Evidence of a maternal effect that protects against water stress in larvae of the American dog tick, Dermacentor variabilis (Acari: Ixodidae)

We report that the ability to absorb water vapor from the air in larvae of the American dog tick, Dermacentor variabilis, changes depending upon moisture conditions where the eggs develop. When development occurs at lower relative humidities, resultant larvae can replenish water stores, maintain water balance, and survive at relative humidities as low as 75-85% RH, a range that agrees with previously published values for the critical equilibrium humidity or CEH. In contrast, exposure to high relative humidity conditions during development elevates the CEH to 93-97% RH. These larvae can survive only at relative humidities that are close to saturation, as 93% RH is a dehydrating atmosphere. For these larvae, absorption at 97% RH can be prevented by blocking the mouthparts with wax, indicating that an upward shift has occurred in the moisture threshold where the active mechanism for water vapor absorption operates. Based on transfer experiments between low and high relative humidities, the CEH of larvae is determined by the relative humidity experienced by the mother rather than the moisture conditions encountered by eggs after they are laid. The fact that no changes in body water content, dehydration tolerance limit and water loss rate were observed implies that adjustments to the CEH conferred by the mother have the adaptive significance of enabling larvae to maintain water balance by limiting the range of hydrating atmospheres.     

Ripe pollen carbohydrate changes in Trachycarpus fortunei: the effect of relative humidity

Pollen of the palm Trachycarpus fortunei was kept at 25°C and relative humidities (RH) of 20, 55 and 98%. Changes in viability, water content and carbohydrates were measured over 2–17 days. Water content remained almost constant at 20 and 50% RH and increased dramatically at 98%. Pollen viability and germination rate remained almost constant over 14 days at 20% RH and decreased to about 2% after 7–9 days at 55% and to even less at 98% RH. Although the three experimental conditions were constant, qualitative and quantitative variations in pollen carbohydrates were recorded, even after pollen had lost its viability. The quantities of mono-, di- and polysaccharides varied with the period of pollen storage at the various RH. The greatest changes in glucose, fructose and sucrose content were recorded at 55 and 98% RH. At these relative humidities, maximum glucose and fructose content and minimum sucrose content occurred at maximum water content. Starch was not present in mature pollen but appeared and peaked after 7–9 days of pollen storage at 55 and 98%. Appearance of starch coincided with an increase in pectin content. PAS-positive cytoplasmic polysaccharides showed an increasing trend at 20% RH. A relation was found between pollen viability, water content and monosaccharide content. Pollen viability and germination capacity remained high at 20% RH for 14 days. At this relative humidity, pollen water, glucose and fructose contents remained almost constant, while sucrose reached its maximum value. The fluctuations of more complex carbohydrates (starch, pectins and PAS-positive cytoplasmic polysaccharides) were less easy to interpret. Changes observed under experimental conditions could simulate processes occurring in nature during pollen presentation and dispersal.     

Water uptake in the cat flea Ctenocephalides felis (Pulicidae: Siphonaptera)

To counteract water loss due to excretion, cuticular transpiration and respiration, various groups of arthropods have developed mechanisms for active uptake of water vapor from unsaturated air. In this study, active uptake capabilities and water loss rates were examined in the various developmental stages of the cat flea, Ctenocephalides felis. To determine critical equilibrium humidity, the lowest relative humidity at which active water uptake can occur, pre-desiccated immature and adult fleas were placed in a series of humidity regimes ranging from 44 to 93% RH. Active uptake occurred in larval stages at relative humidities above 53% and in pre-pupae at 75-93% RH. Pupae and adults did not demonstrate active uptake at any humidity. Optimal uptake for larvae occurred between 20 and 30 degrees C. When placed over Drierite (<10% RH), larval and adult stages demonstrated a higher rate of water loss than pre-pupal and pupal stages. Active water uptake is necessary to ensure proper development of the larvae of C. felis. Active uptake ceases after the larval-pupal ecdysis and it appears that adults have lost the ability to actively uptake water.     

Water loss and metabolic water in starving Argas reflexus nymphs (Acari: Argasidae)

Basic components of the water balance were determined in A. reflexus unfed second instar nymphs kept at 30 degrees C and different relative humidities in darkness. At 2.5% and 32.5% RH, A. reflexus survived for 170+/-60 and 246+/-71 days, respectively. At 56%, 75.5% and 96.5% RH, the experiment was terminated after 168 days without any mortality. The initial water content of hydrated A. reflexus kept at 85% RH was 70.3+/-1.8% while the water content was close to 50% in ticks dehydrated at /=56% suggesting that A. reflexus increased its oxidative metabolism under dehydrating conditions and thus delayed lethal dehydration. Interestingly, the dry mass of dead ticks was almost identical irrespective of whether the ticks had previously been kept at 2.5% and 32.5% RH, i.e. irrespective of their different survival periods. This raises the question whether the ticks had died by dehydration or by exhaustion of energy reserves.     

