Endosperm dormancy breakage in olive seeds

Seeds of Olea europaea L. ssp. oleaster Hoffm. and Link freed from the sclerous endoearp and incubated in water at 15 or 25°C in darkness or in 12:12 h white light:dark conditions, did not germinate, due to dormancy imposed by the endosperm. Seeds also did not germinate when incubated in abscisic acid, gibberellic acid, kinetin or zeatin in darkness and at cither 15 or 25°C. SAN 9789 |4-chloro-5-(methylamine)-2-(a,a,a-trifluoro-m-tolyl)-3-(2H)-pyridazmone] did not promote germination at 15°C but it did to a 75% level at 25°C. This promoting effect of SAN was counteracted by abscisic acid. Cultures of naked embryos grew equally well in the presence or absence of SAN 9789. 6-Benzylaminopurine promoted whole seed germination to a 15% level.     

Dormancy of<Emphasis Type="Italic"> Arabidopsis</Emphasis> seeds and barley grains can be broken by nitric oxide

Seeds of Arabidopsis thaliana (L.) Heynh. and grains of barley (Hordeum vulgare L.) were used to characterize the affects of nitric oxide (NO) on seed dormancy. Seeds of the C24 and Col-1 ecotypes of Arabidopsis are almost completely dormant when freshly harvested, but dormancy was broken by stratification for 3 days at 4°C or by imbibition of seeds with the NO donor sodium nitroprusside (SNP). This effect of SNP on dormancy of Arabidopsis seeds was concentration dependent. SNP concentrations as low as 25 M reduced dormancy and stimulated germination, but SNP at 250 M or more impaired seedling development, including root growth, and inhibited germination. Dormancy was also reduced when Arabidopsis seeds were exposed to gasses that are generated by solutions of SNP. Nitrate and nitrite, two other oxides of nitrogen, reduced the dormancy of Arabidopsis seeds, but much higher concentrations of these were required compared to SNP. Furthermore, the kinetics of germination were slower for seeds imbibed with either nitrate or nitrite than for seeds imbibed with SNP. Although seeds imbibed with SNP had reduced dormancy, seeds imbibed with SNP and abscisic acid (ABA) remained strongly dormant. This may indicate that the effects of ABA action on germination are downstream of NO action. The NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3 oxide (cPTIO) strengthened dormancy of unstratified and briefly stratified Arabidopsis seeds. Dormancy of three cultivars of barley was also reduced by SNP. Furthermore, dormancy in barley grain was strengthened by imbibition of grain with cPTIO. The data presented here support the conclusion that NO is a potent dormancy breaking agent for seeds and grains. Experiments with the NO scavenger suggest that NO is an endogenous regulator of seed dormancy.Abbreviations ABA Abscisic acid - cPTIO 2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3 oxide - GA Gibberellin - SNP Sodium nitroprusside - NO_x Gaseous oxides of nitrogen     

Participation of auxin and abscisic acid in the regulation of seasonal variations in cambial activity and xylogenesis

Summary The current notion that hormonal level and cell response are clearly correlated has often been challenged recently. During the period of cambial activity, auxin content seems to control the intensity of mitosis and some features of the resulting wood, but not the duration of the active period itself. During cambial rest, the indole-3-acetic acid (IAA) level often remains high in the cambium, but the cell sensitivity to auxin is low. The decrease of auxin transport in autumn is sometimes interpreted as a major qualitative change affecting the pattern of transport, and sometimes as a secondary change occurring later than rest onset. The causes of the seasonal variation of cambial response remain unknown. A hypothesis is proposed that accounts for the structural-functional changes occurring in cambial cells during the onset of dormancy. Abscisic acid (ABA) may reduce wood production and xylem cell enlargement in late summer. An important amount of ABA may be present in the cambial zone in autumn after drought stress and in spring in the young growing shoot. Changes in ABA level do not appear to be clearly correlated with the different steps of cambial rest and activity. Beyond the role of ABA as a stress mediator, its participation in the annual regulation of cambial activity remains unclear. Its distribution in the most alkaline compartments may account for the particularities of its seasonal activity. The involvement of IAA and ABA in cambial growth is discussed within the scope of a possible annual alternation of two different metabolisms in the cambial cell.Abbreviations ABA abscisic acid - DPA dihydrophaseic acid - GA gibberellic acid - GC-MS gas chromatography-mass spectrometry - IAA indole-3-acetic acid - PA phaseic acid - RNA ribonucleic acid - SICM single ion current monitoring - SIM selected ion monitoring     

