半夏倒苗前后的细胞组织结构

探讨高温胁迫下半夏倒苗前后的组织学结构的变化,为揭示半夏倒苗的生物学机理提供参考依据。在半夏植株高15cm左右时,给予(32±1)℃的高温胁迫,于不同胁迫天数取半夏叶柄,经爱氏苏木精染液染色,用石蜡切片法制片,在显微镜下观察并照相。结果表明,随着高温胁迫时间的延长,半夏叶柄的维管组织结构被破坏越来越严重,细胞壁、细胞膜破裂,原生质外渗,核膜破裂,核仁溢出,有的细胞内核仁消失。     

Kinetics of nitrogen mineralization in Costa Rican soils: Model evaluation and pretreatment effects

Present methods for determining critical nutrient concentrations in plants and soils are unsatisfactory if concentrations change with time while the crop is growing. In such cases the critical concentration can only be applied in relation to growth rate at any given moment. For interpreting field experiments this introduces considerable difficulties: two possible approaches to these problems are suggested, one of which uses a simple simulation model. Results from a Brussels sprout nitrogen experiment are used to show how, using this approach, a single critical sap nitrate concentration (380 mg NO₃ N.l^–1 for 95% of potential growth rate) may serve to explain the results at all growth stages in three seasons.     

天目山米心水青冈群落物种组成特点与萌条更新

由于特定的温湿需求,中国的水青冈多分布于亚热带山地,而分布于欧洲和北美的水青冈则为温带的优势种。本文对浙江天目山自然保护区内米心水青冈群落物种组成特点和更新进行了研究。结果表明：在3个30 m×30 m样方中共发现132种高等植物,分属于51科86属;种-面积关系符合Arrhenius模型,lg S=0.384 lg A+0.6443;log-series模型能很好地模拟米心水青冈群落中乔木层种-多度关系(R²=0.9596);乔木层优势种为壳斗科的米心水青冈、短柄枹、锥栗等;灌木层优势种有伞形绣球、宜昌荚蒾等;草本层优势种为箬竹、苔草等;群落物种多样性较高,而灌木层和草本层物种多样性与乔木层多样性呈负相关;群落结构表明,天目山米心水青冈群落是稳定的顶极群落,萌条更新在米心水青冈群落中十分常见,55%的乔木层物种具有萌条现象;尤其是米心水青冈,萌条数与母株的胸径呈显著的正相关。     

Polysaccharide production benefits dry storage survival of the biocontrol agent Pseudomonas fluorescens S11:P:12 effective against several maladies of stored potatoes

Pseudomonas fluorescens S11:P:12 (NRRL B-21133) is a biological control agent able to suppress several potato diseases and sprouting. Notably, it produces a polysaccharide during liquid cultivation, and the objective of this work was to determine the role of this material in the bio-control process. First, the polysaccharide was isolated, purified and identified as marginalan, which accumulated to ~3.3 g/L in cultures. The bioactivity of isolated marginalan applied alone or in combination with washed cells of strain S11:P:12 was tested in potato bioassays of dry rot and pink rot suppressiveness and sprout inhibition. Since the formulation and storage of a dried biocontrol product is preferred for commercial use, the impact of marginalan on cell survival during drying and storage was also studied. Washed bacteria formulated with 0–6.6 g/L polysaccharide were either applied to Hyflo granules, then slowly dried for 24 h with airflow at 50–60% relative humidity, or in 1-µL droplets placed in replicate wells of a micro-plate, then quickly dried for 1 h in a biohazard hood. Both Hyflo and micro-plate dry storage results indicated that marginalan significantly reduced cell death after drying, such that the final stable viable cell density was 2.5–5 orders of magnitude greater, respectively, than if no marginalan were included with cells. Marginalan had no significant impact on disease or sprout suppression by strain S11:P:12, and its main benefit to biocontrol was viable cell preservation during drying and storage. When marginalan was formulated with other selected P. fluorescens strains, its benefits to drying and storage survival were again evident (especially after 4°C instead of 25°C storage), but its effects were more subtle than for strain S11:P:12, and dry rot suppression was not impacted.     

