Changes in sensitivity of Amaranthus retroflexus L seeds to ethylene during preincubation. II. Effects of alternating temperature and burial in soil

Abstract. The effects of diurnally alternating temperatures and of prolonged burial in the soil on germination response of redroot pigweed ( Amaranthus retroflexus L.) seeds to ethylene were investigated. Percentage germination in a 12 h/12 h, 23° C/35° C temperature regime roughly equalled that observed at constant 35° C, and greatly exceeded that observed at 30°C. Preincubation for 61 d in alternating temperatures, which were gradually increased to simulate soil warming in spring, caused little germination in the absence of ethylene, but considerably enhanced sensitivity to ethylene. Seeds kept in soil in the same temperature regime failed to show the response to ethylene, and the soil itself removed ethylene from the soil atmosphere.
After burial in a field plot either over winter or during the summer, seeds had a very low ethylene response threshold (0.01−0.05 cm³ m⁻³) and strong response to ethylene (70–95% germination at 51 cm³ m⁻³ compared to 1–20% without ethylene). Germinability of seeds buried overwinter declined between 10 May (85%) and 24 May (7%), and 90% of those recovered on or after 24 May had a visible rupture in the seed coat. Apparently, germination had begun during burial, but was arrested by unknown causes in an early phase and was followed by seed deterioration.
Although the role of ethylene in germination of buried seeds remains uncertain, the greatly enhanced sensitivity to ethylene observed in pigweed seeds after burial deserves further investigation.     

Some effects of nitrate-treated soil upon the sensitivity of buried redroot pigweed (Amaranthus retroflexus L.) seeds to ethylene, temperature, light and carbon dioxide

Abstract Fresh dormant redroot pigweed (Amaranthus retroflexus L.) seeds were buried 5 cm deep in the field at Stoneville, MS in November 1981. Potassium nitrate (200 kg ha ¹) or nothing was applied to the soil in the fall of 1981 and the late winter of 1982. Seeds were recovered at intervals under darkness during the following 2 years and tested for responses to ethylene, temperature, light and carbon dioxide. During the first overwintering, nitrate enhanced loss of primary dormancy and increases seed sensitivity to temperature, light and ethylene. The loss of dormancy reached a maximum at 25 to 30 weeks (early summer) after burial. Examination of the recovered seeds indicated that about 80% of the non-treated seeds and 98% of the nitrate-treated seeds germinated in situ during the period of maximum loss of dormancy. Thus, after one overwintering period, about 20% of the original buried seed population remained dormant in nontreted soil and 2% remained dormant in the nitratetreated soil. After the second overwintering, the percentages of dormant seeds remaining in nontreated or treated soil were both only 1–2%. Nitrate reduced dormancy and enhanced germination in early summer following the first overwintering. Regardless of treatment, the remaining 1 2% of seeds in soil after the second year were of low sensitivity to the germination stimuli (ethylene, temperature, light) and constituted the long-lived portion of the original seed population.     

Effects of ethylene and some other environmental factors on different stages of germination in red root pigweed (Amaranthus retroflexus L.) seeds*

Abstract. Ethylene was found to promote two distinct processes during germination of redroot pigweed (Amarantus retroflexus L.) seeds: embryo expansion that splits the seed coat (incomplete germination), and radicle penetration through the more elastic endosperm (complete germination). The two events can be separated in time by subjecting seeds to low water potential or low CO₂ levels, which arrest germination of some seeds at the incomplete stage. Ethylene applications to incompletely germinated seeds promote complete germination, with a response threshold near 0.02 cm³ m^?3 and saturation near 0.5 cm³ m^?3. Higher ethylene concentrations (0.5 to 50 cm³ m^?3) given during the first day of seed imbibition also increase the percentage of seeds which initiate embryo expansion and split the seed coat. Light and elevated CO₂ also promote radicle penetration of the endosperm in seeds incubated under water stress. The results support the view that the germination pause at the incomplete stage is an adaptation to environmental stresses that can be overcome with exogenous ethylene or certain other stimuli.     

