Polyamines as biomarkers for plant regeneration capacity: improvement of regeneration by modulation of polyamine metabolism in different genotypes of indica rice

Study on the relationship between the changes in polyamine content and seedless grapes embryo rescue breeding

This study was envisaged to investigate the physiological reasons affecting the embryo development and abortion of seedless grapes on the basis of the previous embryo rescue breeding techniques of seedless grapes. Specifically, the relationship between the embryo rescue breeding of seedless grapes and the change of polyamine content was evaluated, in order to provide hybrid germplasm in the breeding of new seedless grape cultivars. Four ovules of 4 naturally pollinated Eurasian seedless grape cultivars, including 'Thompson Seedless' grape (hereinafter referred to as 'Seedless White' grape), 'Flame Seedless' grape, 'Heshi Seedless' grape and 'Ruby Seedless' grape were employed for the study. Changes in the endogenous polyamine content, exogenous polyamine content, and the suitable combination of exogenous polyamines in the seedless grape berries and isolated ovules were determined during the best embryo rescue period. Furthermore, the effect of different exogenous polyamine contents on the germination and seedling rate of different seedless grape embryos was analyzed. In the best embryo rescue period, the number of ovules had different effects on the content of polyamines. For seedless grape cultivars with 4 ovules, a high content of polyamines was found to be more beneficial in the embryonic development. The existence of embryos had different effects on the development of embryos. In the ovules with embryo, an increase in the content of polyamine was beneficial to the growth and development of the ovule. Different ratios of exogenous polyamines had varying effects on the embryonic development. Putrescine (Put) exhibited the greatest effect on the embryonic development. Further, correlation analysis showed that different combinations of exogenous polyamines had varying effects on the embryonic development. A maximal ovule development was observed in the combination of exogenous polyamines of putrescine2+spermidine2+spermine1. For maximal embryo germination and seeding formation, the optimal combination was putrescine2+spermidine2+spermine2. Irrespective to the number of ovules or the existence of embryos, the results indicated that a high content of endogenous polyamines promoted the growth and development of embryos. The embryo rescue efficiency of different exogenous polyamines was different, and the appropriate combination of exogenous polyamines was beneficial to the growth and development of ovules, with a high development rate of the ovule and seedling.

The effects of genotypes and media composition on callogenesis, regeneration and cell suspension culture of chamomile (Matricaria chamomilla L.)

Background

Chamomile is an important herb being used widely for medicinal purposes. Its multitherapeutic, cosmetic, and nutritional values have been established through years of traditional and scientific use and research. Increased use of medicinal plants necessitates rational use as well as sustainable production of such genetic resources. Plant in vitro micro-propagation poses unique opportunities for sustainable production of medicinal herbs, their regrowth and conservation. The present study aimed to investigate the effects of different explants, plant growth regulators (PGRs) combinations and media type on callogenesis, in vitro regeneration and cell suspension of six chamomile genotypes to enhance its sustainable production.

Methods

The shoot, lateral sprout, and leaf derived explants of six chamomile genotypes including Isfahan, Shiraz, Kazeron, Goral, Sharokashari and Presso were used for direct and indirect regeneration. For indirect regeneration various doses of NAA and kinetin were used to induce calli which were cultured on MS media containing PGRs for direct and indirect regeneration. Later, cell suspension was established and morphological characterization of CrO₃ stained cells was carried out using microscopy.

Results and Discussion

Our findings revealed that the highest callus percentage and callus volume were observed from lateral sprouts and shoots of genotype Isfahan on MS medium containing 1 mg/L NAA and 1 mg/L kinetin. The in vitro regeneration was found to be genotype dependent while 77% and 77.5% was the highest percentage for indirect and direct regeneration, respectively. Additionally, the maximum shoot number (two shoots/explant) and shoot length (2.22 cm) were also observed in Isfahan genotype. Cell suspension culture showed the highest fresh weight (18.59 g) and dry weight (1.707 g) with 0.75 g inoculum of the callus derived from lateral sprouts cultured on MS medium. Microscopy of CrO₃ stained cells was carried on each 3rd day for 27 days that revealed larger and spongier cells in the early days as compared to final days when the cell number was greater but cell size was smaller.

Conclusion

The callogenesis, organogenesis, and cell suspension culture of chamomile may be genotype dependent. Hence, optimization of media ingredients and culture conditions is of utmost importance for devising tissue culture based conservation strategy of any chamomile genotype and secondary metabolite production.

