The physiological basis of seed dormancy in Avena fatua VI. Respiration and the stimulation of germination by ethanol

Ethanol induced germination in several partly after-ripened dormant lines of Avena fatua L. The dose-response curves for the stimulation of germination and for oxygen uptake were similar, indicating that ethanol may stimulate germination by promoting oxygen uptake. A time-sequence study showed that ethanol stimulated oxygen uptake by as much as 70% prior to the first visible signs of germination. A similar methanol treatment failed to induce germination or significantly elevate oxygen uptake, indicating that the promotive effects of ethanol are not common to all alcohols. The stimulation of both germination and oxygen uptake by ethanol was not inhibited significantly by salicylhydroxamic acid, an inhibitor of alternative respiration. Thus, stimulation of germination and oxygen uptake by ethanol does not require the operation of the alternative pathway of respiration. Similarly, the stimulation of germination and oxygen uptake by ethanol were not inhibited by sodium azide, an inhibitor of cytochrome-mediated respiration. However, both germination and oxygen uptake were prevented when salicylhydroxamic acid and sodium azide were administered together. Thus, stimulation of these events by ethanol requires only the operation of one or other of these pathways of respiration; a specific requirement for the operation of the alternative pathway of respiration does not exist. The function of ethanol as a promoter of respiration is discussed with reference to dormancy and involvement of the Krebs cycle.     

The physiological basis of seed dormancy in Avena fatua. VII. Action of organic acids and pH

Citric, succinic, fumaric, malic, pyruvic and lactic acids induced germination in two genetically pure dormant lines of Avena fatua L. The sensitivity to these acids was low immediately after harvest and increased markedly after a period of dry after-ripening. Because the acids could only overcome dormancy in partly after-ripened caryopses, the mode of their action in these caryopses differed from that of another germination promotor, ethanol, and was similar to that of the germination promoter, sodium nitrate. The mode of action of the organic acids on the partly after-ripened caryopses through lowering pH was indicated by the observation that other non-metabolic weak acids could also break dormancy while neutral pH value salt solutions of some of the tested acids were inactive. The dose-response curves of citric acid for the stimulation of germination and for oxygen uptake were similar, indicating that this organic acid may stimulate germination by promoting oxygen uptake. A time sequence study showed that citric acid stimulated oxygen uptake before the first visible signs of germination. Stimulation of germination and oxygen uptake over a range of pH values showed that those values of pH which stimulated germination also stimulated oxygen uptake, indicating that the ability to stimulate oxygen uptake was not confined to organic acids. The stimulation of both germination and oxygen uptake by citric acid was not inhibited by salicylhydroxamic acid, an inhibitor of alternative respiration, therefore stimulation of both germination and oxygen uptake by citric acid does not require the operation of the alternative pathway of respiration. The function of weak acids as promoters of oxygen uptake is discussed with reference to the breakage of dormancy in partly after-ripened caryopses and the involvement of various respiratory pathways is indicated.     

The physiological basis of seed dormancy in Avena fatua L. I. Action of the respiratory inhibitors sodium azide and salicylhydroxamic acid

The dormancy breaking effect of sodium azide was studied in seeds of several genetically pure lines of Avena fatua L. isolated from field populations. Sodium azide (0.8 and 1 m M ) induced germination in several dormant lines (characterized by long term dormancy) after two weeks of treatment. By about five weeks, germination was nearly complete in azide treated seeds as compared to little or no germination in controls. (2-chloroethyl) trimethylammonium chloride (an inhibitor of gibberellin biosynthesis) completely inhibited the azide effect suggesting that stimulation of germination by azide requires gibberellin biosynthesis. Azide was very effective in breaking dormancy in lines AN-51, AN-86, AN-127 and AN-265, but failed to induce germination in Montana 73. In this line there was a synergism between azide and gibberellic acid in promotion of germination. Thus, at least two metabolic blocks are involved in the stimulation of germination in this line. Salicylhydroxamic acid (an inhibitor of alternative respiration) at 3 m M completely inhibited the germination induced by 1 m M azide. At this concentration, salicylhydroxamic acid did not inhibit germination in 1) genetically nondormant seeds (line SH-430), 2) afterripened seeds of a dormant line (AN-51), and 3) gibberellic acid-treated dormant seeds. These findings suggest that salicylhydroxamic acid-sensitive process(es), presumably alternative respiration, is necessary for the stimulation of germination in the presence of azide, but not in the germination of genetically nondormant, gibberellic acid-treated dormant, or afterripened seeds.     

