15 and 40 days post anthesis (DPA) stages was studied in six wheat genotypes namely HD 2967, GLU 1101, PBW 343, BW 9022, PH-132–4840 and PBW 550. Supra-optimal N doses (150 kg Nha–1 and 180 kg Nha–1) accentuated glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT) and alkaline inorganic pyrophosphatase activities in correspondence with an increase in amino acid, protein and sugar content in both roots and internodes in all the six genotypes. Activities of analyzed enzymes were significantly high at 15 days post anthesis (DPA) stage and thereafter declined at maturity (40 DPA) in parallel with decrease in amino acid contents. Maximum activity of GOT, GPT and AIP was observed in HD 2967 and GLU 1101 genotypes along with higher build up of proteins and amino acids which resulted in higher grain yield. Activity of GPT was comparatively high over GOT, indicating its major role towards protein synthesis. Grain filling processes in terms of proteins and amino acids were positively correlated with GOT and GPT activities while sugars were correlated to AIP. Thus, nitrogen acquisition and assimilation resulted in favoured utilization of N in form of amino acid and proteins accumulation while sugar content was also stimulated. Due to immense activities of aminotransferases and higher contents of amino acids and proteins in GLU 1101 and HD 2967 genotypes at optimal dose and higher dose of N, these genotypes hold future potential for developing new cultivars with better grain quality characteristics.

Impact of light and sucrose supplementation on cellular differentiation, metabolic shift and modulation of gene expression in hairy roots of Daucus carota

Green hairy root cultures of Daucus carota were subjected to gradually lowered sucrose concentrations to understand the modulation of secondary metabolism upon carbon-starved conditions. An apparent negative correlation with the sucrose concentrations in the media was observed with chloroplast development, as confirmed by both histological studies and relevant biochemical assays. Expansion of relative vascular area and well-developed multi-layered endodermis were evidenced in green hairy roots with low sucrose concentrations as compared to normal hairy roots cultivated with 2% sucrose under dark condition. Thus, anatomical modulation was evident in photo-oxidatively stressed green hairy roots because of their maintenance under continuous illumination. This was demonstrated further by the expression analysis of glutathione peroxidase and NADPH reductase genes which showed upregulation in green hairy roots maintained in ½ MS media containing 0.5% sucrose as compared to normal hairy roots. The amount of phenolic marker compound p-hydroxybenzoic acid was reduced to half, while enhanced levels of emitted terpenoid volatiles were noticed in these carbon-starved green hairy roots. Analysis of primary metabolites in green hairy roots showed increased levels of amino acids and sugar alcohols accumulation. Further, analysis revealed the elevated accumulation of organic acids which have significant bearing towards redirection of primary metabolites leading to the formation of enhanced terpenoid volatiles in green hairy roots. Thus, our study revealed the impact of light and sucrose supplementation towards cellular differentiation and redirection of secondary metabolism in hairy roots of D. carota.

Fusarium oxysporum affects differently the hydrogen peroxide levels and oxidative metabolism in susceptible and resistant bean roots

This study aimed at investigating the role of enzymes related to the oxidative metabolism and hydrogen peroxide in susceptible and resistant plants of common bean to Fusarium oxysporum f. sp. phaseoli (Fop). Fop inoculation increased H2O2 levels only in roots of resistant plants. Despite this, no hypersensitive cells were induced. In the enzymatic metabolism, two distinct phases were observed in resistant roots; the first one at 1 day after inoculation (dai) characterized by an increase in guaiacol peroxidase, superoxide dismutase and ascorbate peroxidase, and decrease in catalase and lipoxygenase activities, and the second one at 3–4 dai characterized by activity peaks of NADPH oxidase, superoxide dismutase and ascorbate peroxidase. Overall, the metabolism oxidative was more drastically modified in resistant roots than in susceptible ones. Our results demonstrate that Fop infection affects differently the oxidative metabolism in a genotype-dependent manner.