棉铃虫蛹期在极端湿度下的失水动态

研究了极端相对湿度 (0%、9%、22.5%、80%、90%和100%) 对棉铃虫Helicoverpa armigera蛹期发育、存活和水分动态的影响。发育蛹在25℃下,相对湿度≤9%时, 不能羽化;湿度为22.5%时,羽化率不足20%; 高湿不影响它们的存活。在同样温度下,湿度≥9%时,滞育蛹在一个月内都极少死亡;在此期间,滞育终止率随湿度降低而升高。各湿度处理组发育蛹和滞育蛹从1日龄起的累计失水率都与其日龄呈线性相关。三个低湿处理组发育蛹中死亡个体在死亡前的平均累计失水率都在32%以上。滞育蛹经0%湿度处理一个月,平均仅失水22.4%;在湿度≥90%时的同期失水率不超过3.6%。在30℃下,发育蛹在4 h内测定的表皮渗透力最大,分别是9.0(♀)和10.7(♂) μg/(cm²·h·mm Hg); 滞育蛹的相应值出现在2 h内, 分别为 4.7(♀)和5.4(♂) μg/(cm²·h·mm Hg)。     

四种石斛兰种胚发育进程研究

以玫瑰石斛、尖刀唇石斛、短棒石斛、兜唇石斛种子为材料,进行种胚非共生萌发研究,并对其种子形态和胚的发育进程进行了显微观察。结果表明:处于球形胚阶段的石斛兰种子,种胚吸胀后突破种皮,发育至吸收毛和芽生长点出现后,种胚形成原球体;种子萌芽后胚尚未成熟,只进入心形胚阶段。呈纺锤形种子的种皮两端形状不同,一端存在结点,呈弯曲状的尖形,另一端种皮呈收拢的圆口形。4种石斛兰种子,玫瑰石斛种子最长,为两端狭长的纺锤形;兜唇石斛种子最短,呈两端稍细的纺锤形。玫瑰石斛、短棒石斛、尖刀唇石斛种子胚培养需要5～10 d萌发;兜唇石斛种子和胚皆偏小,萌发需要30 d。石斛兰种胚和种皮吸水膨胀后,种胚向种皮的一端移动、脱出或种胚撕裂种皮中央后突破而出,形成裸胚。玫瑰石斛种子撕裂种皮后主要从种皮中央突破;短棒石斛、尖刀唇石斛、兜唇石斛部分种胚从种皮一端脱出,部分种胚则从中央撑破种皮脱出。充分膨胀、变绿后萌芽的裸胚,存在极性,顶部芽生长点萌动,下部出现成群散射状吸收毛。     

A Study on Pollen Morphology of Some Chinese Genera in Tribe Anthemideae

This paper deals with pollen grains of 9 chinese genera of Trib. Anthemideae Cass., which include the genera: Ajania Poljak., Hippolytia Poljak., Stilpnolepis Krasch., Elachanthemum Ling et Y. R. Ling, Filifolium Kitam., Ajaniopsis Shih, Kaschgaria Poljak., Neopallasia Poljak., Seriphidium Poljak., Pollen grains of these genera are isopolar, radially symmetrical, 3-colporate, NPC 345, spheroidal, sometimes suboblate or subprolate. Polar axis 20.0-30.0μm equatorial axis 20.0 -30.0μm. The exine consists of three layers: tectum, columellae and nexine. Exine thickness 3.2-5.6μm, usually the columellae is the thickest. According to the differences of exine ornamentation, they are divided into two main groups: 1. with distinct spines, including the genera Ajania Poljak., Hippolytia Poljak., Stilpnolepis Krasch., 2.with indistinct spinules, including the genera Elachanthemum Ling et Y.R.Ling, Filifolium Kitam., Ajaniopsis Shih, Kaschgaria., Neopallasia Poljak.,Seriphidium Polj     

