Arrestment of carbohydrate metabolism during anaerobic dormancy and aerobic acidosis inArtemia embryos: determination of pH-sensitive control points

Summary Changes in concentrations of trehalose, glycogen, glycerol, some glycolytic intermediates and adenylate nucleotides that occur during aerobic development have been compared to those seen during anaerobic dormancy and aerobic acidosis in gastrula-stage embryos ofArtemia. The latter two incubation conditions are known to foster large drops in intracellular pH (Busa et al. 1982; Busa and Crowe 1983).During aerobic development, trehalose levels decline while glycogen and glycerol are synthesized (Fig. 1). These transitions are blocked during both anaerobic dormancy and aerobic acidosis, but are resumed by return of embryos to aerobic incubation (Fig. 1). Thus, it is concluded that carbohydrate catabolism in hydrated embryos is directly modulated by intracellular pH. Changes in metabolite levels (Figs. 2–4) reveal that this process is controlled primarily at the trehalase and hexokinase reactions with a less-pronounced negative crossover point noted at the phosphofructokinase step. Each of these reactions is shown to be nonequilibrium by comparing the mass action ratio to the equilibrium constant (Table 1).When embryos are placed under anaerobic conditions, ATP levels drop dramatically while AMP increases in concentration (Fig. 5). These changes are reflected in a drop in adenylate energy charge from a control value of 0.73 to 0.42 (Fig. 6). Aerobic acidosis only leads to a slight decrease in energy charge, emphasizing that shifts in adenylate poolsAbbreviations pH _i intracellular pH - glyceraldehyde 3-P glyeraldehyde 3-phosphate - DHAP dihydroxyacetone phosphate - glucose 6-P glucose 6-phosphate - fructose 6-P fructose 6-phosphate - fructose 1,6-P ₂ fructose 1,6-bisphosphate - HK hexokinase - PFK phosphofructokinase - MAR mass action ratio - K _eq equilibrium constant     

Control of seed dormancy in Nicotiana plumbaginifolia: post-imbibition abscisic acid synthesis imposes dormancy maintenance

The physiological characteristics of seed dormancy in Nicotiana plumbaginifolia Viv. are described. The level of seed dormancy is defined by the delay in seed germination (i.e the time required prior to germination) under favourable environmental conditions. A wild-type line shows a clear primary dormancy, which is suppressed by afterripening, whereas an abscisic acid (ABA)-deficient mutant shows a non-dormant phenotype. We have investigated the role of ABA and gibberellic acid (GA₃) in the control of dormancy maintenance or breakage during imbibition in suitable conditions. It was found that fluridone, a carotenoid biosynthesis inhibitor, is almost as efficient as GA₃ in breaking dormancy. Dry dormant seeds contained more ABA than dry afterripened seeds and, during early imbibition, there was an accumulation of ABA in dormant seeds, but not in afterripened seeds. In addition, fluridone and exogenous GA₃ inhibited the accumulation of ABA in imbibed dormant seeds. This reveals an important role for ABA synthesis in dormancy maintenance in imbibed seeds. Received: 31 December 1998 / Accepted: 9 July 1999     

Transition from primary dormancy to secondary dormancy in cocklebur seeds

Abstract The transition from primary dormancy to secondary dormancy was examined using upper cocklebur (Xanthium pennsylvanicum Wallr.) seeds. The non-after-ripened seeds with primary dormancy responded to chilling, anoxia, KCN, and NaN₃ with an increase in germination. However, their maximal responses to these treatments only occurred after a period of water imbibition, probably a reflection of the increasing growth potential of the axial tissue which was accompanied by the increase in the capacities of respiration and ethylene production. On the other hand, the establishment of secondary dormancy was accompanied by a decrease in respiration and ethylene production of seeds, and in the growth potential of both axial and cotyledonary tissues. The decrease in growth potential of these tissues occurred regardless of whether they were excised from after-ripened seeds or non-after-ripened seeds. It is inferred that the primary dormancy of cocklebur seeds is a state maintained in un-germinated seeds for a long time through a spontaneous transition to secondary dormancy.     

