Phenotypic plasticity rather than locally adapted ecotypes allows the invasive alligator weed to colonize a wide range of habitats

Both phenotypic plasticity and locally adapted ecotypes may contribute to the success of invasive species in a wide range of habitats. Here, we conducted common garden experiments and molecular marker analysis to test the two alternative hypotheses in invasive alligator weed (Alternanthera philoxeroides), which colonizes both aquatic and terrestrial habitats. Ninety individuals from three pairs of aquatic versus terrestrial populations across southern China were analyzed, using inter simple sequence repeat (ISSR) marker, to examine population differentiation in neutral loci. Two common gardens simulating aquatic and terrestrial habitats were set up to examine population differentiation in quantitative traits. We found no evidence of population differentiation in both neutral loci and quantitative traits. Most individuals shared the same ISSR genotype. Meanwhile, plants from different habitats showed similar reaction norms across the two common gardens. In particular, plants allocated much more biomass to the belowground roots in the terrestrial environment, where alligator weed may lose part or all of the aboveground shoots because of periodical or accidental disturbances, than those in the aquatic environment. The combined evidence from molecular marker analysis and common garden experiments support the plasticity hypothesis rather than the ecotype hypothesis in explaining the adaptation of alligator weed in a wide range of habitats.     

Genetic diversity of alligator weed ecotypes is not the reason for their different responses to biological control

Biological control of alligator weed Alternanthera philoxeroides (Mart.) Griseb. using Agasicles hygrophila, a Chrysomelid beetle, has been successful in limiting growth in water, but not on land. In order to understand a possible genetic basis of this difference, technique using inter-simple sequence repeats (ISSR) markers was applied to analyse genetic diversity of this invasive weed. No genetic variation was detected not only within or between populations growing in the same habitats, but also between land- and water-grown populations. Thus we consider that the genetic variation is not the baseline factor resulting in the biological control difference in China. The differential success of pupation by the beetle may be related to the phenotypic plasticity of the plant stem diameter, rather than to genotypic factors.     

Temperature dependence of UV radiation effects in Arctic and temperate isolates of three red macrophytes

The temperature dependence of UV effects was studied for Arctic and temperate isolates of the red macrophytes Palmaria palmata, Coccotylus truncatus and Phycodrys rubens. The effects of daily repeated artificial ultraviolet B and A radiation (UVBR: 280–320?nm, UVAR: 320–400?nm) treatments were examined for all isolates at 6, 12 and 18?°C by measuring growth, optimal quantum yield of PSII (F_v/F_m) and cyclobutane-pyrimidine dimer (CPD) accumulation. Furthermore, possible ecotypic differences in UV sensitivity between Arctic and temperate isolates were evaluated. Large species-specific differences in UV sensitivity were observed for all parameters: the lower subtidal species C. truncatus and P. rubens were highly sensitive to the UV treatments, whereas P. palmata, which predominantly occurs in the upper subtidal zone, was not affected by these treatments. Only minor differences were found between Arctic and temperate isolates, suggesting that no differences in UV sensitivity have evolved in these species. Relative growth rates were temperature-dependent, whereas species-specific UV effects on growth rates were relatively independent of temperature. In contrast, the species-specific decrease in F_v/F_m and its subsequent recovery were temperature-dependent in all species. UV effects on F_v/F_m were lower at 12 and 18?°C compared with 6?°C. In addition, UV effects on F_v/F_m decreased in the course of the experiment at all temperatures, indicating acclimation to the UV treatments. CPDs accumulated during the experiment in both isolates of P. rubens, whereas CPD concentrations remained low for the other two species. CPD accumulation appeared to be independent of temperature. The results suggest that summer temperatures occurring in temperate regions facilitate repair of UV-induced damage and acclimation to UV radiation in these algae compared with Arctic temperatures. Because the differences in UV effects on F_v/F_m, growth and CPD accumulation were relatively small over a broad range of temperatures, it was concluded that the influence of temperature on UV effects is small in these species.     