Local Evolution of Seed Flotation in Arabidopsis

Arabidopsis seeds rapidly release hydrophilic polysaccharides from the seed coat on imbibition. These form a heavy mucilage layer around the seed that makes it sink in water. Fourteen natural Arabidopsis variants from central Asia and Scandinavia were identified with seeds that have modified mucilage release and float. Four of these have a novel mucilage phenotype with almost none of the released mucilage adhering to the seed and the absence of cellulose microfibrils. Mucilage release was modified in the variants by ten independent causal mutations in four different loci. Seven distinct mutations affected one locus, coding the MUM2 β-D-galactosidase, and represent a striking example of allelic heterogeneity. The modification of mucilage release has thus evolved a number of times independently in two restricted geographical zones. All the natural mutants identified still accumulated mucilage polysaccharides in seed coat epidermal cells. Using nuclear magnetic resonance (NMR) relaxometry their production and retention was shown to reduce water mobility into internal seed tissues during imbibition, which would help to maintain seed buoyancy. Surprisingly, despite released mucilage being an excellent hydrogel it did not increase the rate of water uptake by internal seed tissues and is more likely to play a role in retaining water around the seed.     

Seed coat cell turgor responds rapidly to air humidity in chickpea and faba bean

The turgor pressure in cells of chickpea (Cicer arietinum L.) and faba bean (Vicia faba L.) seed coats was measured with a pressure probe. Measurements were made under in situ conditions by removing a section of wall from a pod, which remained attached to the plant, and exposing the intact seed. If the pod wall was removed and the turgor measurements made under ambient laboratory conditions of 50% to 70% relative humidity (RH), cell turgor pressure declined over time, typically reaching 0 MPa. If the pod wall was removed and the turgor measurements made under conditions of 100% RH, however, cell turgor pressure was stable over time, relatively uniform within the seed coat tissue, and was found to be 0.1-0.3 MPa for chickpea, and 0.1-0.2 MPa for faba bean. In both species there was a marked decline in cell turgor, beginning within about 60 s, when humidification was discontinued. The decline in cell turgor occurred regardless of the depth of the cell within the seed coat tissue, and this decline could be stopped, but not entirely reversed, when humidification was restored. An increase in cell turgor could also be caused by wetting of the seed. These responses indicate that a very rapid water exchange can occur within the seed coat tissue in situ. The rapid and, in some cases, relatively permanent loss of seed coat cell turgor in the absence of humidification raises serious concerns regarding desiccation artefacts which may be involved in the empty seed coat technique, often used to study seed carbon and water relations in grain legumes.     

Effect of temperature and relative humidity on the rate of development,fecundity and life table parameters of the red spider mite Oligonychus mangiferus (Rahman and Sapra) (Acari: Tetranychidae)

Studies on biology of Oligonychus mangiferus (Rahman and Sapra) at combination of eight constant temperatures and relative humidities (RHs) viz., 7.0°C with 85% RH, 10°C with 80% RH, 15.0°C with 75% RH, 23.0°C with 70% RH, 31.0°C with 65% RH, 34.0°C with 65% RH, 36.0°C with 60% RH and 40.0°C with 55% RH revealed that the optimal condition for the development of these mites are 15.0–31.0°C and 65–75% RH. The highest temperature and the lowest RH accelerated the rate of development and induced more reproduction of O. mangiferus. Its population also multiplied 30.81 times in a generation time of 27.36 days at 31.0°C and 65% RH, while the same population only increased 7.46 times in a generation time of 48.07 days at 15.0°C and 75% RH. Fecundity was highest at 31.0°C and 65% RH with 46.43 eggs per female. The highest intrinsic rate of natural increase was observed at 31.0°C as 0.125 per day.     

白沙蒿种子萌发特性的研究 I. 粘液瘦果的结构和功能

白沙蒿(Artemisia sphaerocephala Krasch.)是中国西北部沙漠的流动及固定沙丘上广泛分布的优势种灌木。瘦果小而轻,借助显微镜和扫描电镜对瘦果的形态结构进行了观察,其种子的种皮与果皮愈合,果皮外层为很厚的粘液层,其粘液层在遇湿后迅速吸水膨胀,其重量增至原来的589倍。在自然生境中,粘液物质将沙粒粘附于瘦果的周围,使瘦果的重量发生变化。瘦果能长时间在水上漂浮,粘液物质有助于种子的萌发和苗的发育。白沙蒿产生三种不同颜色的瘦果,其种子具有不同的萌发速率但最终达到相同的萌发率。研究表明瘦果的粘液物质对白沙蒿种子的传播与萌发具有重要的生态意义。     