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.

Variations in polyamine conjugates in maize (Zea mays L.) seeds contaminated with aflatoxin B1: a dose-response relationship

BACKGROUND

Cereal seeds, such as maize seeds, are frequently contaminated with aflatoxin B1 (AFB1), one of the most dangerous naturally occurring carcinogens. In plants, phenolamides are involved in biotic stress response. The data on variations of phenolamides in AFB1-containing seeds are limited.

RESULTS

Five polyamine conjugates, including two spermidine and three putrescine conjugates, were tentatively identified in methanolic extracts, using HPLC-DAD-MS. The ratio of putrescine to spermidine conjugates changed with increasing AFB1 concentration in a logistic dose-response manner, with a ratio of below 1 up to a concentration of 51.51 μg kg^-1 , and approximately 2.54 and 3 at higher concentrations of 177.4 and 308.13 μg kg^-1 , respectively. The observed variations of the total antioxidant activity and the total phenolic content may support this biphasic behaviour of the seeds against AFB1 stress.

CONCLUSIONS

The obtained data are a contribution to the understanding of the roles of polyamine conjugates in seed defence to increasing AFB1 concentrations. According to our knowledge, this study reports for the first time the biphasic response of maize seeds to increasing AFB1 contamination level, comprising the induction of polyamine conjugate accumulation and variation in the ratio of conjugates. This dose-response relationship may provide useful information in the field of agricultural and food chemistry as an indicator of AFB1 contamination level and, hence, for selecting an appropriate seed quality. © 2020 Society of Chemical Industry.

Somatic Embryogenesis Induction in Woody Species: The Future After OMICs Data Assessment

Very early somatic embryogenesis has been recognized as a powerful method to propagate plants in vitro. For some woody species and in particular for some coniferous trees, somatic embryogenesis induction has become a routine procedure. For the majority, the application of this technology presents yet many limitations especially due to the genotype, the induction conditions, the number of embryos produced, maturation, and conversion, among other factors that compromise the systematic use of somatic embryogenesis for commercial purposes especially of woody species and forest trees in particular. The advancements obtained on somatic embryogenesis in Arabidopsis and the development of OMIC technologies allowed the characterization of genes and the corresponding proteins that are conserved in woody species. This knowledge will help in understanding the molecular mechanisms underlying the complex regulatory networks that control somatic embryogenesis in woody plants. In this revision, we report on developments of OMICs (genomics, transcriptomics, metabolomics, and proteomics) applied to somatic embryogenesis induction and its contribution for understanding the change of fate giving rise to the expression of somatic embryogenesis competence.

Introgression, Generational Expression and Salinity Tolerance Conferred by the Pea DNA Helicase 45 Transgene into Two Commercial Rice Genotypes, BR28 and BR47

DNA helicase (PDH45) from the pea plant (Pisum sativum) is a member of the DEAD box protein family and plays a vital regulatory role in saline stress tolerance in plants. We previously reported that over-expression of PDH45 gene confers both seedling and reproductive stage salinity tolerance to a Bangladeshi rice landrace, Binnatoa (BA). In this study, transgenic BA-containing PDH45 (♂) was crossed with two different farmer-popular BRRI rice varieties (♀), BR28 and BR47, in a contained net house. F1 plants positive for the transgene and having recipient phenotype were advanced from F1 to F5. Expression of the PDH45 gene was detected in all generations. The expression level of PDH45 was 200-fold higher in the donor compared to the two recipient genotypes but without any effect on their salt stress tolerance ability in various assays. Under 120 mM NaCl stress at seedling stage, all rice genotypes showed vigorous growth, higher chlorophyll content, lower electrolyte leakage and lower LDS (Leaf Damage Score) compared to their corresponding wild types. At the reproductive stage under continuous salinity stress at 80 mM NaCl, the cross-bred lines BR28 and BR47 showed significantly better spikelet fertility and yield per plant, which were two- and 2.5-folds, respectively, than their corresponding wild types. The PDH45 transgene was observed to increase the expression of 6 salt stress-related downstream genes at 150 mM NaCl stress to similar differential degrees in the donor and recipient genotypes. However, the expression of OsLEA was significantly higher in transgenic BR28 compared to transgenic BR47, where the latter shows comparatively higher salt tolerance. The study shows stability of transgene expression across generations. It also demonstrates that there may be an effect of background genotype on transgene expression. Moreover, some downstream effects of the transgene may also be genotype-specific.

