Hygroreceptor identification and response characteristics in the stick insectCarausius morosus

Summary Simultaneous recordings were made from 3 sensory units in an easily identifiable sensillum on the 12th antennal segment ofCarausius morosus. Impulse frequency (F) of one unit rose sharply when either the temperature (T) or the partial pressure of water vapor (Pw) was suddenly lowered. F of another rose sharply either when T was suddenly lowered or Pw was raised. F of the third was hardly affected by sudden changes in T but rose abruptly when Pw fell (Fig. 1). The reactions of the first may be explained by enthalpic cooling and is considered a cold cell. Those of the second may be attributed to changes in relative humidity (Hr) and is thus termed a moist cell. The third is taken to be the latter's antagonist, a dry cell.A 90%-probability that a single moist cell of average differential sensitivity will correctly discriminate between two humidity levels is not reached until the difference between the two is 38% Hr. The dry cell requires a difference of only 7.5% (Table 1). The basis for discrimination is a single presentation of each level.The power to discriminate Hr steps is better in both cell types. For a single moist cell of average differential sensitivity the difference required between the steps for a 90%-probability of correct discrimination is only 6.3% Hr; for the dry cell, 3.5% Hr. Basis for discrimination: a single presentation of each step. Step range: 5% to 55% Hr.Abbreviations F impulse frequency in impulses per second (imp/s) - Hr orHR relative humidity in % - Ps saturation pressure of water vapor in torr - Pw partial pressure of water vapor in torr - r correlation coefficient - T temperature in °C Dedicated to Prof. Dr. F. Schaller on the occasion of his 65th birthday     

Response characteristics of a cold receptor in the stick insectCarausius morosus

Summary The cold cell in the easily identified mound-shaped sensillum on the 12th segment ofCarausius morosus' antennae responds to downward temperature (T) steps from about 15 °C with a sharp rise in impulse frequency (F). Responses to similar steps from higher initial temperatures are smaller (Figs. 1, 3, 4). As initialT increases from 16 °C to 31 °C, differential sensitivity to downward steps falls off by a factor of 27: to yield an average increase inF of 1 imp/s, steps down from 31 °C must increase by 1.7 °C; steps down from 16 °C, by only 0.06 °C (Fig. 5). Resolving power forT-steps at mid-range initial temperatures is about 0.7 °C, i.e. the probability that a single cold cell at average differential sensitivity will correctly discriminate between twoT steps 0.7 °C apart is 90% when the cell is presented with each step just once.The same cold cell also displays a clear dependence on steadyt between 14 °C and 24 °C (Figs. 7, 8). The static discharge rate of a single cell at average differential sensitivity has a resolving power of about 0.9 °C for steadyT. — The static discharge is not affected by the amount of water vapor in the stimulating air (Fig. 9).Abbreviations F impulse frequency in impulses per second (imp/s) - Pw partial pressure of water vapor in torr - r correlation coefficient - T temperature in °C - T step change inT     

Warm and cold receptors of two sensilla on the foreleg tarsi of the tropical bont tickAmblyomma variegatum

Summary A pair of antagonistic thermal receptors has been identified in each of two long, tapering, poreless setae located distally on the foreleg tarsi of the tropicalbont tick,Amblyomma variegatum (Fig. 1). One, the cold receptor, responds to a rapiddrop in temperature (T) with a sudden rise in impulse frequency (F). The other, a warm receptor, responds to a rapidrise inT with a sudden rise inF (Figs. 2, 4). These two units are unusual for sharing their seta with two other units which are mechanosensitive. The four are distinguishable on the basis of spike amplitude and form (Fig. 3). Hence the thermal sensitivity displayed is hardly attributable to the pair of cells with tubular bodies but rather to the two extending up into the seta (for structure, see Hess and Vlimant 1982, 1983 a).As based on the first 100 ms of the response, differential sensitivity to rapidT change is –16.1± 10.4 (imp/s)/°C for cold units, 17.6 ± 9.5 (imp/s)/°C for warm (Table 1). As progressively larger segments of the spike train are employed to determineF, differential sensitivity of the warm unit drops off much more quickly than that of the cold (Table 2, Figs. 5, 6). In the cold unit resolving power (the difference in rapid temperature change discriminable with 90% probability by a pair of responses of a single unit at average sensitivity) continues to increase as the segment of the spike train determiningF is lengthened (from 0.58 °C for 100 ms segments to 0.41 °C for 1,100 ms segments). Resolving power of the warm unit, on the other hand, tends to decrease as longer segments are employed (from 0.52 °C for the first 100 ms to 0.80 °C for the first 1,100 ms). These relationships provoke the question of whether the spike trains may be evaluated in the CNS in different fashions.Abbreviations b slope of characteristic curve - F impulse frequency in impulses per second (imp/s) - n number of individuals examined - Pw partial pressure of water vapor in Torr - r correlation coefficient - s SD of responses from characteristic curve - SD standard deviation - T temperature in °C - T difference inT Refers to difference between initial and end temperature in abruptT changes     

