Methyl jasmonate alters N partitioning, N reserves accumulation and induces gene expression of a 32-kDa vegetative storage protein that possesses chitinase activity in Medicago sativa taproots

Histological, chemical and gene expression differences between western redcedar seedlings resistant and susceptible to cedar leaf blight

Introduction

Western redcedar (Thuja plicata) is an important species in the Cupressaceae both at economic and cultural levels in the Pacific Northwest of North America. In adult trees, the species produces one of the most weathering-resistant heartwoods among conifers, making it one of the preferred species for outdoor applications. However, young T. plicata plants are susceptible to infection with cedar leaf blight (Didymascella thujina), an important foliar pathogen that can be devastating in nurseries and small-spaced plantations. Despite that, variability in the resistance against D. thujina in T. plicata has been documented, and such variability can be used to breed T. plicata for resistance against the pathogen.

Objective

This investigation aimed to discern the phenotypic and gene expression differences between resistant and susceptible T. plicata seedlings to shed light on the potential constitutive resistance mechanisms against cedar leaf blight in western redcedar.

Methods

The study consisted of two parts. First, the histological differences between four resistant and four susceptible families that were never infected with the pathogen were investigated. And second, the differences between one resistant and one susceptible family that were infected and not infected with the pathogen were analyzed at the chemical (C, N, mineral nutrients, lignin, fiber, starch, and terpenes) and gene expression (RNA-Seq) levels.

Results

The histological part showed that T. plicata seedlings resistant to D. thujina had constitutively thicker cuticles and lower stomatal densities than susceptible plants. The chemical analyses revealed that, regardless of their infection status, resistant plants had higher foliar concentrations of sabinene and α-thujene, and higher levels of expression of transcripts that code for leucine-rich repeat receptor-like protein kinases and for bark storage proteins.

Conclusion

The data collected in this study shows that constitutive differences at the phenotypic (histological and chemical) and gene expression level exist between T. plicata seedlings susceptible and resistant to D. thujina. Such differences have potential use for marker-assisted selection and breeding for resistance against cedar leaf blight in western redcedar in the future.

Defense Priming in Nicotiana tabacum Accelerates and Amplifies 'New' C/N Fluxes in Key Amino Acid Biosynthetic Pathways

In the struggle to survive herbivory by leaf-feeding insects, plants employ multiple strategies to defend themselves. One mechanism by which plants increase resistance is by intensifying their responsiveness in the production of certain defense agents to create a rapid response. Known as defense priming, this action can accelerate and amplify responses of metabolic pathways, providing plants with long-lasting resistance, especially when faced with waves of attack. In the work presented, short-lived radiotracers of carbon administered as 11CO2 and nitrogen administered as 13NH3 were applied in Nicotiana tabacum, to examine the temporal changes in 'new' C/N utilization in the biosynthesis of key amino acids (AAs). Responses were induced by using topical application of the defense hormone jasmonic acid (JA). After a single treatment, metabolic partitioning of recently fixed carbon (designated 'new' carbon and reflected as 11C) increased through the shikimate pathway, giving rise to tyrosine, phenylalanine and tryptophan. Amplification in 'new' carbon fluxes preceded changes in the endogenous (12C) pools of these AAs. Testing after serial JA treatments revealed that fluxes of 'new' carbon were accelerated, amplified and sustained over time at this higher rate, suggesting a priming effect. Similar results were observed with recently assimilated nitrogen (designated 'new' nitrogen reflected as 13N) with its partitioning into serine, glycine and glutamine, which play important roles supporting the shikimate pathway and downstream secondary metabolism. Finally, X-ray fluorescence imaging revealed that levels of the element Mn, an important co-factor for enzyme regulation in the shikimate pathway, increased within JA treated tissues, suggesting a link between plant metal ion regulation and C/N metabolic priming.

Proteomics (SWATH-MS) informed by transcriptomics approach of tropical herb Persicaria minor leaves upon methyl jasmonate elicitation

BACKGROUND

Jasmonic acid (JA) and its derivative, methyl JA (MeJA) are hormonal cues released by plants that signal defense response to curb damages from biotic and abiotic stresses. To study such response, a tropical herbal plant, Persicaria minor, which possesses pungent smell and various bioactivities including antimicrobial and anticancer, was treated with MeJA. Such elicitation has been performed in hairy root cultures and plants such as Arabidopsis and rice, yet how MeJA influenced the proteome of an herbal species like P. minor is unknown.

METHOD

In this study, P. minor plants were exogenously elicited with MeJA and leaf samples were subjected to SWATH-MS proteomics analysis. A previously published translated transcriptome database was used as a reference proteome database for a comprehensive protein sequence catalogue and to compare their differential expression.

RESULTS

From this proteomics informed by transcriptomics approach, we have successfully profiled 751 proteins of which 40 proteins were significantly different between control and MeJA-treated samples. Furthermore, a correlation analysis between both proteome and the transcriptome data sets suggests that significantly upregulated proteins were positively correlated with their cognate transcripts (Pearson's r = 0.677) while a weak correlation was observed for downregulated proteins (r = 0.147).

DISCUSSION

MeJA treatment induced the upregulation of proteins involved in various biochemical pathways including stress response mechanism, lipid metabolism, secondary metabolite production, DNA degradation and cell wall degradation. Conversely, proteins involved in energy expensive reactions such as photosynthesis, protein synthesis and structure were significantly downregulated upon MeJA elicitation. Overall protein-transcript correlation was also weak (r = 0.341) suggesting the existence of post-transcriptional regulation during such stress. In conclusion, proteomics analysis using SWATH-MS analysis supplemented by the transcriptome database allows comprehensive protein profiling of this non-model herbal species upon MeJA treatment.

Three members of Medicago truncatula ST family are ubiquitous during development and modulated by nutritional status (MtST1) and dehydration (MtST2 and MtST3)

BACKGROUND

ShooT specific/Specific Tissue (ST) belong to a protein family of unknown function characterized by the DUF2775 domain and produced in specific taxonomic plant families, mainly Fabaceae and Asteraceae, with the Medicago truncatula ST family being the largest. The putative roles proposed for this family are cell elongation, biotic interactions, abiotic stress and N reserve. The aim of this work was to go deeper into the role of three M. truncatula ST proteins, namely ST1, ST2 and ST3. Our starting hypothesis was that each member of the family could perform a specific role, and hence, each ST gene would be subjected to a different type of regulation.