Physiological response and phenolic metabolism in tomato (Solanum lycopersicum) mediated by silicon under Ralstonia solanacearum infection

Bacterial wilt, caused by Ralstonia solanacearum (Rs) is a serious soil-borne disease and silicon can enhance tomato resistance against this disease. However, few studies have focused on the mechanisms of Si-mediated pathogen resistance from the rhizosphere perspective. In this study, two tomato genotypes, HYT (susceptible) and H7996 (resistant), were used to investigate the effects of silicon application on disease inhibition, root growth, and organic acid content in both roots and root exudates under R. solanacearum infection. The results showed that Si application significantly suppressed bacterial wilt in HYT, but had no effect in H7996. Silicon concentrations in roots, stems and leaves of tomato were significantly increased by Si treatment under R. solanacearum inoculation. In HYT, Si application increased root dry weight by 22.8–51.6% and leaf photosynthesis by 30.6–208.0%, and reduced the concentrations of citric acid in root exudates by 71.4% and in roots by 83.5%. However, organic acids did not influence R. solanacearum growth. Results also demonstrated that salicylic acid (SA) content in roots was significantly increased by silicon addition for H7996 and exogenous SA application could reduce bacterial wilt disease index. Collectively, these results suggest that Si-modulated phenolic compound metabolism in roots or root exudates, especially citric acid and SA, may be a potential mechanism in the amelioration of bacterial wilt disease by Si.

Effect of treated wastewater on growth and secondary metabolites production of two Eucalyptus species

The use of Treated Waste Water (TWW) as an alternative to limit water use in agriculture practices in the context of global warming is of particular importance, especially in countries where water resources are limited. In this study, we assessed the effect of TWW irrigation on two Eucalyptus species (E. camaldulensis and E. occidentalis) in their early stages of growth (up to one year after seedling and transplantation) in pot experiment and compared to Well-Water (WW) irrigation. Changes in plant growth traits/ characteristics including plant height, stem diameter, number of leaves and Leaf Mass per Area (LMA) were analysed as well as the modification of root and leaves secondary metabolic profiles and total phenolic contents. Soil physico-chemical parameters were also measured before and after the experiment.Our results showed that both species do not have the same response to TWW irrigation: while most growth recorded parameters were most affected in E. camaldulensis after one year of growth with TWW, E. occidentalis had its leaf number significantly increased with TWW after seven months. Leaves were lighter and smaller than the ones obtained with WW irrigation after four months but the reduction of weight and area was proportional in such a way that LMA was not affected and this effect was transitory. Such effect was not observed with E. camaldulensis.Concerning root and leaf secondary metabolite profiles, changes in both plant part extract compositions were observed according to irrigation type, though these were weak compared to plant species identity. Common metabolic patterns following TWW irrigation could be showed in both species like for example the increase of quercetin glucosinnapate in leaf extracts or the decrease of two peduncalagin isomers detected as major compounds in the same extracts. Though some differences were also observed, particularly, E. occidentalis had more compounds decreased in its roots than E. camaldulensis when irrigated with TWW while in leaves the tendency was inverted. Total phenolic content was decreased in both species and for both plant parts, but this diminution was more pronounced in E. occidentalis roots. We also noticed modifications in soil parameters after TWW exposure and some were dependant on the species of Eucalyptus like for example soil organic matter content which increased with TWW in the case of E. occidentalis, whereas it decreased for E. camaldulensis. All these results let us hypothesize that E. occidentalis possess better adaptation capabilities to TWW irrigation than E. camaldulensis and that these might be related to changes in root metabolism.