Antennal warm and cold receptors of the cave beetle,Speophyes lucidulus delar., in sensilla with a lamellated dendrite

Summary Electrophysiological examination of the 2 black-hair sensilla on the antennae of both larval stages of the cave beetle,Speophyes lucidulus, has revealed in each a pair of antagonistic thermal receptors (Fig. 1). Each sensillum was known to house the dendrites of 2 sensory cells which are associated with the extensively lamellated dendrite of a third (Corbière-Tichané 1971). One unit, a cold receptor, responds to temperature drops of 1 to 7 °C from initial temperatures between 9 and 14 °C with impulse frequencies up to 200 imp/s (Figs. 3, 4). Its antagonist, encountered less than 10% as often, is a warm receptor which responds with similar impulse frequencies to rapid rises in temperature from the same 9–14 °C (Figs. 3, 6). As indicated by the average gain of 24 imp/s for an increase of 1 °C in temperature drop, the cold unit appears almost twice as sensitive to sudden temperature change as the warm unit (14 (imp/s) °C). Examination of response scatter indicates that the average cold unit should on the basis of a single pair of responses be able to designate the greater of two temperature drops between 1 and 7 °C with 90% probability when they differ by 0.7 °C (Fig. 5). Though not yet definitive, evidence is accumulating that the third physiological unit is a dry air receptor.Abbreviations F impulse frequency in imp/s - Fc F as calculated - Fm F as measured - imp impulses - Pw partial pressure of water vapor in air - Ps saturation pressure of water vapor - r regression coefficient - T temperature - difference in Supported by the Deutsche Forschungsgemeinschaft, Sonder forschungsbereich 4, Projekt DThe authors wish to express their indebtedness to Dr. Renate Beinhauer, Faculty of Natural Sciences I — Mathematics, Univ. of Regensburg, for her help in applying statistical methods in determining resolving power.     

Humidity-invoked upwind orientation of shore insects (Bambidion obtusidens, coleoptera: Carabidae)

Because insects cannot rely solely on kinetic responses to locate upwind humidity resources, an alternative mechanism involving the perception of windborne humidity fluctuations was investigated. In a wind tunnel, upwind responses of adult shore insects (Bembidion obtusidens Fall, Carabidae, Coleoptera) were invoked by pulsed (1.25-Hz) increases (1.7%) of relative humidity at ambient relative humidities of 32, 42, 52, and 62% but not at 72 and 86%. Conversely, upwind responses to pulsed decreases (1.8%) occurred at 65, 72, and 86% but not at 32, 42, and 52% ambient relative humidities. These results suggest that perception by moist-air and dry-air hygroreceptors of turbulence-induced pulses of moist air or of dry air in their habitat trigger positive anemotactic orientation of these insects to upwind humidity resources.     

