Development of beta-1,3-glucanase activity in germinated tomato seeds

Phytotoxic Effects of Catnip (Nepeta meyeri Benth.) on Early Growth Stages Development and Infection Potential of Field Dodder (Cuscuta campestris Yunck)

Dodder (Cuscuta campestris Yunck.) is one of the most devastating parasitic plants, which reduces quantity and quality of crops. The inhibitory effect of catnip (Nepeta meyeri Benth.) extracts on germination and some seedling characteristics of the C. campestris were investigated in three phases in a laboratory and greenhouse. Aqueous extracts from different organs of N. meyeri were used in bioassays. The N. meyeri extracts reduced germination percent, root and shoot growth, and dry weight of C. campestris seedlings. Moreover, results showed an inhibitory effect of the N. meyeri extracts on the activity of alpha-amylase, protease, and beta-1,3-glucanase enzymes in C. campestris germinating seeds. Under greenhouse conditions, C. campestris seeds were planted with 30-day-old alfalfa plants and irrigated with N. meyeri extracts. The application of extracts from different organs of N. meyeri reduced emergence percent and length of stem and hampered C. campestris attachment to alfalfa. N. meyeri extracts also inhibited the activity of antioxidant enzymes and increased the accumulation of hydrogen peroxide and the malondialdehyde in C. campestris seedlings. The strongest inhibitory effects were observed from flower, leaf, and stem extracts of N. meyeri, respectively. However, after C. campestris attachment to alfalfa plants, treatment by N. meyeri extracts did not exhibit any effect on infestation efficiency and C. campestris growth traits. According to these findings, N. meyeri extract, especially from flower and leaf, may be recommended as a potent bio-control agent to control germination and early stage development of C. campestris.

Comparing the contents, functions and neonicotinoid take-up between floral and extrafloral nectar within a single species (Hemerocallis citrina Baroni)

BACKGROUND AND AIMS

Many angiosperms can secrete both floral (FN) and extrafloral (EFN) nectar. However, much remains unclear about how EFN and FN differ in secretion, composition and ecological function, especially when both FN and EFN are secreted on flowers of the same species.

METHODS

Hemerocallis citrina flowers secrete both FN and EFN. The FN and EFN traits including volume, presentation pattern and temporal rhythms of secretion were compared by field observation. Sugar and amino acid contents were analysed using regular biochemical methods, whereas the proteome was investigated by combined gel-based and gel-free approaches. Animal feeders on FN and EFN were investigated by field observation. Hemerocallis citrina plants were exposed by soil drenching to two systemic insecticides, acetamiprid and imidacloprid, and the concentration of these in FN and EFN was measured by ultra-high performance liquid chromatography coupled with mass spectrometry.

KEY RESULTS

Hemerocallis citrina FN was concentrated and sucrose dominant, secreted in the mature flower tube and served as a reward for pollinators. Conversely, EFN was hexose rich, more dilute and less rich in sugar and amino acids. EFN was secreted on the outside of developing floral buds, and was likely to attract predatory animals for defence. EFN had fewer phenolics, but more pathogenesis-related components, such as chitinase and glucanase. A significantly different proteomic profile and enzymatic activities between FN and EFN suggest that they had different biosynthesis mechanisms. Both neonicotinoid insecticides examined became present in both nectar types soon after application, but in greater concentration within EFN; EFN also attracted a wider range of insect species than FN.

CONCLUSIONS

Hemerocallis citrina FN and EFN differed in production, composition and ecological function. The EFN pathway could be a significant way for neonicotinoids to enter the wild food chain, and must be considered when evaluating the risks to the environment of other systemic insecticides.

