Control of wild carrot somatic embryo development by antioxidants : a probable mode of action of 2,4-dichlorophenoxyacetic Acid

Exogenous Glutathione Promotes the Proliferation of Pinus koraiensis Embryonic Cells and the Synthesis of Glutathione and Ascorbic Acid

Somatic embryogenesis (SE), which leads to the formation of embryonic callus (EC) tissue, is the most promising method for large-scale production and selective breeding of woody plants. However, in many species, SE suffers from low proliferation rates, hindering the production of improved plant materials. One way of improving proliferation rates is achieved by improving the redox status of the culture medium. In this study, we investigated the effects of exogenous glutathione (GSH) and L-buthionine sulfoximine (BSO, the inhibitor of glutathione synthase) on the EC proliferation rate in Korean pine (Pinus koraiensis), using cell lines with both high (F: 001#-001) and low (S: 001#-010) proliferation potential. We found that exogenous GSH promoted cell proliferation in both cell lines, while exogenous BSO inhibited proliferation in both cell lines. At 35 d with exogenous GSH treatment, the fresh weight of F and S cell lines increased by 35.48% and 48.39%, respectively, compared with the control. The exogenous application of GSH increased the intracellular levels of GSH, total GSH (T-GSH), oxidized glutathione (GSSG), ascorbic acid (ASA), total ASA (T-ASA), and the ratios of GSH:T-GSH and ASA:T-ASA in both F and S cell lines. Furthermore, exogenous GSH increased the activity of both glutathione reductase (GR) and dehydroascorbate reductase (DHAR) while decreasing the activity of ascorbate peroxidase (APX) in both cell lines. It appears that the application of exogenous GSH promotes a reducing cultural environment, which is conducive to EC proliferation in Korean pine. By helping to reveal the mechanism whereby GSH regulates redox homeostasis in Korean pine EC cells, we have laid the foundation for a large-scale breeding of Korean pine somatic embryogenesis technology system.

Antioxidants Application Enhances Regeneration and Conversion of Date Palm (Phoenix dactylifera L.) Somatic Embryos

Many embryogenic systems have been designed to generate somatic embryos (SEs) with the morphology, biochemistry, and vigor uniformity of zygotic embryos (ZEs). During the current investigation, several antioxidants were added to the maturation media of the developing somatic embryos of date palm. Explant material was a friable embryogenic callus that was placed in maturation media containing ABA at 0.5 mg L⁻¹, 5 g L⁻¹ polyethylene glycol, and 10 g L⁻¹ phytagel. Furthermore, α-tocopherol or reduced glutathione (GSH) were used separately at (25 and 50 mg L⁻¹). These treatments were compared to a widely used date palm combination of reduced ascorbic acid (ASC) and citric acid at 150 and 100 mg L⁻¹, respectively, and to the medium free from any antioxidants. The relative growth percentage of embryogenic callus (EC), globularization degree, differentiation%, and SEs number were significantly increased with GSH (50 mg L⁻¹). Additionally, the latter treatment significantly enhanced the conversion% of SEs and the number of secondary somatic embryos (SSEs). ASC and citric acid treatment increased leaf length, while α-tochopherol (50 mg L⁻¹) elevated the number of leaves plantlet⁻¹. GSH at 50 mg L⁻¹ catalyzed the activities of polyphenol oxidase (PPO) and peroxidase (POD) in EC and enhanced the accumulation of proteins in SEs.

