Aminoacylation of four tRNA species in lupin (Lupinus luteus) cotyledons

During germination of lupin seeds, the levels of in-vivo tRNA aminoacylation increase in different ways, depending on the species of tRNA. Column chromatography of tRNA on reverse-phase-chromatography (RPC-5) has shown the presence of 4 peaks of isoleucyl-tRNA, 5 of leucyl-tRNA, 5 of lysyl-tRNA, 2 of tyrosyl-tRNA, and 4 of valyl-tRNA. Cochromatography of periodate treated and control tRNA preparations, labeled with radioactive amino acids, indicates identical aminoacylation in vivo of isoaccepting tRNAs during plant development. One isoacceptor of isoleucine tRNA changes its elution profile after periodate treatment.Abbreviation RPC-5 reverse-phase-chromatography     

Sucrose metabolism in lima bean seeds

Developing and germinating lima bean (Phaseolus lunatus var Cangreen) seeds were used for testing the sucrose synthase pathway, to examine the competition for uridine diphosphate (UDP) and pyrophosphate (PPi), and to identify adaptive and maintenance-type enzymes in glycolysis and gluconeogenesis. In developing seeds, sucrose breakdown was dominated by the sucrose synthase pathway; but in the seedling embryos, both the sucrose synthase pathway and acid invertase were active. UDPase activity was low and seemingly insufficient to compete for UDP during sucrose metabolism in seed development or germination. In contrast, both an acid and alkaline pyrophosphatase were active in seed development and germination. The set of adaptive enzymes identified in developing seeds were sucrose synthase, PPi-dependent phosphofructokinase, plus acid and alkaline pyrophosphatase; and, the adaptive enzymes identified in germinating seeds included the same set of enzymes plus acid invertase. The set of maintenance enzymes identified during development, in the dry seed, and during germination were UDP-glucopyrophosphorylase, neutral invertase, ATP and UTP-dependent fructokinase, glucokinase, phosphoglucomutase, ATP and UTP-dependent phosphofructokinase and sucrose-P synthase.     

喀什霸王的结实和种子萌发特性

喀什霸王(Zygophyllum kaschgaricum)是生长于中国新疆南部荒漠环境的稀有种及二级保护植物。当前, 该物种在自然种群中呈分散式及片段化分布, 且种群密度低, 种群老龄化较严重。因此, 为了了解该物种种子萌发特性及其对荒漠环境的响应, 该文采用室内控制实验方法, 对该物种的自然坐果率、结籽率、种子吸水特性、种子休眠和萌发特性及对干旱胁迫的响应进行了比较研究。结果表明: 喀什霸王在自然种群中的坐果率及结籽率较低, 且种子的败育率较高。不同干藏时间种子的吸水速率间存在显著差异; 随着干藏时间的延长, 种子的吸水率逐步增强。刚成熟的种子在不同温度及光周期下均可萌发; 其中高温(10/20 ℃, 20/30 ℃)及黑暗条件下的萌发率比低温(10/5 ℃, 5/2 ℃)及光照条件下的萌发率高。不同干藏时间的种子在不同浓度赤霉素(GA₃)下的萌发率均较高; 但低温储藏时间对该物种种子的打破休眠及萌发率没有促进作用。以上结果说明该物种存在非深度生理休眠; 而干藏时间、高温且黑暗及高浓度(50 mmoloL ^-1) GA₃是打破休眠及促进种子萌发的最合适条件。高温条件下的干旱胁迫对喀什霸王种子萌发具有抑制作用; 春季和秋季降水量决定种子的萌发率。总之, 喀什霸王种子在物候上表现出的春秋季萌动及非深度生理休眠以提高幼苗存活力及保障种群稳定性, 是一种对新疆南部干旱及高温胁迫荒漠环境的适应策略。     

Changes in RNA and Protein Metabolism Associated with Alterations in the Germination Efficiency of Sunflower Seeds