Influence of Two Nitrogen Forms on Hormone Metabolism in Potential Storage Roots and Storage Root Number of Sweetpotato

In this study, we investigated the effects of two N forms on sweetpotato [Ipomoea batatas (L.) Lam.] root growth and development, zeatin riboside (ZR) and indole‐3‐acetic acid (IAA) concentrations in potential storage roots, and storage root number per plant. During the period 2015 to 2016, field experiments were performed using the sweetpotato cultivars ‘Shangshu 19’ and ‘Jixu 23’, which involved the following three treatments: no application of N fertilizer, application of 60 kg N hm−2 ammonium N, and application of 60 kg N hm−2 amide N. Our results indicated that during storage root formation, compared with the control treatment, the ammonium N treatment led to a significantly higher number of thick roots. However, the ammonium N treatment significantly reduced the average diameter of thick roots during early storage root formation and increased the average diameter during late storage root formation. Compared with the control treatment, ammonium N treatment inhibited the expression of Ibkn1, Ibkn2, and SRD1 genes during the early stage of storage root formation and also reduced the activities of IAA oxidase, peroxidase, and polyphenol oxidase enzymes, thereby ultimately reducing the ZR and IAA concentrations in potential storage roots. The opposite pattern was observed during the late stage of storage root formation. During the canopy closure period, compared with the control treatment, ammonium N treatment significantly increased the number of storage roots with diameters of 0.5 to 5.0 cm but decreased the number of storage roots with diameters &gt;5.0 cm. At harvest, the ammonium N treatment had resulted in the highest storage root yield and storage root number per plant.

Effect of konjac glucomannan coating on antioxidant capacity and phenolic metabolism in fresh-cut lotus roots

Effect of konjac glucomannan coating on antioxidant capacity and phenolic metabolism in fresh-cut lotus roots

Responses of Bougainvillea spectabilis to elevated atmospheric CO2 under galaxolide (HHCB) pollution and the mechanisms of its rhizosphere metabolism

Due to the discovery of synthetic musks in soil and the gradual increase in atmospheric carbon dioxide (CO2), it is important to reveal the potential implications of these compounds for bioremediation systems. Hence, this study was conducted to investigate the combined influence of galaxolide (HHCB) and elevated CO2 on an ornamental remediation plant. We conducted pot experiments with Bougainvillea spectabilis, an ornamental remediation plant, in which the biomass, HHCB and chlorophyll contents, and rhizosphere metabolism of the plants were analyzed. We showed that B. spectabilis exhibited high tolerance under combined HHCB and elevated CO2 stresses. The addition of HHCB alone to the soil did not significantly reduce the biomass components of B. spectabilis, whereas the presence of elevated CO2 (750 μL L−1) alone showed a relatively strong ability to increase plant biomass, especially that of the leaves. An elevated CO2 concentration stimulated the absorption of low doses of HHCB by the roots. Regarding the root metabolites of B. spectabilis, carbohydrates and organic acids were highly correlated with HHCB concentration, and amino acids were well correlated with CO2 concentration. Our study indicates that B. spectabilis may be well suited to remove HHCB from contaminated soil under elevated CO2 levels, and the root metabolism of this plant provides information about HHCB contamination and elevated CO2 conditions.

Modification of plant cell wall chemistry impacts metabolome and microbiome composition in Populus PdKOR1 RNAi plants

AimsWe examined the effect of downregulating PdKOR1 gene, an endo-β-1,4-glucanase gene family member previously characterized to affect cellulose biosynthesis and cell wall composition in Populus, on the secondary metabolome and microbiome of field-grown Populus deltoides.MethodsWe revealed differences in metabolite profiles of PdKOR1 RNAi and control roots using gas chromatography-mass spectrometry, and microbiome identification via Illumina MiSeq 16S and ITS2 rRNA sequencing in root endospheres and rhizospheres.ResultsPdKOR1 RNAi root metabolites differed from control plants: free amino acids (valine, isoleucine, alanine) were reduced while caffeoyl-shikimates, salicylic-acid derivatives, and flavonoid metabolites increased in PdKOR1 RNAi roots. The Actinobacterial family Micromonosporaceae were more abundant in RNAi root endospheres, whereas Nitrospirae was reduced in PdKOR1 RNAi rhizospheres. Ascomycota were lower and Basidiomycota greater in PdKOR1 rhizospheres. Bacterial and fungal community composition, as measured by Bray-Curtis dissimilarity, differed between PdKOR1 RNAi and control rhizospheres and endospheres.ConclusionsThese results indicate that modification of plant cell walls via downregulation of PdKOR1 gene in Populus impacts carbon metabolism in roots and concomitant alterations in root-associated microbial communities. Such an understanding of functional and ecological implications of biomass chemistry improvement efforts is critical to address the goals of sustainable bioenergy crop production and management.