Somatic embryogenesis in Larix: the state of art and perspectives

Clonal propagation of conifers using somatic embryogenesis is essential for the selection of tree species, and for the implementation of afforestation and reforestation. In combination with cryopreservation, somatic embryogenesis creates the basis for the development of economically valuable lines of clones and elite genotypes. The industrial use of such genetically verified clone lines in forestry can significantly increase forest productivity compared to any conventional methods for improving tree crops that are available. Larch is considered as one of the main conifer candidates for large-scale reforestation, not only due to the vastness of its habitat, but also due to the unique quality of its wood, rapid growth and high ecological plasticity. However, the vast majority of larch species are characterized by uneven yields and extremely low seed quality. In this regard, obtaining planting material for reforestation from larch seeds on seed plantations is not advisable, but can be successfully implemented in afforestation programs using somatic embryogenesis technologies. Research on the somatic embryogenesis of larch has been conducted for over 30 years, which allowed considerable experience in this field to be accumulated. To date, the conditions for the initiation and maintenance of embryogenic cultures, as well as for the formation and development of somatic embryos have been determined. Significant progress has been made in the study of both the factors affecting these processes and the molecular mechanisms that underlie the various stages of embryogenesis. Nevertheless, despite the successes achieved, knowledge available today on the somatic embryogenesis of representatives of the genus Larix is still not enough to develop technologies for producing valuable plant-breeding material in vitro. This review analyzes the current state of research on the problem of somatic embryogenesis of representatives of the genus Larix. Particular attention is paid to the choice of explants for somatic embryogenesis, the composition of the media for cultivation, the dependence of the potential of somatic embryogenesis on the duration of cultivation, and the genetic control of somatic embryogenesis.

Identification of novel genes potentially involved in somatic embryogenesis in chicory (Cichorium intybus L.)

BACKGROUND

In our laboratory we use cultured chicory (Cichorium intybus) explants as a model to investigate cell reactivation and somatic embryogenesis and have produced 2 chicory genotypes (K59, C15) sharing a similar genetic background. K59 is a responsive genotype (embryogenic) capable of undergoing complete cell reactivation i.e. cell de- and re-differentiation leading to somatic embryogenesis (SE), whereas C15 is a non-responsive genotype (non-embryogenic) and is unable to undergo SE. Previous studies 1 showed that the use of the beta-D-glucosyl Yariv reagent (beta-GlcY) that specifically binds arabinogalactan-proteins (AGPs) blocked somatic embryo production in chicory root explants. This observation indicates that beta-GlcY is a useful tool for investigating somatic embryogenesis (SE) in chicory. In addition, a putative AGP (DT212818) encoding gene was previously found to be significantly up-regulated in the embryogenic K59 chicory genotype as compared to the non-embryogenic C15 genotype suggesting that this AGP could be involved in chicory re-differentiation 2. In order to improve our understanding of the molecular and cellular regulation underlying SE in chicory, we undertook a detailed cytological study of cell reactivation events in K59 and C15 genotypes, and used microarray profiling to compare gene expression in these 2 genotypes. In addition we also used beta-GlcY to block SE in order to identify genes potentially involved in this process.

RESULTS

Microscopy confirmed that only the K59, but not the C15 genotype underwent complete cell reactivation leading to SE formation. beta-GlcY-treatment of explants blocked in vitro SE induction, but not cell reactivation, and induced cell wall modifications. Microarray analyses revealed that 78 genes were differentially expressed between induced K59 and C15 genotypes. The expression profiles of 19 genes were modified by beta-GlcY-treatment. Eight genes were both differentially expressed between K59 and C15 genotypes during SE induction and transcriptionally affected by beta-GlcY-treatment: AGP (DT212818), 26 S proteasome AAA ATPase subunit 6 (RPT6), remorin (REM), metallothionein-1 (MT1), two non-specific lipid transfer proteins genes (SDI-9 and DEA1), 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase), and snakin 2 (SN2). These results suggest that the 8 genes, including the previously-identified AGP gene (DT212818), could be involved in cell fate determination events leading to SE commitment in chicory.

CONCLUSION

The use of two different chicory genotypes differing in their responsiveness to SE induction, together with beta-GlcY-treatment represented an efficient tool to discriminate cell reactivation from the SE morphogenetic pathway. Such an approach, together with microarray analyses, permitted us to identify several putative key genes related to the SE morphogenetic pathway in chicory.