Transcriptional and proteomic insights into phytotoxic activity of interspecific potato hybrids with low glycoalkaloid contents

BACKGROUND

Glycoalkaloids are bioactive compounds that contribute to the defence response of plants against herbivore attack and during pathogenesis. Solanaceous plants, including cultivated and wild potato species, are sources of steroidal glycoalkaloids. Solanum plants differ in the content and composition of glycoalkaloids in organs. In wild and cultivated potato species, more than 50 steroidal glycoalkaloids were recognized. Steroidal glycoalkaloids are recognized as potential allelopathic/phytotoxic compounds that may modify the growth of target plants. There are limited data on the impact of the composition of glycoalkaloids on their phytotoxic potential.

RESULTS

The presence of α-solasonine and α-solamargine in potato leaf extracts corresponded to the high phytotoxic potential of the extracts. Among the differentially expressed genes between potato leaf bulks with high and low phytotoxic potential, the most upregulated transcripts in sample of high phytotoxic potential were anthocyanin 5-aromatic acyltransferase-like and subtilisin-like protease SBT1.7-transcript variant X2. The most downregulated genes were carbonic anhydrase chloroplastic-like and miraculin-like. An analysis of differentially expressed proteins revealed that the most abundant group of proteins were those related to stress and defence, including glucan endo-1,3-beta-glucosidase acidic isoform, whose expression level was 47.96× higher in potato leaf extract with low phytotoxic.

CONCLUSIONS

The phytotoxic potential of potato leaf extract possessing low glycoalkaloid content is determined by the specific composition of these compounds in leaf extract, where α-solasonine and α-solamargine may play significant roles. Differentially expressed gene and protein profiles did not correspond to the glycoalkaloid biosynthesis pathway in the expression of phytotoxic potential. We cannot exclude the possibility that the phytotoxic potential is influenced by other compounds that act antagonistically or may diminish the glycoalkaloids effect.

A conserved GH17 glycosyl hydrolase from plant pathogenic Dothideomycetes releases a DAMP causing cell death in tomato

To facilitate infection, pathogens deploy a plethora of effectors to suppress basal host immunity induced by exogenous microbe-associated or endogenous damage-associated molecular patterns (DAMPs). In this study, we have characterized family 17 glycosyl hydrolases of the tomato pathogen Cladosporium fulvum (CfGH17) and studied their role in infection. Heterologous expression of CfGH17-1 to 5 by potato virus X in different tomato cultivars showed that CfGH17-1 and CfGH17-5 enzymes induce cell death in Cf-0, Cf-1 and Cf-5 but not in Cf-Ecp3 tomato cultivars or tobacco. Moreover, CfGH17-1 orthologues from other phytopathogens, including Dothistroma septosporum and Mycosphaerella fijiensis, also trigger cell death in tomato. CfGH17-1 and CfGH17-5 are predicted to be β-1,3-glucanases and their enzymatic activity is required for the induction of cell death. CfGH17-1 hydrolyses laminarin, a linear 1,3-β-glucan with 1,6-β linkages. CfGH17-1 expression is down-regulated during the biotrophic phase of infection and up-regulated during the necrotrophic phase. Deletion of CfGH17-1 in C. fulvum did not reduce virulence on tomato, while constitutive expression of CfGH17-1 decreased virulence, suggesting that abundant presence of CfGH17-1 during biotrophic growth may release a DAMP that activates plant defence responses. Under natural conditions CfGH17-1 is suggested to play a role during saprophytic growth when the fungus thrives on dead host tissue, which is in line with its high levels of expression at late stages of infection when host tissues have become necrotic. We suggest that CfGH17-1 releases a DAMP from the host cell wall that is recognized by a yet unknown host plant receptor.

Identification of a Vitis vinifera endo-β-1,3-glucanase with antimicrobial activity against Plasmopara viticola

Inducible plant defences against pathogens are stimulated by infections and comprise several classes of pathogenesis-related (PR) proteins. Endo-β-1,3-glucanases (EGases) belong to the PR-2 class and their expression is induced by many pathogenic fungi and oomycetes, suggesting that EGases play a role in the hydrolysis of pathogen cell walls. However, reports of a direct effect of EGases on cell walls of plant pathogens are scarce. Here, we characterized three EGases from Vitis vinifera whose expression is induced during infection by Plasmopara viticola, the causal agent of downy mildew. Recombinant proteins were expressed in Escherichia coli. The enzymatic characteristics of these three enzymes were measured in vitro and in planta. A functional assay performed in vitro on germinated P. viticola spores revealed a strong anti-P. viticola activity for EGase3, which strikingly was that with the lowest in vitro catalytic efficiency. To our knowledge, this work shows, for the first time, the direct effect against downy mildew of EGases of the PR-2 family from Vitis.

