Polyamine levels during the development of zygotic and somatic embryos of Pinus radiata

The Chemical Environment at Maturation Stage in Pinus spp. Somatic Embryogenesis: Implications in the Polyamine Profile of Somatic Embryos and Morphological Characteristics of the Developed Plantlets

Changes in the chemical environment at the maturation stage in Pinus spp. somatic embryogenesis will be a determinant factor in the conversion of somatic embryos to plantlets. Furthermore, the study of biochemical and morphological aspects of the somatic embryos could enable the improvement of somatic embryogenesis in Pinus spp. In the present work, the influence of different amino acid combinations, carbohydrate sources, and concentrations at the maturation stage of Pinus radiata D. Don and Pinus halepensis Mill. was analyzed. In P. radiata, the maturation medium supplemented with 175 mM of sucrose and an increase in the amino acid mixture (1,100 mgL^-1 of L-glutamine, 1,050 mgL^-1 of L-asparagine, 350 mgL^-1 of L-arginine, and 35 mgL^-1 of L-proline) promoted bigger embryos, with a larger stem diameter and an increase in the number of roots in the germinated somatic embryos, improving the acclimatization success of this species. In P. halepensis, the maturation medium supplemented with 175 mM of maltose improved the germination of somatic embryos. The increase in the amount of amino acids in the maturation medium increased the levels of putrescine in the germinated somatic embryos of P. halepensis. We detected significant differences in the amounts of polyamines between somatic plantlets of P. radiata and P. halepensis; putrescine was less abundant in both species. For the first time, in P. radiata and P. halepensis somatic embryogenesis, we detected the presence of cadaverine, and its concentration changed according to the species.

Stage-specific protein regulation during somatic embryo development of Carica papaya L. 'Golden'

Somatic embryogenesis is an important biotechnological technique for large-scale propagation of elite genotypes. Identifying stage-specific compounds associated with somatic embryo development can help elucidate the ontogenesis of Carica papaya L. somatic embryos and improve tissue culture protocols. To identify the stage-specific proteins that are present during the differentiation of C. papaya somatic embryos, proteomic analyses of embryos at the globular, heart, torpedo and cotyledonary developmental stages were performed. Mass spectrometry data have been deposited in the ProteomeXchange with the dataset identifier PXD021107. Comparative proteomic analyses revealed a total of 801 proteins, with 392 classified as differentially accumulated proteins in at least one of the developmental stages. The globular-staged presented a higher number of unique proteins (16), and 7 were isoforms of 60S ribosomal proteins, suggesting high translational activity at the beginning of somatic embryogenesis. Proteins related to mitochondrial metabolism accumulated to a high degree at the early developmental stages and then decreased with increasing development, and they contributed to cell homeostasis in early somatic embryos. A progressive increase in the accumulation of vicilin, late embryogenesis abundant proteins and chloroplastic proteins that lead to somatic embryo maturation was also observed. The differential accumulation of acetylornithine deacetylase and S-adenosylmethionine synthase 2 proteins was correlated with increases in putrescine and spermidine contents, which suggests that both polyamines should be tested to determine whether they increase the conversion rates of globular- to cotyledonary-staged somatic embryos. Taken together, the results showed that somatic embryo development in C. papaya is regulated by the differential accumulation of proteins, with ribosomal and mitochondrial proteins more abundant during the early somatic embryo stages and seed maturation proteins more abundant during the late stages.

Citrus Polyamines: Structure, Biosynthesis, and Physiological Functions

Polyamines (PAs) are ubiquitous biogenic amines found in all living organisms from bacteria to Archaea, and Eukaryotes including plants and animals. Since the first description of putrescine conjugate, feruloyl-putrescine (originally called subaphylline), from grapefruit leaves and juice, many research studies have highlighted the importance of PAs in growth, development, and other physiological processes in citrus plants. PAs appear to be involved in a wide range of physiological processes in citrus plants; however, their exact roles are not fully understood. Accordingly, in the present review, we discuss the biosynthesis of PAs in citrus plants, with an emphasis on the recent advances in identifying and characterizing PAs-biosynthetic genes and other upstream regulatory genes involved in transcriptional regulation of PAs metabolism. In addition, we will discuss the recent metabolic, genetic, and molecular evidence illustrating the roles of PAs metabolism in citrus physiology including somatic embryogenesis; root system formation, morphology, and architecture; plant growth and shoot system architecture; inflorescence, flowering, and flowering-associated events; fruit set, development, and quality; stomatal closure and gas-exchange; and chlorophyll fluorescence and photosynthesis. We believe that the molecular and biochemical understanding of PAs metabolism and their physiological roles in citrus plants will help citrus breeding programs to enhance tolerance to biotic and abiotic stresses and provide bases for further research into potential applications.