Proteins and polyamines during dormancy breaking of European beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) seeds

The studies were carried out on Fagus sylvatica seeds during stratification and their germination. After imbibition beechnuts were subjected to cold (3 °C — temperature which breaks dormancy) or warm (15 °C — temperature unable to break dormancy) stratification and alternatively were treated with polyamine synthesis inhibitors: canavanine and DFMO (difluoromethylornithine). After cold stratification in embryo axes we found (using 2-D electrophoresis) about 150 new proteins absent in dry seeds. Exogenous spermidine increased the protein synthesis, percent of germinated seeds and accelerated breaking of dormancy. In contrast, canavanine and DFMO decreased dynamic of protein synthesis, quantity of proteins probably synthesised de novo, and percent of germinated seeds. The maximum of polyamine content in embryo axes during cold stratification preceded such the maximum during warm stratification. Irrespective of the influence of PAs and inhibitors of PA synthesis, the comparison of electrophoregrams and autoradiograms showed that different groups synthesised de novo appeared after different periods of cold stratification. Probably the part of this protein is associated with Fagus sylvatica seeds dormancy breaking.     

濒危植物海南龙血树种子休眠机理及其生态学意义

通过对中国西双版纳与泰国都有分布和栽培的641种植物的傣、泰土著名字相似性比较,发现这两个民族具有基本相同的民间植物命名的“双名法”。西双版纳傣族与泰国的兰纳地区、北—东北部和其它地区泰族的植物土著名相同、相似的分别占0.69、0.57和0.37,主要包括药用植物在内的经济植物和与南传上座部佛教文化密切相关的植物。其主要成因包括他们的语言文字、宗教信仰、生活习俗等的傣、泰历史渊源及其所具有的传统文化密切程度相关。其中,兰纳地区地处泰国北部,它不仅邻近西双版纳,而且在历史上,它们曾经同属于“兰纳王国”,两地的边界曾是“犬牙交错”,成为“曼比勐农”（兄弟之邦）。这样,使包括土著名字在内的佛教植物、野生植物和栽培植物等的交流比泰国其它地区更加密切,相似性便最高。西双版纳傣族和兰纳泰族被视为尚存的标准“Tai”人区。因此,该研究对于中国Dai、泰国Thai、缅甸Siam和老挝Laos等国家民族的科学文化交流及其植物资源的利用和保护等具有重要的意义。 关键词： 民族植物学研究, 中国西双版纳傣族与泰国泰族, 相同植物的民间命名方法, 相似的植物土著名字, 相似的历史渊源成因, 科学与文化交流的意义     

Dynamics of carbohydrates in the embryo axes of horse chestnut seeds during their transition from dormancy to germination

It was shown that the content of carbohydrates and their composition in embryo axes of horse chestnut seeds changed as seeds acquired a capability of dormancy release and germination. Sucrose prevailed among carbohydrates, comprising to 150–160 mg/g dry wt. During the first half of the seed imbibition time, oligosaccharides, namely raffinose and stachyose, degraded, whereas the contents of glucose and fructose were very low. The second half of the imbibition period (until radicle protrusion) was characterized by a cessation of oligosaccharide breakdown and accumulation of monosaccharides. Carbohydrate balance showed that the contribution of oligosaccharide breakdown to sucrose and monosaccharide accumulation was rather small, and monosaccharides accumulated mostly at the expense of sucrose gradually coming from cotyledons during imbibition. The trend of carbohydrate metabolism in imbibing axial organs was similar during the entire period of a seed dormancy release in the course of stratification. A readiness for the commencement of these processes during the entire dormancy period implies that carbohydrate conversions in embryo axes are not a trigger for a dormancy release. Monosaccharide accumulation in embryo axes before radicle protrusion produces an increase in the osmotic pressure, as compared to that provided by sucrose, by approximately 20%. Recalcitrance of the horse chestnut seeds is discussed in relation to the role of carbohydrates and other endogenous osmotica in the establishment of osmotic properties.     