Germination responses of a non-dormant seed population of Amaranthus patulus Bertol. to constant temperatures in the sub-optimal range

Abstract. The germination responses of a nondormant seed population of Amaranthus patulus Bertol, at constant sub-optimal temperatures in the range of 10–34°C were analysed through a detailed time-course study. Although a final germination percentage of nearly 100% was attained at temperatures above 18°C, it fell abruptly to zero with decreasing temperature from 17 to 10°C. The final germination percentage, v. temperature plotted on a normal probability scale yielded a straight line, indicating normality of the lower limit temperature within seed population with an estimated mean of 13.75°C and a standard deviation of 1.50°C. Simple linear relationships were obtained between the temperature and the germination rates, i.e., the reciprocals of the time taken to germinate by the subpopulations with 20–80% germination. The linear relationships were characterized by similar base temperatures or theoretical limit temperatures of about 11°C but there was a variation in the required 'thermal times' (θ), the distribution of which could be approximated for the seed population by the following distribution function: where m is the median of the distribution and A is a parameter characterizing the pattern of the distribution. When the germination rates were calculated after subtracting 10–14 h from the time actually consumed in germination, linear Arrhenius relationships were obtained. The apparent activation energy estimated from the linear regression of Arrhenius plot was approximately 100 kJ mol⁻¹ with all 20–80% subpopulations.     

外来杂草反枝苋对农作物的化感作用及其风险评价

利用改进的差时播种共培法,以麦田伴生恶性杂草播娘蒿为对照,在实验室条件下研究反枝苋根系分泌物及其不同浓度残枝浸提液对小麦、玉米、油菜种子萌发及生长的影响.结果显示:(1)反枝苋幼苗的根系分泌物能够显著抑制作物根长和苗高的生长;(2)反枝苋不同浓度浸提液均能抑制作物种子的萌发,其抑制作用随浓度的增加而增强;(3)除0.025 g·mL-1处理对小麦根长和苗高、玉米苗高有促进作用外,其余各浓度反枝苋浸提液对作物幼苗的根长和苗高有不同程度的抑制,且对根长的抑制作用更强;(4)反枝苋对作物幼苗的抑制作用强于恶性杂草播娘蒿,风险评估定量分析结果认定反枝苋为陕西省高度危险性植物.     

反枝苋群落优势种的种间关联性分析

根据野外95个样方的调查数据,运用2×2列联表的χ₂检验、Jaccard关联指数、Pearson相关系数和Spearman秩相关系数对山西省中南部地区反枝苋群落的25个优势种,共300个种对的种间关联性和相关性进行分析。研究结果表明:1)群落总体呈负相关趋势,优势种的分布相对独立,群落结构较为松散,显著和极显著关联的种对较少;2）χ₂检验与关联度指数有机结合才能更为准确的反映种间关系;3）Spearman秩相关系数灵敏度高,分析结果较χ₂检验与Pearson相关系数更为合理准确;4）根据25个优势种对环境的适应方式和主导生态因素结合PCA排序,将它们划分为4个生态种组,各生态种组内的种对具有相同的资源利用方式和生态要求。     

Responsiveness of Amaranthus retroflexus seeds to ethephon, 1-aminocyclopropane 1-carboxylic acid and gibberellic acid in relation to temperature and dormancy

Dormant Amaranthus retroflexus seeds do not germinate in the dark at temperatures below 35°C. Fully dormant seeds germinate only at 35–40°C whereas non-dormant ones germinate within a wider range of temperatures (15 to 40°C). Germination of non-dormant seeds requires at least 10% oxygen, but the sensitivity of seeds to oxygen deprivation increases with increasing depth of dormancy. 10^–6 to 10^–4 M ethephon, 10^–3 M 1-aminocyclopropane 1-carboxylic acid (ACC) and 10^–3 M gibberellic acid (GA₃) break this dormancy. In the presence of 10^–3 M GA₃ dormant seeds are able to germinate in the same range of temperatures as non-dormant seeds. The stimulatory effect of GA₃ is less dependent on temperature than that of ethephon, while ACC stimulates germination only at relatively high temperatures (25–30°C). The results obtained are discussed in relation to the possible involvement of endogenous ethylene in the regulation of germination of A. retroflexus seeds.Abbreviations ACC 1-aminocyclopropane 1-carboxylic acid - GA₃ gibberellic acid - SD standard deviation     