Thermoregulation by rhesus monkeys at different absolute humidities

The effect of relative humidity on thermoregulation has been well examined. Because the same relative humidity represents very different absolute humidities at different ambient temperatures, the present study was designed to examine the interaction of temperature and absolute humidity on the thermal balance of rhesus monkeys, Macaca mulatta. Thermal balance was examined in six unacclimated, unanesthetized, female rhesus monkeys at ambient temperatures of 25, 30, 35, and 40 °C and absolute humidities of 6, 22, and 40 torr. Monkeys were capable of achieving thermal balance under all conditions except at 40 °C with 40 torr absolute humidity, where experiments were stopped after rectal temperature exceeded 40.5 °C. At 40 °C, monkeys increased evaporative heat loss through both respiration and sweating; the slope of the relationship between evaporative heat loss and core temperature was attenuated by increases in absolute humidity. In contrast, absolute humidity had no direct effect on metabolic rate. The rise in body temperature under the conditions of high heat/high humidity was therefore most attributable to humidity-dependent decreases in evaporative heat loss.Abbreviations E_tot total evaporative heat loss - HR heart rate - K thermal conductance - M metabolic rate - RQ respiratory quotient - T_c core temperature - T_sk mean skin temperature - VCO₂ carbon dioxide production - VO₂ oxygen consumptionCommunicated by G. Heldmaier     

Diurnal variation in photochemical dynamics and surface reflectance of the desiccation-tolerant moss,Tortula ruralis

Most desiccation-tolerant plants alter shoot structure during drying, making it possible to use changes in surface reflectance as a proxy measure of plant water status. Diurnal courses of surface reflectance (albedo) and chlorophyll fluorescence parameters of the ectohydric moss, Tortula ruralis (Hedw.) Gaertn, were measured to assess the coordination between anatomical and physiological features under field conditions. Albedo showed a sigmoidal relationship with relative humidity and the deviation of moss mat temperature from dew point. Maximum photosynthetic quantum yield (F _v/F _m) also displayed a sigmoidal relationship pooled across three days differing in light, temperature, and relative humidity. Depending on the light conditions and rapidity of drying during the morning, there were distinct differences in the ability of T. ruralis to establish thermal dissipation of excess light energy (NPQ) across a range of light levels following rehydration through the day. These findings suggest that there is a coordinated suite of architectural and physiological characteristics maintaining the photosynthetic integrity of these plants in highly variable arid and semi-arid environments.     

Immunohistochemical comparison of whisker pad cutaneous innervation in Swiss Webster and hairless mice

To establish the mouse mutant, hairless (Hr), as a useful model for future analyses of target–ending interactions, we assessed the cutaneous innervation in the whisker pad after loss of primary hair targets. Postnatal (P) development of fur in Hr begins similarly to that of “normal” Swiss Webster (SW) mice. Around P10, hairs are shed and the follicles rendered permanently incompetent. Hair loss progresses rostrocaudally until the entire skin is denuded. Substantial alterations in the distribution and density of sensory and autonomic endings in the mystacial pad vibrissal and intervibrissal fur innervation were discovered. Pilo-neural complexes innervating fur hairs were dismantled in Hr. Epidermal innervation in SW was rich; only a few endings expressed growth-associated protein-43?kdal (GAP), suggesting limited changes in axonal elongation. Innervation in Hr formed a dense layer passing upward through the thickened epidermis, with substantial increases among all types of endings. Vibrissal follicle–sinus complexes were also hyperinnervated. Endings in Hr vibrissae and fur were strongly GAP-positive, suggesting reorganization of innervation. Dermal and vascular autonomic innervation in both strains co-localized tyrosine hydroxylase and neuropeptide Y, but only in Hr did neuropeptide Y co-localize calcitonin gene-related peptide (CGRP) and express GAP immunolabeling. Stereological quantitation of trigeminal ganglia revealed no differences in neuron number between Hr and SW, although there were small increases in cell volume in Hr trigeminal ganglion cells. These results suggested that a form of collateral sprouting was active in Hr mystacial pads, not in response to local injury, but as a result of loss of primary target tissues.     