Thermospermine Synthase (ACL5) and Diamine Oxidase (DAO) Expression Is Needed for Zygotic Embryogenesis and Vascular Development in Scots Pine

Unlike in flowering plants, the detailed roles of the enzymes in the polyamine (PA) pathway in conifers are poorly known. We explored the sequence conservation of the PA biosynthetic genes and diamine oxidase (DAO) in conifers and flowering plants to reveal the potential functional diversification of the enzymes between the plant lineages. The expression of the genes showing different selective constraints was studied in Scots pine zygotic embryogenesis and early seedling development. We found that the arginine decarboxylase pathway is strongly preferred in putrescine production in the Scots pine as well as generally in conifers and that the reduced use of ornithine decarboxylase (ODC) has led to relaxed purifying selection in ODC genes. Thermospermine synthase (ACL5) genes evolve under strong purifying selection in conifers and the DAO gene is also highly conserved in pines. In developing Scots pine seeds, the expression of both ACL5 and DAO increased as embryogenesis proceeded. Strong ACL5 expression was present in the procambial cells of the embryo and in the megagametophyte cells destined to die via morphologically necrotic cell death. Thus, the high sequence conservation of ACL5 genes in conifers may indicate the necessity of ACL5 for both embryogenesis and vascular development. Moreover, the result suggests the involvement of ACL5 in morphologically necrotic cell death and supports the view of the genetic regulation of necrosis in Scots pine embryogenesis and in plant development. DAO transcripts were located close to the cell walls and between the walls of adjacent cells in Scots pine zygotic embryos and in the roots of young seedlings. We propose that DAO, in addition to the role in Put oxidation for providing H2O2 during the cell-wall structural processes, may also participate in cell-to-cell communication at the mRNA level. To conclude, our findings indicate that the PA pathway of Scots pines possesses several special functional characteristics which differ from those of flowering plants.

The Response of Picea abies Somatic Embryos to UV-B Radiation Depends on the Phase of Maturation

Ultraviolet-B (UV-B) radiation is a key environmental signal which initiates diverse responses that affect the metabolism, development, and viability of plants. In keeping with our previous studies, we concentrated primarily on how UV-B radiation affects Norway spruce [Picea abies (L.) Karst.] somatic embryo maturation and how phenolics and polyamines (PAs) are linked to the defense response invoked by UV-B irradiation. We treated clusters of Norway spruce embryogenic culture (EC) with UV-B during the five stages of embryo maturation (early, cylindrical, precotyledonary, cotyledonary, and mature embryos). For the first time, we take an advantage of the unique environmental scanning electron microscope AQUASEM II to characterize somatic embryos in their native state. The severity of the irradiation effect on embryonal cell viability was shown to be dependent on the intensity of radiation as well as the stage of embryo development, and might be related to the formation of protoderm. The response of early embryos was characterized by an increase in malondialdehyde (MDA), a marked decrease in PA contents and a decline in phenolics. The reduced ability to activate the defense system seems to be responsible not only for the severe cell damage and decrease in viability but also for the inhibition of embryo development. The significant reduction in spermidine (Spd), which has been reported to be crucial for the somatic embryo development of several coniferous species, may be causally linked to the limited development of embryos. The pronounced decrease in cell wall-bound ferulic acid might correspond to failure of somatic embryos to reach more advanced stages of development. Embryos at later stages of development showed stress defense responses that were more efficient against UV-B exposure.

Polyamine- and Amino Acid-Related Metabolism: The Roles of Arginine and Ornithine are Associated with the Embryogenic Potential

The mechanisms that control polyamine (PA) metabolism in plant cell lines with different embryogenic potential are not well understood. This study involved the use of two Araucaria angustifolia cell lines, one of which was defined as being blocked, in that the cells were incapable of developing somatic embryos, and the other as being responsive, as the cells could generate somatic embryos. Cellular PA metabolism was modulated by using 5 mM arginine (Arg) or ornithine (Orn) at two time points during cell growth. Two days after subculturing with Arg, an increase in citrulline (Cit) content was observed, followed by a higher expression of genes related to PA catabolism in the responsive cell line; whereas, in the blocked cell line, we only observed an accumulation of PAs. After 14 d, metabolism was directed towards putrescine accumulation in both cell lines. Exogenous Arg and Orn not only caused a change in cellular contents of PAs, but also altered the abundance of a broader spectrum of amino acids. Specifically, Cit was the predominant amino acid. We also noted changes in the expression of genes related to PA biosynthesis and catabolism. These results indicate that Arg and Orn act as regulators of both biosynthetic and catabolic PA metabolites; however, we suggest that they have distinct roles associated with embryogenic potential of the cells.