Canola seed germination and seedling emergence from pre-hydrated and re-dried seeds subjected to salt and water stresses at low temperatures

Low soil temperatures and low water potentials reduce and delay the seed germination of canola (Brassica rapa L., B. napus L.) in western Canada. Germination is also very sensitive to the salinity effects of nitrogen fertiliser placed with the seed, especially when the seed bed is relatively dry. The effects of pre-hydration and re-drying treatment on canola (Brassica rapa L. cv. Tobin) seed germination and seedling emergence at 10°C subjected to either a water or salt stress were determined. Low water potentials, induced by polyethylene glycol (PEG 8000), low soil moisture, or high concentrations of salts, reduced both germination and seedling emergence, and increased the time to 50% germination and emergence of seeds at 10°C. At equal osmotic potentials, Na₂SO₄ was less inhibitory on low temperature germination than either NaCl or PEG, suggesting that the sulphate ion partially alleviated the inhibitory effects of low water potential. Solutions of NaCI produced more abnormal seedlings compared to Na₂SO₄, suggesting that NaCl was more toxic than Na₂SO₄ during seedling development. Pre-hydration and re-drying partially overcame the inhibitory effects of both low water potential and salts on seed germination and seedling emergence at 10°C. The seed treatment increased the germination rate in Petri dishes and seedling emergence from a sandy loam soil. Water potentials or soil water contents required to inhibit 50% germination or emergence at 10°C were lower for treated seeds compared to control seeds. Salt concentrations inhibiting 50% emergence were higher for treated seeds than control seeds. Neither treated nor control seeds produced seedlings which emerged if the soil water content was lower than 9% or when the soil was continuously irrigated with salt solutions of 100 mmol kg^-1 of NaCl or 50 mmol kg^-1 of Na₂SO₄. These results suggest that the pre-hydration and re-drying treatment did not lower the base water potentials at which seedling emergence could occur. Abnormal seedlings were observed in both treated and control seeds, particularly if the soil was watered with NaCl solutions; however, the seed treatment reduced the number of abnormal seedlings.     

ACC conversion to ethylene by sunflower seeds in relation to maturation,germination and thermodormancy

Conversion of exogenous 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene was studied in sunflower (Helianthus annuus L., cv. Mirasol) seeds in relation to germinability. Ethylene production from ACC decreased during seed maturation, and non-dormant mature seeds were practically unable to synthesize ethylene until germination and growth occurred, indicating that ethylene forming enzyme (EFE) activity developed during tissue imbibition and growth. ACC conversion to ethylene was reduced by the presence of pericarp, and in young seedlings it was less in cotyledons than in growing axes.ACC conversion to ethylene by cotyledons from young seedlings was optimal at c. 30°C, and was strongly inhibited at 45°C. Pretreatment of imbibed seeds at high temperature (45°C) induced a thermodormancy and a progressive decrease in EFE activity.Abscisic acid and methyl-jasmonate, two growth regulators which inhibit seed germination and seedling growth, and cycloheximide were also shown to inhibit ACC conversion to ethylene by cotyledons of 3-day-old seedlings and by inbibed seeds.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - CH cycloheximide - EFE ethylene forming enzyme - IAA indole-3-acetic acid - Me-Ja methyl-jasmonate     

A bimodal germination response to temperature in cocklebur seeds. I. Cyanide-sensitive and cyanide-resistant respirations

