Heat increases germination of water-permeable seeds of obligate-seeding <Emphasis Type="Italic">Darwinia</Emphasis> species (Myrtaceae)

We examined the response of seeds to heat in four geographically restricted and one widespread species of shrubby Darwinia from the fire-prone region of southeastern Australia. These shrubs are killed by fire and rely on seed germination after a fire to maintain populations. We replicated the germination trials across several sites and several fruiting seasons for most species. Seeds had a high level of viability and were largely dispersed in a dormant state, except in D. glaucophylla, where seed dormancy varied significantly across fruiting seasons. The indehiscent fruit of all species readily imbibes moisture when wet and seeds are not considered to be ‘hard-seeded’. All species had increased seed germination in response to a limited range of heating temperatures (generally 80–100°C). Higher temperatures killed increasing proportions of seeds. This pattern was broadly consistent across species, population and seasons, although the proportion of seeds whose germination was promoted by heat varied from high (D. diminuta, D. fascicularis, D. glaucophylla) to moderate (D. biflora, D. procera). Our work highlights the importance of heat as a mechanism for influencing germination in species that are not hard-seeded. Consequently, soil temperatures during a fire should strongly influence post-fire germination levels in Darwinia. The roles of other cues that promote germination, i.e. smoke, seasonal temperatures and their interactions with heat, remain to be investigated.     

贵州毕节喀斯特地区优势植物种子萌发特性初步研究

对采自贵州毕节地区的11种植物的种子萌发特性进行了初步研究,结果表明：①盐肤木、火棘、化香、云贵金丝桃与白栎种子在4周之内能够萌发;除云贵鹅耳枥胚坏死之外（萌发实验前后对种子进行解剖）,其他5种植物的种子都未萌发,处于不同的休眠状态。②盐肤木、化香、云贵金丝桃的种子光照时的萌发率远高于黑暗时的萌发率,具有显著差异,尤其是云贵金丝桃,因此3种植物种子均属于喜光性种子;而火棘与白栎种子有无光照都可以萌发,而且萌发率没显著差异,因此属于光不敏感或光中性种子。③盐肤木、云贵金丝桃的种子在30℃较高温条件下萌发最好;白栎、火棘种子在15℃、20℃低温条件下萌发更好;化香种子萌发温度既不能低于20℃也不能高于25℃。④刺异叶花椒种子吸水率高达85%,胚包埋在胚乳之中非常微小、未分化,因此可以初步判定属于形态休眠或者形态生理休眠;而平枝荀子、西域旌节花、云南旌节花种子吸水率都在20%以上,胚长/种子长都超多1/2,并且胚已发育完全,应属于生理休眠;小果蔷薇种子吸水率约27%,胚长/种子长都达2/3,并且通过对种子的解剖发现胚还未发育,应属于形态生理休眠。     

Comparison of egg period, hatching rate, and first-instar nymphs among three species of stonefly

Egg period was compared among several temperature conditions (11°C, 16°C, 20°C, 23°C) in Sweltsa sp., Stavsolus japonicus, and Isoperla aizuana (Plecoptera). The shortest mean egg incubation period was 27.8 days at 20°C in Sweltsa sp., 118.1 days at 16°C in Stavsolus japonicus, and 162.0 days at 20°C in Isoperla aizuana on average. Egg hatching rate was also the highest at the water temperature that provided the shortest egg incubation period. Based on laboratory data, eggs of Sweltsa sp. were considered to be deposited in May and hatched in June in the field. Thus, they must have spent the summer as nymphs in the field. Eggs of Stavsolus japonicus and Isoperla aizuana were considered to be deposited in April to May and hatched in September to October in the field. Visible eyes of Stavsolus japonicus and Isoperla aizuana appeared in August. It is likely that the long egg period of Stavsolus japonicus and Isoperla aizuana reflects that these two species spend the summer as dormant eggs in the field.     

Tubercle bacilli generate a novel cell wall-associated pigment after long-term anaerobic culture

Many cases of tuberculosis result from reactivation of previously acquired latent infections. Models to study such persister forms often involve gradual depletion of oxygen during culture as poor aeration is a characteristic of non-progressive TB granulomas. Anaerobically cultured bacilli develop a thickened outer-most cell wall layer. Here, we analyzed this layer from anaerobically cultured Mycobacterium tuberculosis and Mycobacterium bovis BCG. By six weeks of anaerobiosis a pigment was detected at levels > 60-fold higher in anaerobic than aerobic bacilli. This pigment was responsible for the electron-dense appearance of the thickened cell wall layer and gave an electrospray mass spectrometry peak at 409 Da (M+Na)+ or (M+H)+. We termed this pigment APP1, anaerobically produced pigment 1, the first pigment identified in M. tuberculosis.     

Inflorescence bud proteins of Pistacia vera

 The Pistacia vera L. (common name pistachio) is a unique dioecious and deciduous tree species, which is productive under harsh desert climates. We have identified and purified an Inflorescence Bud Protein of 32 kDa (IBP32) from male pistachio trees. There is a close correlation between its accumulation and inflorescence bud development and its disappearance and flowering. Using antibodies raised against this protein, we have identified in female trees the IBP32 and in addition a 27 kDa protein (IBP27), which appears to be specific to female inflorescence buds. The accumulation and disappearance of IBP27 follows the same pattern as that of IBP32. These proteins are glycoproteins rich in glycine and alanine and are highly hydrophilic. Based on the analytical results and immunological cross-reactivity between dehydrin antibodies and the IBPs, it is assumed that the latter are dehydrin-like and may protect inflorescence bud meristems against cold injury during dormancy. The IBPs are the major proteins of the pistachio bud, therefore they may also serve as nitrogen storage during winter for inflorescence bud growth in spring. Received: 17 October 1997 / Accepted: 6 March 1998     