Glutathione redox regulation of in vitro embryogenesis

Production of embryos in culture via either somatic embryogenesis or androgenesis has long been used as a propagation tool and as a model system in the investigation of structural, physiological, and molecular events governing embryo development. Despite the similar external morphology to their zygotic counterparts, cultured embryos often fail to develop properly and convert into viable plants during post-embryonic growth. These deficiencies are the results of structural and physiological deviations ascribed to sub-optimal culture conditions. In an attempt to enhance embryo yield and quality we have conducted a series of investigations into the role of glutathione during embryogenesis. Changes in the glutathione redox state represent a key metabolic switch which triggers embryo growth. The imposition of a reduced environment during the early embryonic phases promotes cellular proliferation and increases the number of immature embryos, possibly by promoting the synthesis of nucleotides in support of energetic processes and mitotic activity. Continuation of embryo development is best achieved if the glutathione pool is experimentally switched towards an oxidized state; a condition which favors histodifferentiation and post-embryonic growth in both angiosperm and gymnosperms species. Among the structural events favored by the imposed oxidized environment is the proper formation of the shoot apical meristem (SAM), which acquires a "zygotic-like" appearance. The apical poles of treated embryos are well organized and display a proper expression and localization of meristem marker genes. These conditions are not met in control embryos which form abnormal SAMs characterized by the presence of intercellular spaces and differentiation of meristematic cells. Such meristems fail to reactivate at germination resulting in embryo abortion. Physiological and molecular studies have further demonstrated that the oxidized glutathione environment induces several responses, including changes in ascorbate metabolism, abscisic acid and ethylene synthesis, as well as alterations in storage product deposition patterns. This review attempts to relate these responses to the improved embryonic performance and proposes improved culture conditions to be applied for those cell lines and species recalcitrant to in vitro embryogenesis.

Altered HBK3 expression affects glutathione and ascorbate metabolism during the early phases of Norway spruce (Picea abies) somatic embryogenesis

Plant homeobox genes play an important role in plant development, including embryogenesis. Recently, the function of a class I homeobox of knox 3 gene, HBK3, has been characterized in the conifer Picea abies (L.) Karst (Norway spruce) [8]. During somatic embryogenesis, expression of HBK3 is required for the proper differentiation of proembryogenic masses into somatic embryos. This transition, fundamental for the overall embryogenic process, is accelerated in sense lines over-expressing HBK3 (HBK3-S) but precluded in antisense lines (HBK3-AS) where the expression of this gene is experimentally reduced. Altered HBK3 expression resulted in major changes of ascorbate and glutathione metabolism. During the initial phases of embryogeny the level of reduced GSH was higher in the HBK3-S lines compared to their control counterpart. An opposite profile was observed for the HBK3-AS lines where the glutathione redox state, i.e. GSH/GSH + GSSG, switched towards its oxidized form, i.e. GSSG. Very similar metabolic fluctuations were also measured for ascorbate, especially during the transition of proembryogenic masses into somatic embryos (7 days into hormone-free medium). At this stage the level of reduced ascorbate (ASC) in the HBK3-AS lines was about 75% lower compare to the untransformed line causing a switch of the ascorbate redox state, i.e. ASC/ASC + DHA + AFR, towards its oxidized forms, i.e. DHA + AFR. Changes in activities of several ascorbate and glutathione redox enzymes, including dehydroascorbate reductase (EC 1.8.5.1), ascorbate free radical reductase (EC 1.6.5.4) and glutathione reductase (GR; EC 1.6.4.2) were responsible for these metabolic differences. Data presented here suggest that HBK3 expression might regulate somatic embryo yield through alterations in glutathione and ascorbate metabolism, which have been previously implicated in controlling embryo development and maturation both in vivo and in vitro.

Buthionine sulfoximine (BSO)-mediated improvement in cultured embryo quality in vitro entails changes in ascorbate metabolism, meristem development and embryo maturation

Applications of buthionine sulfoximine (BSO), an inhibitor of GSH (reduced glutathione), which switches the cellular glutathione pool towards the oxidized form GSSG, positively influences embryo quality by improving the structure of the shoot apical meristem and promoting embryo maturation, both of which improve the post-embryonic performance of the embryos. To investigate the mechanisms underlying BSO-mediated improvement in embryo quality the transcript profiles of developing Brassica napus microspore-derived embryos cultured in the absence (control) or presence of BSO were analyzed using a 15,000-element B. napus oligo microarray. BSO applications induced major changes in transcript accumulation patterns, especially during the late phases of embryogenesis. BSO affected the transcription and activities of key enzymes involved in ascorbate metabolism, which resulted in major fluctuations in cellular ascorbate levels. These changes were related to morphological characteristics of the embryos and their post-embryonic performance. BSO applications also activated many genes controlling meristem formation and function, including ZWILLE, SHOOTMERISTEMLESS, and ARGONAUTE 1. Increased expression of these genes may contribute to the improved structural quality of the shoot poles observed in the presence of BSO. Compared to their control counterparts, middle- and late-stage BSO-treated embryos also showed increased accumulation of transcripts associated with the maturation phase of zygotic embryo development, including genes encoding ABA-responsive proteins and storage- and late-embryogenic abundant (LEA) proteins. Overall these transcriptional changes support the observation that the BSO-induced oxidized glutathione redox state allows cultured embryos to reach both morphological and physiological maturity, which in turn guarantees successful regeneration and enhanced post-embryonic growth.