Differences in the nature of thermodormancy and far-red dormancy in lettuce seeds

Lettuce seeds cv. Noran germinate at 23°C in light as well as in darkness. However dormancy can be induced either by a long exposure (24 h) to far-red radiation or by an exposure of 48–72 h to a temperature of 37°C. The difference in response of these two types of dormant seeds to conditions inducing germination indicate that in both types P_fr is inactivated, but that a dark process required for immediate action of P_fr does not proceed at 37°C as it does during far-red radiation.     

Changes in endogenous abscisic acid levels during dormancy release and maintenance of mature seeds: studies with the Cape Verde Islands ecotype,the dormant model of<Emphasis Type="Italic"> Arabidopsis thaliana</Emphasis>

Mature seeds of the Cape Verde Islands (Cvi) ecotype of Arabidopsis thaliana (L.) Heynh. show a very marked dormancy. Dormant (D) seeds completely fail to germinate in conditions that are favourable for germination whereas non-dormant (ND) seeds germinate easily. Cvi seed dormancy is alleviated by after-ripening, stratification, and also by nitrate or fluridone treatment. Addition of gibberellins to D seeds does not suppress dormancy efficiently, suggesting that gibberellins are not directly involved in the breaking of dormancy. Dormancy expression of Cvi seeds is strongly dependent on temperature: D seeds do not germinate at warm temperatures (20–27°C) but do so easily at a low temperature (13°C) or when a fluridone treatment is given to D seeds sown at high temperature. To investigate the role of abscisic acid (ABA) in dormancy release and maintenance, we measured the ABA content in both ND and D seeds imbibed using various dormancy-breaking conditions. It was found that dry D seeds contained higher amounts of ABA than dry ND after-ripened seeds. During early imbibition in standard conditions, there was a decrease in ABA content in both seeds, the rate of which was slower in D seeds. Three days after sowing, the ABA content in D seeds increased specifically and then remained at a high level. When imbibed with fluridone, nitrate or stratified, the ABA content of D seeds decreased and reached a level very near to that of ND seeds. In contrast, gibberellic acid (GA₃) treatment caused a transient increase in ABA content. When D seeds were sown at low optimal temperature their ABA content also decreased to the level observed in ND seeds. The present study indicates that Cvi D and ND seeds can be easily distinguished by their ability to synthesize ABA following imbibition. Treatments used here to break dormancy reduced the ABA level in imbibed D seeds to the level observed in ND seeds, with the exception of GA₃ treatment, which was active in promoting germination only when ABA synthesis was inhibited.Abbreviations ABA Abscisic acid - Cvi Cape Verde Islands - D Dormant - GA Gibberellin - GA₃ Gibberellic acid - ND Non dormant     

Antagonistic effects of abscisic acid and gibberellic acid on the breaking of dormancy of Fagus sylvatica seeds

Study of the factors involved in the dormancy of Fagus sylvatica seeds shows that such dormancy is due partly to the seed coats and partly to endogenous factors. Seed coat removal accelerates both the release from dormancy and the effects of the other treatments that abolish it. The dormancy of these seeds is eliminated by cold treatment at 4°C over a period longer than 8 weeks, and exogenous application of abscisic acid (ABA) reverses the effects of low temperature, the seeds remaining in an ungerminated state. Additionally, ABA reduces protein synthesis but slightly increases RNA synthesis, which suggests its involvement in the synthesis of RNAs related to this process. In vitro translation of the RNAs isolated from these seeds shows that ABA delays the disappearance of at least 2 polypeptides (of ca 22 and 24 kDa), which are abundant in dormant seeds and under conditions that prevent the release from dormancy, but which disappear under treatments that abolish it. Exogenous application of gibberellic acid (GA₃) proved to be efficient in breaking the dormancy of these seeds and in substituting for cold treatment as well as in antagonizing the effects of ABA on the synthesis of both DNA and proteins. GA₃ also accelerates the disappearance of the two polypeptides abundant in dormant seeds and in ABA-treated seeds. These findings suggest that both ABA and GA₃ could be involved in the regulation of nucleic acid and protein metabolism during dormancy, acting antagonistically in these processes and, specifically, in the regulation of the synthesis of the two proteins that appear to play a role in the maintenance of dormancy in these seeds.     