Isolation and Characterization of ScGluD2, a New Sugarcane beta-1,3-Glucanase D Family Gene Induced by Sporisorium scitamineum, ABA, H2O2, NaCl, and CdCl2 Stresses

Beta-1,3-glucanases (EC 3.2.1.39), commonly known as pathogenesis-related (PR) proteins, play an important role not only in plant defense against fungal pathogens but also in plant physiological and developmental processes. However, only a limited number of sugarcane beta-1,3-glucanase genes have been isolated. In the present study, we identified and characterized a new beta-1,3-glucanase gene ScGluD2 (GenBank Acc No. KF664181) from sugarcane. An X8 domain was present at the C terminal region of ScGluD2, suggesting beta-1,3-glucan-binding function. Phylogenetic analysis showed that the predicted ScGluD2 protein was classified into subfamily D beta-1,3-glucanase. Localization of the ScGluD2 protein in the plasma membrane was determined by tagging it with green fluorescent protein. The expression of ScGluD2 was more up-regulated in sugarcane smut-resistant cultivars in the early stage (1 or 3 days) than in the susceptible ones after being challenged by the smut pathogen, revealing that ScGluD2 may be involved in defense against the invasion of Sporisorium scitamineum. Transient overexpression of ScGluD2 in Nicotiana benthamiana leaves induced a defense response and exhibited antimicrobial action on the tobacco pathogens Pseudomonas solanacearum and Botrytis cinerea, further demonstrating that ScGluD2 was related to the resistance to plant pathogens. However, the transcripts of ScGluD2 partially increased (12 h) under NaCl stress, and were steadily up-regulated from 6 to 24 h upon ABA, H2O2, and CdCl2 treatments, suggesting that ABA may be a signal molecule regulating oxidative stress and play a role in the salt and heavy metal stress-induced stimulation of ScGluD2 transcripts. Taken together, ScGluD2, a novel member of subfamily D beta-1,3-glucanase, was a stress-related gene of sugarcane involved in plant defense against smut pathogen attack and salt and heavy metal stresses.

Fibres from flax overproducing β-1,3-glucanase show increased accumulation of pectin and phenolics and thus higher antioxidant capacity

BACKGROUND

Recently, in order to improve the resistance of flax plants to pathogen infection, transgenic flax that overproduces β-1,3-glucanase was created. β-1,3-glucanase is a PR protein that hydrolyses the β-glucans, which are a major component of the cell wall in many groups of fungi. For this study, we used fourth-generation field-cultivated plants of the Fusarium -resistant transgenic line B14 to evaluate how overexpression of the β-1,3-glucanase gene influences the quantity, quality and composition of flax fibres, which are the main product obtained from flax straw.

RESULTS

Overproduction of β-1,3-glucanase did not affect the quantity of the fibre obtained from the flax straw and did not significantly alter the essential mechanical characteristics of the retted fibres. However, changes in the contents of the major components of the cell wall (cellulose, hemicellulose, pectin and lignin) were revealed. Overexpression of the β-1,3-glucanase gene resulted in higher cellulose, hemicellulose and pectin contents and a lower lignin content in the fibres. Increases in the uronic acid content in particular fractions (with the exception of the 1 M KOH-soluble fraction of hemicelluloses) and changes in the sugar composition of the cell wall were detected in the fibres of the transgenic flax when compared to the contents for the control plants. The callose content was lower in the fibres of the transgenic flax. Additionally, the analysis of phenolic compound contents in five fractions of the cell wall revealed important changes, which were reflected in the antioxidant potential of these fractions.