Precise knowledge of seed quality after harvest and during storageis of particular importance for seed producers. We analyseddifferent sunflower seed lots (Helianthus annuusL.) characterizedby extremes of germination ability. We used RNA analysis tostudy possible changes in gene expression in seeds unable togerminate. Total RNA content was very small in dry seeds showinga low germination ability. Capacity for total RNA synthesisat the onset of imbibition was also reduced in these seeds.In addition, correlations were found between these parametersand germination ability at 19 °C. We demonstrated a highcorrelation between the amount of total RNA in the dry seed,the capacity of RNA synthesis at the onset of imbibition andthe seed moisture content at the time of the harvest. The abilityof dry seed mRNAs to be translatedin vitrowas also reduced andseven polypeptides, from stored mRNAs, were characteristic ofthe cotyledons from high germinability seeds. Germination canthus be affected at several levels including membrane, enzymaticand nucleic acid deteriorations. Gene expression; germination ability; Helianthus annuusL.; marker; protein; RNA; seed; sunflower     

Drought tolerance of Periploca sepium during seed germination: antioxidant defense and compatible solutes accumulation

Periploca sepium Bunge is a native and widespread shrub on the Loess Plateau, an arid and semi-arid region in China. To understand the adaptability of its seed germination to dry environments, we investigated the germination rate, water relations, lipid peroxidation, antioxidant capacity and accumulation of major organic solutes during seed germination under water deficit conditions. Results showed that seeds pre-treated by hydration–dehydration or ?0.9 MPa PEG germinated faster than control seeds, indicating strong resistance of P. sepium to drought condition. The re-dried seeds showed higher proline, total free amino acids (TFAA) and soluble proteins (SP) contents than control dry seeds, indicating the maintenance of physiological advancement when dehydrated. Osmotic stress made seed germination stay on the plateau phase (phase II). However, germinating seeds moved into phase III immediately once transferred into distilled water. Large increases in SP and soluble sugars (SS) of both re-dried and osmotic stressed seeds help themselves to resist drought stress. The re-hydrated seeds showed significantly higher levels of proline, TFAA, SP and SS than control seeds. The largely accumulated SS during osmotic stress declined sharply when transferred into distilled water. Our data demonstrate that P. sepium’s tolerance to drought stresses during germination is associated with enhanced activity of antioxidant enzymes and accumulation of some compatible solutes. Seed physiological advancement progressed slowly under low water conditions and it was maintained when seeds were air dried. This strategy ensures high and more rapid seed germination of P. sepium under drying and wetting conditions in drought-prone regions.     

The Effects of Priming and Ageing on Resistance to Deterioration of Tomato Seeds

The influence of seed priming and ageing treatments on viabilityand rate of germination of tomato (Lycopersicon esculentum Mill.)seeds was examined under both long-term and controlled-deteriorationstorage conditions. Seeds of a single lot of tomato were eitherprimed or aged to increase or decrease the rate of germination(Argerich and Bradford, 1989). They were then stored at 6% moisturecontent (dry weight basis) at either 4 ?C or 30 ?C for 1 year.Both viability and germination rate were unaffected by eitherstorage temperature in control seeds, or by 4 ?C storage inprimed or aged seeds. At 30 ?C, however, viability and germinationrate of primed and aged seeds was markedly reduced after 6 monthsof storage. The temperature dependence of the germination rateand the spread of germination times within the population wasalso adversely affected by high temperature storage, particularlyfor primed seeds. Under controlled deterioration conditions(13.5% moisture content and 50 ?C), the rate of loss of viabilitywas greater for primed seed than for control or aged seeds.The relationship between seed viability and the mean germinationrate, however, was not influenced by the seed treatments. Thesedata are analysed in relation to current models of seed deteriorationduring storage and seed repair during priming. The results indicatethat enhancement of seed germination rates by priming treatmentssimultaneously lowers the resistance of seeds to deterioration.Primed tomato seeds must, therefore, be considered to be vigorousseeds with a reduced storage life. Key words: Tomato, controlled deterioration, seed germination rate, seed viability     

Yeast seryl tRNA synthetase: two sets of substrate sites involved in aminoacylation.