Multi-strain co-cultures surpass blends for broad spectrum biological control of maladies of potatoes in storage

Pseudomonas fluorescens strains S11:P:12, P22:Y:05, and S22:T:04 and Enterobacter cloacae strain S11:T:07 have been documented to suppress four important storage potato maladies – dry rot, late blight, pink rot, and sprouting. This research investigates the efficacy and consistency of strain mixtures produced by co-culturing strains together in one vessel or by blending them together after separate cultivations in pure cultures. Pure and co-cultures were produced in flask or fermentor cultures, viable cell concentrations were assessed using a nutrient-based selective plating method to identify and enumerate strains, and the efficacy of treatments was assessed with respect to dry rot, pink rot, late blight or sprout suppression. Experiments were designed to analyze dry rot suppression versus all strain combinations and the combination method (co-culture or blend). Results of a two-way analysis of variance of disease with strain composition and combination method showed that significantly better dry rot suppression was obtained by co-cultures (30.3±2.4% relative disease) than by similar strain blends of pure cultures (41.3±2.4%) (P<0.001). During a 3-year study, both biocontrol efficacy and consistency were assessed in 16 laboratory and small pilot trials simulating commercial storages. Three-strain co-culture had a lower mean disease rating than the blend in 9 of 16 experiments examining control of the three diseases and sprouting. The co-culture led other treatments in incidences of significant malady reduction relative to the control: 14 of 16 attempts for co-culture, 11 of 16 attempts for blend, 10 of 13 attempts for pure S11:P:12, 8 of 13 attempts for S22:T:04, and 9 of 13 attempts for P22:Y:05. Using relative performance indices to rank treatment performance across all experiments, the co-culture treatment ranked significantly higher than the blend. A synergy analysis suggested that co-culturing strains stimulated inter-strain activities to boost biocontrol efficacy and consistency, a feature not developed in strains grown separately and mixed just prior to addition to potatoes.     

A novel plant membrane proteoglycan which causes anorexia in animals

Hunger and satiety are complex interplay of several factors in human and animal species. Reduced food intake has also been observed under various pathological conditions. Earlier, we have been able to isolate an endogenous glycoprotein from erythrocyte membranes, which causes anorexia in rats. In the present study, a similar anorexigenic proteoglycan from Mung bean sprout membranes has been isolated and purified. The proteoglycan (50 kDa) consisted of 70–85% carbohydrate with galactose, glucose galactosamine and mannose as the main sugars. Protein part on analysis showed higher glutamic acid and serine content. This proteoglycan reduces food intake when injected in rats deprived of food for 96 hr as well as normally fed rats, mice and rabbits without any rebound. The TCA-soluble proteoglycan from different plant sources have also been compared for their anorexigenic activity. The similarities observed among plant and animal cell membrane proteoglycans with satietins isolated from human blood plasma could be due to membrane origin of satietins. (Mol Cell Biochem120: 111–117, 1993)     

A comparison of the chemical flavour composition of some brussels sprouts cultivars grown at different crop spacings

Variations in the chemical flavour composition of six cultivars of Brussels sprout were determined for plants grown at three different crop spacings (30, 45 and 60 cm from nearest neighbours). Appreciable variations in the chemical composition of the flavour extracts were observed and it was possible to distinguish the better flavoured cultivars in all cases. In general, flavour strength increased the closer together the plants were grown. The results indicate a crude yet simple method for the production of Brussels sprouts of varying flavour and flavour strength.     