RESULTS

The search for cis-acting regulatory elements (CREs) in silico in pST1, pST2 and pST3 promoters showed prevalence of tissue/organ specific motifs, especially root- and seed-specific ones. Light, hormone, biotic and abiotic related motifs were also present. None of these pSTs showed the same combination of CREs, or presented the same activity pattern. In general, pST activity was associated with the vascular cylinder, mainly in roots. Promoter activation was highly specific and dissimilar during reproductive development. The ST1, ST2 and ST3 transcripts accumulated in most of the organs and developmental stages analysed - decreasing with age - and expression was higher in the roots than in the aerial parts and more abundant in light-grown plants. The effect of the different treatments on transcript accumulation indicated that ST1 behaved differently from ST2 and ST3, mainly in response to several hormones and dehydration treatments (NaCl or mannitol), upon which ST1 transcript levels decreased and ST2 and ST3 levels increased. Finally, the ST1 protein was located in the cell wall whereas ST2 and ST3 were present both in the cytoplasm and in the cell wall.

CONCLUSIONS

The ST proteins studied are ubiquitous proteins that could perform distinct/complementary roles in plant biology as they are encoded by differentially regulated genes. Based on these differences we have established two functional groups among the three STs. ST1 would participate in processes affected by nutritional status, while ST2 and ST3 seem to act when plants are challenged with abiotic stresses related to water stress and in physiologically controlled desiccation processes such as the seed maturation.

A case of neofunctionalization of a Putranjiva roxburghii PNP protein to trypsin inhibitor by disruption of PNP-UDP domain through an insert containing inhibitory site

The attainment of new function by a protein is achieved through convergent/divergent evolution. In present work, the sequence analysis of a 34kDa protein from Putranjiva roxburghii, earlier reported as a potent trypsin inhibitor, showed resemblance to some of the wound inducible and vegetative storage proteins. A detailed sequence analysis revealed that these proteins belong to PNP-UDP family. In case of P. roxburghii protein, an approximately 46 residue insert disrupts the PNP domain. Similar disruption of PNP domain is observed in related plant proteins. The characterization of recombinant full length and truncated (without 46 residue insert) forms of P. roxburghii PNP family protein (PRpnp) unraveled that trypsin inhibitory active site is located within the insert. The truncated form containing uninterrupted PNP domain showed strong PNP enzymatic activity where it hydrolyzed the N-glycosidic bond of inosine and guanosine. The full length protein, however, showed weak PNP enzyme activity which may be due to presence of the insert. These results indicate towards the neofunctionalization of PRpnp to a potent trypsin inhibitor through an insert containing inhibitory residue to cater to the needs of plant defense. The similar wound inducible and vegetative storage proteins may have also evolved due to evolutionary needs.

Transcriptomic Analysis of Responses to Imbalanced Carbon: Nitrogen Availabilities in Rice Seedlings

The internal C:N balance must be tightly controlled for the normal growth and development of plants. However, the underlying mechanisms, by which plants sense and balance the intracellular C:N status correspondingly to exogenous C:N availabilities remain elusive. In this study, we use comparative gene expression analysis to identify genes that are responsive to imbalanced C:N treatments in the aerial parts of rice seedlings. Transcripts of rice seedlings treated with four C:N availabilities (1:1, 1:60, 60:1 and 60:60) were compared and two groups of genes were classified: high C:low N responsive genes and low C:high N responsive genes. Our analysis identified several functional correlated genes including chalcone synthase (CHS), chlorophyll a-b binding protein (CAB) and other genes that are implicated in C:N balancing mechanism, such as alternative oxidase 1B (OsAOX1B), malate dehydrogenase (OsMDH) and lysine and histidine specific transporter 1 (OsLHT1). Additionally, six jasmonate synthetic genes and key regulatory genes involved in abiotic and biotic stresses, such as OsMYB4, autoinhibited calcium ATPase 3 (OsACA3) and pleiotropic drug resistance 9 (OsPDR9), were differentially expressed under high C:low N treatment. Gene ontology analysis showed that high C:low N up-regulated genes were primarily enriched in fatty acid biosynthesis and defense responses. Coexpression network analysis of these genes identified eight jasmonate ZIM domain protein (OsJAZ) genes and several defense response related regulators, suggesting that high C:low N status may act as a stress condition, which induces defense responses mediated by jasmonate signaling pathway. Our transcriptome analysis shed new light on the C:N balancing mechanisms and revealed several important regulators of C:N status in rice seedlings.

Genome-wide analysis and differential expression of chitinases in banana against root lesion nematode (Pratylenchus coffeae) and eumusa leaf spot (Mycosphaerella eumusae) pathogens

Knowledge on structure and conserved domain of Musa chitinase isoforms and their responses to various biotic stresses will give a lead to select the suitable chitinase isoform for developing biotic stress-resistant genotypes. Hence, in this study, chitinase sequences available in the Musa genome hub were analyzed for their gene structure, conserved domain, as well as intron and exon regions. To identify the Musa chitinase isoforms involved in Pratylenchus coffeae (root lesion nematode) and Mycosphaerella eumusae (eumusa leaf spot) resistant mechanisms, differential gene expression analysis was carried out in P. coffeae- and M. eumusae-challenged resistant and susceptible banana genotypes. This study revealed that more number of chitinase isoforms (CIs) were responses upon eumusa leaf spot stress than nematode stress. The nematode challenge studies revealed that class II chitinase (GSMUA_Achr9G16770_001) was significantly overexpressed with 6.75-fold (with high fragments per kilobase of exon per million fragments mapped (FPKM)) in resistant genotype (Karthobiumtham-ABB) than susceptible (Nendran-AAB) genotype, whereas when M. eumusae was challenge inoculated, two class III CIs (GSMUA_Achr9G25580_001 and GSMUA_Achr8G27880_001) were overexpressed in resistant genotype (Manoranjitham-AAA) than the susceptible genotype (Grand Naine-AAA). However, none of the CIs were found to be commonly overexpressed under both stress conditions. This study reiterated that the chitinase genes are responding differently to different biotic stresses in their respective resistant genotypes.