Metabolic engineering provides insight into the regulation of thiamin biosynthesis in plants

Thiamin (or thiamine) is a water-soluble B-vitamin (B1), which is required, in the form of thiamin pyrophosphate, as an essential cofactor in crucial carbon metabolism reactions in all forms of life. To ensure adequate metabolic functioning, humans rely on a sufficient dietary supply of thiamin. Increasing thiamin levels in plants via metabolic engineering is a powerful strategy to alleviate vitamin B1 malnutrition and thus improve global human health. These engineering strategies rely on comprehensive knowledge of plant thiamin metabolism and its regulation. Here, multiple metabolic engineering strategies were examined in the model plant Arabidopsis thaliana. This was achieved by constitutive overexpression of the three biosynthesis genes responsible for B1 synthesis, HMP-P synthase (THIC), HET-P synthase (THI1), and HMP-P kinase/TMP pyrophosphorylase (TH1), either separate or in combination. By monitoring the levels of thiamin, its phosphorylated entities, and its biosynthetic intermediates, we gained insight into the effect of either strategy on thiamin biosynthesis. Moreover, expression analysis of thiamin biosynthesis genes showed the plant’s intriguing ability to respond to alterations in the pathway. Overall, we revealed the necessity to balance the pyrimidine and thiazole branches of thiamin biosynthesis and assessed its biosynthetic intermediates. Furthermore, the accumulation of nonphosphorylated intermediates demonstrated the inefficiency of endogenous thiamin salvage mechanisms. These results serve as guidelines in the development of novel thiamin metabolic engineering strategies.     

珙桐枝皮中的生物碱甙成分研究

从珙桐枝皮甲醇提取物的水溶性部分得到3个配糖体化合物,经核磁共振和质谱等光谱分析鉴定为1个喹啉类生物碱甙-pumiloside(1)和2个吲哚类生物碱甙-vincosamide(2),strictosidinic acid(3),其中pumiloside是抗肿瘤物质喜树碱的一种生物合成前体,这3个化合物均为首次从该植物中分得。     

Metabolome and transcriptome profiling of Theobroma cacao provides insights into the molecular basis of pod color variation

Journal of Plant Research - The Theobroma cacao presents a wide diversity in pod color among different cultivars. Although flavonoid biosynthesis has been studied in many plants, molecular...     

Abscisic acid relationships in the chill-related dormancy mechanism in apple seeds

Abscisic acid (ABA) levels in seeds from three cultivars of apple (Malus domestica Borkh.) which have substantially different chilling requirements were investigated by gas chromatography mass-spectrometry selected ion monitoring (GCMS-SIM) during stratification. The ABA content of dormant unchilled seeds was similar in the three cultivars, suggesting no relationship between the chilling requirement of those seeds and their ABA status. That chilling is not related to ABA changes during stratification was confirmed by warm (20°C) and cold (5°C) stratification experiments. ABA content dropped rapidly and nearly identically under both temperature regimes, but only cold stratification promoted germination. The decline in ABA during stratification was due in large part to leaching from the seed coat and nucellar membrane; the ABA content of the embryo remained nearly constant. The radicle in intact seeds stratified at 5°C began growing 20–30 days after the ABA in the seed coat and nucellar membrane had nearly disappeared. Radicle growth did not occur in unchilled seeds, even though ABA had leached from them as well. It is possible that the leaching of ABA from the seed allows certain promotive forces to develop, but if so, these can develop only at chilling temperatures. Studies were also conducted on 2-trans ABA relationships to apple seed dormancy, but no association was evident.Report No. 12, Department of Fruit and Vegetable Science, Cornell University.     