Alterations of the glutathione redox state improve apical meristem structure and somatic embryo quality in white spruce (Picea glauca)

In white spruce, an improvement of somatic embryo number and quality can be achieved through experimental manipulations of the endogenous levels of reduced (GSH) and oxidized (GSSG) glutathione. An optimal protocol for embryo production included an initial application of GSH in the maturation medium, followed by replacement with GSSG during the remaining maturation period. Under these conditions, the overall embryo population more than doubled, and the percentage of fully developed embryos increased from 22% to almost 70%. These embryos showed improved post-embryonic growth and conversion frequency. Structural studies revealed remarkable differences between embryo types, especially in storage product deposition pattern and organization of the shoot apical meristem (SAM). Compared with their control counterparts, glutathione-treated embryos accumulated a larger amount of starch during the early stages of development, and more protein and lipid bodies during the second half of development. Differences were also noted in the organization of SAMs. Shoot meristems of control embryos were poorly organized and were characterized by the presence of intercellular spaces, which caused separation of the subapical cells. Glutathione-treated embryos had well-organized meristems composed of tightly packed cells which lack large vacuoles. The improved organization of the shoot apical meristems in treated embryos was ascribed to a lower production of ethylene. Differences in meristem structure between control and treated embryos were also related to the localization pattern of HBK1, a shoot apical meristem 'molecular marker' gene with preferential expression to the meristematic cells of the shoot pole. Expression of this gene, which was localized to the apical cells in control embryos, was extended to the subapical cells of treated embryos. Overall, it appears that meristem integrity and embryo quality are under the direct control of the glutathione redox state.

The traditional diet of Greece and cancer

The term 'Mediterranean diet', implying that all Mediterranean people have the same diet, is a misnomer. The countries around the Mediterranean basin have different diets, religions and cultures. Their diets differ in the amount of total fat, olive oil, type of meat, wine, milk, cheese, fruits and vegetables; and the rates of coronary heart disease and cancer, with the lower death rates and longer life expectancy occurring in Greece. The diet of Crete represents the traditional diet of Greece prior to 1960. Analyses of the dietary pattern of the diet of Crete shows a number of protective substances, such as selenium, glutathione, a balanced ratio of n-6/n-3 essential fatty acids (EFA), high amounts of fibre, antioxidants (especially resveratrol from wine and polyphenols from olive oil), vitamins E and C, some of which have been shown to be associated with lower risk of cancer, including cancer of the breast. Epidemiological studies and animal experiments indicate that n-3 fatty acids exert protective effects against some common cancers, especially cancers of the breast, colon and prostate. Many mechanisms are involved, including suppression of neoplastic transformation, cell growth inhibition, and enhanced apoptosis and anti-angiogenicity, through the inhibition of eicosanoid production from n-6 fatty acids; and suppression of cyclooxygenase 2 (COX-2), interleukin 1 (IL-1) and IL-6 gene expression by n-3 fatty acids. Recent intervention studies in breast cancer patients indicate that n-3 fatty acids, and docosahexaenoic acid (DHA) in particular, increase the response to chemopreventive agents. In patients with colorectal cancer, eicosapentaenoic acid (EPA) and DHA decrease cell proliferation, and modulate favourably the balance between colonic cell proliferation and apoptosis. These findings should serve as a strong incentive for the initiation of intervention trials that will test the effect of specific dietary patterns in the prevention and management of patients with cancer.