Nodule performance within a changing environmental context

Global climate models predict that future environmental conditions will see alterations in temperature, water availability and CO2 concentration ([CO2]) in the atmosphere. Climate change will reinforce the need to develop highly productive crops. For this purpose it is essential to identify target traits conditioning plant performance in changing environments. N2 fixing plants represent the second major crop of agricultural importance worldwide. The current review provides a compilation of results from existing literature on the effects of several abiotic stress conditions on nodule performance and N2 fixation. The environmental factors analysed include water stress, salinity, temperature, and elevated [CO2]. Despite the large number of studies analysing [CO2] effects in plants, frequently they have been conducted under optimal growth conditions that are difficult to find in natural conditions where different stresses often occur simultaneously. This is why we have also included a section describing the current state of knowledge of interacting environmental conditions in nodule functioning. Regardless of the environmental factor considered, it is evident that some general patterns of nodule response are observed. Nodule carbohydrate and N compound availability, together with the presence of oxygen reactive species (ROS) have proven to be the key factors modulating N2 fixation at the physiological/biochemical levels. However, with the exception of water availability and [CO2], it should also be considered that nodule performance has not been characterised in detail under other limiting growth conditions. This highlights the necessity to conduct further studies considering these factors. Finally, we also observe that a better understanding of these metabolic effects of changing environment in nodule functioning would require an integrated and synergistic investigation based on widely used and novel protocols such as transcriptomics, proteomics, metabolomics and stable isotopes.

ScChi, encoding an acidic class III chitinase of sugarcane, confers positive responses to biotic and abiotic stresses in sugarcane

Chitinases (EC 3.2.2.14), expressed during the plant-pathogen interaction, are associated with plant defense against pathogens. In the present study, a positive correlation between chitinase activity and sugarcane smut resistance was found. ScChi (GenBank accession no. KF664180), a Class III chitinase gene, encoded a 31.37 kDa polypeptide, was cloned and identified. Subcellular localization revealed ScChi targeting to the nucleus, cytoplasm and the plasma membrane. Real-time quantitative PCR (RT-qPCR) results showed that ScChi was highly expressed in leaf and stem epidermal tissues. The ScChi transcript was both higher and maintained longer in the resistance cultivar during challenge with Sporisorium scitamineum. The ScChi also showed an obvious induction of transcription after treatment with SA (salicylic acid), H2O2, MeJA (methyl jasmonate), ABA (abscisic acid), NaCl, CuCl2, PEG (polyethylene glycol) and low temperature (4 °C). The expression levels of ScChi and six immunity associated marker genes were upregulated by the transient overexpression of ScChi. Besides, histochemical assay of Nicotiana benthamiana leaves overexpressing pCAMBIA 1301-ScChi exhibited deep DAB (3,3'-diaminobenzidinesolution) staining color and high conductivity, indicating the high level of H2O2 accumulation. These results suggest a close relationship between the expression of ScChi and plant immunity. In conclusion, the positive responses of ScChi to the biotic and abiotic stimuli reveal that this gene is a stress-related gene of sugarcane.

Differences in the arbuscular mycorrhizal fungi-improved rice resistance to low temperature at two N levels: aspects of N and C metabolism on the plant side

We performed an experiment to determine how N and C metabolism is involved in the low-temperature tolerance of mycorrhizal rice (Oryza sativa) at different N levels and examined the possible signaling molecules involved in the stress response of mycorrhizal rice. Pot cultures were performed, and mycorrhizal rice growth was evaluated based on treatments at two temperatures (15 °C and 25 °C) and two N levels (20 mg pot(-1) and 50 mg pot(-1)). The arbuscular mycorrhizal fungi (AMF) colonization of rice resulted in different responses of the plants to low and high N levels. The mycorrhizal rice with the low N supplementation had more positive feedback from the symbiotic AMF, as indicated by accelerated N and C metabolism of rice possibly involving jasmonic acid (JA) and the up-regulation of enzyme activities for N and C metabolism. Furthermore, the response of the mycorrhizal rice plants to low temperature was associated with P uptake and nitric oxide (NO).

Flexible resource allocation during plant defense responses

Plants are organisms composed of modules connected by xylem and phloem transport streams. Attack by both insects and pathogens elicits sometimes rapid defense responses in the attacked module. We have also known for some time that proteins are often reallocated away from pathogen-infected tissues, while the same infection sites may draw carbohydrates to them. This has been interpreted as a tug of war in which the plant withdraws critical resources to block microbial growth while the microbes attempt to acquire more resources. Sink-source regulated transport among modules of critical resources, particularly carbon and nitrogen, is also altered in response to attack. Insects and jasmonate can increase local sink strength, drawing carbohydrates that support defense production. Shortly after attack, carbohydrates may also be drawn to the root. The rate and direction of movement of photosynthate or signals in phloem in response to attack is subject to constraints that include branching, degree of connection among tissues, distance between sources and sinks, proximity, strength, and number of competing sinks, and phloem loading/unloading regulators. Movement of materials (e.g., amino acids, signals) to or from attack sites in xylem is less well understood but is partly driven by transpiration. The root is an influential sink and may regulate sink-source interactions and transport above and below ground as well as between the plant and the rhizosphere and nearby, connected plants. Research on resource translocation in response to pathogens or herbivores has focused on biochemical mechanisms; whole-plant research is needed to determine which, if any, of these plant behaviors actually influence plant fitness.

Novel application of 2-[(18)F]fluoro-2-deoxy-D-glucose to study plant defenses

INTRODUCTION

Since its first use in humans in 1976, 2-[¹⁸F]fluoro-2-deoxy-d-glucose (¹⁸FDG) continues to serve as a tracer to measure tissue glucose metabolism in medical imaging. Here we demonstrate a novel use for this tracer to study glycoside biosynthesis in plants as a measure of plant response to defense induction.

METHODS

Coupling autoradiography with radio high-performance liquid chromatography analysis of tissue extracts, we examined the combined effects of leaf wounding and treatment using the potent plant defense hormone, methyl jasmonate (MeJA), to measure tracer distribution and tracer use in secondary defense chemistry in Arabidopsis thaliana. We hypothesized that competing sinks like roots and reproductive tissues, as well as vascular architecture, would impact the induction of phenolic defenses of the plant that make use of glucose in glycoside formation by altering distribution and metabolic utilization of ¹⁸FDG.

RESULTS

Our studies showed that leaf orthostichy defined the major route of ¹⁸FDG transport in both vegetative and reproductive plants when a single petiole was cut as the entry point for tracer introduction. However, when nonorthostichous leaves were damaged and treated with MeJA, ¹⁸FDG was transported in its intact form to these leaves 3 h later, where it was incorporated into phenolic glycosides.

CONCLUSIONS

Our work demonstrates a new use for ¹⁸FDG in plant science with insights into carbohydrate allocation that contradict conclusions of previous studies showing transport of resources away from damaged sites.