Plant nucleoside diphosphate kinase 1: A housekeeping enzyme with moonlighting activity

ABSTRACTNucleoside diphosphate kinase (NDPK) catalyzes the interconversion of nucleoside diphosphates and triphosphates using ATP as phosphate donor. This housekeeping enzyme is present in several subcellular compartments. The main isoform (NDPK1) is located in the cytosol and is highly expressed in meristems and provascular tissues. The manipulation of NDPK1 levels in transgenic potato roots demonstrates that this enzyme plays a key role in the transfer of energy between the cytosolic adenine and uridine nucleotide pools and in the distribution of carbon between starch and cellulose. Modulation of the expression of NDPK1 also alters the homeostasis of root respiration, glycolytic flux, reactive oxygen species production and growth. Herein, we propose a model summarizing the effects of the manipulation of NDPK1 levels on root metabolism. The model also accounts for G-quadruplex DNA binding, a moonlighting activity recently attributed to NDPK1, which possibly contributes to the metabolic phenotype of transgenic roots.

Root architecture and nitrogen metabolism in roots of apple rootstock respond to exogenous glucose supply in low carbon soil

To investigate the response of root architecture and nitrogen metabolism of apple rootstock to glucose supply in low-carbon (C) soil, Malus baccata (L.) Borkh. in gravel soil was treated with glucose C equal to the soil microbial biomass carbon (MBC)-C value (G&lt;sub&gt;1&lt;/sub&gt;), five times the soil MBC value (G&lt;sub&gt;2&lt;/sub&gt;), or with no glucose (CK). The roots samples were harvested after treatments for 7, 15 and 30 days. The roots tended to become larger, more dichotomous and showed a larger link branching angle in G&lt;sub&gt;1&lt;/sub&gt; and G&lt;sub&gt;2&lt;/sub&gt; than in CK, especially in the G&lt;sub&gt;1&lt;/sub&gt; treatment for 30 days. Plant height and biomass were increased by G1. Nitrate (NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;-N) and nitrite (NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;–&lt;/sup&gt;-N) contents were increased, but ammonium (NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;-N) concentration was decreased in the roots treated with G&lt;sub&gt;1&lt;/sub&gt; and G&lt;sub&gt;2&lt;/sub&gt; in all treatment periods. Also, the activities and transcript levels of nitrate reductase, glutamine synthetase, glutamate dehydrogenase, glutamate synthase were generally increased in roots treated with glucose, especially under G&lt;sub&gt;1&lt;/sub&gt;. The activities of glutamic oxalacetic transaminases and glutamic-pyruvic transaminase were higher under G&lt;sub&gt;1&lt;/sub&gt; than under either G&lt;sub&gt;2&lt;/sub&gt; or CK. Exogenous carbon source that equals to the native MBC effectively regulated the root architecture and supported increasing nitrogen absorption and metabolism in plants growing under carbon-restricted conditions.

The newly synthesized plant growth regulator S-methylmethionine salicylate may provide protection against high salinity in wheat

High salinity is one of the major environmental factors limiting the productivity of crop species worldwide. Improving the stress tolerance of cultivated plants and thus increasing crop yields in an environmentally friendly way is a crucial task in agriculture. In the present work the ability of a new derivative, S-methylmethionine-salicylate (MMS), to improve the salt tolerance of wheat plants was tested parallel with its related compounds salicylic acid and S-methylmethionine. The results show that while these compounds are harmful at relatively high concentration (0.5 mM), they may provide protection against high salinity at lower (0.1 mM) concentration. This was confirmed by gas exchange, chlorophyll content and chlorophyll-a fluorescence induction measurements. While osmotic adjustment probably plays a critical role in the improved salt tolerance, neither Na or K transport from the roots to the shoots nor proline synthesis are the main factors in the tolerance induced by the compounds tested. MMS, S-methylmethionine and Na-salicylate had different effects on flavonol biosynthesis. It was also shown that salt treatment had a substantial influence on the SA metabolism in wheat roots and leaves. Present results suggest that the investigated compounds can be used to improve salt tolerance in plants.