Seryl tRNA synthetase from Saccharomyces Carlsbergensis C836 contains two sets of sites for tRNASer, L-serine, and Mg2+-ATP, both of which are involved in aminoacylation. This is based on the following experimental results: (a) at low serine concentrations, second order kinetics in tRNASer are observed; (b) biphasic kinetics result when the amino acid is the varied substrate indicating anticooperative binding of two serine molecules to the synthetase; (c) when two molecules of serine are bound the rate of aminoacylation increases strongly and becomes first order in tRNASer; (d) the involvement of more than one site for Mg2+ and ATP is deduced from systematic variations of the concentrations of Mg2+ and ATP. Implications of the anticooperative binding of the substrates for possible reaction mechanisms are discussed. The results indicate that under normal conditions, the activity of seryl tRNA synthetase is regulated mainly by tRNASer while at high serine concentrations regulation by the amino acid itself prevails.     

Patterns of protein oxidation in Arabidopsis seeds and during germination

Increased cellular levels of reactive oxygen species are known to occur during seed development and germination, but the consequences in terms of protein degradation are poorly characterized. In this work, protein carbonylation, which is an irreversible oxidation process leading to a loss of function of the modified proteins, has been analyzed by a proteomic approach during the first stages of Arabidopsis (Arabidopsis thaliana) seed germination. In the dry mature seeds, the legumin-type globulins (12S cruciferins) were the major targets. However, the acidic alpha-cruciferin subunits were carbonylated to a much higher extent than the basic (beta) ones, consistent with a model in which the beta-subunits are buried within the cruciferin molecules and the alpha-subunits are more exposed to the outside. During imbibition, various carbonylated proteins accumulated. This oxidation damage was not evenly distributed among seed proteins and targeted specific proteins as glycolytic enzymes, mitochondrial ATP synthase, chloroplastic ribulose bisphosphate carboxylase large chain, aldose reductase, methionine synthase, translation factors, and several molecular chaperones. Although accumulation of carbonylated proteins is usually considered in the context of aging in a variety of model systems, this was clearly not the case for the Arabidopsis seeds since they germinated at a high rate and yielded vigorous plantlets. The results indicate that the observed specific changes in protein carbonylation patterns are probably required for counteracting and/or utilizing the production of reactive oxygen species caused by recovery of metabolic activity in the germinating seeds.     

Proliferating cell nuclear antigen expression in maize seed development and germination: Regulation by phytohormones and its association with putative cell cycle proteins

The proliferating cell nuclear antigen (PCNA) plays a fundamental role in DNA replication and repair and recently, it has been found associated to proteins that control the G1 phase of the cell cycle, such as cyclin D. Maize PCNA cDNA has been cloned and overexpressed in order to raise antibodies. The expression of PCNA has been followed during seed development and seed germination using the homologous antibodies. The protein was found at a constant level during seed development up to 48 days after pollination (DAP) and then the amount declined to very low levels, similar to those found in dry seeds. Upon germination, PCNA levels rose gradually reaching a peak by 20 h germination. Imbibition in the presence of cytokinins (Benzyladenine, BA) produced a sharp increase in amount during the first 3–6 h germination, whereas imbibition in the presence of abscisic acid (ABA) did not alter the pattern of expression as compared with control seeds. Immunoprecipitation experiments showed that PCNA was associated to a putative cyclin D protein during germination and this association was altered by phytohormones. While the complex PCNA-cyclin D-like protein was present along the first 15 h of germination under control conditions, it was dissociated after 6 h if embryo axes germinated in the presence of BA or ABA. However, complex dissociation in the presence of BA was due to degradation of the putative cyclin D protein while in the presence of ABA the putative cyclin D was still present. These results are discussed in the context of seed germination and the cell cycle.     