Integrated transcriptomic and proteomic profiling of white spruce stems during the transition from active growth to dormancy

In the autumn, stems of woody perennials such as forest trees undergo a transition from active growth to dormancy. We used microarray transcriptomic profiling in combination with a proteomics analysis to elucidate processes that occur during this growth-to-dormancy transition in a conifer, white spruce (Picea glauca[Moench] Voss). Several differentially expressed genes were likely associated with the developmental transition that occurs during growth cessation in the cambial zone and the concomitant completion of cell maturation in vascular tissues. Genes encoding for cell wall and membrane biosynthetic enzymes showed transcript abundance patterns consistent with completion of cell maturation, and also of cell wall and membrane modifications potentially enabling cells to withstand the harsh conditions of winter. Several differentially expressed genes were identified that encoded putative regulators of cambial activity, cell development and of the photoperiodic pathway. Reconfiguration of carbon allocation figured centrally in the tree's overwintering preparations. For example, genes associated with carbon-based defences such as terpenoids were down-regulated, while many genes associated with protein-based defences and other stress mitigation mechanisms were up-regulated. Several of these correspond to proteins that were accumulated during the growth-to-dormancy transition, emphasizing the importance of stress protection in the tree's adaptive response to overwintering.

Multiple biological functions of sporamin related to stress tolerance in sweet potato (Ipomoea batatas Lam)

The initial investigation of the nature of the proteins in the tuber of sweet potato (Ipomoea batatas Lam.) revealed a globulin-designated "ipomoein," which was reported by Jones and Gersdorff, (1931). Later, "ipomoein" was renamed "sporamin" and was found to be a major storage protein that accounted for over 80% of the total protein in the tuberous root. To date, sporamin has been studied by a series of biochemical and molecular approaches. The first purification of sporamin into two major fractions, A and B, was successfully completed in 1985. Several characteristics of the protein, such as the diversification of the nucleotide sequences in the gene family, the protein structure, the biological functions of storage, defense, inhibitory activity and ROS scavenging, were identified. In the past decade, sporamin was classified as a Kunitz-type trypsin inhibitor, and its insect-resistance capability has been examined in transgenic tobacco and cauliflower plants, indicating the multiple functions of this protein has evolved to facilitate the growth and development of sweet potato. Sporamin is constitutively expressed in the tuberous root and is not normally expressed in the stem or leaves. However, this protein is expressed systemically in response to wounding and other abiotic stresses. These dual expression patterns at the transcriptional level revealed that the complex regulatory mechanism of sporamin was modulated by environmental stresses. The versatile functions of sporamin make this storage protein a good research model to study molecular evolution, regulatory mechanisms and physiological functions in plants. This review summarizes and discusses recent approaches and future perspectives in agricultural biotechnology.

A comparative proteomic analysis of the early response to compatible symbiotic bacteria in the roots of a supernodulating soybean variety

To reveal the processes involved in the early stages of symbiosis between soybean plants and root nodule bacteria, we conducted a proteomic analysis of the response to bacterial inoculation in the roots of supernodulating (En-b0-1) and non-nodulating (En1282) varieties, and their parental normal-nodulating variety (Enrei). A total of 56 proteins were identified from 48 differentially expressed protein spots in normal-nodulating variety after bacterial inoculation. Among 56 proteins, metabolism- and energy production-related proteins were upregulated in supernodulating and downregulated in non-nodulating varieties compared to normal-nodulating variety. The supernodulating and non-nodulating varieties responded oppositely to bacterial inoculation with respect to the expression of 11 proteins. Seven proteins of these proteins was downregulated in supernodulating varieties compared to non-nodulating variety, but expression of proteasome subunit alpha type 6, gamma glutamyl hydrolase, glucan endo-1,3-beta glucosidase, and nodulin 35 was upregulated. The expression of seven proteins mirrored the degree of nodule formation. At the transcript level, expression of stem 31kDa glycoprotein, leucine aminopeptidase, phosphoglucomutase, and peroxidase was downregulated in the supernodulating variety compared to the non-nodulating variety, and their expression in the normal-nodulating variety was intermediate. These results suggest that suppression of the autoregulatory mechanism in the supernodulating variety might be due to negative regulation of defense and signal transduction-related processes.

Photosynthesis, N(2) fixation and taproot reserves during the cutting regrowth cycle of alfalfa under elevated CO(2) and temperature

Future climatic conditions, including rising atmospheric CO(2) and temperature may increase photosynthesis and, consequently, plant production. A larger knowledge of legume performance under the predicted growth conditions will be crucial for safeguarding crop management and extending the area under cultivation with these plants in the near future. N(2) fixation is a key process conditioning plant responsiveness to varying growth conditions. Moreover, it is likely to increase under future environments, due to the higher photosynthate availability, as a consequence of the higher growth rate under elevated CO(2). However, as described in the literature, photosynthesis performance is frequently down-regulated (acclimated) under long-term exposure to CO(2), especially when affected by stressful temperature and water availability conditions. As growth responses to elevated CO(2) are dependent on sink-source status, it is generally accepted that down-regulation occurs in situations with insufficient plant C sink capacity. Alfalfa management involves the cutting of shoots, which alters the source-sink relationship and thus the photosynthetic behaviour. As the growth rate decreases at the end of the pre-cut vegetative growth period, nodulated alfalfa plants show photosynthetic down-regulation, but during regrowth following defoliation, acclimation to elevated CO(2) disappears. The shoot harvest also leads to a drop in mineral N uptake and C translocation to the roots, resulting in a reduction in N(2) fixation due to the dependence on photosynthate supply to support nodule function. Therefore, the production of new shoots during the first days following cutting requires the utilization of reduced C and N compounds that have been stored previously in reserve organs. The stored reserves are mediated by phytohormones such as methyl jasmonate and abscisic acid and in situations where water stress reduces shoot production this potentially enables the enhancement of taproot protein levels in nodulated alfalfa, which may lead to these plants being in better condition in the following cut/regrowth cycle. Furthering our knowledge of legume performance under predicted climate change conditions will be crucial for the development of varieties with better adaptation that will achieve greater and more efficient production values. Furthermore, for this purpose it will be necessary to improve existing methodologies and create new ones for phenotype characterization. Such knowledge will provide key information for future plant breeding programs.

Herbivore-induced resource sequestration in plants: why bother?