嗜卷书虱实验种群生命表的研究

在不同温度和湿度条件下对嗜卷书虱进行饲养,分别组建春实验种群特定年龄和特定时间生命表,并应用Morris模式及SWeibull频数分布以探讨温、湿度与嗜卷书虱种群数量变动的关系。结果表明,温、湿度对存活率的作用是影响该实验种群趋势指数（I）值最重要的因子,在适宜温、湿度条件下,种群存活曲线属DeeveyⅠ型,而在不太适宜条件下则属DeeveyⅢ型,理论上30.63℃时周限增长率（λ）最大,达1.0628倍／天,该虫发育和繁殖的最适温区为28-30℃,最适相对湿度在80％左右。     

绢蒿属8种植物果实微形态特征及其分类学意义

为寻找绢蒿属系统学的新证据,应用解剖镜和扫描电镜对我国8种绢蒿属植物的果实微形态特征进行了比较观察。结果表明,绢蒿属8种植物果实形状相似性较高,呈倒卵形或长倒卵形,直或稍弯曲;果脐圆形,常偏向一侧;顶端中央均可见花柱残留物,边缘具衣领状环;果实表面纹饰为搓板状和不规则皱褶纹饰。这些果实微形态特征中,果实的表面纹饰具有一定的差异,特别是次级结构,可作为绢蒿属植物区分种的参考性状之一。     

Biochemical and physiological studies of certain ticks (Ixodoidea): effects of relative humidity and starvation on the water balance and behavior of adult Argas (Persicargas) arboreus (Argasidae).

The effects of high (96%) and low (0%) relative humidities (RH) and starvation on the total body weight, water content, dry weight content, and humidity responses of unfed adult Argas (Persicargas) arboreus (Argasidae) were determined each 15 days for a period of 105 days. High RH caused an increase of 6.7% in females and 7.2% in males of total body weight after 15 days followed by very slow decrease reaching 4.5% in females and 5.4% in males of initial body weight after 105 days. Low RH caused continuous decrease to 46.2% in females and 53.7% in males of the initial body weight after 105 days. After 105-day starvation at 96% RH, the initial value of the water content increased by 3% in females and 5% in males; at 0% RH this value decreased by 52% in females and 59% in males. The initial value of the dry weight content decreased by 23% in females and 26% in males at 96% RH and by 33% in females and 43% in males at 0% RH. Newly molted adults were hygronegative and at 96% RH remained so. At 0% RH, the hygronegative reaction gradually decreased and changed to hygropositive after 60 days in females and 90 days in males. Survival of 80 control ticks after 105 days was 96% at 96% RH and 54% at 0% RH.     

种皮和环境温度对橡胶树种子萌发的影响

在人工气候箱控制的条件下,研究了种皮和环境温度对橡胶树(Hevea brasiliensis)种子萌发的影响.结果表明,种皮对橡胶树种子的吸水和萌发具有明显的机械限制作用;去除种皮后种子萌发速率加快,萌发指数增大,但萌发率从83.8%下降到47.8%,幼苗活力指数从332.3下降到187.9.15℃以下的温度明显推迟种子萌发,且萌发率下降.去除种皮后的种仁萌发率、萌发指数和幼苗活力指数均随着温度的升高而增大;有种皮种子的萌发率、萌发指数和幼苗活力指数分别在20℃(94.7%)、30℃(1.86)和25℃(374.4)时最大,而萌发速率系数随着温度的升高先增大后减小.在橡胶树栽培和胶园建设中,可利用种皮对种仁水分散失的限制作用以及对低温的不敏感性,有效延长橡胶树种子的贮藏时间,提高萌发率和籽苗质量.     

GC-MS分析伊犁绢蒿挥发油化学成分

利用水蒸气蒸馏法提取伊犁绢蒿挥发油,出油率为0．25％。采用色谱-质谱-计算机联用技术,从检出的30个成分中鉴定出28个,所鉴定成分占挥发油色谱总峰面积的98．66％。其主要化学成分为α-苎酮(78．74％)、樟脑(6．17％)、桧烯醇乙酸酯(1．94％)、β-苎酮(1．40％)、乙酸乙酯(1．14％)等,占总挥发油成分的89．46％。     

Effect of relative humidity of hot air on the heat resistance of Bacillus cereus spores