Abstract. Pre-imbibed cocklebur ( Xanthium penn-sylvanicum Wallr.) seeds displayed bimodal germination-temperature responses with two optima at 8 and 33° C. Such germination responses occurred subsequent to bimodal respiration-temperature upsurges at lower and higher temperature regions. At lower temperatures, cocklebur seeds respired predominantly through a cyanide-sensitive cytochrome pathway. A rise in temperature resulted in a marked increase in flux via an alternative pathway, a propyl gallate- (PG) or benzohydroxamic-acid- (BHAM) sensitive pathway, thus resulting in an increase in the ratio of this pathway relative to the cytochrome pathway. Both an increased capacity for the alternative pathway and an increase in the ratio of this pathway to the cytochrome pathway were obtained when pre-imbibed seeds were exposed to either 8 or 33°C for a short period. The effects of low temperature were reduced as the exposure time was prolonged beyond 3d, resulting in a reduction in germination. Neither PG nor BHAM had an inhibitory effect on the chilling-induced germination, but the germination-stimulating effect of high temperatures was less pronounced in the presence of PG or BHAM. At high temperatures, on the other hand, KCN and NaN₃ were ineffective or, rather, slightly inhibited germination. It was thus concluded that low and high temperatures exert their germination-stimulating effects by an essentially similar manner which increases fluxes both via the cytochrome pathway and, especially, via the alternative pathway and, as a result, raises the ratio of the latter to the former.     

Polyamines and ethylene in the removal of embryonal dormancy in apple seeds

Putrescine (Put), spermidine (Spd) and spermine (Spm) were found in seeds of apple ( Malus domestica Borkh. cv. Antonovka), in amounts that increased in the order given. The levels slowly decreased during 30 days of stratification. Exogenous polyamines (PAs) affected germination of isolated embryos in a way dependent on the type of polyamine, its concentration, and the state of the embryo dormancy. The effect of Put and Spd on germination was stimulatory, while that of Spm was inhibitory. Stimulation of germination was also observed when embryos were treated with arginine, ornithine and methionine. Canavanine inhibited germination, and this effect was reversed by arginine or Put. Ethephon, aminooxyacetic acid (AOA) and aminoethoxyvinylglycine (AVG) present during seed stratification had no effect on the levels of endogenous PAs. Put and Spd did not change ethylene production, neither during seed stratification nor during embryo germination, whereas Spm reduced ethylene evolution. The data suggest that Spm plays a role in the maintenance of dormancy by preventing ethylene production, while Put and Spd participate in dormancy removal, independently of ethylene.     

The effect of ethylene, octanoic acid and a plant-derived smoke extract on the germination of light-sensitive lettuce seeds

The effects of an aqueous plant-derived smoke extract, octanoic acid and ethylene on germination of light-sensitive Grand Rapids lettuce seeds were investigated. The smoke extract brought about a concentration dependent increase in germination and a complete inhibition of germination at high concentrations. Octanoic acid could not induce germination. Ethylene at concentrations over 5 L L^–1 increased lettuce seed germination, but not to the same degree as smoke. Aqueous smoke in combination with ethylene showed a synergistic effect on germination at suboptimal smoke concentrations. At high smoke concentrations the effect of ethylene was almost completely inhibited. Octanoic acid in combination with ethylene brought about a higher level of germination than with ethylene alone, but only at the highest concentration of octanoic acid tested (1 mM). Standardized hexane and dichloromethane-partitioned smoke extracts and octanoic acid were subjected to TLC separation. The R _f -fractions in the smoke lanes showing activity in the lettuce seed bioassay did not correspond to the R _f -value of octanoic acid. As aqueous smoke can withstand autoclaving and can be separated by TLC and HPLC without loosing activity it is unlikely that the activity of aqueous smoke is linked to ethylene. It thus appears that the active compound in smoke is neither octanoic acid nor ethylene.Abbreviations TLC thin layer chromatography - HPLC High performance liquid chromatography     

Ontogenetic variation in response to temperature change in the control of seed dormancy of Rumex obtusifolius L. and Rumex crispus L.