Herbivores can cause numerous changes in primary plant metabolism. Recent studies using radioisotopes, for example, have found that insect herbivores and related cues can induce faster export from leaves and roots and greater partitioning into tissues inaccessible to foraging herbivores. This process, termed induced resource sequestration, is being proposed as an important response of plants to cope with herbivory. Here, we review the evidence for resource sequestration and suggest that associated allocation and ecological costs may limit the benefit of this response because resources allocated to storage are not immediately available to other plant functions or may be consumed by other enemies. We then present a conceptual model that describes the conditions under which benefits might outweigh costs of induced resource sequestration. Benefits and costs are discussed in the context of differences in plant life-history traits and biotic and abiotic conditions, and new testable hypotheses are presented to guide future research. We predict that intrinsic factors related to life history, ontogeny and phenology will alter patterns of induced sequestration. We also predict that induced sequestration will depend on certain external factors: abiotic conditions, types of herbivores, and trophic interactions. We hope the concepts presented here will stimulate more focused research on the ecological and evolutionary costs and benefits of herbivore-induced resource sequestration.

Stability of AtVSP in the insect digestive canal determines its defensive capability

We have previously demonstrated that Arabidopsis vegetative storage protein (AtVSP) is an acid phosphatase that has anti-insect activity in in vitro feeding assays [Liu et al., 2005. Plant Physiology 139, 1545-1556]. To investigate the functionality of AtVSP in planta as an anti-insect defense protein, we produced AtVSP-overexpressing as well as AtVSP-silenced transgenic Arabidopsis lines, and evaluated impact on the polyphagous American grasshopper Schistocerca americana. Grasshoppers showed no significant difference in weight gain and growth rate when feeding on wild type, overexpressing, or silenced lines, respectively. In addition, AtVSP protein was undetectable in either the midgut or frass of grasshoppers reared on transgenic plants suggesting that AtVSP was unable to withstand proteolytic degradation. To determine the stability of the AtVSP protein in grasshopper digestive canal, midgut extracts from various nymphal stages were incubated with bacterially expressed AtVSP for different periods of time. AtVSP was hydrolyzed rapidly by grasshopper midgut extract, in stark contrast with its fate when incubated with cowpea bruchid midgut extract. Multiple proteases have been detected in the midgut of grasshoppers, which may play important roles in determining the insect response to AtVSP. Results indicate that stability of an anti-insect protein in insect guts is a crucial property integral to the defense protein.

Chestnut species and jasmonic acid treatment influence development and community interactions of galls produced by the Asian chestnut gall wasp, Dryocosmus kuriphilus

Jasmonic acid (JA) is a plant-signaling hormone involved in defenses against insects and pathogens as well as the regulation of nutrient partitioning. Gall wasps (Hymenoptera: Cynipidae) induce the formation of galls on their host plants, which house immature wasps and provide them with nutrition and protection. The goal of this study was to investigate the effects of JA application on gall development and defenses. Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae) galls on American chestnut, Castanea dentata (Marsh.) Borkhausen (Fagales: Fagaceae), and Chinese chestnut, C. mollissima Blume, were treated with JA or a JA- inhibitor, diethyldithiocarbamic acid (DIECA), to determine the effects of these treatments on gall characteristics and defenses. Chinese chestnut galls treated with JA had greater volume and dry weight, thicker sclerenchyma layers, and fewer external fungal lesions compared with controls. Galls from both chestnut species treated with JA contained a lower proportion of empty chambers, and elevated tannin levels compared with controls. The effects of DIECA on galls were generally opposite from those of JA. American chestnut galls treated with DIECA had lower dry weight and fewer feeding punctures caused by the lesser chestnut weevil compared with controls. Galls from both chestnut species that were treated with DIECA were smaller and had more external fungal lesions compared with controls. Compared to American chestnut galls, Chinese chestnut galls had increased parasitism rates and fewer gall wasps. This study is the first to investigate the effects of JA on an insect gall, and indicates that JA treatments benefit gall wasps by increasing gall size and defenses.

Methyl jasmonate elicits rapid changes in carbon and nitrogen dynamics in tomato

• Evidence is emerging to support the notion that in response to herbivory, plants undergo changes in their primary metabolism and are able to fine-tune the allocation of new and existing resources and temporarily direct them to storage organs. • We hypothesized that simulated herbivory increases the export of resources out of the affected tissues and increases allocation to roots. We used short-lived radioisotopes to study in vivo the dynamics of newly incorporated (11)CO(2) and (13)NH(3). Methyl jasmonate (MeJA), a known defense elicitor, was applied to the foliage of tomato plants and 4 h later we monitored leaf uptake, export and whole-plant allocation of [(11)C]photosynthate and [(13)N]amino acids. • There was a marginally significant decrease in the fixation of (11)CO(2), and an increase in the export of newly acquired carbon and nitrogen out of MeJA-treated leaves. The proportion of nitrogen allocated to roots increased, whereas the proportion of carbon did not change. • These results are in agreement with our hypotheses, showing a change in the allocation of resources after treatment with MeJA; this may reduce the chance of resources being lost to herbivores and act as a buffer to biotic stress by increasing the potential for plant regrowth and survival after the attack.

Partitioning of new carbon as ¹¹C in Nicotiana tabacum reveals insight into methyl jasmonate induced changes in metabolism

We examined the timeline by which methyl jasmonate (MeJA) reprograms new carbon partitioning into key metabolite pools. The radioactive isotope ¹¹C (t(¹/₂) 20.4 min), administered to intact leaves of Nicotiana tabacum L. (cv Samsun) as ¹¹CO(2) gas enabled us to measure changes in new carbon partitioning into soluble sugar and amino acid pools of [¹¹C]photosynthate. A 500 μM MeJA treatment resulted in a decrease in the [¹¹C]soluble sugar pool and an increase in the [¹¹C]amino acid pool after 4 h. This pattern was more pronounced 15 h after treatment. We also examined the timeline for ¹¹C-partitioning into aromatic amino acid metabolites of the shikimate pathway. [¹¹C]Tyrosine, [C¹¹C]phenylalanine and [¹¹C]tryptophan were elevated 1.5-fold, 12-fold and 12-fold, respectively, relative to controls, 4 h after MeJA treatment, while endogeneous pools were unchanged. This suggests that only new carbon is utilized during early stages of defense induction. By 15 h, [C¹¹C]tyrosine and [¹¹C]phenylalanine returned to baseline while [¹¹C]tryptophan was elevated 30-fold, suggesting that MeJA exerts selective control over the shikimate pathway. Finally, we measured trans-cinnamic acid levels as a gauge of downstream phenolic metabolism. Levels were unchanged 4 h after MeJA treatment relative to controls, but were increased 2-fold by 15 h, indicating a lag in response of secondary metabolism.