The functional analysis of Type I postplasmic/PEM mRNAs in embryos of the ascidian Halocynthia roretzi

Maternal factors, such as a muscle determinant macho-1 mRNA that is localized to the posterior-vegetal cortex (PVC) of fertilized ascidian eggs, are crucial for embryonic axis formation and cell fate specification. Maternal mRNAs that show an identical posterior localization pattern to that of macho-1 in eggs and embryos are called Type I postplasmic/PEM mRNAs. We investigated the functions of five of the nine Type I mRNAs so far known in Halocynthia roretzi: Hr-Wnt-5, Hr-GLUT, Hr-PEM3, Hr-PEN1, and Hr-PEN2. Suppression of their functions with specific antisense morpholino oligonucleotides (MOs) had effects on the formation of various tissues: Hr-Wnt-5 on notochord, muscle, and mesenchyme, although zygotic function of Hr-Wnt-5 is responsible for notochord formation; Hr-GLUT on notochord, mesenchyme, and endoderm; and Hr-PEN2 on muscle, mesenchyme, and endoderm. On the other hand, Hr-PEM3 and Hr-PEN1 MOs seemed to have no effect. We conclude that the functions of at least some localized maternal Type I postplasmic/PEM mRNAs are necessary for early embryonic patterning in ascidians.     

Incubation water loss,shell conductance,and pore dimensions in Adelie Penguin eggs

Summary In order to understand water loss regulation of bird eggs in very dry climates eggs of the Adelie Penguin were studied at Cape Bird, Ross Island, Antarctica. During incubation 125 g Adelie Penguin eggs lose about 447 mg of water per day, resulting in an overall estimated loss, during 35 days of incubation, of 13% of their initial mass. The eggshell conductance of 13.1 mg H₂O·day^-1·torr^-1 occurs from 9100 pores with an effective radius and pore length of 11 m and 600 m, respectively. In this study the water vapor pressure of the egg was 44 torr, estimated from the egg temperature of 35.9°C. Ambient temperature was-4°C, with an absolute humidity of less than 3 torr, resulting in an overall vapor pressure difference between the egg and the environment of 41 torr. This difference was divided between the egg and nest conductance in a ratio of ca. 1:5.     

Effects of relative humidity on development, fecundity and survival of three storage mites

The developmental rate of immature stages and the reproduction of adults of Tyrophagus putrescentiae (Schrank), T. neiswanderi Johnston and Bruce and Acarus farris (Oudemans) were examined at 70, 80 and 90% r.h. and a constant temperature of 25°C. At 70% r.h., T. putrescentiae and A. farris immature stages failed to reach the protonymph stage as 100% of the larvae died, whereas T. neiswanderi was able to complete development. The developmental time of all immature stages for the three species was significantly increased as relative humidity was reduced. The mobile stages were particularly susceptible, as the time needed to complete their development at lower relative humidities suffered greater increases than the egg stage. At 70% r.h., T. putrescentiae and A. farris were not able to lay eggs and only 24% of T. neiswanderi pairs were fertile. The reproductive parameters of the three species at the relative humidities at which they were able to lay eggs showed significant differences, except for the percentage of fertile mating at 80 and 90% r.h. As relative humidity increased, preoviposition period was reduced and fecundity and daily fecundity was increased, whereas the oviposition period showed different patterns for the three species. The intrinsic rate of increase (r _m ) of T. neiswanderi at 70% r.h. was negative indicating that, at these conditions, mite populations of this species will diminish until they disappear. As relative humidity increased from 80 to 90% r.h. this parameter was almost twofold for both Tyrophagus species. The r _m obtained for A. farris at 90% r.h. was similar to that of T. neiswanderi at the same humidity while at 80% r.h. it was very small so that the population doubling time was more than 84 days. The influence of relative humidity on biology of these mites and its practical application as control measure are discussed.     

Structure of the filamentous bacteriophage,Pf3, by X-ray fiber diffraction

Fiber diffraction data have been obtained for the filamentous bacteriophage Pf3. The virus crystallizes on a hexagonal net with lattice constants a = b = 5.61 nm and c = 7.50 nm at 0% relative humidity and a = 6 = 6.20 nm and c = 7.99 nm at 98% relative humidity. The X-ray diffraction pattern resembles those of two other bacteriophages, Pf 1 and Xf, and therefore belongs to class II. The data are consistent with a 27₅ helix symmetry with an axial rise of 0.277 (dry) to 0.296 (wet) nm.     