Bottlenecks in bog pine multiplication by somatic embryogenesis and their visualization with the environmental scanning electron microscope

Somatic embryogenesis (SE) is an important biotechnological technique used for the propagation of many pine species in vitro. However, in bog pine, one of the most endangered tree species in the Czech Republic, limitations were observed, which negatively influenced the development and further germination of somatic embryos. Although initiation frequency was very low-0.95 %, all obtained cell lines were subjected to maturation. The best responding cell line (BC1) was used and subjected to six different variants of the maturation media. The media on which the highest number of early-precotyledonary/cotyledonary somatic embryos was formed was supplemented with 121 μM abscisic acid (ABA) and with 6 % maltose. In the end of maturation experiments, different abnormalities in formation of somatic embryos were observed. For visualization and identification of abnormalities in meristem development during proliferation and maturation processes, the environmental scanning electron microscope was used. In comparison to the classical light microscope, the non-commercial environmental scanning electron microscope AQUASEM II has been found as a very useful tool for the quick recognition of apical meristem disruption and abnormal development. To our knowledge, this is the first report discussing somatic embryogenesis in bog pine. Based on this observation, the cultivation procedure could be enhanced and the method for SE of bog pine optimized.

Elucidation of the polyamine biosynthesis pathway during Brazilian pine (Araucaria angustifolia) seed development

Polyamines (PAs), such as spermidine and spermine, as well as amino acids that are substrates for their biosynthesis, are known to be essential for plant development. However, little is known about the gene expression and metabolic switches associated with the ornithine/arginine and PA biosynthetic pathway during seed development in conifers. To understand these metabolic switches, the enzyme activity of arginine decarboxylase and ornithine decarboxylase, as well as the contents of PAs and amino acids were evaluated in three Araucaria angustifolia (Bertol. Kuntze) seed developmental stages in combination with expression profile analyses of genes associated with the ornithine/arginine and PA biosynthetic pathway. Twelve genes were selected for further analysis and it was shown that the expression profiles of AaADC and AaSAMDC were up-regulated during zygotic embryo development. Polyamines and amino acids were found to accumulate differently in embryos and megagametophytes, and the transition from the globular to the cotyledonary stage was marked by an increase in free and conjugated spermidine and spermine contents. Putrescine is made from arginine, which was present at low content at the late embryogenesis stage, when high content of citrulline was observed. Differences in amino acids, PAs and gene expression profiles of biosynthetic genes at specific seed stages and at each seed transition stage were investigated, providing insights into molecular and physiological aspects of conifer embryogenesis for use in future both basic and applied studies.

Moderate stress responses and specific changes in polyamine metabolism characterize Scots pine somatic embryogenesis

Somatic embryogenesis (SE) is one of the methods with the highest potential for the vegetative propagation of commercially important coniferous species. However, many conifers, including Scots pine (Pinus sylvestris L.), are recalcitrant to SE and a better understanding of the mechanisms behind the SE process is needed. In Scots pine SE cultures, embryo production is commonly induced by the removal of auxin, addition of abscisic acid (ABA) and the desiccation of cell masses by polyethylene glycol (PEG). In the present study, we focus on the possible link between the induction of somatic embryo formation and cellular stress responses such as hydrogen peroxide protection, DNA repair, changes in polyamine (PA) metabolism and autophagy. Cellular PA contents and the expression of the PA metabolism genes arginine decarboxylase (ADC), spermidine synthase (SPDS), thermospermine synthase (ACL5) and diamine oxidase (DAO) were analyzed, as well as the expression of catalase (CAT), DNA repair genes (RAD51, KU80) and autophagy-related genes (ATG5, ATG8) throughout the induction of somatic embryo formation in Scots pine SE cultures. Among the embryo-producing SE lines, the expression of ADC, SPDS, ACL5, DAO, CAT, RAD51, KU80 and ATG8 showed consistent profiles. Furthermore, the overall low expression of the stress-related genes suggests that cells in those SE lines were not stressed but recognized the ABA+PEG treatment as a signal to trigger the embryogenic pathway. In those SE lines that were unable to produce embryos, cells seemed to experience the ABA+PEG treatment mostly as osmotic stress and activated a wide range of stress defense mechanisms. Altogether, our results suggest that the direction to the embryogenic pathway is connected with cellular stress responses in Scots pine SE cultures. Thus, the manipulation of stress response pathways may provide a way to enhance somatic embryo production in recalcitrant Scots pine SE lines.