Potassium deficiency induces the biosynthesis of oxylipins and glucosinolates in Arabidopsis thaliana

BACKGROUND

Mineral fertilization and pest control are essential and costly requirements for modern crop production. The two measures go hand in hand because plant mineral status affects plant susceptibility to pests and vice versa. Nutrient deficiency triggers specific responses in plants that optimize nutrient acquisition and reprogram metabolism. K-deficient plants illustrate these strategies by inducing high-affinity K-uptake and adjusting primary metabolism. Whether and how K deficient plants also alter their secondary metabolism for nutrient management and defense is not known.

RESULTS

Here we show that K-deficient plants contain higher levels of the phytohormone jasmonic acid (JA), hydroxy-12-oxo-octadecadienoic acids (HODs) and 12-oxo-phytodienoic acid (OPDA) than K-sufficient plants. Up-regulation of the 13-LOX pathway in response to low K was evident in increased transcript levels of several biosynthetic enzymes. Indole and aliphatic glucosinolates accumulated in response to K-deficiency in a manner that was respectively dependent or independent on signaling through Coronatine-Insensitive 1 (COI1). Transcript and glucosinolate profiles of K-deficient plants resembled those of herbivore attacked plants.

CONCLUSIONS

Based on our results we propose that under K-deficiency plants produce oxylipins and glucosinolates to enhance their defense potential against herbivorous insects and create reversible storage for excess S and N.

The underestimated role of roots in defense against leaf attackers

Plants have evolved intricate strategies to withstand attacks by herbivores and pathogens. Although it is known that plants change their primary and secondary metabolism in leaves to resist and tolerate aboveground attack, there is little awareness of the role of roots in these processes. This is surprising given that plant roots are responsible for the synthesis of plant toxins, play an active role in environmental sensing and defense signaling, and serve as dynamic storage organs to allow regrowth. Hence, studying roots is essential for a solid understanding of resistance and tolerance to leaf-feeding insects and pathogens. Here, we highlight this function of roots in plant resistance to aboveground attackers, with a special focus on systemic signaling and insect herbivores.

Vegetative storage protein with trypsin inhibitor activity occurs in Sapindus mukorassi, a sapindaceae deciduous tree

A vegetative storage protein (VSP) with trypsin inhibitor activity in a deciduous tree, Sapindus mukorassi, was characterized by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western-blot, immuno-histochemical localization, light- and electro-microscopy, together with analysis of proteinase inhibitor activity of the purified VSP in vitro. There were two proteins with molecular masses of about 23 and 27 kDa in a relatively high content in the bark tissues of terminal branches of S. mukorassi in leafless periods. The proteins decreased markedly during young shoot development, indicating their role in seasonal nitrogen storage. Immuno-histochemical localization with the polyclonal antibodies raised against the 23 kDa protein demonstrated that the 23 kDa protein was the major component of protein inclusions in protein-storing cells. The protein inclusions were identified by protein-specific staining and should correspond to the electron-dense materials in different forms in the vacuoles of phloem parenchyma cells and phloem ray parenchyma cells under an electron microscope. So, the 23 kDa protein was a typical VSP in S. mukorassi. The 23 and 27 kDa proteins shared no immuno-relatedness, whereas the 23 kDa protein was immuno-related with the 22 kDa VSP in lychee and possessed trypsin inhibitor activity. The 23 kDa protein may confer dual functions: nitrogen storage and defense.

Proteomic analysis of soybean nodule cytosol

An isolation procedure for soybean (Glycine max L. cv Williams 82) nodule cytosol proteins was developed which greatly improved protein resolution by two-dimensional polyacrylamide gel electrophoresis. The most abundant proteins were selected and analyzed by mass spectrometry. The identified proteins were categorized by function (% of total proteins analyzed): carbon metabolism (28%), nitrogen metabolism (12%), reactive oxygen metabolism (12%) and vesicular trafficking (11%). The first three categories were expected based on the known physiological functions of the symbiotic nitrogen fixation process. The number of proteins involved in vesicular trafficking suggests a very active exchange of macromolecules and membrane components. Among the 69 identified proteins were the enzymes of the three carbon portion of glycolysis, which were further characterized to support their roles in the sucrose synthase pathway to provide malate for the bacteroids. Proteomic analysis provides a functional tool by which to understand and further investigate nodule function.

Vegetative storage protein in Litchi chinensis, a subtropical evergreen fruit tree, possesses trypsin inhibitor activity

BACKGROUND AND AIMS

Vegetative storage proteins (VSPs) are commonly bioactive in herbaceous plants but few VSPs with bioactivity have been identified in trees. In addition, information on the characterization of VSPs in evergreen trees is limited. The objective of this study was to characterize the VSPs with bioactivity in evergreen trees. Methods The VSP in lychee (Litchi chinensis), an evergreen fruit tree, was characterized by a combination of cytological, biochemical and molecular biological techniques.

KEY RESULTS

The VSP in lychee was a 22-kDa protein. It accumulated in the large central vacuoles of protein-storing cells (PSCs) in two distinguishable forms, granular and floccular. The PSCs were of a novel type. The 22-kDa protein is distributed in mature leaves, bark tissues of branches, trunk and large roots, paralleling the distribution of PSCs. Its homologues were present in mature seed. During young shoot development and fruiting, the 22-kDa protein decreased apparently, suggesting a nitrogen-storage function. The 22-kDa protein had several isoforms encoded by a small multigene family. One gene member, LcVSP1, was cloned. The LcVSP1 had no intron and contained a 675 bp open reading frame encoding a putative protein of 225 amino acids. LcVSP1 was homologous to Kunitz trypsin inhibitors. The 22-kDa protein inhibited trypsin and chymotrypsin, but had no inhibitory effect on subtilisin.

CONCLUSIONS

Lychee is rich in a 22-kDa VSP with trypsin inhibitor activity. The VSP plays an important role in nitrogen storage while its possible defensive function remains to be elucidated.

Elevated atmospheric CO2 and strain of rhizobium alter freezing tolerance and cold-induced molecular changes in alfalfa (Medicago sativa)

BACKGROUND AND AIMS

The objective of the study was to assess the impact of elevated CO2 in interaction with rhizobial strains on freezing tolerance and cold-induced molecular changes in alfalfa.

METHODS

Alfalfa inoculated with two different strains of rhizobium (A2 and NRG34) was grown and cold acclimated (2 weeks at 2 degrees C) under either 400 (ambient) or 800 micromol mol(-1) (elevated) CO2.