Importance of methionine biosynthesis for Arabidopsis seed germination and seedling growth

Proteomics of Arabidopsis seeds revealed the differential accumulation during germination of two housekeeping enzymes. The first corresponded to methionine synthase that catalyses the last step in the plant methionine biosynthetic pathway. This protein was present at low level in dry mature seeds, and its level was increased strongly at 1-day imbibition, prior to radicle emergence. Its level was not increased further at 2-day imbibition, coincident with radicle emergence. However, its level in 1-day imbibed seeds strongly decreased upon subsequent drying of the imbibed seeds back to the original water content of the dry mature seeds. The second enzyme corresponded to S -adenosylmethionine synthetase that catalyses the synthesis of S -adenosylmethionine from methionine and ATP. In this case, this enzyme was detected in the form of two isozymes with different p I and M r. Both proteins were absent in dry mature seeds and in 1-day imbibed seeds, but specifically accumulated at the moment of radicle protrusion. Arabidopsis seed germination was strongly delayed in the presence of dl -propargylglycine, a specific inhibitor of methionine synthesis. Furthermore, this compound totally inhibited seedling growth. These phenotypic effects were largely alleviated upon methionine supplementation in the germination medium. The results indicated that methionine synthase and S -adenosylmethionine synthetase are fundamental components controlling metabolism in the transition from a quiescent to a highly active state during seed germination. Moreover, the observed temporal patterns of accumulation of these proteins are consistent with an essential role of endogenous ethylene in Arabidopsis only after radicle protrusion.     

Changes in Levels and Integrity of Ribosomal RNA During Seed Maturation and Germination in Carrot (Daucus carota L.)

Thompson, S., Bryant, J. A. and Brocklehurst, P. A. 1987. Changesin levels and integrity of ribosomal RNA during seed maturationand germination in carrot (Daucus carota L.).—J. exp.Bot. 38: 1343–1350. Amounts and integrity (percentage of complete un-nicked molecules)of ribosomal RNA (rRNA) during germination in carrot seed lotsof differing vigour and viability were examined using aqueousand formamide gel electrophoresis. In unaged seed, amounts ofrRNA per seed in dry seed are not related to maturity, vigouror viability. However, rRNA in immature seed is more vulnerableto damage by ageing than rRNA in mature seed; thus, amountsof rRNA per seed in aged seed are indicators of vigour and viability.On imbibition of aged or unaged seed, more rRNA fragmentationoccurs in immature seed than in mature seed, and the time atwhich the effects of synthesis outweigh the effects of degradationis earlier during germination in mature than in immature seed. Key words: rRNA, seed maturation, seed germination, Daucus carota L.     

The Time Required for Dormancy Release in Arabidopsis Is Determined by DELAY OF GERMINATION1 Protein Levels in Freshly Harvested Seeds

Seed dormancy controls the start of a plant's life cycle by preventing germination of a viable seed in an unfavorable season. Freshly harvested seeds usually show a high level of dormancy, which is gradually released during dry storage (after-ripening). Abscisic acid (ABA) has been identified as an essential factor for the induction of dormancy, whereas gibberellins (GAs) are required for germination. The molecular mechanisms controlling seed dormancy are not well understood. DELAY OF GERMINATION1 (DOG1) was recently identified as a major regulator of dormancy in Arabidopsis thaliana. Here, we show that the DOG1 protein accumulates during seed maturation and remains stable throughout seed storage and imbibition. The levels of DOG1 protein in freshly harvested seeds highly correlate with dormancy. The DOG1 protein becomes modified during after-ripening, and its levels in stored seeds do not correlate with germination potential. Although ABA levels in dog1 mutants are reduced and GA levels enhanced, we show that DOG1 does not regulate dormancy primarily via changes in hormone levels. We propose that DOG1 protein abundance in freshly harvested seeds acts as a timer for seed dormancy release, which functions largely independent from ABA.     

Common and distinct responses in phytohormone and vitamin E changes during seed burial and dormancy in Xyris bialata and X. peregrina