Abscisic acid,abscisic acid-esters and phaseic acid in vegetative terminal buds of Acer pseudoplatanus during emergence from winter dormancy

Levels of free-abscisic acid and boundabscisic acid (alkaline hydrolyzable abscisic acidesters) in replicated samples of terminal vegetative buds of sycamore trees were measured during natural emergence from winter dormancy by gas chromatographic methods together with isotope dilution estimation of recovery rates. Not until after the buds had been released from true dormancy in January by winter chilling did any clear change occur in either abscisic acid (ABA) fraction, or in total ABA, on any basis of comparison. The percentage of total ABA present as the free acid declined at the end of true dormancy to approximately two-thirds of its value in the earlier winter months. It is concluded that glucosylation of ABA is unlikely to play a major part in the mechanism of release from dormancy in vegetative sycamore buds. At the end of true dormancy there was a large transient increase in what appeared to be phaseic acid, but this was not accompanied by any marked decrease in either free- or bound-ABA.Abbreviations ABA abscisic acid - TLC thin layer chromatography - GLC gas chromatography     

Regulation of carotenoid and ABA accumulation during the development and germination of Nicotiana plumbaginifolia seeds

Abscisic acid (ABA) is derived from epoxycarotenoid cleavage and regulates seed development and maturation. A detailed carotenoid analysis was undertaken to study the contribution of epoxycarotenoid synthesis to the regulation of ABA accumulation in Nicotiana plumbaginifolia developing seeds. Maximal accumulation of xanthophylls occurred at mid-development in wild type seeds, when total ABA levels also peaked. In contrast, in ABA-deficient mutants xanthophyll synthesis was delayed, in agreement with the retardation in seed maturation. Seed dormancy was restored in mutants impaired in the conversion of zeaxanthin into violaxanthin by zeaxanthin epoxidase (ZEP), by the introduction of the Arabidopsis AtZEP gene under the control of promoters inducing expression during later stages of seed development compared to wild type NpZEP, and in dry and imbibed seeds. Alterations in the timing and level of ZEP expression did not highly affect the temporal regulation of ABA accumulation in transgenic seeds, despite notable perturbations in xanthophyll accumulation. Therefore, major regulatory control of ABA accumulation might occur downstream of epoxycarotenoid synthesis.     

The dual role of temperature in the regulation of the seasonal changes in dormancy and germination of seeds of Polygonum persicaria L.

Summary The role of temperature in the regulation of seasonal changes in dormancy and germination was studied in seeds of Polygonum persicaria. Seeds were buried in the field and under controlled conditions. Portions of seeds were exhumed at regular intervals and germination was tested over a range of conditions. Seeds of P. persicaria exhibited a seasonal dormancy pattern that clearly showed the typical features of summer annuals, i.e. dormancy was relieved at low winter temperatures, the germination peak occurred in spring and dormancy was re-induced in summer. The expression of the dormancy pattern was influenced by the temperature at which germination was tested. At 30°C exhumed seeds germinated over a much longer period of the year than at 20° or 10°C. Nitrate added during the germination test occasionally stimulated germination. The seasonal changes in dormancy of buried seeds were regulated by the field temperature. Soil moisture and nitrate content did not influence the changes in dormancy. The fact that, on the one hand, field temperature determined the changes in dormancy and, on the other hand, germination itself was influenced by temperature, was used to describe the seasonal germination pattern of P. persicaria with a model. Germination of exhumed seeds in Petri dishes at field temperature was accurately described with this model. Germination in the field was restricted to the period where the range of temperatures over which germination could proceed (computed with the model) and field temperature overlapped.     