The Effect of Exogenous Spermidine Concentration on Polyamine Metabolism and Salt Tolerance in Zoysiagrass (Zoysia japonica Steud) Subjected to Short-Term Salinity Stress

Salt stress, particularly short-term salt stress, is among the most serious abiotic factors limiting plant survival and growth in China. It has been established that exogenous spermidine (Spd) stimulates plant tolerance to salt stress. The present study utilized two zoysiagrass cultivars commonly grown in China that exhibit either sensitive (cv. Z081) or tolerant (cv. Z057) adaptation capacity to salt stress. The two cultivars were subjected to 200 mM salt stress and treated with different exogenous Spd concentrations for 8 days. Polyamine [diamine putrescine (Put), tetraamine spermine (Spm), and Spd], H2O2 and malondialdehyde (MDA) contents and polyamine metabolic (ADC, ODC, SAMDC, PAO, and DAO) and antioxidant (superoxide dismutase, catalase, and peroxidase) enzyme activities were measured. The results showed that salt stress induced increases in Spd and Spm contents and ornithine decarboxylase (ODC), S-adenosylmethionine decarboxylase (SAMDC), and diamine oxidase (DAO) activities in both cultivars. Exogenous Spd application did not alter polyamine contents via regulation of polyamine-degrading enzymes, and an increase in polyamine biosynthetic enzyme levels was observed during the experiment. Increasing the concentration of exogenous Spd resulted in a tendency of the Spd and Spm contents and ODC, SAMDC, DAO, and antioxidant enzyme activities to first increase and then decrease in both cultivars. H2O2 and MDA levels significantly decreased in both cultivars treated with Spd. Additionally, in both cultivars, positive correlations between polyamine biosynthetic enzymes (ADC, SAMDC), DAO, and antioxidant enzymes (SOD, POD, CAT), but negative correlations with H2O2 and MDA levels, and the Spd + Spm content were observed with an increase in the concentration of exogenous Spd.

Effect of antibiotics on callus regeneration during transformation of IR 64 rice

We report here the effect of antibiotics on the regeneration potential of recalcitrant indica rice cultivar, IR64. Different protocols reporting high-efficiency agro-bacterium-mediated transformation of mature seed-derived regenerative calli were used and compared. The putative transgenic (T0) plants were analyzed for integration of the transgene through polymerase chain reaction and Southern blotting analyses. It was observed that the high-efficiency transformation of scutellar-derived regenerative calli could be obtained by using maltose as a carbon source and increased quantity of 2,4-D on a medium containing a higher concentration of gelling agent. The percentage of regeneration is greatly affected by the presence of antibiotics.

Regulation of polyamine metabolism in Pyropia cinnamomea (W.A. Nelson), an important mechanism for reducing UV-B-induced oxidative damage

It is generally accepted that ultraviolet (UV) radiation can have adverse affects on phototrophic organisms, independent of ozone depletion. The red intertidal seaweed Pyropia cinnamomea W.A. Nelson (previously Porphyra cinnamomea Sutherland et al. 2011), similar to many other intertidal macrophytes, is exposed to high levels of UV radiation on a daily basis due to emersion in the upper littoral zone. It has been shown that seaweeds, like higher plants, respond to an increased activity of antioxidative enzymes when exposed to stress. However, earlier investigations have shown that P. cinnamomea also compensates for stress due to UV radiation by increasing polyamine (PA) levels, especially bound-soluble and bound-insoluble PAs. The PA precursor putrescine (PUT) can be synthesized via two enzymatic pathways: arginine decarboxylase (ADC) and ornithine decarboxylase (ODC). Both of these enzymes showed increased activity in P. cinnamomea under UV stress. In higher plants, ADC is the enzyme responsible for increased PA levels during stress exposure, while ODC is correlated with cell division and reproduction. However, there are contrary findings in the literature. Using two irreversible inhibitors, we identified the enzyme most likely responsible for increased PUT synthesis and therefore increased stress tolerance in P. cinnamomea. Our results show that changes in the PA synthesis pathway in P. cinnamomea under UV stress are based on an increased activity of ADC. When either inhibitor was added, lipid hydroperoxide levels increased even under photosynthetically active radiation, suggesting that PAs are involved in protection mechanisms under normal light conditions as well. We also show that under optimum or low-stress conditions, ODC activity is correlated with PUT synthesis.