Temperature and humidity are the main factors influencing seed viability, dormancy and longevity of buried seeds. Unfortunately, very little is known about such processes in species of tropical regions, where temperature does not show major seasonal variations. The extent to which germination capacity, phytohormones and vitamin E levels were altered after burial of seeds of Xyris bialata and X. peregrina (Xyridaceae), two species endemic to rupestrian fields of Brazil, was examined. After 2 months of burial, seed germination capacity remained constant, which is associated with decreases in ABA and IAA content in both species. During this period, zeatin levels also decreased in X. bialata, but not in X. peregrina, the latter showing much lower levels of ABA. During the summer (rainy season), seeds of both species experienced a progressive, but severe, decrease in germination capacity, which reversed at the end of the winter (dry season), thus suggesting secondary dormancy. This dormancy appeared to be caused by drastic decreases in GAs, rather than increases in ABA. Levels of GA(4) decreased to non-detectable values during dormancy in both species. Furthermore, zeatin levels decreased in X. bialata but not in X.peregrina during this period. Both species accumulated γ-tocopherol as the major vitamin E form, and levels of this antioxidant remained constant or even increased during seed burial; however, X. bialata seeds showed a significant decrease in α-tocopherol during seed burial and dormancy. It is concluded that in X. peregrina and X. bialata, (i) burial causes significant changes in the phytohormone levels of seeds; (ii) secondary dormancy is induced in seeds; (iii) a GA(4) decrease, rather than an ABA increase, seems to be involved in the induction of secondary dormancy; and (iv) reductions in α-tocopherol in buried seeds are not necessarily indicative of reduced germination capacity.     

小花草玉梅种子萌发过程中常见内源激素含量的变化及萌发机制

植物内源激素在调节种子休眠和萌发过程中具有极其重要的作用。本研究运用反式高效液相色谱(RP-HPLC)与紫外检测器联用的方法对小花草玉梅干种子、吸胀种子和露白种子中的赤霉素GAs、脱落酸ABA、玉米素ZT和生长素IAA含量进行了检测,旨在研究植物内源激素水平在种子萌发过程中的变化是否直接关系着小花草玉梅种子在光照或黑暗条件下的萌发能力。结果显示,种子吸胀过程中,光照促进了ZT同时抑制了ABA的积累,并且ZT对ABA萌发抑制作用的解除也受光的促进,露白种子中的ABA/ZT,ABA/GAs和(ABA+IAA)/(GAs+ZT)水平在黑暗条件下高于光照条件,上述均是导致光照条件下种子萌发率较高的重要原因;相对于干种子,IAA含量在种子吸胀初期急速下降,(ABA+IAA)/(GAs+ZT)在种子萌发过程中有所降低,而ABA/GAs却表现出明显的上升趋势;各激素水平所受光照的影响均在种子开始露白时显著减弱,另外,吸胀第9天是小花草玉梅种子萌发过程中激素变化的一个关键的时间节点。总之,种子萌发并非直接关系着GA含量的升高和ABA含量的降低。因光照直接促进了小花草玉梅种子的萌发,本研究认为高寒草甸充...     

Control of the Germination Responses of Amaranthus retroflexus L. Seeds by their Parental Photothermal Environment

Germination responses of the seeds of Amaranthus retroflexusL. were affected by the photoperiod, temperature, and levelof solar radiation experienced by their parent plants. Seedsfrom parents grown continuously in short days (SD, 8 h) lostpost-harvest dormancy more rapidly and had a higher dark germination,as well as a greater responsiveness (at 30?C) to pretreatmentsat low temperature (5 or 10?C) and to short illuminations, thanseeds from parents grown continuously in long days (LD, 16 h).Dark germination and responsiveness of the seeds to promotivetreatments were both higher when their parents were transferredat flowering from LD to SD than when grown continuously in LD.These responses were lower when their parents were similarlytransferred from SD to LD than when grown continuously in SD.The promotive effects of parental post-flowering SD on darkgermination (at 30?C) were enhanced by reduction of parentaltemperature (from 27/22?C to 22/17?C), but the responsivenessof the seeds to low temperature pretreatment was reduced. Inflorescencesdeveloping in LD produced seed with higher germinability whenfloweringwas not induced (LD throughout) than when it was induced (eitherby SD till flowering, or by three SD cycles when 4–5 leavesappeared). Reduced levels of solar radiation had opposite effectsin the different parental photoperiods: dark germination andthe responsiveness to low temperature pretreatments were reducedin LD, but were increased in SD. Differences in the germination responses resulting from differencesin the parental environment could not be correlated with differencesin seed coat thickness or seed dry weight.     