The physiological basis of seed dormancy in Avena fatua IV. Alternative respiration and nitrogenous compounds

Sodium nitrate and nitrite induced germination in a partly after-ripened dormant line of Avena fatua L. The dose-response curves for their stimulation of germination and oxygen uptake were similar, indicating that these compounds may stimulate germination by promoting oxygen uptake. Time-sequence studies showed that nitrate and nitrite stimulated oxygen uptake as much as 70% prior to the first signs of germination. A similar ammonium chloride treatment failed to induce germination or elevate the rate of oxygen uptake, indicating that nitrate and nitrite may promote these events by acting as electron acceptors. The stimulation of germination and oxygen uptake by nitrate and nitrite were not significantly inhibited by salicylhydroxamic acid, an inhibitor of alternative respiration. Thus, stimulation of germination and oxygen uptake by nitrate and nitrite do not require the operation of the alternative pathway of respiration. The stimulation of germination and oxygen uptake by nitrate and nitrite were not inhibited by sodium azide, an inhibitor of cytochrome-mediated respiration; however both germination and oxygen uptake were prevented when salicylhydroxamic acid and sodium azide were applied together. Thus, stimulation of germination and oxygen uptake by nitrate and nitrite require the operation of only one or other of the pathways of respiration; however a specific requirement for the operation of the alternative pathway of respiration does not exist. The function of these compounds as promotors of respiration is discussed with reference to dormancy and the involvement of the Krebs cycle.     

Avena fatua L. seed and seedling nutrient dynamics as influenced by mycorrhizal infection of the maternal generation

Abstract. The objective of this study was to determine how mycorrhizal infection of one generation of plants influences the nutrient dynamics of seeds and seedlings comprising the subsequent generation. We showed that, for Avena fatua L., seeds produced by mycorrhizal (M) plants consistently contained significantly more phosphorus (particularly the phytate P and residual P fractions) than seeds produced by non-mycorrhizal (NM) plants. We also followed the development of spikelets produced by M and NM plants. The rates of increase in spikelet dry weight and nitrogen content were largely unaffected by mycorrhizal infection. However, the rate of P accumulation into spikelets was significantly increased by mycorrhizal infection. Greater endosperm P reserves in seeds produced by M plants were associated with greater rates of P accumulation in resultant seedlings. Moreover, offspring plants (all NM) produced by M mother plants had significantly higher root and rhizosphere phosphatase, ATPase and phytase activities than offspring plants produced by NM mother plants. This persistent maternal effect has never before been described. Our results suggest that mycorrhizal infection of one generation of plants may have substantial positive effects on the offspring generation, and thus, may influence plant population dynamics.     

Induction of vivipary in Avena fatua

An investigation was conducted under controlled conditions to determine whether treatments designed to maximize the availability of water during seed development could induce viviparous germination in wild oats ( Avena fatua L.). Panicles of three genetic lines, which differed in their degree of dormancy, were kept in darkness at ca 100% RH and 20±1°C and were either supplied with water through the cut end of the rachis or left attached to the plant which was exposed to light. In the non-dormant line, germination of both primary and secondary caryopses on excised panicles increased with their stage of development when treated, i.e., 0, 5 and 10 days after anthesis. Germination of primary caryopses varied between 70 and 80% and was similar on both isolated and attached panicles treated at 10 and 5 days after anthesis, respectively. The percentage germination was considerably lower in all treatments of the two dormant lines and was inversely related to the genetically determined difference in their degree of dormancy. In these dormant lines germination was significantly lower on the intact plant than on the detached panicles. Water potential measurements suggested that this difference may be due partly to the transpiration-induced negative ψ_xyin the stem which may contribute to the inhibition of embryo growth and thus to the prevention of viparous germination.     

