Post‐dispersal seed predation and its relations with seed traits: a thirty‐species‐comparative study

Post‐dispersal seed predation is a key process determining the variability in seed survival in forests, where most seeds are handled by rodents. Seed predation is thought to affect seedling regeneration, colonization ability and spatial distribution of plants. Basic seed traits are the essential factors affecting rodent foraging preferences and thus seed survival and seedling recruitment. Many studies have discussed several seed traits and their effects upon seed predation by rodents. However, the results of those previous studies are usually equivocal, likely because few seed traits and/or plant species tend to be incorporated into these studies. In order to elucidate the relationships between seed predation and seed traits, we surveyed the predation of 48 600 seeds in a natural pine forest, belonging to 30 species, for three consecutive years. The results demonstrated that: (i) seed size and seed coat hardness did not significantly affect seed predation; (ii) total phenolics had a negative effect upon seed predation; (iii) positive effects of nitrogen content upon seed predation were found. From our study, it seems that the better strategy to prevent heavy predation is for plants to produce seeds with higher total phenolics content rather than physical defenses (i.e. hard seed coat) or larger seeds. Additionally, rodent foraging preference may depend more on Nitrogen content than other nutrient content of seeds.     

First report of seed dispersal by ants in Dicentra peregrina (Papaveraceae), an alpine plant in the Japanese Alps

Seed dispersal by ants, known as myrmecochory, is commonly observed among various plant taxa. The seeds of these plants have an elaiosome to attract ants. In Japan, myrmecochory has been well studied in several lowland plant species, but not in highland plant species that grow above the tree line. We investigated whether the seeds of Dicentra peregrina, known as the “queen of the alpine plants” in Japan, are carried by Formica gagatoides ants at 2510 m a.s.l. on Mt Norikura, Kita‐Alps, Japan. We observed F. gagatoides workers picking up D. peregrina seeds by grasping the elaiosome and carrying the seeds into their nests. We inferred from the observed ant behavior and the seed morphology that D. peregrina is a myrmecochorous species.     

Biomass harvest of invasive Typha promotes plant diversity in a Great Lakes coastal wetland

Ecological and financial constraints limit restoration efforts, preventing the achievement of desired ecological outcomes. Harvesting invasive plant biomass for bioenergy has the potential to reduce feedback mechanisms that sustain invasion, while alleviating financial limitations. Typha × glauca is a highly productive invasive wetland plant that reduces plant diversity, alters ecological functioning, its impacts increase with time, and is a suitable feedstock for bioenergy. We sought to determine ecological effects of Typha utilization for bioenergy in a Great Lakes coastal wetland by testing plant community responses to harvest‐restoration treatments in stands of 2 age classes and assessing community resilience through a seed bank study. Belowground harvesting increased light penetration, diversity, and richness and decreased Typha dominance and biomass in both years post‐treatment. Aboveground harvesting increased light and reduced Typha biomass in post‐year 1 and in post‐year 2, increased diversity and richness and decreased Typha dominance. Seed bank analysis revealed that young stands (<20 years) had greater diversity, richness, seedling density, and floristic quality than old stands (>30 years). In the field, stand‐age did not affect diversity or Typha dominance, but old stands had greater Typha biomass and slightly higher richness following harvest. Harvesting Typha achieved at least 2 desirable ecological outcomes: reducing Typha dominance and increasing native plant diversity. Younger stands had greater potential for native recovery, indicated by more diverse seed banks. In similar degraded wetlands, a single harvest of Typha biomass would likely result in significant biodiversity and habitat improvements, with the potential to double plant species richness.     

Effectiveness of dry heat as a seed sterilisation technique: Implications for ex situ conservation

Seed-borne pathogens are a daily issue for ex situ collection managers who try to solve it using various chemicals more or less harmful to the staff and the plant material stored. The most common physical method for seed sterilisation is moist heat, in contrast to dry heat which is used much less frequently. Consequently, the efficiency of dry heat as disinfection method and the behaviour of seeds undergoing this treatment are currently poorly known, especially for wild species. In this study, seed viability was estimated by performing germination tests according to standard procedures. Germination tests were conducted on 13,200 seeds from 66 wild species of temperate regions belonging to 22 different families. Results indicate that dry seeds exposed to 60°C during 1hour were less infected by seed-borne pathogens in 14% of the cases, whereas no change has been registered in the other cases. For all 66 studied species, no decrease in germination percentage was detected after the heat treatment. Given its positive effect on infection control without affecting seed viability, dry heat treatment as proposed here opens opportunities for seed bank managers, but also for the disinfection of herbarium collections.     

Biospeckle activity in coffee seeds is associated non‐destructively with seedling quality

Seeds age during storage, resulting in a decline in germination and seedling quality. Seed quality tests are important to monitor this decline. However, such tests are usually destructive and require large seed numbers and long time. For coffee seeds the standard germination test and assessment of seedling quality takes 30 days. Biospeckle has been used previously as a non‐destructive optical tool to monitor biological activity in a range of tissues. Biospeckle was applied 3–6 days after imbibition (DAI) to investigate an association with coffee seedling quality after 30 days. Two distinct areas of biospeckle activity were demonstrated, concurring with the locations of the embryonic axis and the cotyledons in the apical and central seed parts, respectively. Moisture content analysis revealed that embryos of imbibed seeds contained more water than endosperm. Different areas within the endosperm did not differ in moisture content, while the moisture content of the axis was higher than that of the cotyledons, and this did not change from 4 DAI. Therefore, it was concluded that high biospeckle activity was not the result of increased water content in any seed part, but more likely of growth and metabolism in the axis and cotyledons, which had been described previously. A threshold biospeckle ratio apical : central of 1.02 after 6 days distinguished between seeds that produced dead and viable seedlings after 30 days and provided similar results as a tetrazolium test, a widely acknowledged but destructive test for seed quality. Thus, biospeckle data provided a non‐destructive early parameter for seedling quality, based on embryo growth during germination.     