Hygro- and thermoreceptive tarsal organ in the spider Cupiennius salei

Extracellular recordings were made from moist cells, dry cells and warm cells in the tip pore sensilla of the spider tarsal organ. Stimulation consisted of a rapid shift from an adapting air stream to another one at different levels of partial pressure of water vapor or of temperature. The moist and the dry cells respond antagonistically to sudden changes in humidity. Both hygroreceptors are unusual in being excited in a synergistic manner by pungent vapors of very volatile, polar substances. Presumably, the hygrosensitivity is superimposed on basically chemosensitive receptors. A moist cell at average differential sensitivity is able to discriminate two successive upward steps in humidity when they differ by 11% relative humidity. For a single dry cell, the difference required for a correct discrimination between two downward humidity steps is 10% relative humidity. The moist and the dry cells are unique in that they occur in combination with warm cells. A single warm cell at average differential sensitivity is able to resolve differences in warming steps down to 0.4°C.Abbreviations HR relative humidity - T temperature     

Effect of different eriophyid and tetranychid mango mite species on development,longevity, fecundity and predation of Typhlodromus mangiferus Zaher and El-Brolossy (Acari: Phytoseiidae)

Effects on development, longevity, fecundity and predation of the predatory phytoseiid mite Typhlodromus mangiferus Zaher and El-Brolossy were studied in the laboratory at different temperatures and relative humidities using four prey mite species: the motile stages of the eriophyid mango bud mite Aceria mangiferae Sayed, the eriophyid leaf coating and webbing mite Cisaberoptus kenyae Keifer, the eriophyid mango rust mite Metaculus mangiferae (Attiah) and nymphs of the tetranychid mango red mite Oligonychus mangiferus (Rahman and Sabra). The increase of different temperatures and decrease of relative humidities from 25°C and 60% to 30°C and 55% and 35°C and 50% shortened development and increased reproduction and prey consumption. The developmental durations were almost similar when the predator was fed on eriophyids compared to that on tetranychid. The maximum reproduction (2.70, 2.08, 1.97 and 1.66 eggs/ ♀ /day) was recorded at the highest temperature and the lowest relative humidity, while the minimum reproduction (1.7, 1.54, 1.53, and 1.06 eggs/ ♀ /day) was noted at the lowest temperature and highest relative humidity with all mango prey species. Life table parameters indicated that feeding of T. mangiferus on A. mangiferae led to the highest reproduction rate (rm = 0.204 and 0.139 females/female/day), while feeding on O. mangiferus gave the lowest reproduction rate (rm = 0.137 and 0.116) at 35°C and 50% relative humidity and 25°C and 60% relative humidity, respectively. T. mangiferus seems to be a voracious predator of both mango eriophyid and tetranychid mites. The adult female daily consumed about 127 A. mangiferae, 97 C. kenyae, 86 M. mangiferae, and 18 O. mangiferus at 35°C and 50% relative humidity, while it devoured only 99.81, 86, 81, and 15 individuals, respectively at 25°C and 60% relative humidity. The present study revealed that each injurious mite is thought to be profitable prey species to T. mangiferus as a facultative predator.     

Desiccation Tolerance and Global Change: Implications for Tropical Bryophytes in Lowland Forests

Global change puts an increasing pressure on tropical forests and their inherent diversity by the risk of longer droughts and drier microclimatic conditions within the forest. How organisms will respond is uncertain, especially for organisms highly depending on their microclimatic environment such as bryophytes. An adequate tolerance to desiccation is important to face these changes, however, little is known for tropical bryophytes. We investigated for the first time the desiccation tolerance of epiphytic bryophytes from contrasting microsites at the tropical lowland forest in French Guiana. Using chlorophyll‐fluorescence (F_v/F_m) as an indicator of recovery, we tested: (1) desiccation tolerance for short (3 d) and long (9 d) desiccation events; (2) different desiccation intensities; and (3) recovery by rehydration with water vapor. Species from the canopy were well adapted to desiccation events. Thirteen of 18 species maintained more than 75 percent of their photosynthetic capacity after recovery at the strongest desiccation treatment of 9 d at 43 percent relative humidity (RH). In contrast, species from the understory were sensitive and withstood desiccation only at humid conditions of 75 percent RH and higher. The photosystem of the studied bryophytes was reactivated efficiently in equilibration with water vapor only—a yet neglected phenomenon in bryology. A novel introduced desiccation tolerance index allows global comparison of desiccation tolerances and highlights the sensitivity of understory species. Our results suggest that decreasing humidity caused by climate change and forest degradation could be a concerning threat for understory species.     