Temperature control of germination and its possible role in the survival of a non-dormant population of Avena fatua

Germination of freshly harvested seeds of a non-dormant (ND) line (Stonehouse 319) of wild oats ( Avena fatua L.) was inhibited by incubation of the seeds at relatively high temperatures of 25 and 30°C. The germination inhibition in these seeds appeared to be a case of thermo-inhibition which was the direct effect of hightemperature treatment (HIT), since it did not persist after transferring the seeds to an optimum germination temperature of 20°C. Even a prolonged HTT of 30°C for over 5 weeks did not prevent germination of about 80% of the seeds transferred to 20°C. However, in a significant proportion of the seeds, thermo-dormancy was induced by 10 days of HTT at 30°C if the seeds were then incubated at sub-optimal temperatures of 5 to 15°C. This thermo-dormancy would appear to be 'restrictive' in form, since its expression was restricted to very specific conditions. Relatively low inclubation temperaturs of 5 and 10°C markedly slowed germination whether HTT was applied or not. The results suggest that thermo-inhibition and thermo-dormancy, induced during seasonal temperature fluctuations, may provide a survival mechanism for seeds of such ND lines as Stonehouse 319.     

Dormancy-associated embryonic mRNAs and proteins in imbibing Avena fatua caryopses

The mechanisms controlling seed dormancy maintenance and release are not understood. To characterize the molecular events accompanying dormancy release, two-dimensional gel electrophoresis was used to monitor changes in soluble proteins and in vitro translation products of embryonic mRNA populations during imbibition of dormant and nondormant (after-ripened) Avena fatua L. caryopses. No differences were observed between in vitro translation products of mRNA extracted from dry dormant and nondormant embryos. However, the expression patterns of several imbibition- and germination-associated mRNAs were temporally modulated during the first 24 h of imbibition. Two dormancy-associated mRNAs, represented by polypeptides D₁ and D₂, were differentially overexpressed in dormant embryos after 3 h of imbibition. mRNA levels for D₁ and D₂ were about 8- and 3-fold higher, respectively, in dormant embryos than in nondormant embryos after 3 h of imbibition. Overexpression of D₁ continued through 12 h of imbibition, while expression of both mRNAs fell to low and equivalent amounts in dormant and nondormant embryos after 24 h. Similar dormancy-associated changes in two soluble proteins were observed during imbibition. The results demonstrate that steady-state levels of specific mRNAs and proteins change during early imbibition of dormant and nondormant A. fatua embryos and indicate that these changes may be associated with differential gene expression responsible for the maintenance of dormancy.     

The physiological basis of seed dormancy in Avena fatua. VIII. Action of malonic acid

Adkins, S. W., Symons, S. J. and Simpson, G. M. 1988. The physiological basis of seed dormancy in Avena fatua . VIII. Action of malonic acid - Physiol. Plant, 72: 477–482.
A low concentration of malonic acid (50 m M ) induced germination in four genetically pure dormant lines of Avena fatua L. Sensitivity to this treatment was poor immediately after harvest but increased markedly during after-ripening, indicating that the mode of action of malonic acid (50 m M ) was similar to that of another organic acid, citric acid. Over the concentration range (10–50 m M ) where malonic acid promoted germination, oxygen uptake was also stimulated, and this was before the first visible signs of germination. At higher concentrations (100–300 m M ) where there was no promotion of germination, malonic acid strongly inhibited oxygen uptake. These results show that malonic acid has a dual effect on oxygen uptake and subsequent germination. Low concentrations (10–50 m M ) act by stimulating the Krebs cycle and germination through an acidification reaction like citric acid, and high concentrations (100–300 m M ) act by inhibiting germination through enzymatic restraint of the Krebs cycle.
The stimulation of both oxygen uptake and germination by three established germination promoters (sodium nitrate, citric acid and ethanol) was inhibited by a high concentration of malonic acid (200 m M ) but unaffected by a low concentration (50 m M ). These results show that oxygen uptake, and hence the activity of the Krebs cycle, are important processes involved in the dormancy breaking mechanism of these three promotors.     