Abstract After the onset of imbibition, the dormant seeds of Rumex obtusifolius and R. crispus are stimulated to germinate by a change from an initial low temperature to a warmer temperature for a relatively brief period: the warmer that temperature the shorter is the optimum period spent at it, and this optimum value is unaffected by the initial temperature. The optimum period is more critical in R. crispus than in R. obtusifolius (about 1 h and 2.5 to 4 h, respectively, for a warmer temperature of 35°C in the dark); in the light the length of the period at the warmer temperature is less critical in both species. The sensitivity of the seeds to the change to the warmer temperature increases with time from the start of imbibition at a rate which is positively related to the initial temperature. In R. obtusifolius maximum sensitivity was typically reached after 3 to 5 d when the initial temperature was 20°C and then remained constant, or declined only slightly, over the period investigated (10 d). At the same initial temperature, however, R. crispus showed a cyclical pattern of sensitivity with peaks occurring at 3–4 d intervals from the start of imbibition.     

The presence of two types of β-cyanoalanine synthase in germinating seeds and their responses to ethylene

Germinating seeds of many species contain two types of β-cyanoalanine synthase (CAS, EC 4.4.1.9) that convert HCN to β-cyanoalanine. One is cytoplasmic CAS (cyt-CAS), which is precipitated by 50 to 60% (NH₄)₂SO₄ and has a pH optimum of 10.5. Cytoplasmic CAS is present at high levels in dry seed and its activity does not increase during imbibition. The activity of cyt-CAS is not affected by exogenously applied ethylene (C₂H₄), except in rice ( Oryza sativa cv. Sasanishiki). The second type of CAS found in seed is mitochondrial CAS (mit-CAS), which is precipitated by 60 to 70% (NH₄)₂SO₄ and has a pH optimum of 9.5. Mitochondrial CAS is present at low levels in dry seed, and its activity increases greatly during imbibition in the seeds of all species tested. Exposure to C₂H₄ stimulated mit-CAS activity in seeds of rice, barley ( Hordeum vulgare cv. Hadakamugi). cucumber ( Cucumis sativus cv. Kagafushinari) and cocklebur ( Xanthium pennsylvanicum ). The increase in the mit-CAS activity in cocklebur in response to C₂H₄ commenced alter a lag period of 2 to 3 h when the duration of soaking was short (16 h), but commenced without a lag period when the seeds were soaked for three months. Application of both chloramphenicol and cycloheximide to the axial and cotyledonary tissues of cocklebur seeds strongly inhibited growth as well as the increase in mit-CAS activity. It is postulated that the mit-CAS is synthesized de novo during imbibition and that its activity is regulated by C₂H₄, CO₂ which also promotes seed germination in some species, was ineffective m stimulating mit-CAS activity in cocklebur seeds.     

光照和温度对百合属6种植物种子萌发的影响

对不同光照和温度条件对条叶百合（Lilium callosum Sieb.et Zucc.)、大花卷丹[L. leichtlinii Hook.f var.maximowicaii(Regel)Baker]、有斑百合[L.concolor Salisb.var.pulchellum(Fisch.)Regel]、川百合[L.davidii Duchartre)、毛百合（L. dauricum Ker-Gawl.)和东北百合（L.distichum Nakai)种子萌发的影响进行了研究。结果表明：光照对有斑百合、川百合和毛百合种子萌发有明显促进作用,可缩短种子萌发时间,提高种子萌发率。24h光照下种子萌发完全所需天数比12h光照少,种子萌发率以24h光照最佳。避光条件下温度对大花卷丹、有斑百合、毛百合、川百合及东北百合种子萌发率和萌发速度有影响,对条叶百合种子影响最大,其种子萌发最适温度为20℃,5～6d开始萌动,2～3周萌发完全,随着温度的升高或降低其种子萌发率下降。光照条件下,变温对种子萌发影响不明显。子叶留土类型的毛百合种子有二次休眼现象,9000lx光照能代替低温解除二次休眼。经不同前处理的百合种子萌发率和萌发速度不同。     