An ATP-synthesizing system in seeds

Using onion seed powder, a semi-in vitro system for ATP synthesis in seeds has been developed. The system requires AMP, phosphoenolpyruvate (PEP) and orthophosphate with apparent Km values of 0.8, 1.5 and 3.0 mM, respectively. ATP synthesis is pH-dependent with a sharp optimum at pH 6.4, it exhibits linearity with time up to 40 min, and with a seed powder concentration between 25 and 150 mg ml^-1. The system is stimulated by low concentrations (<25 mM) of K⁺ and Mg²⁺ but is inhibited by higher concentrations of K⁺ and Mg²⁺ as well as by low concentrations of Li⁺, Na⁺ and especially Ca²⁺. The maximal rate is about 5 pmol min^-1 mg seed powder^-1 in dry onion seeds. During seed imbibition the rate of activity increases by about 120% after 3 h, reaching a plateau which is steady up to 18 h, when the radicle emerges. A comparison of the ATP content in seeds during the early period of imbibition with the capacity of ATP synthesis at this stage reveals that the described system could provide, during germination, 100 times more ATP than that found in imbibed seeds. The system is shown to be present in ten different types of seeds.     

Ubiquitination and ATP levels in garden pea seeds

Developing and germinating pea seeds contain high levels of ubiquitin conjugated to proteins as detected on western blots. In contrast, the level of dry seed protein-ubiquitin conjugates in vivo appears low, with mainly free ubiquitin present. The ubiquitination of endogenous dry pea seed proteins is observed in vitro, relying only on already present endogenous ubiquitin, suggesting the enzymatic machinery for ubiquitination is present in the dry seed. Energy source in the form of ATP increased the formation of large molecular mass conjugates, although some conjugation took place without added ATP. The usefulness of dry seeds, having low levels of ATP which can then be manipulated in the in vitro reaction is discussed. ATP and ubiquitin degrading activities are detected in the crude in vitro system, pointing to the need to purify the individual components, or to seek specific inhibitors of the undesirable secondary reactions.     

Polyamine distribution among maize embryonic tissues and its relation to seed germination

Polyamines are known to participate in the control of cell division. In the present report, the levels and distribution of polyamines in the embryonic tissues of maize seeds were studied to relate them to the reinitiation of cell division during seed germination. Results indicate higher contents of polyamines in scutellum than in axis tissues of dry seeds. After germination, larger increments of the three polyamines were obtained in axes, rather than in scutella. Seeds of low viability did not show putrescine increments after germination. It is suggested that spermidine and spermine are directly related to the germination process.     

Analysis of how ant behaviors affect germination in a tropical myrmecochore Calathea microcephala (P. & E.) Koernicke (Marantaceae): Microsite selection and aril removal by neotropical ants,Odontomachus, Pachycondyla,and Solenopsis (Formicidae)

Summary The evolutionary effects of a tropical ant-seed interaction are examined by posing questions about the fate of Calathea seeds carried by neotropical ants. Where do ants take seeds and what do they do with them? How do ant behaviors affect seed germination? Treatment of seeds by ants is determined by a series of seed-fate trials in captive colonies. There is no evidence of seed predation by ants. Odontomachus laticeps, Pachycondyla spp, and Solenopsis geminata rapidly displace seeds to ant nests, determine the microsites of seeds, and remove the seed arils for food. The seed arils are rich in lipids. The effects on germination of microsite selection and aril removal are quantitatively evaluated. Seeds which are immediately taken to a consistently moist spot germinate readily; 72% germinate, with a mean germination speed of 29 days. For such seeds aril removal does not significantly affect germination. In contrast, seeds which experience a delay before encountering appropriate germination conditions seem to exhibit an induced dormancy (sensu, Harper 1977) and a lower germination percentage. They take longer to germinate (up to 85 days) even after conditions become appropriate. It appears that their germination is enhanced by aril removal, which may act as an environmental cue to break dormancy. Such a mechanism would indicate that ant-handling of seeds is predictive of favorable conditions for seedling growth and establishment. The exact nature of such conditions and the effects on plant population dynamics remain to be seen.