Role of reactive oxygen species in the regulation of Arabidopsis seed dormancy

Freshly harvested seeds of Arabidopsis thaliana, Columbia (Col) accession were dormant when imbibed at 25°C in the dark. Their dormancy was alleviated by continuous light during imbibition or by 5 weeks of storage at 20°C (after-ripening). We investigated the possible role of reactive oxygen species (ROS) in the regulation of Col seed dormancy. After 24 h of imbibition at 25°C, non-dormant seeds produced more ROS than dormant seeds, and their catalase activity was lower. In situ ROS localization revealed that germination was associated with an accumulation of superoxide and hydrogen peroxide in the radicle. ROS production was temporally and spatially regulated: ROS were first localized within the cytoplasm upon imbibition of non-dormant seeds, then in the nucleus and finally in the cell wall, which suggests that ROS play different roles during germination. Imbibition of dormant and non-dormant seeds in the presence of ROS scavengers or donors, which inhibited or stimulated germination, respectively, confirmed the role of ROS in germination. Freshly harvested seeds of the mutants defective in catalase (cat2-1) and vitamin E (vte1-1) did not display dormancy; however, seeds of the NADPH oxidase mutants (rbohD) were deeply dormant. Expression of a set of genes related to dormancy upon imbibition in the cat2-1 and vet1-1 seeds revealed that their non-dormant phenotype was probably not related to ABA or gibberellin metabolism, but suggested that ROS could trigger germination through gibberellin signaling activation.     

Physiological characteristics and related gene expression of after‐ripening on seed dormancy release in rice

After‐ripening is a common method used for dormancy release in rice. In this study, the rice variety Jiucaiqing (Oryza sativa L. subsp. japonica) was used to determine dormancy release following different after‐ripening times (1, 2 and 3 months). Germination speed, germination percentage and seedling emergence increased with after‐ripening; more than 95% germination and 85% seedling emergence were observed following 1 month of after‐ripening within 10 days of imbibition, compared with <45% germination and 20% seedling emergence in freshly harvested seed. Hence, 3 months of after‐ripening could be considered a suitable treatment period for rice dormancy release. Dormancy release by after‐ripening is mainly correlated with a rapid decline in ABA content and increase in IAA content during imbibition. Subsequently, GA₁/ABA, GA₇/ABA, GA₁₂/ABA, GA₂₀/ABA and IAA/ABA ratios significantly increased, while GA₃/ABA, GA₄/ABA and GAs/IAA ratio significantly decreased in imbibed seeds following 3 months of after‐ripening, thereby altering α‐amylase activity during seed germination. Peak α‐amylase activity occurred at an earlier germination stage in after‐ripened seeds than in freshly harvested seeds. Expression of ABA, GA and IAA metabolism genes and dormancy‐related genes was regulated by after‐ripening time upon imbibition. Expression of OsCYP707A5, OsGA2ox1, OsGA2ox2, OsGA2ox3, OsILR1, OsGH3‐2, qLTG3‐1 and OsVP1 increased, while expression of Sdr4 decreased in imbibed seeds following 3 months of after‐ripening. Dormancy release through after‐ripening might be involved in weakening tissues covering the embryo via qLTG3‐1 and decreased ABA signalling and sensitivity via Sdr4 and OsVP1.     

Hormonal and environmental regulation of seed germination in flixweed (<Emphasis Type="Italic">Descurainia sophia</Emphasis>)

Flixweed is one of the most abundant weeds in North America and China, and causes a reduction in crop yields. Dormancy of flixweed seeds is deep at maturity and is maintained in soil for several months. To identify regulators of seed dormancy and germination of flixweed, the effect of environmental and hormonal signals were examined using dormant and non-dormant seeds. The level of dormancy was decreased during after-ripening and stratification, but long imbibition (over 5 days) at 4 °C in the dark resulted in the introduction of secondary dormancy. The strict requirement of duration of cold treatment for the break of dormancy may play a role in the seasonal regulation of germination. The germination of non-dormant flixweed seeds was critically regulated by red (R) and far-red (FR) light in a photoreversible manner. Sodium nitroprusside, a donor of nitric oxide (NO), promoted germination of half-dormant seeds, suggesting that NO reduced the level of seed dormancy. As has been shown in other related species, light elevated sensitivity to GA₄ in dark-imbibied flixweed seeds, but cold treatment did not affect GA₄-sensitivity unlike in Arabidopsis. Taken together, our results indicate that seed germination in flixweed and its close relative Arabidopsis is controlled by similar as well as distinct mechanisms in response to various endogenous and environmental signals.     