Mechanism exploration on nitrogen metabolism and secondary metabolism in Atropa belladonna hairy roots treated with yeast extract

In order to study the mechanism of nitrogen metabolism and secondary metabolism in Atropa belladonna hairy roots treated with yeast extract, yeast extract（YE） was added to the culture medium. Then the changes of physiological and biochemical indexes of A. belladonna hairy roots after treatment with YE were detected. The results are as follows，the activity of key enzymes of nitrogen metabolism changed differently. Compared with the control group (CK), the activity of nitrate reductase (NR) and glutamine synthetase (GS) were significantly increased, while the activity of glutamate dehydrogenase (GDH) was not changed significantly. The content of nitrate nitrogen, ammonium nitrogen had a significant decrease,but the content of soluble protein, free amino acid, total nitrogen are significantly more than CK. Moreover, YE treatment led to the increase of the content precursor amino acids (ornithine and arginine) and precursor putrescine in secondary metabolic pathways of A. belladonna. The expression level of gene putrescine N-methyl transferase (pmt), tropinone reductase-I (trI) and hyoscyamine 6-β-hydroxylase(h6h) all increased in a different rate caused by YE treatment, which eventually led to the increase of the yield of tropane alkaloids. The yield of hyoscyamine and scopolamine were 3.09 and 1.85 folds than that of CK after 16 days treatment time. The results indicated that YE can induce more synthesis of tropane alkaloids by increasing the activity of key enzymes in nitrogen metabolism to provide more synthetic materials for secondary metabolism, meanwhile it regulated the expression level of some genes of key metabolic enzyme to accelerate secondary metabolism.

Effects of nitrogen forms on carbohydrate metabolism and storage‐root formation of sweet potato

AbstractIn this study, we examined the effects of different forms of nitrogen (N) fertilizer on carbohydrate metabolism and storage root formation in sweet potato [Ipomoea batatas L. (Lam.) cv. Shangshu 19 and cv. Jixu 23] in 2015–2016. Two fertilizer treatments, ammonium nitrogen (AN) and amide nitrogen (XN), were applied at 60 kg ha−1 in a two‐factor split‐plot design. The effects of nitrogen form on the morphology of adventitious roots, carbohydrate metabolism in potential storage roots, and number of storage roots per plant in sweet potato were investigated. The results show that during the early growth phase, the AN treatment significantly increased the number of adventitious roots, root tips, root length density, and fresh weight of roots (in pot trials). This treatment also significantly decreased the sucrose concentration of potential storage roots and increased the activities of cell wall, vacuolar, and cytoplasmic invertases. However, XN‐treated potential storage roots showed a relatively high starch concentration, activities of sucrose synthase and ADP‐glucose pyrophosphorylase, and transcription of sporamin genes. At the canopy closure period, the AN treatment significantly increased the number of storage roots of 0.5–5.0 cm in diameter and decreased the number of those &gt; 5 cm in diameter compared to the control. The XN treatment induced the opposite effects. In the harvesting period, the AN treatment produced the highest storage root yield and number of storage roots per plant. Thus, in field trials the AN treatment induced a greater increase in production by increasing the number of storage roots.