Dormancy in somatic embryos and seeds ofVitis: changes in endogenous abscisic acid during embryogeny and germination

Abscisic acid (ABA) in extracts of somatic embryos and seeds of Gloryvine (Vitis vinifera L.xV. rupestris Scheele) was measured by gas chromatography-mass spectrometry-selected ion monitoring using deuterated ABA, (±)-[C-3Me-²H₃]ABA, ([²H₃]ABA) as internal standard. The ABA content increased rapidly during embryogeny (0.035 ng/embryo at the globular stage to 0.22 ng/embryo at the mature stage). The level of ABA in the tissues of somatic embryos, expressed in ng/mg dry weight, decreased from the globular stage (0.76 ng/mg) to the mature stage (0.25 ng/mg). Chilling (4° C) induced normal germination of seeds and mature somatic embryos and precocious germination of globular, heart-shaped and torpedoshaped somatic embryos. In all cases chilling led to a marked reduction in endogenous ABA. Exogenous (±)-ABA inhibited the germination of chilled somatic embryos.Abbreviations ABA abscisic acid - [²H₃]ABA (±)-[C-3Me-²H₃]-abscisic acid - BHT 2,6-di-t-butyl-4-methylphenol - GC-MS gas chromatography-mass spectrometry - Me-ABA and Me-[²H₃]ABA methyl esters of ABA and [²H₃]ABA, respectively - SIM selected ion monitoring     

Structure of the calmodulin alphaII-spectrin complex provides insight into the regulation of cell plasticity

AlphaII-spectrin is a major cortical cytoskeletal protein contributing to membrane organization and integrity. The Ca2+-activated binding of calmodulin to an unstructured insert in the 11th repeat unit of alphaII-spectrin enhances the susceptibility of spectrin to calpain cleavage but abolishes its sensitivity to several caspases and to at least one bacterially derived pathologic protease. Other regulatory inputs including phosphorylation by c-Src also modulate the proteolytic susceptibility of alphaII-spectrin. These pathways, acting through spectrin, appear to control membrane plasticity and integrity in several cell types. To provide a structural basis for understanding these crucial biological events, we have solved the crystal structure of a complex between bovine calmodulin and the calmodulin-binding domain of human alphaII-spectrin (Protein Data Bank ID code 2FOT). The structure revealed that the entire calmodulin-spectrin-binding interface is hydrophobic in nature. The spectrin domain is also unique in folding into an amphiphilic helix once positioned within the calmodulin-binding groove. The structure of this complex provides insight into the mechanisms by which calmodulin, calpain, caspase, and tyrosine phosphorylation act on spectrin to regulate essential cellular processes.     

Conditions of induction of secondary dormancy in apple after breaking of primary dormancy by anaerobiosis and low temperature

Dormant embryos of Pyrus malus L. cv. Golden delicious, isolated from the fruits at harvest time or after a few months storage at 10 to 15°C, were kept under anaerobic conditions in order to eliminate primary dormancy. Germination tests were then carried out at different temperatures, using three modes of culture depending on the nature of the contact between the embryo and the medium. In CM the distal part of the two cotyledons was immersed in the medium. In RM only the embryonic axis was immersed. In C/2M the embryo was placed flat on the medium, the radicle and the external surface of one cotyledon being in contact with it.
Results showed that primary dormancy was released progressively depending on the duration of the anaerobic treatment. After a treatment of 11 or 13 days the last symptoms of primary dormancy were only apparent when germination tests were carried out at high temperatures (26–30°C) or in CM mode of culture.
When the embryos were kept at 4°C during 3 months inside the fruits, subsequent germination was inhibited at high temperature and in CM mode of culture. When the embryos were kept under anaerobic conditions (7 days) after the chilling treatmem inside the fruits, germination was no longer inhibited. It is concluded that the inhibition of germination at high temperature and in CM mode of culture is due to the persistence of traces of primary dormancy. Therefore, these conditions do not seem to induce secondary dormancy in apple embryos.
After elimination of primary dormancy by anaerobiosis. only application of (±) abscisic acid (3.8 and 19 μM) inhibited germination. These results support the idea that ABA is an important factor in the induction of dormancy. However, the question remains whether this secondary embryo dormancy has the same characteristics as the original primary dormancy.     