Rethinking the common garden in invasion research

In common garden experiments, a number of genotypes are raised in a common environment in order to quantify the genetic component of phenotypic variation. Common gardens are thus ideally suited for disentangling how genetic and environmental factors contribute to the success of invasive species in their new non-native range. Although common garden experiments are increasingly employed in the study of invasive species, there has been little discussion about how these experiments should be designed for greatest utility. We argue that this has delayed progress in developing a general theory of invasion biology. We suggest a minimum optimal design (MOD) for common garden studies that target the ecological and evolutionary processes leading to phenotypic differentiation between native and invasive ranges. This involves four elements: (A) multiple, strategically sited garden locations, involving at the very least four gardens (2 in the native range and 2 in the invaded range); (B) careful consideration of the genetic design of the experiment; (C) standardization of experimental protocols across all gardens; and (D) care to ensure the biosafety of the experiment. Our understanding of the evolutionary ecology of biological invasions will be greatly enhanced by common garden studies, if and only if they are designed in a more systematic fashion, incorporating at the very least the MOD suggested here.     

Performance of active Photosystem II centers in photoinhibited pea leaves

Effects of photoinhibition on photosynthesis in pea (Pisum sativum L.) leaves were investigated by studying the relationship between the severity of a photoinhibitory treatment (measured as F_v/F_m) and several photoacoustic and chlorophyll a fluorescence parameters. Because of the observed linear relationship between the decline of F_v/F_m and the potential oxygen evolution rate determined by the photoacoustic method, the parameter F_v/F_m was used as an indicator for the severity of photoinhibition. Our analysis revealed that part of the Photosystem II (PS II) reaction centers is inactive in oxygen evolution and is also less sensitive to photoinhibition. Correcting the parameter q_P (fraction of open PS II reaction centers) for inactive PS II centers unveiled a strong increase of q_P in severely inhibited pea leaves, indicating that the inactivated active centers do no longer contribute to q_P and that photoinhibition has an all or none effect on PS II centers. Analysis of q_E (energy quenching) demonstrated its initial increase possibly associated with dephosphorylation of LHC II. Analysis of q_I (photoinhibition dependent quenching) showed that the half-time of recovery of q_I increases steeply below an F_v/F_m of 0.65. This increase of the relaxation half-time corresponds with a decrease of the electron transport rate J and tentatively indicates that the supply of ATP, needed for the recovery, starts to decrease. The data indicate the necessity of correcting for inactive centers in order to make valuable conclusions about effects of photoinhibition on photosynthetic parameters.     

Growth under UV-B radiation increases tolerance to high-light stress in pea and bean plants

Pea (Pisum sativum L.) and bean (Phaseolus vulgaris L.) plants were exposed to enhanced levels of UV-B radiation in a growth chamber. Leaf discs of UV-B treated and control plants were exposed to high-light (HL) stress (PAR: 1200 mol m^–2 s^–1) to study whether pre-treatment with UV-B affected the photoprotective mechanisms of the plants against photoinhibition. At regular time intervals leaf discs were taken to perform chlorophyll a fluorescence and oxygen evolution measurements to assess damage to the photosystems. Also, after 1 h of HL treatment the concentration of xanthophyll cycle pigments was determined. A significantly slower decline of maximum quantum efficiency of PSII (F _v/F _m), together with a slower decline of oxygen evolution during HL stress was observed in leaf discs of UV-B treated plants compared to controls in both plant species. This indicated an increased tolerance to HL stress in UV-B treated plants. The total pool of xanthophyll cycle pigments was increased in UV-B treated pea plants compared to controls, but in bean no significant differences were found between treatments. However, in bean plants thiol concentrations were significantly enhanced by UV-B treatment, and UV-absorbing compounds increased in both species, indicating a higher antioxidant capacity. An increased leaf thickness, together with increases in antioxidant capacity could have contributed to the higher protection against photoinhibition in UV-B treated plants.     