KEY RESULTS

Plants acclimated under 400 micromol mol(-1) CO2 were more freezing tolerant than those maintained under 800 micromol mol(-1). Cryoprotective sugars typically linked with the acquisition of freezing tolerance such as sucrose, stachyose and raffinose increased in roots in response to low temperature but did not differ between CO2 treatments. Similarly high CO2 did not alter the expression of many cold-regulated (COR) genes although it significantly increased the level of transcripts encoding a COR gene homologous to glyceraldehyde-3-phosphate-dehydrogenase (GAPDH). A significant effect of rhizobial strain was observed on both freezing tolerance and gene expression. Plants of alfalfa inoculated with strain A2 were more freezing tolerant than those inoculated with strain NRG34. Transcripts of COR genes homologous to a pathogenesis-related protein (PR-10) and to a nuclear-targeted protein were markedly enhanced in roots of alfalfa inoculated with strain A2 as compared with strain NRG34. Transcripts encoding the vegetative storage proteins (VSPs) beta-amylase and chitinase were more abundant in roots of non-acclimated plants inoculated with strain NRG34 than with strain A2.

CONCLUSIONS

Taken together, the results suggest that elevated CO2 stimulates plant growth and reduces freezing tolerance. The acquisition of cold tolerance is also influenced by the rhizobial strain, as indicated by lower levels of expression of COR genes and sustained accumulation of VSP-encoding transcripts in alfalfa inoculated with strain NRG34 as compared with strain A2.

An antifungal peptide from passion fruit (Passiflora edulis) seeds with similarities to 2S albumin proteins

An actual worldwide problem consists of an expressive increase of economic losses and health problems caused by fungi. In order to solve this problem, several studies have been concentrating on the screening of novel plant defence peptides with antifungal activities. These peptides are commonly characterized by having low molecular masses and cationic charges. This present work reports on the purification and characterization of a novel plant peptide of 5.0 kDa, Pe-AFP1, purified from the seeds of passion fruit (Passiflora edulis). Purification was achieved using a Red-Sepharose Cl-6B affinity column followed by reversed-phase chromatography on Vydac C18-TP column. In vitro assays indicated that Pe-AFP1 was able of inhibiting the development of the filamentous fungi Trichoderma harzianum, Fusarium oxysporum, and Aspergillus fumigatus with IC50 values of 32, 34, and 40 microg ml(-1), respectively, but not of Rhyzoctonia solani, Paracoccidioides brasiliensis and Candida albicans. This protein was also subjected to automated N-terminal amino acid sequence, showing high degree of similarities to storage 2S albumins, adding a new member to this protein-defence family. The discovery of Pe-AFP1 could contribute, in a near future, to the development of biotechnological products as antifungal drugs and transgenic plants with enhanced resistance to pathogenic fungi.

Nitrogen reserves, spring regrowth and winter survival of field-grown alfalfa (Medicago sativa) defoliated in the autumn

AIMS

The objective of the study was to characterize variations in proline, arginine, histidine, vegetative storage proteins, and cold-inducible gene expression in overwintering roots of field-grown alfalfa, in response to autumn defoliation, and in relation to spring regrowth and winter survival.

METHODS

Field trials, established in 1996 in eastern Canada, consisted of two alfalfa cultivars ('AC Caribou' and 'WL 225') defoliated in 1997 and 1998 either only twice during the summer or three times with the third defoliation taken 400, 500 or 600 growing degree days (basis 5 degrees C) after the second summer defoliation.

KEY RESULTS

The root accumulation of proline, arginine, histidine and soluble proteins of 32, 19 and 15 kDa, characterized as alfalfa vegetative storage proteins, was reduced the following spring by an early autumn defoliation at 400 or 500 growing degree days in both cultivars; the 600-growing-degree-days defoliation treatment had less or no effect. Transcript levels of the cold-inducible gene msaCIA, encoding a glycine-rich protein, were markedly reduced by autumn defoliation in 'WL 225', but remained unaffected in the more winter-hardy cultivar 'AC Caribou'. The expression of another cold-inducible gene, the dehydrin homologue msaCIG, was not consistently affected by autumn defoliation. Principal component analyses, including components of root organic reserves at the onset of winter, along with yield and plant density in the following spring, revealed that (a) amino acids and soluble proteins are positively related to the vigour of spring regrowth but poorly related to winter survival and (b) winter survival, as indicated by plant density in the spring, is associated with higher concentrations of cryoprotective sugars in alfalfa roots the previous autumn.

CONCLUSIONS

An untimely autumn defoliation of alfalfa reduces root accumulation of specific N reserves such as proline, arginine, histidine and vegetative storage proteins that are positively related to the vigour of spring regrowth but poorly related to winter survival.

Arabidopsis vegetative storage protein is an anti-insect acid phosphatase

Indirect evidence previously suggested that Arabidopsis (Arabidopsis thaliana) vegetative storage protein (VSP) could play a role in defense against herbivorous insects. To test this hypothesis, other AtVSP-like sequences in Arabidopsis were identified through a Basic Local Alignment Search Tool search, and their transcriptional profiles were investigated. In response to methyl jasmonate application or phosphate starvation, AtVSP and AtVSP-like genes exhibited differential expression patterns, suggesting distinct roles played by each member. Arabidopsis VSP2 (AtVSP2), a gene induced by wounding, methyl jasmonate, insect feeding, and phosphate deprivation, was selected for bacterial expression and functional characterization. The recombinant protein exhibited a divalent cation-dependent phosphatase activity in the acid pH range. When incorporated into the diets of three coleopteran and dipteran insects that have acidic gut lumen, recombinant AtVSP2 significantly delayed development of the insects and increased their mortality. To further determine the biochemical basis of the anti-insect activity of the protein, the nucleophilic aspartic acid-119 residue at the conserved DXDXT signature motif was substituted by glutamic acid via site-directed mutagenesis. This single-amino acid alteration did not compromise the protein's secondary or tertiary structure, but resulted in complete loss of its acid phosphatase activity as well as its anti-insect activity. Collectively, we conclude that AtVSP2 is an anti-insect protein and that its defense function is correlated with its acid phosphatase activity.

beta-1,3-Glucanase Activity in Peanut Seed (Arachis hypogaea) is Induced by Inoculation with Aspergillus flavus and Copurifies with a Conglutin-Like Protein