Proteomic analysis and polyamines, ethylene and reactive oxygen species levels of Araucaria angustifolia (Brazilian pine) embryogenic cultures with different embryogenic potential

Somatic embryogenesis is an important biotechnological tool in the large-scale propagation of elite genotypes and ex situ conservation of conifer species. Protocols for the induction and proliferation of embryogenic cultures (ECs) of Brazilian pine (Araucaria angustifolia (Bert.) O. Ktze) are well established, although the proper formation of mature somatic embryos (SEs) is still problematic. Thus, the identification of molecular markers for the screening of ECs able to respond to maturation conditions (abscisic acid and osmotic agents) is highly desirable. To develop molecular markers for the early detection of ECs able to develop well-formed SEs under maturation conditions, we analyzed the proteins found during the proliferation phase of A. angustifolia cell lines with different embryogenic capabilities, with one cell line being responsive to maturation conditions (R cell line), and one cell line that presented blocked development of SEs (B cell line). In addition, based on the peptides identified, polyamine levels (free and conjugate), ethylene production and reactive oxygen species (ROS) emission were analyzed using both EC lines (R and B cell lines). A marked difference in the biochemistry of ECs between these two cell lines was observed. Eleven proteins that were differentially expressed in the cell lines were identified by the combination of two-dimensional electrophoresis (2-DE) and MALDI-TOF/TOF mass spectrometry. Among these, S-adenosylmethionine synthase, the enzyme associated with polyamines and ethylene biosynthesis, was observed exclusively in the R cell line, while a protein linked to the oxidative stress subunit F of NADH dehydrogenase was observed exclusively in the B cell lines. Additionally, B cell lines showed higher levels of diamine putrescine and lower levels of ethylene. Higher values of ethylene and ROS were observed for the cell line that showed normal development of SEs. Altogether, our results open new perspectives in the optimization of culture conditions for A. angustifolia somatic embryogenesis, as well as establishing biochemical markers for the early selection of ECs during maturation trials.

Polyamines affect the cellular growth and structure of pro-embryogenic masses in Araucaria angustifolia embryogenic cultures through the modulation of proton pump activities and endogenous levels of polyamines

Polyamines (PAs) are abundant polycationic compounds involved in many physiological processes in plants, including somatic embryogenesis. This study investigates the role of PAs on cellular growth and structure of pro-embryogenic masses (PEMs), endogenous PA and proton pump activities in embryogenic suspension cultures of Araucaria angustifolia. The embryogenic suspension cultures were incubated with putrescine (Put), spermidine (Spd), spermine (Spm) and the inhibitor methylglyoxal-bis(guanylhydrazone) (MGBG), respectively (1 mM). After 24 h and 21 days, the cellular growth and structure of PEMs, endogenous PA contents and proton pump activities were analyzed. The addition of Spm reduced the cellular growth and promoted the development of PEMs in embryogenic cultures, which could be associated with a reduction in the activities of proton pumps, such as H(+) -ATPase P- and V-types and H(+) -PPases, and alterations in the endogenous PA contents. Spm significantly affected the physiology of the A. angustifolia somatic embryogenesis suspension, as it potentially affects cellular growth and structure of PEMs through the modulation of proton pump activities. This work demonstrates the involvement of exogenous PAs in the modulation of cellular growth and structure of PEMs, endogenous PA levels and proton pump activities during somatic embryogenesis. To our knowledge, this study is the first to report a relationship between PAs and proton pump activities in these processes. The results obtained in this study offer new perspectives for studies addressing the role of PAs and proton pump on somatic embryogenesis in this species.

Polyamine metabolism during exponential growth transition in Scots pine embryogenic cell culture

Polyamine (PA) metabolism was studied in liquid cultures of Scots pine (Pinus sylvestris L.) embryogenic cells. The focus of the study was on the metabolic changes at the interphase between the initial lag phase and the exponential growth phase. PA concentrations fluctuated in the liquid cultures as follows. Putrescine (Put) concentrations increased, whereas spermidine (Spd) concentrations decreased in both free and soluble conjugated PA fractions. The concentrations of free and soluble conjugated spermine (Spm) remained low, and small amounts of excreted PAs were also found in the culture medium. The minor production of secondary metabolites reflected the undifferentiated stage of the embryogenic cell culture. Put was produced via the arginine decarboxylase (ADC) pathway. Futhermore, the gene expression data suggested that the accumulation of Put was caused neither by an increase in Put biosynthesis nor by a decrease in Put catabolism, but resulted mainly from the decrease in the biosynthesis of Spd and Spm. Put seemed to play an important role in cell proliferation in Scots pine embryogenic cells, but the low pH of the culture medium could also, at least partially, be the reason for the accumulation of endogenous Put. High Spd concentrations at the initiation of the culture, when cells were exposed to stress and cell death, suggested that Spd may act not only as a protector against stress but also as a growth suppressor, when proliferative growth is not promoted. All in all, Scots pine embryogenic cell culture was proved to be a favourable experimental platform to study PA metabolism and, furthermore, the developed system may also be beneficial in experiments where, e.g., the effect of specific stressors on PA metabolism is addressed.