Chilling and freezing stress in live oaks (Quercus section Virentes): intra- and inter-specific variation in PS II sensitivity corresponds to latitude of origin

Sensitivity to cold and freezing differs between populations within two species of live oaks (Quercus section Virentes Nixon) corresponding to the climates from which they originate. Two populations of Quercus virginiana (originating from North Carolina and north central Florida) and two populations of the sister species, Q. oleoides, (originating from Belize and Costa Rica) were grown under controlled climate regimes simulating tropical and temperate conditions. Three experiments were conducted in order to test for differentiation in cold and freezing tolerance between the two species and between the two populations within each species. In the first experiment, divergences in response to cold were tested for by examining photosystem II (PS II) photosynthetic yield (ΔF/F _m′) and non-photochemical quenching (NPQ) of plants in both growing conditions after short-term exposure to three temperatures (6, 15 and 30°C) under moderate light (400 μmol m⁻² s⁻¹). Without cold acclimation (tropical treatment), the North Carolina population showed the highest photosynthetic yield in response to chilling temperatures (6°C). Both ecotypes of both species showed maximum ΔF/F _m′ and minimum NPQ at their daytime growth temperatures (30°C and 15°C for the tropical and temperate treatments, respectively). Under the temperate treatment where plants were allowed to acclimate to cold, the Q. virginiana populations showed greater NPQ under chilling temperatures than Q. oleoides populations, suggesting enhanced mechanisms of photoprotective energy dissipation in the more temperate species. In the second and third experiments, inter- and intra-specific differentiation in response to freezing was tested for by examining dark-adapted F _v/F _m before and after overnight freezing cycles. Without cold acclimation, the extent of post-freezing declines in F _v/F _m were dependent on the minimum freezing temperature (0, −2, −5 or −10°C) for both populations in both species. The most marked declines in F _v/F _m occurred after freezing at −10°C, measured 24 h after freezing. These declines were continuous and irreversible over the time period. The North Carolina population, however, which represents the northern range limit of Q. virginiana, showed significantly less decline in F _v/F _m than the north central Florida population, which in turn showed a lower decline in Fv/F _m than the two Q. oleoides populations from Belize and Costa Rica. In contrast, after exposure to three months of chilling temperatures (temperate treatment), the two Q. virginiana populations showed no decline in F _v/F _m after freezing at −10°C, while the two Q. oleoides populations showed declines in F _v/F _m reaching 0.2 and 0.1 for Costa Rica and Belize, respectively. Under warm growth conditions, the two species showed different F ₀ dynamics directly after freezing. The two Q. oleoides populations showed an initial rise in F ₀ 30 min after freezing, followed by a subsequent decrease, while the Q. virginiana populations showed a continuous decrease in F ₀ after freezing. The North Carolina population of Q. virginiana showed a tendency toward deciduousness in response to winter temperatures, dropping 58% of its leaves over the three month winter period compared to only 6% in the tropical treatment. In contrast, the Florida population dropped 38% of its leaves during winter. The two populations of the tropical Q. oleoides showed no change in leaf drop during the 3-months winter (10% and 12%) relative to their leaf drop over the same timecourse in the tropical treatment. These results indicate important ecotypic differences in sensitivity to freezing and cold stress between the two populations of Q. virginiana as well as between the two species, corresponding to their climates of origin.     

Impacts of chlorination and heat shocks on growth, pigments and photosynthesis of Phaeodactylum tricornutum (Bacillariophyceae)

The main impacts of cooling water from thermal (nuclear) power plants on aquatic organisms were caused by chlorination and temperature increase. In this study, we investigated the impacts of residual chlorine and short-term heat shocks on growth, pigment contents and photosynthesis of Phaeodactylum tricornutum. Growth of P. tricornutum was completely inhibited; Chlorophyll a and carotenoids contents deceased about 63.3% and 61.4% in 24 h treated with 0.2 mg L^− 1 chlorine. The negative effects of chlorination increased with enhanced concentration and prolonged exposure time. Relative electrode transfer rate (rETR) of P. tricornutum was significantly suppressed when treated with 0.2 mg L^− 1 residual chlorine for 24 h. Furthermore, the effective quantum yield (F_v'/F_m') decreased first but then recovered with prolonged exposure when residual chlorine ranged between 0.1 and 0.2 mg L^− 1. The cells were less sensitive to heat shocks compared with chlorination: the rETR and F_v'/F_m' was suppressed only when the temperature exceeded 35 °C for 1 h. When P. tricornutum was exposed to chlorination combined with heat shocks, the rETR was further inhibited at 35 °C. It indicated that both chlorination and heat shocks had negative impacts on the primary producers living in discharging coastal waters; furthermore, there were synergistic effects of heat shocks on chlorination toxicity.     