Recovery of plants from “Near-Lethal” stress

This study reports on the dieback and recovery of red-osier dogwood, Cornus sericea L. plants from near-lethal (NL, sublethal) stress after varying lengths of post-stress environment (PSE). Intact dormant stems were subjected to 47° C for one hour during either October, November or December, and then placed into either constant 0° C or 23° C (dark condition) or kept under natural conditions at Corvallis, OR. Plants exposed to NL-heat stress in October died prior to 9 weeks of 0° C PSE, while none of the plants from other PSE treatments showed signs of injury. For plants exposed to NL-heat stress during November and December, stemdieback occurred at 0° C after 12 and 15 weeks, respectively. None of the plants from the other PSE treatments were injured. Post-stress temperatures of 0° or 5° C following NL-heat in October were lethal while temperatures above 10° C allowed recovery. Post-stress exposure to 0° C injured excised stems within 48 h, whereas irreversible damage to whole plants occurred by two weeks. Dormant plants exposed in October to other stresses, e.g., freezing temperature and hydrogen cyanamide, at NL dosages showed that these stresses also caused plant dieback at 0° C and little or no dieback at 23° C PSE.Abbreviations NL Near-Lethal - PSE Post-Stress Environment     

Membrane turnover in imbibed dormant embryos of the wild oat (Avena fatua L.)

Germinating non-dormant (ND) embryos of wild oat incorporate [³H]glycerol into phospholipid, and a 250% increase in total extractable phospholipid occurs within 72 h. During germination, leveles of phosphatidyl inositol showed the greatest change, increasing approximately 5-fold.Imbibed dormant (D) embryos of the wild oat also incorporate [³H]gycerol into phospholipids, but there is no net synthesis. A continuous turnover of membrane phospholipids could be demonstrated in pulse chase experiments, and although the proportions of most phospholipids does not change, there was a decrease of 50% in phosphatidyl serine.The half-life of [³H]glycerol in the extracted phospholipids of D and ND embryos varies between 35 and 57 h, and in membrane fractions separated on sucrose density gradients the half-lives vary between 26 and 56 h.D embryos induced to germinate with GA and ND embryos in which germination is repressed by ABA show similar phospholipid changes to ND and D embryos respectively, with the exception that the proportion of phosphatidyl serine remained unchanged in the ND-ABA embryos.It is concluded that the continual turnover of membranes of imbibed dormant embryos is consistent with the maintenance of cellular integrity determining the longevity of the seed under natural conditions.Abbreviations D dormant - ND nondormant - ABA abscisic acid - GA gibberellic acid (GA₃)     

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

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

Effects of Dormancy Regulating Chemicals on Innate and Salinity Induced Dormancy in the Invasive <Emphasis Type="Italic">Prosopis juliflora</Emphasis> (Sw.) DC. Shrub

The effect of different types and concentrations of dormancy regulating chemicals (DRCs) on innate and induced dormancy was evaluated under optimal germination conditions in the invasive Prosopis juliflora shrub. Lower concentrations of gibberellic acid (0.3 mM) and kinetin (0.05 mM) were more effective in enhancing germination % and rate at higher concentrations of NaCl, but the reverse was true for thiourea. None of the DRCs alleviated innate dormancy of P. juliflora. Germination % and rate decreased as salinity increased. Percent final germination of non-treated seeds was significantly reduced at 500 mM NaCl and virtually inhibited in 600 mM NaCl. Germination reduction in 500 mM NaCl was not alleviated by any of the DRCs, but inhibition induced at 600 mM NaCl was partially alleviated by all the DRCs. Gibberellic acid had a significantly greater effect than kinetin in alleviating germination inhibition. For restoration of saline soil through the use of P. juliflora, results suggest using DRCs, particularly gibberellic acid and thiourea, as a preseeding treatment can overcome the problem of reduced germination.     

The evolutionary ecology of seed germination of Arabidopsis thaliana: variable natural selection on germination timing

Germination timing of Arabidopsis thaliana displays strong plasticity to geographic location and seasonal conditions experienced by seeds. We identified which plastic responses were adaptive using recombinant inbred lines in a field manipulation of geographic location (Kentucky, KY; Rhode Island, RI), maternal photoperiod (14-h and 10-h days), and season of dispersal (June and November). Transgressive segregation created novel genotypes that had either higher fitness or lower fitness in certain environments than either parent. Natural selection on germination timing and its variation explained 72% of the variance in fitness among genotypes in KY, 30% in June-dispersed seeds in RI, but only 4% in November-dispersed seeds in RI. Therefore, natural selection on germination timing is an extremely efficient sieve that can determine which genotypes can persist in some locations, and its efficiency is geographically variable and depends on other aspects of life history. We found no evidence for adaptive responses to maternal photoperiod during seed maturation. We did find adaptive plasticity to season of seed dispersal in RI. Seeds dispersed in June postponed germination, which was adaptive, while seeds dispersed in November accelerated germination, which was also adaptive. We also found maladaptive plasticity to geographic location for seeds dispersed in June, such that seeds dispersed in KY germinated much sooner than the optimum time. Consequently, bet hedging in germination timing was favorable in KY; genotypes with more variation in germination timing had higher fitness because greater variation was associated with postponed germination. Selection on germination timing varied across geographic location, indicating that germination timing can be a critical stage in the establishment of genotypes in new locations. The rate of evolution of germination timing may therefore strongly influence the rate at which species can expand their range.