CONCLUSION

Overexpression of the β-1,3-glucanase gene has a significant influence on the biochemical composition of flax fibres. The constitutive overproduction of β-1,3-glucanase causes a decrease in the callose content, and the resulting excess glucose serves as a substrate for the production of other polysaccharides. The monosaccharide excess redirects the phenolic compounds to bind with polysaccharides instead of to partake in lignin synthesis. The mechanical properties of the transgenic fibres are strengthened by their improved biochemical composition, and the increased antioxidant potential of the fibres supports the potential use of transgenic flax fibres for biomedical applications.

Molecular characterization and differential expression of beta-1,3-glucanase during ripening in banana fruit in response to ethylene, auxin, ABA, wounding, cold and light-dark cycles

beta-1,3-Glucanases (E.C. 3.2.1.39) are widely distributed enzyme among bacteria, fungi, and higher plants. Analyses of accumulation levels of beta-1,3-glucanase protein in various tissues in banana have clearly indicated abundance of beta-1,3-glucanase protein accumulation in ripe pulp tissue. After cloning of beta-1,3-glucanase from banana pulp (cultivar Cavendish), we have carried out an in silico analysis to investigate the sequential, structural, and phylogenetic characteristics of the putative banana beta-1,3-glucanase protein. As like other ripening specific genes, beta-1,3-glucanase is regulated in response to a wide variety of factors. Therefore, we have analyzed the transcript accumulation pattern and protein levels of beta-1,3-glucanase in response to ethylene, auxin, ABA, wounding and, low temperature in preclimacteric banana fruit. Expression profile analyses have indicated that whereas exogenous application of ethylene strongly stimulated beta-1,3-glucanase transcript accumulation, ABA partially induced the expression of the gene. On the other hand, wound treatment did not induce beta-1,3-glucanase expression. Conversely, auxin and cold treatment negatively regulated beta-1,3-glucanase gene expression and thus inhibited glucanase activity. In addition, beta-1,3-glucanase transcript level was markedly decreased by constant exposure to white light. Protein level and enzymatic activity of beta-1,3-glucanase were substantially increased with considerable decrease in fruit firmness by ethylene treatment and reduced exposure to white light conditions as compared with other treatments. Together, the overall study of beta-1,3-glucanase expression pattern, glucanase activity, and changes in fruit firmness during ripening in various conditions suggest the possible physiological function of beta-1,3-glucanase in fruit pulp softening.

Phytotoxic effects of Sicyos deppei (Cucurbitaceae) in germinating tomato seeds

The phytotoxic effect of allelochemicals is referred to as allelochemical stress and it is considered a biotic stress. Sicyos deppei G. Don (Cucurbitaceae) is an allelopathic weed that causes phytotoxicity in Lycopersicon esculentum, delaying seed germination and severely inhibiting radicle growth. This paper reports in in vitro conditions, the effects of the aqueous leachate of S. deppei-throughout tomato germination times-on (1) the dynamics of starch and sugars metabolism, (2) activity and expression of the cell wall enzymes involved in endosperm weakening that allows the protrusion of the radicle, and (3) whether abscisic acid (ABA) is involved in this altered metabolic processes. Results showed that S. deppei leachate on tomato seed germination mainly caused: (1) delay in starch degradation as well as in sucrose hydrolysis; (2) lower activity of sucrose phosphate synthase, cell wall invertase, and alpha-amylase; being sucrose phosphate synthase (SPS) gene expression down-regulated, and the last two up regulated; (3) also, lower activity of endo beta-mannanase, beta-1,3 glucanase, alpha-galactosidase, and exo-polygalacturonase with altered gene expression; and (4) higher content of ABA during all times of germination. The phytotoxic effect of S. deppei aqueous leachate is because of the sum of many metabolic processes affected during tomato seed germination that finally is evidenced by a strong inhibition of radicle growth.