Effectiveness of potassium sulfate in mitigating salt-induced adverse effects on different physio-biochemical attributes in sunflower (Helianthus annuus L.)

To assess whether foliar application of K+S as potassium sulfate (K₂SO₄) could alleviate the adverse effects of salt on sunflower (Helianthus annuus L. cv. SF-187) plants, a greenhouse experiment was conducted. There were two NaCl levels (0 and 150 mM) applied to the growth medium and six levels of K+S as K₂SO₄ (NS (no spray), WS (spray of water+0.1% Tween 20 solution), 0.5% K+0.21% S, 1.0% K+0.41% S, 1.5% K+0.62% S, and 2.0% K+0.82% S in 0.1% Tween-20 solution) applied two times foliarly to non-stressed and salt-stressed sunflower plants. Salt stress markedly repressed the growth, yield, photosynthetic pigments, water relations and photosynthetic attributes, quantum yield (F_v/F_m), leaf and root K⁺, Mg²⁺, P, Ca²⁺, N as well as K⁺/Na⁺ ratios, while it enhanced the cell membrane permeability, and leaf and root Na⁺ and Cl⁻ concentrations. Foliar application of potassium sulfate significantly improved growth, achene yield, photosynthetic and transpiration rates, stomatal conductance, water use efficiency, leaf turgor and enhanced shoot and leaf K⁺ of the salt-stressed sunflower plants, but it did not improve leaf and root Na⁺, Cl⁻, Mg²⁺, P, Ca²⁺, N as well as K⁺/Na⁺ ratios. The most effective dose of K+S for improving growth and achene yield was found to be 1.5% K+0.62% S and 1% K+0.41% S, respectively. Improvement in growth of sunflower plants due to exogenously applied K₂SO₄ was found to be linked to enhanced photosynthetic capacity, water use efficiency, leaf turgor and relative water content.     

In situ measured seasonal variations in F v/F m of two common Red Sea corals

Pulse amplitude modulated (PAM) fluorometry has been suggested as a tool for estimating environmental stresses on corals. However, information regarding natural changes in maximal quantum yields (F _v/F _m) of corals during “normal” (i.e. non-bleaching) years has been limited. In this study, seasonal variations in F _v/F _m for Stylophora pistillata and Favia favus, measured in situ, correlated with seasonal changes in solar irradiance but not in sea temperature. Interactions between sea temperature and irradiance were further studied by growing these corals and Pocillopora damicornis under controlled conditions. Exposure to high light with normal or high temperatures resulted in lower F _v/F _m values than exposure to low light at both temperatures. Thus, high irradiances may cause decreased F _v/F _m values in corals at least as much as, if not more than, high temperatures. Such seasonal variations should be taken into account when using PAM fluorometry as a diagnostic tool for predicting coral bleaching.     

7种秋海棠叶片斑纹结构及遗传特性分析

以7种(品种)秋海棠为材料,观察叶片斑区和非斑区组织结构、测定叶绿素含量及叶绿素荧光参数F_v/F_m值,分析叶片斑纹的形成原因及银点秋海棠点状斑的遗传特性。结果显示：(1)银点秋海棠、铺地秋海棠、假厚叶秋海棠、‘皮卡’和‘非洲丛林’叶片斑区的上表皮细胞与栅栏组织细胞间存在空隙,非斑区则没有空隙,彩纹秋海棠和‘虎斑’的斑区与非斑区上表皮细胞和栅栏组织细胞间均紧密相连。(2)7种(品种)秋海棠叶片斑区和非斑区都具有完整的叶绿体超微结构,类囊体膜丰富,基质和基粒片层清晰;银点秋海棠、假厚叶秋海棠、‘皮卡’和‘非洲丛林’斑区的叶绿素a、b及总叶绿素含量均低于非斑区,而铺地秋海棠斑区和非斑区差别不大;除假厚叶秋海棠的斑区叶绿素荧光参数F_v/F_m值小于非斑区外,其余6种秋海棠均为斑区高于非斑区。(3)银点秋海棠与无斑种类杂交,杂交后代叶片有斑和无斑的植株约为1∶1,而其自交后代中有斑和无斑的植株比例近3∶1。研究发现,银点秋海棠、铺地秋海棠、假厚叶秋海棠、‘皮卡’和‘非洲丛林’的叶斑属于空隙结构型,彩纹秋海棠和‘虎斑’叶斑属于色素型。银点秋海棠点状叶斑与无斑是1对可遗传的相对性状,白色点状斑为显性性状。     