Characterization of cDNA clones for differentially expressed genes in embryos of dormant and nondormant Avena fatua L. caryopses

The molecular regulation of seed dormancy was investigated using differential display to visualize and isolate cDNAs representing differentially expressed genes during early imbibition of dormant and nondormant Avena fatua L. embryos. Of about 3000 cDNA bands examined, 5 cDNAs hybridized with mRNAs exhibiting dormancy-associated expression patterns during the first 48 h of imbibition, while many more nondormancy-associated cDNAs were observed. Dormancy-associated clone AFD1 hybridized with a 1.5 kb mRNA barely detectable in dry dormant and nondormant embryos that became more abundant in dormant embryos after 24 h of imbibition. Clone AFD2 hybridized with two mRNAs, a 1.3 kb message constitutively expressed in dormant and nondormant embryos and a 0.9 kb message present at higher levels in dormant embryos after 3 h of imbibition. Nondormancy-associated clones AFN1, AFN2 and AFN3 hybridized with 1.5 kb, 1.7 kb and 1.1 kb mRNAs, respectively, that were more abundant in nondormant embryos during imbibition. Expression patterns of some mRNAs in dormant embryos induced to germinate by GA₃ treatment were different than water controls, but were not identical to those observed in nondormant embryos. DNA sequence analysis revealed 76% sequence identity between clone AFN3 and a Citrus sinensis glutathione peroxidase-like cDNA, while significant sequence similarities with known genes were not found for other clones. Southern hybridization analyses showed that all clones represent low (1 to 4) copy number genes.     

The physiological basis of seed dormancy in Avena fatua III. Action of nitrogenous compounds

Sodium nitrate and nitrite (50–100 m M ) induced germination in three out of four genetically pure dormant lines of Avena fatua L. The sensitivity to these treatments was low immediately ater harvest and increased markedly after six months of dry after-ripening. The observation that a fourth dormant line failed to respond suggests at least two metabolic blocks may be involved in expression of dormancy. An inhibitor of gibberellin biosynthesis, 2-chloroethyl trimethylammonium chloride, completely inhibited the dormancy-breaking effect by nitrate and nitrite, indicating a requirement for gibberellin biosynthesis. Among reduced nitrogenous compounds, ammonium chloride and urea failed to break dormancy in all partly after-ripened lines, suggesting that nitrate and nitrite may induce germination through their ability to act as electron acceptors. The sensitivity to all nitrogenous compounds tested increased with the length of after-ripening indicating that the depth of the second dormancy block amy decrease with the time of after-ripening. Other reduced nitrogenous compounds, thiourea and hydroxylamine hydrochloride, promoted some germination in the least dormant, partially after-ripened lines. The function of these compounds as electron acceptors and their similarity in activity to the cytochrome oxidase inhibitor, sodium azide, is discussed with reference to dormancy and the possible involvement of the alternative pathway of respiration.     

Growth, anatomy and morphology of the mesocotyl and the growth of appendages of the wild oat (Avena fatua L.) seedling

Morphological and histological studies were made on the mesocotyl and the emergence of seedlings of a nondormant strain (CS40) of wild oats (Avena fatua L.). The elongation of the mesocotyl was primarily responsible for the emergence of seedlings from deeper levels of soil. The mesocotyl of the seedling is here interpreted as the hypocotyl. The functionally suctorial scutellum together with coleoptile constitutes the first cotyledon and the first true-leaf is regarded as the second cotyledon. The development of tillers from scutellar and first-leaf buds depends on the depth at which level the seeds (caryopses) germinated and the seedlings emerged above the soil surface. The first-leaf axillary buds, regradless of depths, develop into dominant tillers. The scutellar buds, especially at greater depths, remain inhibited. At shallower levels, however, they develop into tillers. The scutellar buds, at deeper levels, behave as reserve ramets which feature adds to the success of the species as a weed in the agricultural prairies.     