Co-Localization of beta-1,3-Glucanases and Callose During Somatic Embryogenesis in Cichorium

During direct somatic embryogenesis in leaves of Cichorium hybrid clone '474', 38 kDa beta-1,3-glucanases are accumulated in the culture medium of the embryogenic hybrid to a higher level when compared with a non-embryogenic cultivar. In the same time, embryogenic cells were surrounded by a cell wall that was characterized by the presence of callose. This callosic deposition disappeared as embryos grew. Callose consisted of beta-1,3-glucan linkages and so represented a possible substrate for beta-1,3-glucanases. Using immunolocalization experiments, we demonstrated that from the three types of callose deposits observed during the culturing of Cichorium leaf explants, only the callose present in the walls surrounding reactivated cells seemed specifically related to somatic embryogenesis. Moreover, callose and the 38-kDa beta-1,3-glucanases were co-localized dispersed throughout the thick and swelled walls of reactivated cells and embryo cell walls. This suggests that callose and beta-1,3-glucanases are implicated in the process of somatic embryogenesis since they were always detected in or quite near embryogenic and embryo cell. This also suggested that beta-1,3-glucanases could be involved in the degradation of this callose.

Characterization and Expression of beta-1,3-Glucanase Genes in Jujube Fruit Induced by the Microbial Biocontrol Agent Cryptococcus laurentii

ABSTRACT Two beta-1,3-glucanase genes were cloned from jujube (Ziziphus jujuba Mill) fruit and designated Glu-1 and Glu-2 (GenBank accession numbers DQ012940 and DQ093571), respectively. The expression of Glu-1 and Glu-2 in jujube fruit in response to wounding and microbial biocontrol agent was evaluated by semi-quantitative reverse-transcription polymerase chain reaction analysis. Wounding and treatment with Cryptococcus laurentii stimulated an increase in beta-1,3-glucanase (EC 3.2.1.39) activity in jujube fruit. Analysis of gene expression proved that Glu-1 was highly induced both by wounding and C. laurentii, whereas Glu-2 was broadly not responsive to the yeast. The expression of Glu-1 was noticeably enhanced with increased concentrations of C. laurentii, suggesting that Glu-1 may play a role in defense responses to fungal pathogens. The results hold true at the levels of gene activation and enzyme accumulation in jujube fruit treated by both stimuli, resulting in a significant decrease in disease incidence and lesion diameter, thus providing evidence that changes in beta-1,3-glucanase activity are related to expression of the genes. Taken together, these findings suggest the possible use of beta-1,3-glucanase activity as a biochemical marker for screening jujube fruit against fungal pathogens, and also provide a mechanistic framework for the functions of beta-1,3-glucanase in defense responses.

Cloning and expression analysis of two beta-1,3-glucanase genes from strawberry

We isolated from strawberry (Fragariae x ananassa Duch) a genomic clone of a beta-1,3-glucanase gene, designated as FaBG2-2. In addition, a related cDNA clone, designated as FaBG2-3, was also isolated. FaBG2-2 and FaBG2-3 are similar in their coding regions, except that FaBG2-2 does not appear to contain a signal peptide coding sequence. The 5' and 3' flanking regions of FaBG2-2 and FaBG2-3 are differentt. Using real-time PCR, the expression patterns of FaBG2-3 and a previously isolated beta-1,3-glucanase gene, FaBG2-1, in strawberry plants infected with Colletotrichum fragariae or Colletotrichum acutatum were analyzed at different time points post-infection. The results showed that expressions of both genes in the leaves of infected plants were induced by the two fungi, but the level of induction was several fold greater with C. fragariae. Comparison of the expression levels of the two genes revealed that the level of FaBG2-3 expression was several hundred to over a thousand fold higher than that of FaBG2-1. Furthermore, the expression levels of the two genes in the leaf, fruit, crown and root of uninfected strawberry plants were analyzed.