The dynamics of nutrient utilization and growth of apple root stock ‘M9 EMLA’ in temporary versus continuous immersion bioreactors

The present study investigated the dynamics of nutrient utilization and various growth and physiological parameters during in vitro proliferation of apple root stock ‘M9 EMLA’ in two different bioreactor systems, i.e. temporary and continuous immersions. Individual shoots obtained from temporary immersion system had higher dry mass and were of better quality than those obtained from continuous immersion. In continuous immersion bioreactor, apple shoots appeared to utilize more nutrients from liquid culture medium than that from temporary immersion. The shoot growth was limited by the availability of phosphate and nitrogen in continuous immersion system. The shoots produced in temporary immersion bioreactor showed higher photosynthetic rate, maximum quantum yield of photosystem-II and slow but steady rate of nutrient absorption, indicating the occurrence of higher photomixotrophic metabolism. The study also showed that high level of antioxidant scavenging enzymes in shoots grown in continuous immersion system induced physiological changes to foster adaptation to stresses.     

Effects of temperature and CO2 enrichment on kinetic properties of NADP+-malate dehydrogenase in two ecotypes of Barnyard grass (Echinochloa crus-galli (L.) Beauv.) from contrasting climates

Summary The apparent energy of activation (E _a), Michaelis-Menten constant (K _mfor oxaloacetate), V _max/K _mratios and specific activities of NADP⁺-malate dehydrogenase (NADP⁺-MDH; EC 1.1.1.82) were analyzed in plants of Barnyard grass from Québec (QUE) and Mississippi (MISS) acclimated to two thermoperiods 28/22°C, 21/15°C, and grown under two CO₂ concentrations, 350 l l^-1 and 675 l l^-1. E _avalues of NADP⁺-MDH extracted from QUE plants were significantly lower than those of MISS plants. K _mvalues and V _max/K _mratios of the enzyme from both ecotypes were similar over the range of 10–30°C but reduced V _max/K _mratios were found for the enzyme of QUE plants at 30 and 40°C assays. MISS plants had higher enzyme activities when measured on a chlorophyll basis but this trend was reversed when activities were expressed per fresh weight leaf or per leaf surface area. Activities were significantly higher in plants of both populations acclimated to 22/28°C. CO₂ enrichment did not modify appreciably the catalytic properties of NADP⁺-MDH and did not have a compensatory effect upon catalysis or enzyme activity under cool acclimatory conditions. NADP⁺-MDH activities were always in excess of the amount required to support observed rates of CO₂ assimilation and these two parameters were significantly correlated. The enhanced photosynthetic performance of QUE plants under cold temperature conditions, as compared to that of MISS plants, cannot be attributed to kinetic differences of NADP⁺-malate dehydrogenase among these ecotypes.     

Effects of NaCl salinity on growth, morphology, photosynthesis and proline accumulation of Salvinia natans

The effects of NaCl salinity on growth, morphology and photosynthesis of Salvinia natans (L.) All. were investigated by growing plants in a growth chamber at NaCl concentrations of 0, 50, 100 and 150 mM. The relative growth rates were high (ca. 0.3 d⁻¹) at salinities up to 50 mM and decreased to less than 0.2 d⁻¹ at higher salinities, but plants produced smaller and thicker leaves and had shorter stems and roots, probably imposed by the osmotic stress and lowered turgor pressure restricting cell expansion. Na⁺ concentrations in the plant tissue only increased three-fold, but uptake of K⁺ was reduced, resulting in very high Na⁺/K⁺ ratios at high salinities, indicating that S. natans lacks mechanisms to maintain ionic homeostasis in the cells. The contents of proline in the plant tissue increased at high salinity, but concentrations were very low (<0.1 μmol g⁻¹ FW), indicating a limited capacity of S. natans to synthesize proline as a compatible compound. The potential photochemical efficiency of PSII (F_v/F_m) of S. natans remained unchanged at 50 mM NaCl but was reduced at higher salinities, and the photosynthetic capacity (ETR_max) was significantly reduced at 50 mM NaCl and higher. It is concluded that S. natans is a salt-sensitive species lacking physiological measures to cope with exposure to high NaCl salinity. At low salinities salts are taken up and accumulate in old leaves, and high growth rates are maintained because new leaves are produced at a higher rate than for plants not exposed to salt.     