ABSTRACT Infection of peanut (Arachis hypogaea) seed by Aspergillus flavus and A. parasiticus is a serious problem that can result in aflatoxin contamination in the seed. Breeding resistant cultivars would be an effective approach to reduce aflatoxin accumulation. The objective of this study was to investigate the expression of the pathogenesis-related (PR) protein beta-1,3-glucanase and the isoform patterns in peanut seed inoculated with A. flavus. Peanut genotypes GT-YY9 and GT-YY20 (both resistant to A. flavus infection) and Georgia Green and A100 (both susceptible to A. flavus infection) were used in this study. The activities of beta-1,3-glucanase were similar in the uninfected seed of all genotypes, but increased significantly in the resistant genotypes after inoculation in comparison with the susceptible genotypes. An in-gel (native polyacrylamide gel electrophoresis [PAGE]) enzymatic activity assay of beta-1,3-glucanase revealed that there were more protein bands corresponding to beta-1,3-glucanase isoforms in the infected seed of resistant genotypes than in the infected seed of susceptible genotypes. Both acidic and basic beta-1,3-glucanase isoforms were detected in the isoelectric focusing gels. Thin-layer chromatography analysis of the hydrolytic products from the reaction mixtures of the substrate with the total protein extract or individual band of native PAGE revealed the presence of enzymatic hydrolytic oligomer products. The individual bands corresponding to the bands of beta-1,3-glucanase isoforms Glu 1 to 5 were separated on the sodium dodecyl sulfate-PAGE, resulting in two bands of 10 and 13 kDa, respectively. The sequences of fragments of the 13-kDa major protein band showed a high degree of homology to conglutin, a storage protein in peanut seed. Conglutin is reported as a peanut allergen, Ara h2. Our data provide the first evidences for peanut having beta-1,3-glucanase activities and the association with the resistance to A. flavus colonization in peanut seed. We have not directly demonstrated that conglutin has beta-1,3-glucanase activity.

Contribution of initial C and N reserves in Medicago sativa recovering from defoliation: impact of cutting height and residual leaf area

We studied the effects of stubble carbon / nitrogen (C / N) reserves or residual leaf area (RLA) on the contribution of taproot C / N reserves to shoot regrowth of Medicago sativa L. after cutting. The study assessed the effects of two cutting heights (6 and 15 cm), two RLAs (0 or 100%), and two initial C / N reserve levels (high N or low N) on forage production, nitrogen (N) distribution, and C / N reserve dynamics within stubble and taproot.

Lipid metabolism in arbuscular mycorrhizal roots of Medicago truncatula

The peroxidation of polyunsaturated fatty acids, common to all eukaryotes, is mostly catalyzed by members of the lipoxygenase enzyme family of non-heme iron containing dioxygenases. Lipoxygenase products can be metabolized further in the oxylipin pathway by several groups of CYP74 enzymes. One prominent oxylipin is jasmonic acid (JA), a product of the 13-allene oxide synthase branch of the pathway and known as signaling substance that plays a role in vegetative and propagative plant development as well as in plant responses to wounding and pathogen attack. In barley roots, JA level increases upon colonization by arbuscular mycorrhizal fungi. Apart from this first result regarding JA, no information is available on the relevance of lipidperoxide metabolism in arbuscular mycorrhizal symbiosis. Thus we analyzed fatty acid and lipidperoxide patterns in roots of Medicago truncatula during mycorrhizal colonization. Levels of fungus-specific fatty acids as well as palmitic acid (16:0) and oleic acid (18:1 n - 9) were increased in mycorrhizal roots. Thus the degree of arbuscular mycorrhizal colonization of roots can be estimated via analysis of fungal specific esterified fatty acids. Otherwise, no significant changes were found in the profiles of esterified and free fatty acids. The 9- and 13-LOX products of linoleic and alpha-linolenic acid were present in all root samples, but did not show significant differences between mycorrhizal and non-mycorrhizal roots, except JA which showed elevated levels in mycorrhizal roots. In both types of roots levels of 13-LOX products were higher than those of 9-LOX products. In addition, three cDNAs encoding CYP74 enzymes, two 9/13-hydroperoxide lyases and a 13-allene oxide synthase, were isolated and characterized. The transcript accumulation of these three genes, however, was not increased in mycorrhizal roots of M. truncatula.

The potassium-dependent transcriptome of Arabidopsis reveals a prominent role of jasmonic acid in nutrient signaling

Full genome microarrays were used to assess transcriptional responses of Arabidopsis seedlings to changing external supply of the essential macronutrient potassium (K(+)). Rank product statistics and iterative group analysis were employed to identify differentially regulated genes and statistically significant coregulated sets of functionally related genes. The most prominent response was found for genes linked to the phytohormone jasmonic acid (JA). Transcript levels for the JA biosynthetic enzymes lipoxygenase, allene oxide synthase, and allene oxide cyclase were strongly increased during K(+) starvation and quickly decreased after K(+) resupply. A large number of well-known JA responsive genes showed the same expression profile, including genes involved in storage of amino acids (VSP), glucosinolate production (CYP79), polyamine biosynthesis (ADC2), and defense (PDF1.2). Our findings highlight a novel role of JA in nutrient signaling and stress management through a variety of physiological processes such as nutrient storage, recycling, and reallocation. Other highly significant K(+)-responsive genes discovered in our study encoded cell wall proteins (e.g. extensins and arabinogalactans) and ion transporters (e.g. the high-affinity K(+) transporter HAK5 and the nitrate transporter NRT2.1) as well as proteins with a putative role in Ca(2+) signaling (e.g. calmodulins). On the basis of our results, we propose candidate genes involved in K(+) perception and signaling as well as a network of molecular processes underlying plant adaptation to K(+) deficiency.

Vegetative storage proteins in overwintering storage organs of forage legumes: roles and regulation

In perennial forage legumes such as alfalfa (Medicago sativa L.) and white clover (Trifolium repens L.), vegetative storage proteins are extensively mobilized to meet the nitrogen requirements of new shoot growth in spring or after cutting in summer. The 32-kDa alfalfa storage protein possesses high homology with class III chitinases, belonging to a group of pathogenesis-related proteins that possess antifreeze protein properties in some species and exhibit chitinolytic activity in vitro. This protein and the corresponding mRNA accumulate in taproots of cold-hardy culti vars during acclimation for winter, and in response to short-day conditions in controlled environments. The 17.3-kDa storage protein of white clover possesses high homology with pathogenesis-related proteins and abscisic- acid-responsive proteins from several legume species and has characteristics common to stress-responsive proteins. Low temperature enhances accumulation of this 17.3-kDa protein and its corresponding transcript. Exogenous abscisic acid stimulates the accumulation of vegetative storage proteins and their transcripts in both legume species. These observations suggest that vegetative storage proteins do not exclusively serve as nitrogen reserves during specific phases of legume development, but may play important adaptive roles in plant protection against abiotic (low temperature) and biotic (pathogen attack) stresses.Key words: nitrogen reserves, vegetative storage proteins, regulation, cold tolerance, chitinase, pathogenesis-related proteins.