Induction and release of secondary seed dormancy in genetically pure lines of Avena fatua

Induction and release of secondary dormancy in genetically pure dormant (AN-51, Mont 73) and non-dormant (CS-40, SH-430) lines of wild oat ( Avena fatua L.) were studied. These lines differed with regard to the optimal period of anaerobiosis necessary for induction of dormancy, and/or the degree (% of seeds acquiring dormancy) and duration of the dormancy induced. Secondary dormancy could be induced more effectively in the after-ripened seeds of dormant lines than in the non-dormant lines, where only a short-term dormancy could be induced (in 5–7 week-old-seeds). Higher anaerobiosis temperatures were more effective in inducing dormancy in all lines studied. Thus, as with primary dormancy, wild oat biotypes exhibit genetic variability in their secondary dormancy behaviour and factors like temperature can modify the expression of this trait.
The germination stimulants kinetin, isopentenyl adenine, sodium azide, potassium nitrate, ethanol and substituted phthalimides, which break primary dormancy in wild oats, stimulated germination of secondarily dormant seeds (line AN-51). Since these chemicals are structurally diverse, primary and secondary dormancies appear to be similar in part in their regulation.
Salicylhydroxamic acid, an inhibitor of cyanide-insensitive (alternative) respiration, did not inhibit: 1, spontaneous release of secondary dormancy in the line SH-430; and 2, stimulation of germination of secondarily dormant AN-51 seeds by various chemicals (except azide), suggesting that this respiratory pathway is not necessary for the release of induced dormancy.     

光照对辽东栎种子萌发和幼苗生长的影响

研究了不同光照梯度[55.4%自然全光照(natural sunlight,NS)、18.9%NS、5.5%NS、2.2%NS、0.5%NS和0.3%NS]对辽东栎种子萌发和幼苗生长的影响.结果表明:辽东栎种子的萌发率和萌发指数在55.4%NS处理达到最大,分别为72.5%和0.22,然后随着光照减弱而逐渐减小,在0.3%NS处理下最小,分别为42.5%和0.11;强光照对种子萌发进程有一定的延迟作用,萌发活力指数随着光照的减弱而增大(0.5%NS处理最大);强光下种子萌发的延迟可能是其对多种命运的权衡性选择.强光照有利于辽东栎幼苗基径和根系生长,以及幼苗干物质的积累,但株高最小(6.06 cm);不同光强处理的辽东栎幼苗具有较大的形态学可塑性,其幼苗阶段对光环境的适应性较强,0.5%NS处理的幼苗比叶面积、比枝长、比根长、叶片叶绿素b含量及叶绿素总量均最大,分别为142.57 cm2.g-1、156.86 cm.g-1、271.87 cm.g-1、0.07 g.cm-2和0.24 g.cm-2,55.4%NS处理下最小,分别为44.89 cm2.g-1、52.84 cm.g-1、101.98 cm.g-1、...     

Seed dormancy in Avena fatua: Interacting effects of nitrate, water and seed coat injury

In experiments conducted under controlled conditions. KNO₃ (50 or 100 m M ) promoted germination of a dormant strain (AN 474) of Avena fatua when either one or two holes were pierced in the lower (adaxial) surface of the caryopsis in contact with the nitrate solution. Germination was increased by increasing either the KNO₃ concentration or the number of holes in the seed coat. The germination response induced by the application of water to a hole pierced in the upper surface of the caryopsis was. increased by pre-treatment of the intact caryopsis with KNO₃. Treatment with either 50 or 100 m M KNO₃ caused a transient reduction in embryo water content of intact cary-opses, but increased the nitrate and amino- N content of pierced caryopses prior to germination. Supplying a 100 m M solution of KNO₃ to pierced caryopses reduced the total water potential and osmotic potential of the embryo, and increased its pressure potential by the same amount as an equimolar solution of KC1; however, while both treatments promoted germination, the KNO₃ induced more rapid germination than the KCI. Both treatments also increased the K⁺ content of the embryo, the KNO₃ again having the greater effect. These results are consistent with the hypothesis, based on our previous investigations, that KNO₃ promotes germination of dormant caryopses by accumulating in the embryo where it acts osmotically to increase water uptake. It is also postulated, that, in contrast to KCI, KNG₃ may combine an osmotic effect on water uptake with a nutritional effect on protein synthesis.     