Up‐regulation of PR1 and less disruption of hormone and sucrose metabolism in roots is associated with lower susceptibility to ‘Candidatus Liberibacter asiaticus’

Huanglongbing (HLB), caused by ‘Candidatus Liberibacter asiaticus’ (Las), is a devastating disease of citrus trees in Florida. Previous work showed that the rootstock cultivar Cleopatra mandarin (Citrus reticulata) has a higher population of Las in roots than Swingle citrumelo (C. paradisi × Poncirus trifoliata). Las reduced fibrous root biomass and sucrose content in Cleopatra mandarin more than in Swingle citrumelo. To understand the mechanisms for susceptibility to Las infection, sucrose and hormone metabolism status were evaluated in Cleopatra mandarin and Swingle citrumelo. In fibrous roots of Cleopatra mandarin, higher expression of genes related to sucrose cleavage was consistent with lower sucrose content compared to noninoculated seedlings at 5 weeks post‐root trimming (wpt). In fibrous roots of Swingle citrumelo, both sucrose content and gene expression related to sucrose cleavage were less disrupted by Las infection compared to Cleopatra mandarin at 5 wpt. Genes associated with salicylic acid (SA), ethylene (ET) and abscisic acid (ABA) synthesis, and ABA signalling, phospholipases D (PLD), and phospholipase A2 (PLA2) were activated by Las infection at 5 wpt in Cleopatra mandarin. Expression of downstream effectors of SA, i.e. NPR1, WRKY70 and PR1, did not change in Cleopatra mandarin, suggesting inhibition of the response to SA by the elevation of ABA, ET and PLD. In contrast, the up‐regulation of PR1, lower response of sucrose metabolism genes and down‐regulation of biosynthesis of phytohormones indicates that Swingle citrumelo activates a more effective defence against this biotrophic pathogen than Cleopatra mandarin.

Formation of a subero-lignified apical deposit in root tip of radish (Raphanus sativus) as a response to copper stress.

Heavy metals induce changes in root metabolism and physiology, which can lead to a complex remodelling of the root system. The final morphological responses of radish (Raphanus sativus) roots exposed to toxic concentrations of the heavy metal (Cu) include root growth inhibition, differentiation of xylem vessels close to the root tip, enhanced suberin lamellae deposition and enhanced lateral root production. Recently, we have found that such changes in root morphology and anatomy are coupled to the formation of a subero-lignified apical deposit (SLAD) very close to the root tip. To clarify the details of the formation of a SLAD in the root tip, we conducted experiments with radish roots exposed to a high Cu concentration (60 µm). Histochemical analysis of lignin and suberin as well as analysis of spatial-temporal characteristics of SLAD formation were performed by bright-field, fluorescence and confocal microscopy. This unique structure, not longer than 100 µm, consists of modified cell walls of the central cylinder that are encircled by a short cylinder of prematurely suberized endodermal cells. A SLAD starts to form, in both primary and lateral roots, after cessation of root elongation, and it is coupled with xylem differentiation and root branching close to the root apex. We noticed that deposition of phenolic substances into a SLAD, mainly suberin in the endodermis, is spatially separated from suberization or lignification in basally located endodermis. Although the main reason for formation of a SLAD is elusive, we suggest that it is a part of stress-induced responses which relate to decreased root growth or permeability in heavy metal stress.

Construction of a network describing asparagine metabolism in plants and its application to the identification of genes affecting asparagine metabolism in wheat under drought and nutritional stress.

A detailed network describing asparagine metabolism in plants was constructed using published data from Arabidopsis (Arabidopsis thaliana) maize (Zea mays), wheat (Triticum aestivum), pea (Pisum sativum), soybean (Glycine max), lupin (Lupus albus), and other species, including animals. Asparagine synthesis and degradation is a major part of amino acid and nitrogen metabolism in plants. The complexity of its metabolism, including limiting and regulatory factors, was represented in a logical sequence in a pathway diagram built using yED graph editor software. The network was used with a Unique Network Identification Pipeline in the analysis of data from 18 publicly available transcriptomic data studies. This identified links between genes involved in asparagine metabolism in wheat roots under drought stress, wheat leaves under drought stress, and wheat leaves under conditions of sulfur and nitrogen deficiency. The network represents a powerful aid for interpreting the interactions not only between the genes in the pathway but also among enzymes, metabolites and smaller molecules. It provides a concise, clear understanding of the complexity of asparagine metabolism that could aid the interpretation of data relating to wider amino acid metabolism and other metabolic processes.