The role of stomata in sensitivity of Betula papyrifera seedlings to SO2 at different humidities

Summary Stomata of paper birch (Betula papyrifera Marsh.) seedlings were more open at high humidity than at low humidity and responded rapidly to changes in vapor pressure deficit. SO₂ at 0.2 or 0.8 l l^-1 caused partial stomatal closure. Seedlings fumigated with SO₂ at 0.2 or 0.5 l l^-1 for 30 h or 0.2 l l^-1 for 75 h took up more SO₂ at high than at low humidity. Differences in pollutant uptake could be explained by stomatal conductance with no need to invoke changes in mesophyll conductance. Betula seedlings were more sensitive to SO₂ when fumigated at high humidity, as manifested in more leaf necrosis, increased leaf abscission, and greater growth inhibition compared to seedlings fumigated at low humidity. Amount of injury to leaves increased with rate of SO₂ uptake, and inhibition of root growth increased with total SO₂ uptake.Abbreviations RH relative humidity - VPD vapor pressure deficit - RGR mean relative growth rate - PPFD photosynthetic photon flux density (400–700 nm) - LDC leaf diffusive conductance - water potential Research supported by the College of Agricultural and Life Sciences, University of Wisconsin-Madison     

陕西中部黄土高原地区空气花粉组成及其与气候因子的关系——以洛川县下黑木沟村为例

空气花粉研究是现代孢粉学、植被变迁与预测的重要内容之一.陕西省黄土高原地区洛川县2007-2009连续2a的空气花粉分析表明:空气花粉组成与区域植被分布特征和植物花期一致.与2007—2008年相比,2008-2009年的花粉总通量及蒿属花粉通量明显增加,但木本植物花粉通量降低,这主要与2008-2009年降水明显偏少密切相关.2007-2008年降雨量高于500 mm,花粉组合中乔木花粉百分比高于30％,表现出森林植被特点;2008-2009年降雨量少于450 mm,花粉组合中草本花粉高于80％,乔木花粉低于10％,更多表现出草原植被特点.但从植被观测来看并没有明显的变化,表明花粉组合较植被对气候变化更为敏感.主要花粉类型与气候因子的相关分析表明:气候因子影响空气花粉的组成及数量.栎属、松属、蔷薇科花粉数量主要受春季温度影响,温度越高花粉数量越多;其他季节花粉数量主要受相对湿度影响,湿度越低,花粉数量越大.榆属花粉数量主要与冬季温度有关,温度越高,花粉数量越高.杨属只受春季温度影响,春季温度越低,花粉数量越多.胡颓子科花粉含量主要受春季相对湿度、风速影响,相对湿度越低,风速越大,花粉数量越多.绝大多数草本花粉数量均主要受春、冬季相对湿度及风速影响,相对湿度越低,风速越大,花粉数量越高;此外,禾本科花粉数量还受春季温度影响,温度越高,花粉数量越多;菊科花粉数量在夏秋季节还受温度、湿度和风速的共同影响,温度越低,湿度越低,风速越大,花粉数量越多.这些结果表明,黄土高原中部地区的空气花粉特征能反映区域植被组成,且对气候变化非常敏感,对认识和预测当地气候变化与植被动态等具有重要意义.     