Polyamines, IAA and ABA during germination in two recalcitrant seeds: Araucaria angustifolia (Gymnosperm) and Ocotea odorifera (Angiosperm)

BACKGROUND AND AIMS

Plant growth regulators play an important role in seed germination. However, much of the current knowledge about their function during seed germination was obtained using orthodox seeds as model systems, and there is a paucity of information about the role of plant growth regulators during germination of recalcitrant seeds. In the present work, two endangered woody species with recalcitrant seeds, Araucaria angustifolia (Gymnosperm) and Ocotea odorifera (Angiosperm), native to the Atlantic Rain Forest, Brazil, were used to study the mobilization of polyamines (PAs), indole-acetic acid (IAA) and abscisic acid (ABA) during seed germination.

METHODS

Data were sampled from embryos of O. odorifera and embryos and megagametophytes of A. angustifolia throughout the germination process. Biochemical analyses were carried out in HPLC.

KEY RESULTS

During seed germination, an increase in the (Spd + Spm) : Put ratio was recorded in embryos in both species. An increase in IAA and PA levels was also observed during seed germination in both embryos, while ABA levels showed a decrease in O. odorifera and an increase in A. angustifolia embryos throughout the period studied.

CONCLUSIONS

The (Spd + Spm) : Put ratio could be used as a marker for germination completion. The increase in IAA levels, prior to germination, could be associated with variations in PA content. The ABA mobilization observed in the embryos could represent a greater resistance to this hormone in recalcitrant seeds, in comparison to orthodox seeds, opening a new perspective for studies on the effects of this regulator in recalcitrant seeds. The gymnosperm seed, though without a connective tissue between megagametophyte and embryo, seems to be able to maintain communication between the tissues, based on the likely transport of plant growth regulators.

Polyamine profiles and biosynthesis in somatic embryo development and comparison of germinating somatic and zygotic embryos of Norway spruce

The polyamine (PA) contents and activities of PA biosynthetic enzymes in Norway spruce somatic embryos [Picea abies L. (Karst.), genotype AFO 541] were studied in relation to anatomical changes during their development, from proliferation to germination, and changes in these variables associated with the germination of mature somatic and zygotic embryos were compared. Activities of PA biosynthetic enzymes steadily increased during the development of somatic embryos, from embryogenic suspensor mass until early cotyledonary stages. In these stages, the spermidine (Spd) level was significantly higher than the putrescine (Put) level, and the increases coincided with the sharp increases in S-adenosylmethionine decarboxylase activity in the embryos. The biosynthetic enzyme activity subsequently declined in mature cotyledonary embryos, accompanied by sharp reductions in PA contents, especially in cellular Put contents in embryos from 6 weeks old through the desiccation phase (although the spermine level significantly increased during the desiccation phase), resulting in a shift in the Spd/Put ratio from ca. 2 in early cotyledonary embryos to around 10 after 3 weeks of desiccation. In mature zygotic embryos, Spd contents were twofold lower, but Put levels were higher, than in mature somatic embryos, hence their Spd/Put ratio was substantially lower (ca. 2, in both embryos and megagametophytes). In addition, the PA synthesis activity profiles in the embryos differed (ornithine decarboxylase and arginine decarboxylase activities predominating in mature somatic and zygotic embryos, respectively). The start of germination was associated with a rise in PA biosynthetic activity in the embryos of both origins, which was accompanied by a marked increase in Put contents in somatic embryos, resulting in the decline of Spd/Put ratio to about 2, similar to the ratio in mature and germinating zygotic embryos. The accumulation of high levels of PAs in somatic embryos may be causally linked to their lower germinability than in zygotic embryos.

Proteomic analysis of somatic embryogenesis in Valencia sweet orange (Citrus sinensis Osbeck)

Two dimensional gel electrophoresis combined with matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) was employed to study the somatic embryogenesis (SE) in Valencia sweet orange (Citrus sinensis Osbeck). Twenty-four differentially expressed proteins were identified at five time points of citrus SE (0, 1, 2, 3, 4 weeks after embryo initiation) covering globular, heart/torpedo and cotyledon-shaped embryo stages. The general expression patterns for these proteins were consistent with those appeared at 4 weeks of citrus SE. The most striking feature of our study was that five proteins were predicted to be involved in glutathione (GSH) metabolism and anti-oxidative stress, and they exhibited different expression patterns during SE. Based on that oxidative stress has been validated to enhance SE, the preferential representation for anti-oxidative proteins suggests that they could have a developmental role in citrus SE. Some proteins involved in cell division, photosynthesis and detoxification were also identified, and their possible roles in citrus SE were discussed.