The crystal structure of Pyrococcus furiosus UMP kinase provides insight into catalysis and regulation in microbial pyrimidine nucleotide biosynthesis

UMP kinase (UMPK), the enzyme responsible for microbial UMP phosphorylation, plays a key role in pyrimidine nucleotide biosynthesis, regulating this process via feed-back control and via gene repression of carbamoyl phosphate synthetase (the first enzyme of the pyrimidine biosynthesis pathway). We present crystal structures of Pyrococcus furiosus UMPK, free or complexed with AMPPNP or AMPPNP and UMP, at 2.4 A, 3 A and 2.55 A resolution, respectively, providing a true snapshot of the catalytically competent bisubstrate complex. The structure proves that UMPK does not resemble other nucleoside monophosphate kinases, including the UMP/CMP kinase found in animals, and thus UMPK may be a potential antimicrobial target. This enzyme has a homohexameric architecture centred around a hollow nucleus, and is organized as a trimer of dimers. The UMPK polypeptide exhibits the amino acid kinase family (AAKF) fold that has been reported in carbamate kinase and acetylglutamate kinase. Comparison with acetylglutamate kinase reveals that the substrates bind within each subunit at equivalent, adequately adapted sites. The UMPK structure contains two bound Mg ions, of which one helps stabilize the transition state, thus having the same catalytic role as one lysine residue found in acetylglutamate kinase, which is missing from P.furiosus UMPK. Relative to carbamate kinase and acetylglutamate kinase, UMPK presents a radically different dimer architecture, lacking the characteristic 16-stranded beta-sheet backbone that was considered a signature of AAKF enzymes. Its hexameric architecture, also a novel trait, results from equatorial contacts between the A and B subunits of adjacent dimers combined with polar contacts between A or B subunits, and may be required for the UMPK regulatory functions, such as gene regulation, proposed here to be mediated by hexamer-hexamer interactions with the DNA-binding protein PepA.     

珙桐群落种间关系的研究

用方差比率法(VR)和在2×2联列表基础上应用Jaccard指数、Dice指数和Pearson相关系数、Spearman秩相关系数对卧龙自然保护区三江珙桐群落种间关系进行了分析,结果表明珙桐群落中主要种群在总体上表现出正关联,群落中种间联结的显著度较低,仅有7对联结显著,珙桐与总状山矾呈显著负联结,与稠李呈极显著负联结。大多数种对间关联程度较低,存在极大排斥性的种对较少,暗示目前珙桐群落处于较成熟阶段。研究种间关系时,种间关联性测定指标结合相关系数分析得出的结果较好,最后对珙桐的保护提出了一些建议。     

Gibberellins do not act against abscisic acid in the regulation of bulb dormancy of Allium wakegi Araki

Abscisic acid (ABA) is involved in bulb dormancy of Alliumwakegi Araki. We examined the antagonistic role of gibberellins(GAs)against ABA in the regulation of this dormancy. The concentrations of ABA andGAs in the basal leaf sheaths or bulbs of A. wakegi cv.Kiharawase were investigated during growth in the field and postharveststorage.The concentration of ABA in the basal leaf sheaths began to increase about onemonth before they began to swell, reached a maximum shortly after bulbharvesting, and decreased during postharvest storage. The plants showed bulbdormancy accompanied with the change in ABA concentration. GA1,GA3, GA4, GA12, GA15, GA19, and GA20 were identified in the basal leaf sheaths of A. wakegi from Kovats retention indices (KRI) andfull-scan mass spectra by gas chromatography - mass spectrometry (GC-MS)analysis. The concentrations of all classes of GAs in the basal leaf sheathsestimated by the dwarf rice micro-drop assay increased transitorily shortlybefore they began to swell, and decreased rapidly during bulb development. Bulbdormancy had already been induced when the concentration of the GAs becamemaximum. All the GAs in the bulbs remained at a low level during postharveststorage, when bulbs were gradually released from dormancy. The concentrationsof GA1+3, GA4, GA15, and GA20 inthe bulbs increased after sprouting of the bulbs planted in moist vermiculite.Hence, the state of bulb dormancy is considered to be independent of the GAconcentrations of in the basal leaf sheaths or bulbs of A.wakegi.