A novel mutation in Hr causes abnormal hair follicle morphogenesis in hairpoor mouse, an animal model for Marie Unna Hereditary Hypotrichosis

Hairpoor mice (Hr ^Hp ) were derived through N-ethyl-N-nitrosourea (ENU) mutagenesis. These mice display sparse and short hair in the Hr ^Hp /+ heterozygous state and complete baldness in the Hr ^Hp /Hr ^Hp homozygous state. This phenotype was irreversible and was inherited in an autosomal semidominant manner. Hair follicles (HFs) of Hr ^Hp /+ mice underwent normal cycling and appeared normal, although smaller than those of the wild-type mice. In contrast, HFs of Hr ^Hp /Hr ^Hp mice became cyst-like structures by postnatal day (P) 21. The number and length of vibrissae decreased in a dose-dependent manner as the number of mutant alleles increased. A positional candidate gene approach was used to identify the gene responsible for the hairpoor phenotype. Genetic linkage analysis determined that the hairpoor locus is 2 cm from D14Mit34 on chromosome 14. Sequence analysis of the exons of the candidate gene hairless revealed a T-to-A transversion mutation at nucleotide position 403 (exon 2), presumably resulting in abolishment of an upstream open reading frame (uORF). In addition, we also found that the near-naked mouse (Hr ^N ), a spontaneously arising mutant, harbors a A402G transition in its genome. Both mutations were in the uATG codon of the second uORF in the 5′ UTR and corresponded to the mutations identified in Marie Unna Hereditary Hypotrichosis (MUHH) patients. In the present study we describe the phenotype, histological morphology, and molecular etiology of an animal model of MUHH, the hairpoor mouse. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. I. C. Baek and J. K. Kim contributed equally to this work.     

Chlorophyll Fluorescence of Lichens Containing Green and Blue-Green Algae During Hydration by Water Vapor Uptake and by Addition of Liquid Water*

The fluorescence yield at room temperature of the lichens Ramalina maciformis and Peltigera rufescens, containing either green or blue-green algae (Cyanobacteria) as phycobionts, has been investigated during rehydration of the dry lichens by water vapor uptake or by wetting with liquid water. In the dry state the fluorescence yield with all reaction centers open, F_o, was low and no variable fluorescence could be induced with both species. Whereas R. maciformis, containing green algae, regained normal fluorescence behavior during water vapor uptake, the photosynthetic apparatus of the blue-green algae-containing P. rufescens stayed inhibited and could be reactivated only by addition of liquid water. During stepwise rehydration at increasing air humidities, a pattern was established for the recovery of the different fluorescence parameters in R. maciformis. At a dry-weight related water content between 30 and 40%, F_o rose sharply. Maximal variable fluorescence yield expressed as (F_v)_m/F_o, strongly increased in the same range of water content and remained constant above a water content of 50%. Non-photochemical fluorescence quenching, q_NP, determined at the end of a period of actinic illumination, decreased with increasing water vapor uptake. While spraying the lichen with liquid water did not induce a further decrease of q_NP, slow dehydration at lowered air humidity led to a minimal value of q_NP at a water content of 65 % indicating optimal photosynthetic rate under these conditions. These results extend the conclusions drawn from earlier gas exchange experiments that blue-green algae-containing lichens are unable to reactivate photosynthesis by water vapor uptake. During a re- and de-hydration cycle, no hysteresis in the hydration dependence of the fluorescence parameters was found. From this and the presence of a stable and low F_o value at prolonged incubation in nearly water vapor saturated air, we conclude that the reactivation of photosynthesis in blue-green algae-containing lichens is not prevented through high diffusion resistances for water.     

Embryogenesis in 100% O2 at reduced pressure

Fertile chicken eggs were incubated in an altitude chamber in a near 100% O₂ atmosphere at 225 torr. Both N₂ and CO₂ were kept under 0.5%. Temperature was a standard 37.5° but a high relative humidity of 90% was required to prevent dehydration. In ten trials involving 382 eggs, hatchability averaged 21% of controls and weight of chicks was 11% less than controls, but embryo mortality was distributed similarly. Low pressureper se and small differences in O₂ tension may have affected the results, but similarities to incubation in 21% O₂-79% He call attention to absence of nitrogen as a possible explanation.Supported in part by NASA grant NGR-008-004.