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.

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.

Polyamines and abiotic stress tolerance in plants

Environmental stresses including climate change, especially global warming, are severely affecting plant growth and productivity worldwide. It has been estimated that two-thirds of the yield potential of major crops are routinely lost due to the unfavorable environmental factors. On the other hand, the world population is estimated to reach about 10 billion by 2050, which will witness serious food shortages. Therefore, crops with enhanced vigour and high tolerance to various environmental factors should be developed to feed the increasing world population. Maintaining crop yields under adverse environmental stresses is probably the major challenge facing modern agriculture where polyamines can play important role. Polyamines (PAs)(putrescine, spermidine and spermine) are group of phytohormone-like aliphatic amine natural compounds with aliphatic nitrogen structure and present in almost all living organisms including plants. Evidences showed that polyamines are involved in many physiological processes, such as cell growth and development and respond to stress tolerance to various environmental factors. In many cases the relationship of plant stress tolerance was noted with the production of conjugated and bound polyamines as well as stimulation of polyamine oxidation. Therefore, genetic manipulation of crop plants with genes encoding enzymes of polyamine biosynthetic pathways may provide better stress tolerance to crop plants. Furthermore, the exogenous application of PAs is also another option for increasing the stress tolerance potential in plants. Here, we have described the synthesis and role of various polyamines in abiotic stress tolerance in plants.

Conversion of protocorm-like bodies of Dendrobium huoshanense to shoots: the role of polyamines in relation to the ratio of total cytokinins and indole-3-acetic acid

In the present paper, a correlation between enhanced conversion of protocorm-like bodies (PLBs) of Dendrobium huoshanense to shoots by free polyamines (PAs) and changes in the levels of endogenous hormones is described. The endogenous levels of free spermidine (Spd) and putrescine (Put) increased during the conversion of PLBs to shoots. The exogenous addition of PAs, mainly Spd or Put at 2.0mM, not only elevated the endogenous levels of PAs but also promoted the frequency of conversion of PLBs to shoots. As compared with control, the enhanced conversion of PLBs to shoots by exogenous PAs was accompanied by an increase in ratio of total cytokinins (CTKs) to indole-3-acetic acid (IAA), which was due to decrease in the endogenous level of IAA and increase in the endogenous level of total CTKs, including the levels of isopentenyladenine+isopentenyladenine 9-riboside and zeatin+zeatin riboside. Analysis of enzyme activities showed that the increased endogenous level of total CTKs by PAs was related to the inhibition of CTK decomposition by CTK oxidase, while the decreased endogenous level of IAA was related to the promotion of IAA decomposition by IAA oxidase. Addition of PA biosynthetic inhibitors, involving alpha-difluoromethylornithine for Put and methylglyoxal(bis)-guanylhydrazone for Spd and Spm, decreased the conversion of PLBs to shoots, the ratio of total CTKs to IAA, and the levels of endogenous Put and Spd. This inhibition could be partly reversed by the application of exogenous Put or Spd.

Genetic transformation of NERICA, interspecific hybrid rice between Oryza glaberrima and O. sativa, mediated by Agrobacterium tumefaciens

We developed an efficient gene transfer method mediated by Agrobacterium tumefaciens for introgression of new rice for Africa (NERICA) cultivars, which are derivatives of interspecific hybrids between Oryza glaberrima Steud. and O. sativa L. Freshly isolated immature embryos were inoculated with A. tumefaciens LBA4404 that harbored binary vector pBIG-ubi::GUS or pIG121Hm, which each carried a hygromycin-resistance gene and a GUS gene. Growth medium supplemented with 500 mg/l cefotaxime and 20 mg/l hygromycin was suitable for elimination of bacteria and selection of transformed cells. Shoots regenerated from the selected cells on MS medium containing 20 g/l sucrose, 30 g/l sorbitol, 2 g/l casamino acids, 0.25 mg/l naphthaleneacetic acid, 2.5 mg/l kinetin, 250 mg/l cefotaxime, and 20 mg/l hygromycin. The shoots developed roots on hormone-free MS medium containing 30 mg/l hygromycin. Integration and expression of the transgenes were confirmed by PCR, Southern blot analysis, and histochemical GUS assay. Stable integration, expression, inheritance, and segregation of the transgenes were demonstrated by molecular and genetic analyses in the T(0) and T(1) generations. Most plants were normal in morphology and fertile. The transformation protocol produced stable transformants from 16 NERICA cultivars. We also obtained transformed plants by inoculation of calluses derived from mature seeds, but the frequency of transformation was lower and sterility was more frequent.