Involvement of polyamine biosynthesis in somatic embryogenesis of Valencia sweet orange (Citrus sinensis) induced by glycerol

Culture of Citrus sinensis embryogenic callus on the embryo-inducing medium (EIM) containing glycerol gave rise to a large number of embryos, whereas very few embryos were observed on the callus growth medium (CGM). In the current paper, attempts were made to investigate whether polyamine biosynthesis was involved in glycerol-mediated somatic embryogenesis. Quantification of free polyamines by high-performance liquid chromatography showed that the cultures on EIM had less putrescine than those on CGM. However, increase in spermidine and spermine was detected in cultures on EIM during the first 20d of culture, coincident with abundant somatic embryogenesis. The globular embryos contained more polyamines than embryos at other stages. Semi-quantitative reverse transcriptase-polymerase chain reaction assay showed that expression levels of all of the five key genes involved in polyamine biosynthesis, with the exception of S-adenosylmethionine decarboxylase, were induced in cultures on EIM, and that their transcriptional levels were increased with maturation of the embryos. Addition of alpha-difluoromethylornithine, a polyamine biosynthesis inhibitor, to EIM resulted in remarkable inhibition of somatic embryogenesis, concurrent with notable reduction of endogenous putrescine and spermidine, particularly at higher concentrations. Exogenous application of 1mM putrescine to EIM together with 5mM alpha-difluoromethylornithine led to dramatic enhancement of endogenous polyamines, which successfully restored somatic embryogenesis. All of these, collectively, demonstrated that free polyamines, at least spermidine and spermine herein, were involved in glycerol-mediated promotion of somatic embryogenesis, which will open a new avenue for establishing a sophisticated system for somatic embryogenesis based on the modulation of endogenous polyamines.

Isolation of mitochondria from embryogenic cultures of Picea abies (L.) Karst. and Abies cephalonica Loud.: characterization of a K+(ATP) channel

A valuable method to isolate and purify mitochondria from embryonal masses of two coniferous species (Picea abies [L.] Karst. and Abies cephalonica Loud.) is described. Crude mitochondria from both species were shown to be intact, oxygen consuming (with malate plus glutammate, succinate and NADH as substrates) and well coupled (respiratory control ratio ca. 4). The oxidation of the substrates was only partially KCN-insensitive (alternative oxidase) in some cases. However, these fractions were contaminated by membranes (e.g. plasmalemma, tonoplast, Golgi and endoplasmic reticulum). After purification by a discontinuous Percoll gradient (18, 23, 40%, v/v), three mitochondrial populations were separated. The 0/18 interface fraction was composed mainly of broken and uncoupled mitochondria, while the other two (18/23 and 23/40 interface fractions) contained intact and coupled mitochondria, but only 23/40 interface fraction revealed to be better purified starting from both coniferous embryonal masses. In the latter purified fraction, the presence of a cyclosporin A-sensitive K (ATP) (+) channel was demonstrated. These findings were discussed in the light of the potential use of these mitochondrial fractions in bioenergetic studies, or in the involvement of these organelles to stress response in conifers.

Spermidine and the ectomycorrhizal fungus Pisolithus tinctorius synergistically induce maturation of Scots pine embryogenic cultures

Exogenous spermidine (Spd) and the ectomycorrhizal (ECM) fungus Pisolithus tinctorius (Pers.) Coker and Couch had a synergistic effect on the maturation of Scots pine (Pinus sylvestris L.) somatic embryos. Induced maturation was expressed as a higher number of cell masses able to form embryos and a greater number of embryos formed per cell mass. In contrast, treatment with P. tinctorius alone on the hormone-free medium resulted in the lowest embryo-forming capacity. Retarded proliferation growth appeared to be required for maturation, but did not explain the synergistic effect of the fungus and exogenous Spd. Simultaneous treatment did not result in lower concentrations of putrescine (Put), Spd or spermine (Spm) in the embryogenic cell masses relative to the separate treatments. Our study is the first report on the use of a specific ECM fungus to induce maturation of somatic embryos, and it indicates that P. tinctorius was able to modify the maturation media in a way that, together with exogenous Spd, positively affected embryogenic cultures of Scots pine. Our study also shows that it is possible to enhance plant development other than root formation by using specific ECM fungi.