Gibberellins regulate seed germination in tomato by endosperm weakening: a study with gibberellin-deficient mutants

The germination of seeds of tomato [Lycopersicon esculentum (L.) Mill.] cv. Moneymaker has been compared with that of seeds of the gibberellin-deficient dwarf-mutant line ga-1, induced in the same genetic background. Germination of tomato seeds was absolutely dependent on the presence of either endogenous or exogenous gibberellins (GAs). Gibberellin A₄₊₇ was 1000-fold more active than commercial gibberellic acid in inducing germination of the ga-1 seeds. Red light, a preincubation at 2°C, and ethylene did not stimulate germination of ga-1 seeds in the absence of GA₄₊₇; however, fusicoccin did stimulate germination independently. Removal of the endosperm and testa layers opposite the radicle tip caused germination of ga-1 seeds in water. The seedlings and plants that develop from the detipped ga-1 seeds exhibited the extreme dwarfy phenotype that is normal to this genotype. Measurements of the mechanical resistance of the surrounding layers showed that the major action of GAs was directed to the weakening of the endosperm cells around the radicle tip. In wild-type seeds this weakening occurred in water before radicle protrusion. In ga-1 seeds a similar event was dependent on GA₄₊₇, while fusicoccin also had some activity. Simultaneous incubation of de-embryonated endosperms and isolated axes showed that wild-type embryos contain and endosperm-weakening factor that is absent in ga-1 axes and is probably a GA. Thus, an endogenous GA facilitates germination in tomato seeds by weakening the mechanical restraint of the endosperm cells to permit radicle protrusion.Abbreviations GA(s) gibberellin(s) - GA₃ gibberellic acid     

Recursive construction of perfect DNA molecules from imperfect oligonucleotides

Making faultless complex objects from potentially faulty building blocks is a fundamental challenge in computer engineering, nanotechnology and synthetic biology. Here, we show for the first time how recursion can be used to address this challenge and demonstrate a recursive procedure that constructs error‐free DNA molecules and their libraries from error‐prone oligonucleotides. Divide and Conquer (D&C), the quintessential recursive problem‐solving technique, is applied in silico to divide the target DNA sequence into overlapping oligonucleotides short enough to be synthesized directly, albeit with errors; error‐prone oligonucleotides are recursively combined in vitro, forming error‐prone DNA molecules; error‐free fragments of these molecules are then identified, extracted and used as new, typically longer and more accurate, inputs to another iteration of the recursive construction procedure; the entire process repeats until an error‐free target molecule is formed. Our recursive construction procedure surpasses existing methods for de novo DNA synthesis in speed, precision, amenability to automation, ease of combining synthetic and natural DNA fragments, and ability to construct designer DNA libraries. It thus provides a novel and robust foundation for the design and construction of synthetic biological molecules and organisms.     

动物与植物种子更新的关系Ⅱ．动物对种子的捕食、扩散、贮藏及与幼苗建成的关系

植物的繁殖体总是面临来自各类生物（如昆虫、脊椎动物、真菌）的捕食风险。因动物捕食引起的种子死亡率影响植物的适合度、种群动态、群落结构和物种多样性的保持。种子被捕食的时间和强度成为植物生活史中发芽速度、地下种子库等特征的主要选择压力,而种子大小、生境类型等因素也影响动物对植物种子的捕食。捕食者饱和现象被认为是植物和种子捕食者之间的高度协同进化作用的结果,是限制动物破坏种子、提高被扩散种子存活率的一种选择压力。大部分群落中的大多数植物种子被动物扩散。种子扩散影响种子密度、种子被捕食率、病原体攻击率、种子与母树的距离、种子到达的生境类型以及建成的植株将与何种植物竞争,从而影响种子和幼苗的存活,最终影响母树及后代植物的适合度。种子被动物扩散后的分布一般遵循负指数分布曲线,大多数种子并没有扩散到离母树很远的地方。捕食风险、生境类型、植被盖度均影响动物对种子的扩散。植物结实的季节和果实损耗的过程也体现了其对扩散机会的适应。许多动物有贮藏植物种子的行为。动物贮藏植物繁殖体的行为,一方面调节食物的时空分布,提高了贮食动物在食物缺乏期的生存概率;另一方面也为种子萌发提供了适宜条件,促进了植物的扩散。于是,植物与贮食动物形成了一种协同进化关系,这种关系可能是自然界互惠关系（mutualism)的一种。影响幼苗存活和建成的因子包括种子贮蒇点的微生境、湿度、坡向、坡度、林冠盖度等。许多果食性动物吃掉果肉后,再将完好的种子反刍或排泄出来。种子经动物消化道处理后,发芽率常有所提高。