Changes in free polyamine titers and expression of polyamine biosynthetic genes during growth of peach in vitro callus

In the present paper, correlation between free polyamines and growth of peach (Prunus persica cv. Yuzora) in vitro callus was investigated. Growth of the callus was divided into three phases based on measurement of fresh weight. Free polyamines, putrescine (Put), spermidine (Spd), and spermine (Spm), could be detected during peach callus growth. Changes in free Put titers followed the callus growth rate, as shown by low and stable levels in the first stage, quick increase at the beginning of the second phase, and slow increase in the last phase, whereas fluctuations of Spd and Spm titers were aberrant from that of Put at early stage. Expressions of five key genes involved in polyamine biosynthesis were characterized, in which only the genes leading to Put synthesis, ADC (arginine decarboxylase) and ODC (ornithine decarboxylase), agreed with callus growth and fluctuation of Put titers. Treatment of the callus with D-arginine, an inhibitor of ADC, led to significant growth inhibition and enormous reduction of endogenous Put, coupled with obvious decrease of mRNA levels of ADC and ODC. Exogenous application of Put partially restored the callus growth, along with resumption of endogenous Put and expression levels of ADC and ODC. Spd and Spm titers experienced minor change in comparison to Put. The data presented here suggested that free Put played an important part in peach callus growth. Putative mechanisms or mode of action underlying the role of Put in peach callus growth and different expression patterns of the genes responsible for polyamine biosynthesis are also discussed.

Polyamines induce rapid biosynthesis of nitric oxide (NO) in Arabidopsis thaliana seedlings

In this study, we examined the regulation by putrescine, spermidine and spermine of nitric oxide (NO) biosynthesis in Arabidopsis thaliana seedlings. Using a fluorimetric method employing the cell-impermeable NO-binding dye diaminorhodamine-4M (DAR-4M), we observed that the polyamines (PAs) spermidine and spermine greatly increased NO release in the seedlings, whereas arginine and putrescine had little or no effect. Spermine, the most active PA, stimulated NO release with no apparent lag phase. The response was quenched by addition of 2-aminoethyl-2-thiopseudourea (AET), an inhibitor of the animal nitric oxide synthase (NOS) and plant NO biosynthesis, and by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-1-oxy-3-oxide (PTIO), an NO scavenger. By fluorescence microscopy, using the cell-permeable NO-binding dye diaminorhodamine-4M acetoxymethyl ester (DAR-4M AM), we observed that PAs induced NO biosynthesis in specific tissues in Arabidopsis seedlings. Spermine and spermidine increased NO biosynthesis in the elongation zone of the Arabidopsis root tip and in primary leaves, especially in the veins and trichomes, while in cotyledons little or no effect of PAs beyond the endogenous levels of NO-induced fluorescence was observed. We conclude that PAs induce NO biosynthesis in plants.

Recent advances in rice biotechnology--towards genetically superior transgenic rice

Rice biotechnology has made rapid advances since the first transgenic rice plants were produced 15 years ago. Over the past decade, this progress has resulted in the development of high frequency, routine and reproducible genetic transformation protocols for rice. This technology has been applied to produce rice plants that withstand several abiotic stresses, as well as to gain tolerance against various pests and diseases. In addition, quality improving and increased nutritional value traits have also been introduced into rice. Most of these gains were not possible through conventional breeding technologies. Transgenic rice system has been used to understand the process of transformation itself, the integration pattern of transgene as well as to modulate gene expression. Field trials of transgenic rice, especially insect-resistant rice, have recently been performed and several other studies that are prerequisite for safe release of transgenic crops have been initiated. New molecular improvisations such as inducible expression of transgene and selectable marker-free technology will help in producing superior transgenic product. It is also a step towards alleviating public concerns relating to issues of transgenic technology and to gain regulatory approval. Knowledge gained from rice can also be applied to improve other cereals. The completion of the rice genome sequencing together with a rich collection of full-length cDNA resources has opened up a plethora of opportunities, paving the way to integrate data from the large-scale projects to solve specific biological problems.