干扰强度对群落中紫茎泽兰种子萌发、幼苗定居和生长的影响

干扰与外来植物入侵密切相关,种子萌发和幼苗定居是植物生活史中最脆弱、也是外来植物入侵最关键的阶段.为研究干扰在恶性外来入侵植物紫茎泽兰成功入侵过程中的作用,采用人工牧草群落代替自然群落,人为干扰(去除不同面积的牧草)模拟自然干扰的方式,研究了紫茎泽兰入侵初期种子萌发、幼苗定居和生长对不同干扰强度的响应与适应.结果表明:...     

光质对杉木种子萌发及幼苗生长的影响

光是影响森林早期天然更新(种子萌发和幼苗生长)的重要因子之一.但光质对杉木(Cunninghamia lanceolata(Lamb.) Hook)早期更新的影响尚不清楚.为探讨光质对杉木种子萌发及幼苗生长的影响机制,以杉木种子为研究对象,通过设置8h白光(W)、8h红光(R)、6h红光-2 h远红光(R-FR)、4h红光-2 h远红光-2 h红光(R-FR-R)、黑暗(D,对照)5种不同光质处理,观察种子萌发及幼苗生长特征.结果表明,不同光质处理对杉木种子萌发影响显著,D和R-FR-R处理促进杉木种子萌发,R处理抑制种子萌发.最后一次照光选择红光处理(R和R-FR-R)能够显著促进杉木幼苗根和子叶的伸长,促进生物量积累以及增加叶生物量分配比例,但抑制茎的伸长,远红光处理则促进茎的生长.杉木种子为光不敏感种子,黑暗处理下萌发率最高,且远红光间断处理能够相对促进其萌发,说明杉木种子可以较好地适应异质光环境.     

The physiological basis of seed dormancy in Avena fatua. IX. Characterization of two dormancy states

The dormancy-breaking effect of several known germination promoters was studied in 9 genetically pure lines of Avena fatua L. during a period of controlled after-ripening. Changes in the germination response show at least two dormancy states in the caryopses of these lines. The first state is overcome by a short period of after-ripening and is insensitive to nitrate and azide, while the second state is more persistent and is sensitive to nitrate and azide. Both states are sensitive to gibberellic acid (OA,) and ethanol. In the most dormant lines a third ethanol-insensitive dormancy state is present. The duration of both major dormancy states was related to several environmental factors influencing plant growth and seed storage. Duration was increased in caryopses produced from plants matured under low temperatures (15°C) and decreased in caryopses produced from plants matured under high temperatures (25°C). Duration was increased in caryopses after-ripened under low temperatures (4°C) and decreased in caryopses after-ripened under high temperatures (45°C). Dehulling the seeds prior to after-ripening reduced the duration of both major dormancy states. The multiple state dormancy system and its environmentally induced plasticity are discussed with reference to previous explanations of the dormancy mechanism in wild oats.     

旋转磁场对小麦种子萌发及幼苗生长的影响

以“淮麦19”小麦种子为研究对象,采用磁场强度为11 mT的旋转磁场进行处理,设定不同的时间梯度(10、20、30、60 min),以未经磁场处理的为对照,研究了不同处理时间下旋转磁场对小麦种子发芽指标及幼苗生理特性的影响。结果表明：旋转磁场处理对小麦种子萌发具有促进作用,不同处理时间下,种子的发芽势、发芽率、发芽指数均有显著提高,随着时间的增加呈现先上升后下降的趋势,以处理30 min为最高,分别比对照提高了8.24％、7.37％、11.24％。经旋转磁场处理后,小麦根系发达,根长、根数均显著高于对照;幼苗生长加快,株高除处理60 min外,其他处理均显著高于对照,以处理30 min为最大,高出对照11.13％;叶片数除处理10 min外,其他处理均高于对照,以处理30 min为最大,比对照高出38.89％,且差异显著。旋转磁场处理显著增加了小麦幼苗的物质积累,不同处理时间表现出不同的效果,对幼苗生物积累量影响最佳的是处理20 min。这说明旋转磁场处理提高了小麦种子的萌发能力,加快了小麦幼苗的生长速度。