光照和温度对沙芥和斧翅沙芥植物种子萌发的影响

研究了生长于不同生境下的沙芥(Pugionium cornutum(L.)Gaertn.)和斧翅沙芥(Pugionium dolabratum Maxim.)种子萌发对光照和温度的响应。结果表明:沙芥和斧翅沙芥种子在光下萌发受到显著(P0.05)的抑制作用,其中沙芥种子萌发受光的抑制作用强于斧翅沙芥种子。在黑暗10—40℃恒温条件下,沙芥和斧翅沙芥种子在15—35℃范围内均可萌发,在15℃和35℃下沙芥种子的萌发要优于斧翅沙芥种子;其种子分别在25℃和30℃下达到最佳的萌发响应,在此条件下斧翅沙芥种子的萌发特性优于沙芥种子。在黑暗变温条件下,沙芥和斧翅沙芥种子在20/30℃(12h/12h)下达到最佳的萌发响应,此处理下的萌发率高于其各自最佳恒温处理下的萌发率,其萌发后幼苗下胚轴和胚根的长度较最佳恒温处理有明显的下降,但它们的干重却差异较小,说明变温处理有利于两种种子的萌发和形成强壮的幼苗。综上所述,沙芥和斧翅沙芥种子在黑暗和20/30℃变温条件下有利于种子萌发和幼苗建成。     

Presence of β-cyanoalanine synthase in unimbibed dry seeds and its activation by ethylene during pre-germination

Evolution of HCN from both rice ( Oryza sativa ) and cocklebur ( Xanthium pennsylvanicum ) seeds increased during a pre-germination period and preceded the evolution of (C₂H₄). These two species were adopted as the representatives of starchy and fatty seeds, respectively. Ethylene promotes seed germination of many species. However, HCN evolution declined abruptly when the radicles emerged and before the peak in C₂H₄ evolution. More-over, both rice and soybean ( Glycine max ) seeds showed some activity of β-cyanoalanine synthase (CAS, EC 4.4.1.9) even in the unimbibed dry state. The activities of CAS in the lower seed of cocklebur and in soybean seeds increased rapidly after emergence of the radicle. However, the CAS of rice seeds, with high activity in the dry state, exhibited a bimodal change, gradually decreasing until radicle emergence had occurred, but then increaing. It is thus likly that HCN evolution during initial imbibition may be derived from cyanogenic reserves and controlled by both pre-existing and subsequently-developing CAS. The exogenous application of C₂H₄ stimulated the activities of CAS in both rice and upper cocklebur seeds and reduced their cyanogen contents. Therefore, the decline of HCN evolution after germination seems to be due to the increased activities of CAS by endogenously produced C₂H₄.     

The effect of ethrel and temperature on the germination of Manihot glaziovii Muell. Arg. seeds

Dormancy in seeds of Manihot glaziovii is overcome at 25°C by application of ethrel at effective ethylene concentrations equal to and greater than 10 ll^–1. Imbibition of seeds in ethrel broadens the temperature optimum for germination but does not prevent the development of secondary dormancy at temperatures of 35°C and greater and 15°C and lower. Secondary dormancy must be due to factors other than reduced ethylene production.     

Location of sugars in barley seeds during germination by NMR microscopy

The distribution and fluctuation of sugars in germinating barley seeds were examined by ¹³C nuclear magnetic resonance (NMR) spectroscopy, ¹H-NMR imaging and ¹H-NMR localized spectroscopy in relation to morphology. Maltose, sucrose, fructose and oils were detected in intact imbibed seeds by ¹³C-NMR spectra. During the first 6 d of germination, the maltose content increased and the oil content gradually decreased, whilst the levels of sucrose and fructose remained constant. Sugars were located by ¹H-NMR images and ¹H-NMR localized spectra in the vascular bundle of the seeds as well as in the solubilized endosperm. They were also detected in the shoots. The sugars detected in an 80% ethanol shoot extract were sucrose and glucose, which were located in the vascular bundles but not in the mesophyll cells of the coleoptile. They were also located in the basal part of the shoot, but not above 7 mm from the scutellum. The data suggest that the sugars are primarily transported through the vascular bundles and, at the same time, rapidly incorporated into mesophyll cells in the leaves.