Development of polyphenol oxidase activity in the micropylar endosperm of tomato seeds

Polyphenol oxidase (PPO) activity increased markedly in the micropylar region of the endosperm of tomato (Lycopersicon esculentum) seeds after radicle protrusion. Tissue-printing analyses demonstrated that the majority of the activity is localized in the micropylar area. The increase in the activity was due to the increase in the amounts of enzyme. Within the micropylar endosperm region, two PPO isozymes were immunologically detected whose apparent molecular masses were estimated to be approximately 58 and 59 kDa, respectively, by SDS-PAGE. Although PPO activity also developed in the lateral portion of the endosperm, the level of this activity was much lower as compared with that in the micropylar region. Furthermore, the isozyme pattern in the lateral portion differed from that in the micropylar portion. The 58 kDa isozyme that was detected in the latter portion was absent, and only 59 kDa PPO was detectable in the former one. When the endosperm tissues were wounded, an enhancement of the enzyme activity was observed in the wounded region. The wound-induced development of the enzyme activity was associated with the induction of 58 kDa isozyme.

Significance of inducible defense-related proteins in infected plants

Inducible defense-related proteins have been described in many plant species upon infection with oomycetes, fungi, bacteria, or viruses, or insect attack. Several types of proteins are common and have been classified into 17 families of pathogenesis-related proteins (PRs). Others have so far been found to occur more specifically in some plant species. Most PRs and related proteins are induced through the action of the signaling compounds salicylic acid, jasmonic acid, or ethylene, and possess antimicrobial activities in vitro through hydrolytic activities on cell walls, contact toxicity, and perhaps an involvement in defense signaling. However, when expressed in transgenic plants, they reduce only a limited number of diseases, depending on the nature of the protein, plant species, and pathogen involved. As exemplified by the PR-1 proteins in Arabidopsis and rice, many homologous proteins belonging to the same family are regulated developmentally and may serve different functions in specific organs or tissues. Several defense-related proteins are induced during senescence, wounding or cold stress, and some possess antifreeze activity. Many defense-related proteins are present constitutively in floral tissues and a substantial number of PR-like proteins in pollen, fruits, and vegetables can provoke allergy in humans. The evolutionary conservation of similar defense-related proteins in monocots and dicots, but also their divergent occurrence in other conditions, suggest that these proteins serve essential functions in plant life, whether in defense or not.

The perisperm-endosperm envelope in Cucumis: structure, proton diffusion and cell wall hydrolysing activity

BACKGROUND

and Aims The envelope surrounding the embryo in cucurbit seed, which consists of a single layer of live endosperm cells covered by lipid- and callose-rich layers, is reported to show semi-permeability and also to act as the primary barrier to radicle emergence. Structure, development and permeability of the envelope and activity of cell wall hydrolases during germination of cucumber and muskmelon seeds were investigated.

METHODS

Sections of seeds were stained with aniline blue and Sudan III. Proton diffusion and endo-beta-mannanase activity were detected by tissue printing. A gel-diffusion assay was performed to quantify endo-beta-mannanase activity, while the activity of beta-glucanase was determined with laminarin as the substrate and glucose formation measured using the GOD-POD method.

KEY RESULTS

The lipid layer differentiated during seed development in cucumber in the epidermis of a multilayered nucellus, whereas the callose layer appeared to develop outside the endosperm cell layer. Accordingly, the envelope has been called the perisperm-endosperm (PE) envelope. Chloroform treatment of seeds, which resulted in a substantial reduction in Sudan staining of the lipid layer, also enhanced the permeability of the PE envelope to 2,3,5-triphenyltetrazolium chloride. Proton diffusion occurred when the PE envelopes from seeds had their inner surface in contact with bromocresol purple-containing agarose gels, but not when their outer surface was in contact. Substantial endo-beta-mannanase activity was present in the caps of the PE envelopes, whereas a marked increase in beta-glucanase activity was observed in radicles prior to germination.