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     

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     

Seed dormancy of Cardiospermum halicacabum (Sapindaceae) from three precipitation zones in Sri Lanka

• This study investigated seed germination of Cardiospermum halicacabum, a medicinally important invasive species.
• We compared mass, moisture content (MC), dormancy and dormancy‐breaking treatments and imbibition and germination of scarified and non‐scarified seeds of C. halicacabum from a low‐elevation dry zone (DZ), low‐elevation wet zone (WZ1) and mid‐elevation wet zone (WZ2) in Sri Lanka to test the hypothesis that the percentage of seeds with water‐impermeable seed coats (physical dormancy, PY) decreases with increased precipitation.
• Seed mass was higher in WZ2 than in DZ and WZ1, while seed MC did not vary among the zones. All scarified DZ, WZ1 and WZ2 and non‐scarified DZ and WZ1 seeds imbibed water, but only a few non‐scarified WZ2 seeds did so. When DZ and WZ1 seeds were desiccated, MC and percentage imbibition decreased, showing that these seeds have the ability to develop PY. GA₃ promoted germination of embryos excised from fresh DZ and WZ1 seeds and of scarified WZ2 seeds.
• At maturity, seeds from DZ and WZ1 had only physiological dormancy (PD), while those from WZ2 had combinational dormancy (PY+PD). Thus, our hypothesis was not supported. Since a high percentage of excised embryos developed into normal seedlings; this is a low‐cost method to produce C. halicacabum plants for medicinal and ornamental purposes.

     

Adenine nucleotides and energy charge during dormancy breaking in embryo axes of <Emphasis Type="Italic">Acer platanoides</Emphasis> and <Emphasis Type="Italic">Fagus sylvatica</Emphasis> seeds

We analysed changes in AMP, ADP, and ATP concentrations and adenylate energy charge in Norway maple (Acer platanoides L.) and European beech (Fagus sylvatica L.) seeds during dormancy breaking (at 3 °C) and in the control variant at 15 °C. Values of the studied indicators in stratified beech seeds were generally higher at 15 °C, at least until germination (+3 °C). By contrast, in maple seeds, the values recorded during dormancy breaking by cold stratification were much higher than at 15 °C. Three peaks (usually in weeks 3, 6, and 8) were observed in maple seeds at 3 °C, but not at 15 °C. Among adenine nucleotides, AMP reached the highest levels in both species in both variants of the experiment.     

The Role of Water Uptake in the Transition of Recalcitrant Seeds from Dormancy to Germination

In recalcitrant seeds of horse chestnut (Aesculus hippocastanum L.) maintaining a high water content during winter, dormancy is determined by the presence and influence of the seed coat, while the axial organs of the embryos excised from these seeds are not dormant. Such axial organs were capable for active water uptake and rapid fresh weight increase, so that their fresh weights exceeded those in intact seeds at the time of radicle protrusion. Fructose plays an essential role in the water uptake as a major osmotically active compound. ABA interferes with the water uptake by the axial organs and thus delays the commencement of their growth. The manifestation of seed response to ABA during the entire dormancy period indicates the presence of active ABA receptors and the pathways of its signal transduction. The content of endogenous ABA in the embryo axes doubled in the middle of dormancy period, which coincided with a partial suppression of water uptake by the axes. During seed dormancy release and imbibition before radicle protrusion, the level of endogenous ABA in axes declined gradually. Application of exogenous ABA can imitate dormancy by limiting water absorption by axial organs. Fusicoccin A (FC A) treatment neutralized completely this ABA effect. Endogenous FC-like ligands were detected in the seed axial organs during dormancy release and germination. Apparently, endogenous FC stimulates water uptake via the activation of plasmalemmal H⁺-ATPase, acidification of cell walls, their loosening, and turgor pressure reduction. FC can evidently counteract the ABA-induced suppression of water uptake by controlling the activity of H⁺-ATPase. It is likely that, in dormant intact recalcitrant seeds, axial organs, maintaining a high water content, are competent to elevate their water content and to start their preparation for germination under the influence of FC when coat-imposed dormancy becomes weaker.     