The Mediterranean diets: What is so special about the diet of Greece? The scientific evidence

The term "Mediterranean diet," implying that all Mediterranean people have the same diet, is a misnomer. The countries around the Mediterranean basin have different diets, religions and cultures. Their diets differ in the amount of total fat, olive oil, type of meat and wine intake; milk vs. cheese; fruits and vegetables; and the rates of coronary heart disease and cancer, with the lower death rates and longer life expectancy occurring in Greece. Extensive studies on the traditional diet of Greece (the diet before 1960) indicate that the dietary pattern of Greeks consists of a high intake of fruits, vegetables (particularly wild plants), nuts and cereals mostly in the form of sourdough bread rather than pasta; more olive oil and olives; less milk but more cheese; more fish; less meat; and moderate amounts of wine, more so than other Mediterranean countries. Analyses of the dietary pattern of the diet of Crete shows a number of protective substances, such as selenium, glutathione, a balanced ratio of (n-6):(n-3) essential fatty acids (EFA), high amounts of fiber, antioxidants (especially resveratrol from wine and polyphenols from olive oil), vitamins E and C, some of which have been shown to be associated with lower risk of cancer, including cancer of the breast. These findings should serve as a strong incentive for the initiation of intervention trials that will test the effect of specific dietary patterns in the prevention and management of patients with cancer.

Oxidative stress in recalcitrant tissue cultures of grapevine

Thiobarbituric acid reactive substances (TBARS), and fluorescent compounds with spectral characteristics typical of products associated with oxidative stress in senescent and aging plant and animal cells, were detected in tissue cultures of the recalcitrant grapevine Vitis vinifera L. cultivar, Sultanina. These compounds increased during the early stages of dedifferentiation (callogenesis) of nodal stem explants. Catalase activity was not detected in the original explant, but was induced during callogenic dedifferentiation. Conversely, superoxide dismutase activity was detectable in the original explant, but diminished during the first week of callus induction. Transfer to callus induction medium promoted a large increase in the sulfhydryl content of nodal tissues. TBARS and fluorescent products accumulated in Sultanina callus during long-term culture (over 6 months). The possibility that oxidative stress may contribute to culture recalcitrance in this vine is discussed.

Variation in free-radical damage in rice cell suspensions with different embryogenic potentials

Levels of free-radical-mediated lipid peroxidation were monitored in cell-suspension cultures of Oryza sativa L. possessing different embryogenic potentials. Oxidative stress was evaluated using assays which sequentially assessed the stages of lipid peroxidation (diene conjugation, peroxidation, and the formation of secondary lipid-peroxidation products). Lipid peroxidation was significantly higher in a cell line which had lost embryogenic ability compared with lines which still retained this capacity. Superoxide dismutase (EC 1.15.1.1) activity did not vary significantly between the embryogenic and previously embryogenic lines; however, catalase (EC 1.11.1.6) and peroxidase (EC 1.11.1.7) activities were significantly lower in the line which had lost embryogenic ability. Metabolic activity as estimated by reduction of triphenyl tetrazolium chloride decreased with diminishing embryogenic potential and was especially low in cell lines which never exhibited embryogenic capabilities. The possible involvement of free radicals in the loss of embryogenic potential of rice cells is discussed.

Common purslane: a source of omega-3 fatty acids and antioxidants

omega-3 fatty acids, alpha-tocopherol, ascorbic acid, beta-carotene and glutathione determined in leaves of purslane (Portulaca oleracea), grown in both a controlled growth chamber and in the wild, were compared in composition to spinach. Leaves from both samples of purslane contained higher amounts of alpha-linolenic acid (18:3w3) than did leaves of spinach. Chamber-grown purslane contained the highest amount of 18:3w3. Samples from the two kinds of purslane contained higher leaves of alpha-tocopherol, ascorbic acid and glutathione than did spinach. Chamber-grown purslane was richer in all three and the amount of alpha-tocopherol was seven times higher than that found in spinach, whereas spinach was slightly higher in beta-carotene. One hundred grams of fresh purslane leaves (one serving) contain about 300-400 mg of 18:3w3; 12.2 mg of alpha-tocopherol; 26.6 mg of ascorbic acid; 1.9 mg of beta-carotene; and 14.8 mg of glutathione. We confirm that purslane is a nutritious food rich in omega-3 fatty acids and antioxidants.