CONCLUSIONS

The lipid layer seems to contribute to the semi-permeability of the PE envelope. The diffusion of protons might create an acidic environment conducive to the activity of cell wall hydrolases, namely endo-beta-mannanase (EC 3.2.1.78) and beta-glucanase [beta(1-->3)glucanohydrolase; EC 3.2.1.6], which, in turn, may play a role in the weakening of the PE envelope necessary for the protrusion of the radicle in cucumber and muskmelon seeds.

The modulating effect of the perisperm-endosperm envelope on ABA-inhibition of seed germination in cucumber

Abscisic acid (ABA) markedly reduced the germination of developing seeds at much lower concentrations (ABA50=0.1 mM) compared with that of mature seeds (ABA50=1.6 mM) in cucumber (Cucumis sativus L. cv. Green long). The perisperm-endosperm (PE) envelope in developing seeds showed partly differentiated lipid and callose layers, considerable ABA biosynthetic activity in endosperm cells, and appreciable permeability to applied ABA. The decrease in the sensitivity of seeds to applied ABA was coincident with the complete development of lipid and callose layers, diminished ABA biosynthetic activity in endosperm cells in imbibed mature seeds, and moderate permeability of the PE envelope to applied ABA. Decoated seeds pretreated with chloroform showed decreased germination (ABA50=0.4 mM) in response to applied ABA and increased ABA permeation through the PE envelope. ABA thus allowed to permeate into embryonic tissues substantially reduced the pregerminative activity of beta-glucanase in the radicles. The structure and biophysical/biochemical properties of the PE envelope seem to modulate the effect of ABA on the germination of developing and mature cucumber seeds.

Cloning, characterization and expression of OsGLN2, a rice endo-1,3-beta-glucanase gene regulated developmentally in flowers and hormonally in germinating seeds

We report here the isolation and characterization of a new endo-1,3-beta-glucanase (1,3-beta-GLU) cDNA, OsGLN2, that is expressed both in flowers and in germinating seeds of rice (Oryza sativa L.). The isolated OsGLN2 gene encoded a protein which displayed 72%, 93% and 92% identity at the amino acid level with those encoded by barley GII, rice Gns4 and glu1 1,3-beta-GLU genes, respectively. A GST-OsGLN2 recombinant protein expressed in Escherichia coli preferentially hydrolyzed Laminaria digitata 1,3;1,6-beta-glucan and liberated only oligosaccharides, suggesting that the enzyme can be classified as a 1,3-beta-GLU. Northern analysis with a 3'-UTR gene-specific probe revealed that OsGLN2 is expressed exclusively in the paleae and lemmas during flowering, and no expression of OsGLN2 was detected in other tissues such as leaf blades, leaf sheaths, stems, nodes and roots in mature rice plants. The OsGLN2 gene is also expressed in germinating seeds, where its expression is predominant in endosperms rather than embryos. In de-embryonated rice half-seeds, addition of gibberellin A3 (GA) greatly enhanced expression of the OsGLN2 gene, while the GA-induced gene expression was suppressed strongly by abscisic acid (ABA). This is the first report, to our knowledge, that OsGLN2 encodes a 1,3-beta-GLU and is expressed specifically in paleae and lemmas during flowering and in germinating seeds, where its expression is enhanced by GA and suppressed by ABA.

Purification and characterization of beta-N-acetylhexosaminidase from maize seedlings