Consistency of polyamine profiles and expression of arginine decarboxylase in mitosis during zygotic embryogenesis of Scots pine

In this study, we show that both arginine decarboxylase (ADC) protein and mRNA transcript are present at different phases of mitosis in Scots pine (Pinus sylvestris) zygotic embryogenesis. We also examined the consistency of polyamine (PA) profiles with the effective temperature sum, the latter indicating the developmental stage of the embryos. PA metabolism was analyzed by fitting statistical regression models to the data of free and soluble conjugated PAs, to the enzyme activities of ADC and ornithine decarboxylase (ODC), as well as to the gene expression of ADC. According to the fitted models, PAs typically had the tendency to increase at the early stages but decrease at the late stages of embryogenesis. Only the free putrescine fraction remained stable during embryo development. The PA biosynthesis strongly preferred the ADC pathway. Both ADC gene expression and ADC enzyme activity were substantially higher than putative ODC gene expression or ODC enzyme activity, respectively. ADC gene expression and enzyme activity increased during embryogenesis, which suggests the involvement of transcriptional regulation in the expression of ADC. Both ADC mRNA and ADC protein localized in dividing cells of embryo meristems and more specifically within the mitotic spindle apparatus and close to the chromosomes, respectively. The results suggest the essential role of ADC in the mitosis of plant cells.

Flower fertilization and fruit development prompt changes in free polyamines and ethylene in damson plum (Prunus insititia L.)

The flower opening of damson plum (Prunus insititia L.) was accompanied by an increase in the content of free-polyamines (PA) in the sepals, petals and sex organs, the ovary being most active in accumulating spermine (Spm). The fertilization process and senescence brought on a decline in ovarian Spm, but stimulated putrescine (Put) and spermidine (Spd) content in the sepals. The endocarp of this climacteric fruit produced only ethylene at the end of the S1 phase and throughout S2, in which there was a great richness in ACC and MACC. The greatest amounts of ACC and MACC were observed in the ripening mesocarp and epicarp. The contribution of the endocarp and epicarp to the total ACC in the developing fruit was very similar. During flowering and S1 and S2 phases, Spd was the most abundant PA; in contrast, during S3 and S4 Put was most abundant. The mesocarp contributed the most to the total content in PA throughout the fruit development. The control of SAM distribution towards ethylene and/or PA appears to differ during the development of the endocarp, as the only peak of free-Put (detected in S2) coincided with the highest ACC accumulation and ethylene production. On the contrary, in S3 it is probable that SAM was transformed preferentially into PA, given that free-Spd and Spm, hardly detectable in S1 and S2, peaked in this phase in which there was no gas production.

In vitro somatic embryogenesis from cell suspension cultures of cowpea [Vigna unguiculata (L.) Walp]

We report, an efficient protocol for plantlet regeneration from the cell suspension cultures of cowpea through somatic embryogenesis. Primary leaf-derived, embryogenic calli initiated in MMS [MS salts (Murashige and Skoog 1962) with B5 (Gamborg et al. 1968) vitamins] medium containing 2,4-Dichlorophenoxyacetic acid (2,4-D), casein hydrolysate (CH), and L: -Glutamic acid-5-amide (Gln). Fast-growing embryogenic cell suspensions were established in 0.5 mg l(-1) 2,4-D, which resulted in the highest recovery of early stages of somatic embryos in liquid MMS medium. Embryo development was asynchronous and strongly influenced by the 2,4-D concentration. Mature monocotyledonary-stage somatic embryos were induced in liquid B5 medium containing 0.1 mg l(-1) 2,4-D, 20 mg l(-1) L: -Proline (Pro), 5 muM Abscisic acid (ABA), and 2% mannitol. B5 medium was found superior for the maturation of somatic embryos compared to MS and MMS media. The importance of duration (5 d) for effective maturation of somatic embryos is demonstrated. A reduction in the 2,4-D level in suspensions increased the somatic embryo induction and maturation with decreased abnormalities. Sucrose was found to be the best carbon source for callus induction while mannitol for embryo maturation and maltose for embryo germination. Extension of hypocotyls and complete development of plantlet was achieved in half-strength B5 medium supplemented with 3% maltose, 2500 mg l(-1) potassium nitrate, and 0.05 mg l(-1) thidiazuron (TDZ) with 32% regeneration frequency. Field-established plants were morphologically normal and fertile. This regeneration protocol assures a high frequency of embryo induction, maturation, and plantlet conversion.

Polyamines and somatic embryogenesis in two Vitis vinifera cultivars

Polyamine content and activities of enzymes of polyamine biosynthesis were assayed during somatic embryogenesis in Vitis vinifera callus cultures of Chardonnay and Brachetto 'a grappolo lungo' (Brachetto g.l.) cultivars. The analyses were carried out on embryogenic callus samples, embryos at different stages and developing plants. Polyamine content, both in the free and PCA-soluble conjugated form, was higher in Brachetto g.l. than in Chardonnay, and putrescine was present at higher concentrations than the other polyamines. In all samples of both cultivars, ornithine decarboxylase activity (ODC, EC 4.1.1.17) was higher than arginine decarboxylase (ADC, EC 4.1.1.19), with a maximum in developing plant roots. S-Adenosylmethionine decarboxylase (SAMDC, EC 4.1.1.50) activity displayed a similar trend. The activities of all three enzymes were detected both in the supernatant and pellet fractions, indicating for the first time the presence of SAMDC activity in the particulate fraction. Particularly in the Chardonnay cultivar, an increase in the mRNAs expression patterns of ODC and SAMDC during morphogenesis from small embryos to plantlets was detected by northern blot, suggesting a direct correlation with enzymatic activities.