Polysome Formation in Light-sensitive Common Purslane Seeds

Common purslane (Portulaca oleracea L.) seeds show light-controlled dormancy. Ribosome profiles from dark-incubated seeds consist of 22 to 26% polysomes. Light induces germination and stimulates polysome formation during the 12-hour lag period preceding radicle protrusion. Polysome levels increase to 29, 35, and 41% with exposure to 3, 6, and 9 hours of light, respectively. Although polysomes form on imbibition in the dark, 6 hours of light stimulates a significant increase in polysome formation which is probably related to early stages of radicle elongation.     

Differential Changes in Levels of mRNAs during Maturation of Wheat Seeds That Are Susceptible and Resistant to Preharvest-Sprouting

Seed dormancy is strongly related to the physiological conditions,especially as they relate to responsiveness to ABA, of embryocells during maturation of seeds. In this study, seeds of Triticumaestivum L. cv. Chihoku, which showed nondormancy at harvest,and line Kitakei-l354 (referred to as Kitakei), which showedpost-harvest dormancy, were collected 30 days after anthesis(DPA 30) and at the mature stage (DPA 60). Poly(A)⁺RNA was extractedfrom the embryos of the seeds and translated in a wheat germsystem. The majority of products of translation from the twogenotypes migrated to the same positions in two-dimensionalgels. Levels of six (for polypeptides h, i, k, m, n, and o)out of 14 Chihoku-specific mRNAs decreased dramatically duringseed maturation, concurrently with the loss of dormancy. Bycontrast, levels of 3 (for polypeptides c, e and f) out of 6Kitakei specific mRNAs were maintained during maturation andduring a 48-h imbibition of the dormant seeds but decreasedat germination. Polypeptides n of Chihoku and e of Kitakei hadthe same molecular size and slightly different pI values. Thesetwo polypeptides may be encoded by the same gene and may playsome role in the maintenance of seed dormancy. Levels of mRNAsfor 10 polypeptides, found in both Chihoku and Kitakei embryosat DPA 30, changed to different extents during maturation. Outof the 10 mRNAs, the relative abundance of 4 mRNAs of Kitakeidid not change dramatically during seed maturation, while inChihoku these mRNAs decreased in level or disappeared duringthe same maturation period. In addition, levels of 2 of these4 mRNAs did not decrease significantly during imbibition ofthe dormant Kitakei seeds but disappeared upon treatment forbreaking of dormancy. The maintenance of these mRNAs in thedormant seeds during maturation and imbibition suggests thatthe respective gene products are involved in the maintenanceof dormancy in wheat seeds. (Received December 5, 1991; Accepted April 1, 1992)     

The effect of ethylene on RNA and protein synthesis in germinating Manketti (Ricinodendron rautanenii Schinz) seeds

Amino acid uptake and protein synthesis were monitored in the embryonic axis, cotyledons and endosperm of manketti seeds (Ricinodendron rautanenii Schinz) during imbition, dormancy and dormancy-breaking by ethylene. Protein synthesis increased in all tissues within 48 h of imbibition and was strongly inhibited by cycloheximide and actinomycin D. No marked increase in protein synthesis was observed following ethylene treatment suggesting that qualitative rather than quantitative changes in protein synthesis were associated with dormancy-breaking. Seed germination was relatively insensitive to treatment with actinomycin D in marked contrast to the inhibition observed with cycloheximide.It is suggested that dormancy-breaking by ethylene may require protein synthesis but not DNA-dependent RNA synthesis.     