Enzymatic activity of beta-N-acetyhexosaminidase (EC 3.2.1.52) was analysed in seeds and young seedings of maize (Zea mays) using di-N-acetylchitobiose as a substrate. Substantial activity was detected in dry seeds. Activity increased before germination (48 h) but exclusively in the embryo. In seedlings, most of the activity was found in the scutellum, and lower levels in shoots and roots immediately after germination. An isoform of the enzyme was purified from scutellum (72 h after the start of imbibition) by heat treatment of crude extract and four steps of chromatography. Purified beta-N-acetyl-hexosaminidase showed a single band on SDS-PAGE of around 70 kDa. This was almost the same as the molecular weight estimated by size exclusion chromatography, indicating a monomeric form of the active enzyme. The relative activity of the enzyme for di-N-acetylchitobiose was about 15 times greater than that for p-nitrophenyl-N-acetylglucosaminide or p-nitrophenyl-N-acetylgalactosaminide. Analysis of the reaction with oligo-N-acetylchitooliogsaccharides [(GlcNAc)n] revealed an exotype enzyme producing predominantly (GlcNAc)n-1 and N-acetylglucosamine. The optimum pH, temperature, and isoelectric point (pl) were 4.5, 55 degrees C, and 6.75, respectively. The activity was almost completely inhibited in the presence of 5 mmol/L Ag+, Hg2+, or Fe3+.

Class I chitinase and beta-1,3-glucanase are differentially regulated by wounding, methyl jasmonate, ethylene, and gibberellin in tomato seeds and leaves

Class I chitinase (Chi9) and beta-1,3-glucanase (GluB) genes are expressed in the micropylar endosperm cap of tomato (Lycopersicon esculentum) seeds just before radicle emergence through this tissue to complete germination. In gibberellin (GA)-deficient mutant (gib-1) seeds, expression of Chi9 and GluB mRNA and protein is dependent upon GA. However, as expression occurs relatively late in the germination process, we investigated whether the genes are induced indirectly in response to tissue wounding associated with endosperm cap weakening and radicle protrusion. Wounding and methyl jasmonate (MeJA) induced Chi9 expression, whereas ethylene, abscisic acid, sodium salicylate, fusicoccin, or beta-aminobutyric acid were without effect. Chi9 expression occurred only in the micropylar tissues when seeds were exposed to MeJA or were wounded at the chalazal end of the seed. Expression of Chi9, but not GluB, mRNA was reduced in germinating seeds of the jasmonate-deficient defenseless1 tomato mutant and could be restored by MeJA treatment. Chi9 expression during germination may be associated with "wounding" from cell wall hydrolysis and weakening in the endosperm cap leading to radicle protrusion, and jasmonate is involved in the signaling pathway for this response. Among these treatments and chemicals (other than GA), only MeJA and wounding induced a low level of GluB expression in gib-1 seeds. However, MeJA, wounding, and particularly ethylene induced both genes in leaves, whereas GA induced only Chi9 in leaves. Although normally expressed simultaneously during tomato seed germination, Chi9 and GluB genes are regulated distinctly and tissue specifically by hormones and wounding.

Class I beta-1,3-glucanase and chitinase are expressed in the micropylar endosperm of tomato seeds prior to radicle emergence

beta-1,3-Glucanase (EC 3.2.1.39) and chitinase (EC 3.2.1.14) mRNAs, proteins, and enzyme activities were expressed specifically in the micropylar tissues of imbibed tomato (Lycopersicon esculentum Mill.) seeds prior to radicle emergence. RNA hybridization and immunoblotting demonstrated that both enzymes were class I basic isoforms. beta-1,3-Glucanase was expressed exclusively in the endosperm cap tissue, whereas chitinase localized to both endosperm cap and radicle tip tissues. beta-1,3-Glucanase and chitinase appeared in the micropylar tissues of gibberellin-deficient gib-1 tomato seeds only when supplied with gibberellin. Accumulation of beta-1,3-glucanase mRNA, protein and enzyme activity was reduced by 100 microM abscisic acid, which delayed or prevented radicle emergence but not endosperm cap weakening. In contrast, expression of chitinase mRNA, protein, and enzyme activity was not affected by abscisic acid. Neither of these enzymes significantly hydrolyzed isolated tomato endosperm cap cell walls. Although both beta-1,3-glucanase and chitinase were expressed in tomato endosperm cap tissue prior to radicle emergence, we found no evidence that they were directly involved in cell wall modification or tissue weakening. Possible functions of these hydrolases during tomato seed germination are discussed.