The heat resistance to hot air of spores of Bacillus cereus (ATCC 14579) attached to carriers of stainless steel or silicone rubber was investigated in a range from 1% to 100% relative humidity (RH). Apart from an initial stage, linear survivor curves were obtained for all relative humidities. Neither the attachment itself nor the material of the carrier had an influence on the resistance. A distinct maximum of heat resistance was found at 40% RH. At 122°C the rate constants at 40% RH were five orders of magnitude smaller than at 100% RH and two orders of magnitude smaller than at 1% RH. At relative humidities of more than 40% the rate constants were strongly temperature dependent, whereas at lower relative humidities they were less temperature dependent. No significant influence of the relative humidity on the Arrhenius activation energy was found within each humidity range. The mean values were 295 kJ mol^-1 for relative humidities of 60% to 100% RH and 165 kJ mol^-1 for 1% to 20% RH. The occurrence of a maximum is ascribed to the existence of two inactivation mechanisms, the first is retarded and the second is accelerated by a reduction of relative humidity. It is assumed that the first mechanism is a protein denaturation. The second mechanism may be an oxidative process.     

Water balance and humidity requirements of house dust mites

The house dust mites,Dermatophagoides farinae, D. pteronyssinus andEuroglyphus maynei, are prevalent in homes in humid geographical areas throughout the world. These mites thrive in humid environments in human dwellings where there is no liquid water to drink. However, their bodies contain 70–75% water by weight, which must be maintained in order to reproduce. Their primary source of water is water vapor which is actively extracted from unsaturated air. At relative humidities above 65–70%, adequate amounts of water can be extracted from unsaturated air to compensate for that lost by all avenues. Active uptake is associated with ingestion of a hyperosmotic solution which is secreted by the supracoxal glands. Active mites do not survive longer than 6–11 days at RHs 50%. They survive extended dry periods by forming a desiccation-resistant protonymphal stage which can survive for months at RHs below the critical humidity for active stages. Feeding rate and allergen production is directly influenced by RH. Mites feed, multiply, and produce more fecal matter at higher RHs than at lower ones.     

Water uptake in germinating pecan (Carya illinoinensis) seed

• Water uptake is the fundamental and essential requirement for seed germination. Pecan seed has a hard woody endocarp that plays an important role during water uptake.
• To explore water uptake during germination, the spatiotemporal pattern of water and effect of the endocarp were analysed using high-field MRI, dye-tracing, wax blocking and SEM of water uptake.
• Isolated seeds completed water uptake in 8 h while whole seeds required 6 days, hence, cracking the endocarp plays an important role. The hilum is the channel through which water enters the seed, while the remainder of the seed coat consist of cells covered with a waxy layer that act as a barrier to water absorption. The region with the highest water content in pecan seed is the edge of the U-shaped region, and water can progressively diffuse from this U-shaped region into the whole kernel.
• We report a new water absorption stage between phase II and phase III of the triphasic model of water uptake of pecan seeds. Cracking the endocarp changed water distribution in pecan seeds, which may trigger further water absorption and radicle elongation.

     

贵州麻若平台泥炭藓沼泽中泥炭藓持水特性及其与土壤营养元素关系研究

泥炭藓属（Sphagnum）植物的持水特性在泥炭湿地形成过程中起着重要作用,研究其与土壤营养元素之间的关系有助于地区湿地保护和退化湿地的修复。以贵州麻若平台分布的泥炭沼泽为对象,采用方差分析、相关性分析和冗余分析等方法对沼泽内泥炭藓的生物量、蓄水量、吸水率和土壤营养元素含量等进行研究。结果显示,该区域泥炭藓物种组成主要包括狭叶泥炭藓（Sphagnum cuspidatum Ehrh.）、多纹泥炭藓（Sphagnum multifibrosum X.J.Li&M.Zang）和卵叶泥炭藓（Sphagnum ovatum Hampe.）3种,狭叶泥炭藓为优势种,占泥炭藓总盖度的87.2%。沼泽中泥炭藓的生物量为（0.62 ±0.01）kg/m²,自然蓄水量为（9.42 ±0.45）kg/m²,饱和吸水率达1827.41%±34.56%,说明泥炭藓具有很强的持水能力。RDA分析表明,泥炭藓的生物量、饱和吸水量和饱和吸水率主要受沼泽土壤总钾、总磷、有效磷、有效氮、有效钾的影响,泥炭藓的鲜重、自然蓄水量和自然吸水率受土壤pH和水位的影响较大。泥炭藓的生物量、饱和蓄水量、饱和吸水率与土壤总钾含量呈正相关,与土壤总磷、有效磷、总钾、有效氮、总氮、有机质含量呈负相关,说明土壤总磷、有效磷、有效钾、有效氮、总氮、有机质对沼泽中泥炭藓的持水能力具有抑制作用。