Seasonal changes in polyamine content of vegetative and reproductive olive organs in relation to floral initiation, anthesis, and fruit development

The concentrations of free and non-free spermidine and spermine in vegetative (leaves, shoot apices) and reproductive (lateral buds, ovaries, fruit tissues) olive organs were determined. The aim was to investigate whether the seasonal fluctuations of these polyamines in different organs correlated to developmental processes such as floral differentiation, shoot growth, anthesis, fertilisation, and fruit growth. Samples were taken from trees of the large-fruited cultivar Chondrolia Chalkidikis and the small-fruited Koroneiki. High levels of both polyamines were determined in buds and shoot apices during the cold period, especially in Ch. Chalkidikis, possibly connected to cold-hardiness exhibited by this cultivar. Two peaks of total spermine in buds, the first occurring in January–February and the second in mid April, coincided with the morphological differentiation of flowers and the inflorescence emergence, respectively. Polyamine levels in ovaries dropped after ovule fertilisation and remained low during the subsequent growth of fruit tissues. Spermidine accumulation, especially in the non-free form, was recorded around the middle of August during a period of intense physiological activity in olive connected to embryo and fruit growth, endocarp hardening, and preceding the second flush of growth in early September. The data showed a direct relationship, in terms of time, of polyamine fluctuations with developmental processes in olive. Whether polyamines act, in this respect, as nitrogen providers or assume a more active regulatory role remains to be elucidated.

Transgenic manipulation of the metabolism of polyamines in poplar cells

The metabolism of polyamines (putrescine, spermidine, and spermine) has become the target of genetic manipulation because of their significance in plant development and possibly stress tolerance. We studied the polyamine metabolism in non-transgenic (NT) and transgenic cells of poplar (Populus nigra x maximowiczii) expressing a mouse Orn decarboxylase (odc) cDNA. The transgenic cells showed elevated levels of mouse ODC enzyme activity, severalfold higher amounts of putrescine, a small increase in spermidine, and a small reduction in spermine as compared with NT cells. The conversion of labeled ornithine (Orn) into putrescine was significantly higher in the transgenic than the NT cells. Whereas exogenously supplied Orn caused an increase in cellular putrescine in both cell lines, arginine at high concentrations was inhibitory to putrescine accumulation. The addition of urea and glutamine had no effect on polyamines in either of the cell lines. Inhibition of glutamine synthetase by methionine sulfoximine led to a substantial reduction in putrescine and spermidine in both cell lines. The results show that: (a) Transgenic expression of a heterologous odc gene can be used to modulate putrescine metabolism in plant cells, (b) accumulation of putrescine in high amounts does not affect the native arginine decarboxylase activity, (c) Orn biosynthesis occurs primarily from glutamine/glutamate and not from catabolic breakdown of arginine, (d) Orn biosynthesis may become a limiting factor for putrescine production in the odc transgenic cells, and (e) assimilation of nitrogen into glutamine keeps pace with an increased demand for its use for putrescine production.

Involvement of ethylene in the maturation of black spruce embryogenic cell lines with different maturation capacities

To examine the possible relationship between ethylene and the capacity of embryogenic cell lines to produce mature somatic embryos of black spruce (Picea mariana (Mill.) B.S.P.), two embryogenic cell lines which exhibit different maturation capacities were used to analyse ethylene biosynthesis and that of its immediate precursor, 1-aminocyclopropane-1- carboxylic acid (ACC). Several compounds known to alter ethylene metabolism were also evaluated for their effect on the number of mature somatic embryos produced. The results showed that in the high capacity cell line, ethylene production and endogenous ACC pools were less than in the low capacity cell line. It was also demonstrated that limiting ethylene biosynthesis by adding inhibitors of ethylene biosynthesis or its physiological action to the maturation medium promoted somatic embryo production for the low capacity cell line. Conversely, lowering ethylene biosynthesis reduced the number of somatic embryos in the high capacity cell line. These results were further substantiated by the finding that the effects of amino-oxyacetic acid (AOA), an inhibitor of ethylene biosynthesis, were partially reversed by adding ethylene to both embryogenic cell lines. It is concluded that ethylene is implicated in somatic embryogenesis of black spruce and that the low capacity cell line had excess, i.e. supraoptimal, ethylene production, whereas the high capacity cell line had nearly optimal ethylene production. The relationship between ethylene and other phytohormones, and the possible effects of the interaction between ethylene and polyamines on the maturation of the somatic embryos are discussed.