The Influence of Dormancy-Inducing Desiccation Treatments on the Respiration and Germination of Sorghum

Seeds of sorghum (Sorghum vulgare Pers.) dried in a forced-air dryer from an initial moisture content of 12 percent to either 10 percent or 7 percent exhibited physiological dormancy. Dormancy was more marked in seeds dried to 7 percent than to 10 percent moisture, and was more pronounced in germination at 15° or 20° than at 25°C. Expression of dormancy at the lower temperatures was influenced decidedly by the four germination media (paper towels, blotters, sand, and soil). Percent dormancy was lowest in towels and highest in soil. Osmotic tension is suggested to be a factor influencing dormancy in these media. Dormancy was relieved by cutting the integumentary membrane or by rehydration of dried seeds. Respiration rates were lower and respiratory quotients higher in dormant seeds than in the controls. Differences in respiration rates were detected within 2 hours after the start of imbibition. Dormancy and differences in respiration rates appear to be associated with changes induced in the seeds by drying.     

The Effects of Kinetin and Gibberellin on the Germination of Dehusked Seeds of Indica and Japonica Rice (Oryza sativaL.) under Anaerobic and Aerobic Conditions

The effects of kinetin and gibberellin were examined under anaerobicconditions (0% oxygen) and aerobic conditions (20% oxygen) onthe germination of dehusked seeds of indica and japonica ricecultivars that had been harvested at different times duringthe formation of seeds. Surjamkhi was used as a representativeof deep dormant indica cultivars and Assam IV as a less dormantindica cultivar. Sasanishiki was used as the japonica rice cultivar.Both phytohormones were applied at a concentration of 10^-3Mwhichproved to have the greatest stimulatory effect in preliminarywork at concentrations of 10^-3–10^-5M. Under aerobic conditions,inhibition of germination by dehusking of Sasanishiki seedsthat had been harvested either 30 or 60 d after anthesis wasovercome by kinetin and all seeds germinated. Complete germinationinduced by kinetin under aerobic conditions was also achievedwith the dehusked seeds of the indica rice cultivar Assam IVthat had been harvested on two occasions and of Surjamkhi thathad been harvested 28 d after anthesis. In contrast, germinationof dehusked japonica seeds stimulated by anaerobiosis was inhibitedby kinetin. The stimulatory effects of gibberellin on the germinationof indica and japonica rice seeds were observed under aerobicand anaerobic conditions. Under anaerobic conditions, the responsesof dehusked indica and japonica rice seeds to kinetin and gibberellindiffered, being negative with kinetin and positive with gibberellin.Under aerobic conditions, the stimulatory effects of kinetinon germination of dehusked seeds were greater than those ofgibberellin. Thus, treatment with kinetin appears to be usefulfor breaking the considerable dormancy commonly observed inthe dehusked seeds of indica rice. Mechanisms are proposed toexplain the stimulatory effects of these phytohormones on thegermination of dehusked seeds of indica and japonica rice underaerobic and anaerobic conditions. Rice; Oryza sativaL.; seed germination; dehusking treatment; gibberellin; indica; japonica; kinetin; oxygen; dormancy; germination inhibition; seed formation     

Cell cycle regulation during development and dormancy in embryos of the annual killifish Austrofundulus limnaeus

Embryos of the annual killifish Austrofundulus limnaeus can enter into a state of metabolic dormancy, termed diapause, as a normal part of their development. In addition, these embryos can also survive for prolonged sojourns in the complete absence of oxygen. Dormant embryos support their metabolism using anaerobic metabolic pathways, regardless of oxygen availability. Dormancy in diapause is associated with high ATP and a positive cellular energy status, while anoxia causes a severe reduction in ATP content and large reductions in adenylate energy charge and ATP/ADP ratios. Most cells are arrested in the G₁/G₀ phase of the cell cycle during diapause and in response to oxygen deprivation. In this paper, we review what is known about the physiological and biochemical mechanisms that support metabolic dormancy in this species. We also highlight the great potential that this model holds for identifying novel therapies for human diseases such as heart attack, stroke and cancer.