香果树根萌苗生长特性及影响因子分析

香果树(Emmenopterys henryi)为我国Ⅱ级野生保护植物,由于生境遭到破坏、过度开发利用以及种群自然更新能力差等原因,导致自然环境下香果树种群数量迅速衰减。运用方差分析、多重比较、主成分分析等方法,对自然环境下香果树种群的根萌苗生长状况及其主要影响因子进行了研究。结果表明:香果树根萌苗的数量随着苗龄的增长逐渐减少,1a根萌苗的死亡率最高;苗高和基径均随苗龄的增大呈指数增长;香果树根萌苗主要生长在母树东南方120°~150°(以正北方为0°按顺时针方向旋转,下同)位置、距母树树干2 m以内及直径2 cm、长度30 cm的露根上;根萌苗苗高受母树方位影响较小,受露根直径、露根长度以及与母树间距离的影响稍大;母树南向(168.75°)根萌苗的基径显著大于其它方向的根萌苗基径;与北向和南向相比,母树东向和西向根萌苗的冠幅较大;根萌苗苗高、基径和冠幅等形态指标均随着与母树树干间距离的增加而降低,但随着露根直径的增加各形态指标均呈先升高后降低的趋势(露根直径6.5 cm时苗高和基径达到最大值),随着露根长度的增加各形态指标呈先降低后升高的趋势;与树冠内根萌苗相比,香果树母树树冠外根萌苗的死亡率较高。主成分分析结果表明,随着林内光照条件的改善、土壤中有机质含量的增加、砾石覆盖率的增加以及适度的人为干扰均有利于香果树根萌苗的生长。因此,减小林冠郁闭度、增加人工抚育措施对维持香果树的种群发展、实现其种群自然更新具有重要作用。     

极端干旱条件下杠柳的落叶相对休眠-复水复苏型生存策略

以3种梯度恒定干旱胁迫(土壤水分分别控制在最大田间持水量的80%、55%和35%)为对照,人工模拟持续自然干旱(干旱15~54 d后复水),研究黄土丘陵区广泛分布的乡土灌木杠柳(Periploca sepium)的形态、耗水、生长、生理在持续干旱、极端干旱以及旱后复水时的变化,探讨长期恒定胁迫及极端干旱下植物的适应性策略。结果表明:(1)在恒定干旱胁迫下,杠柳可调整生长和生理状况使其达到适应有限水分供应的新稳定状态;植株冠层减小,叶片可溶性糖积累以及过氧化物酶活性升高是杠柳适应长期恒定干旱胁迫的重要机制。(2)在长期自然干旱胁迫下,杠柳的形态与生理状况均持续变化。在叶片死亡脱落前,叶片中大量积累的脯氨酸、游离氨基酸和可溶性糖提高了杠柳对干旱胁迫的耐受性;随着干旱胁迫的加剧,杠柳叶片加速衰老死亡、以休眠芽形式进入相对休眠状态。(3)复水后根系和茎复苏长出新芽并补偿生长,新芽中高含量的脯氨酸和游离氨基酸以及高活性状态的SOD和POD表明新芽活跃的生理状态是其补偿生长的重要机制,即杠柳在极端干旱条件下具有落叶相对休眠-复水后复苏型生存策略。     

Effects of Prescribed Fires on Young Valley Oak Trees at a Research Restoration Site in the Central Valley of California

Woodland restoration sites planted with Quercus lobata (valley oak) often have serious invasions of nonnative annual grasses and thistles. Although prescribed fire can effectively control these exotics, restoration managers may be reluctant to use fire if it causes substantial mortality of recently planted saplings. We studied the effects of prescribed fires on the survival and subsequent growth of 5‐ and 6‐year‐old valley oak saplings at a research field near Davis, California. One set of blocks was burned in summer 2003 at a time that would control yellow star thistle, a second set of blocks was burned in spring 2004 at a time that would control annual grasses, and a third set was left unburned. Very few oaks died as a result of either fire (3–4%). Although a large proportion was top‐killed (66–72%), virtually all these were coppiced and most saplings over 300 cm tall escaped top‐kill. Tree height, fire temperature, and understory biomass were all predictive of the severity of sapling response to fire. Although the mean sapling height was initially reduced by the fires, the growth rates of burned saplings significantly exceeded the growth rates of unburned control trees for 2 years following the fires. By 2–3 years after the fires, the mean height of spring‐ and summer‐burned saplings was similar to that of the unburned control saplings. The presence of valley oak saplings does not appear to preclude the use of a single prescribed burn to control understory invasives, particularly if saplings are over 300 cm tall.