古林箐秋海棠叶斑结构对叶色的影响

该研究以古林箐秋海棠(Begonia gulinqingensis)为材料,通过分析叶片形态特征、上表皮光学特性、组织结构、叶绿素含量及叶绿素荧光参数(F_v/F_m),探讨了叶片色斑的形成原因。结果表明:(1)古林箐秋海棠叶斑发生频率和数量无明显规律,但发生部位相对稳定,叶斑主要发生在正对叶柄的两条主脉之间。(2)斑区有两种光反射模式,点状反射和多角形反射,栅栏组织细胞呈近等轴的圆形,排列疏松,与上表皮细胞间存在空隙;非斑区只有点状反射模式,栅栏组织细胞为漏斗型,排列紧密,与上表皮细胞间不存在空隙。(3)斑区和非斑区叶绿体均有密集的堆积基粒和丰富的类囊体膜,斑区叶绿素a、b及总叶绿素含量仅比非斑区分别低24.9%、25.2%、25.1%。(4)叶绿素荧光参数(F_v/F_m)值斑区为0.793,非斑区为0.790。虽然斑区叶绿素含量比非斑区略低,但叶绿体结构完整,且叶绿素荧光参数与非斑区无显著差异。斑区上表皮与栅栏组织细胞间的空隙可使光线到达绿色组织时发生二次反射,在叶片表皮细胞边缘形成白色多边形光反射使该区域相对周围正常叶片区域偏白,基于上述结果可推测古林箐秋海棠的淡绿色块斑形成与特殊的叶片结构有关。     

Spatio-temporal variability in the photosynthetic characteristics of Zostera tasmanica measured by PAM

Rapid light curves (RLCs), based on pulse amplitude modulated (PAM) fluorometry, were used to investigate the spatio-temporal variability in photosynthesis versus irradiance parameters (α, I_k and P_max) and the F_v/F_m ratio of the seagrass Zostera tasmanica (formerly Heterozostera tasmanica). Spatial variation was examined across scales ranging from within a leaf (cms) to across the bed (ms), using a nested analysis of covariance sampling design. Overall, significant variation was identified at all scales examined, excluding the largest scale (area). Patterns of variability differed among individual parameters; however a high percentage of the variation was consistently assigned to the covariates, age (within and between leaves) for all parameters, except P_max.     

Effects of mutations in the beta subunit hinge domain on ATP synthase F1 sector rotation: interaction between Ser 174 and Ile 163

A complex of γ, ε, and c subunits rotates in ATP synthase (F_oF₁) coupling with proton transport. Replacement of βSer174 by Phe in β-sheet4 of the β subunit (βS174F) caused slow γ subunit revolution of the F₁ sector, consistent with the decreased ATPase activity [M. Nakanishi-Matsui, S. Kashiwagi, T. Ubukata, A. Iwamoto-Kihara, Y. Wada, M. Futai, Rotational catalysis of Escherichia coli ATP synthase F1 sector. Stochastic fluctuation and a key domain of the β subunit, J. Biol. Chem. 282 (2007) 20698-20704]. Modeling of the domain including β-sheet4 and α-helixB predicted that the mutant βPhe174 residue undergoes strong and weak hydrophobic interactions with βIle163 and βIle166, respectively. Supporting this prediction, the replacement of βIle163 in α-helixB by Ala partially suppressed the βS174F mutation: in the double mutant, the revolution speed and ATPase activity recovered to about half of the levels in the wild-type. Replacement of βIle166 by Ala lowered the revolution speed and ATPase activity to the same levels as in βS174F. Consistent with the weak hydrophobic interaction, βIle166 to Ala mutation did not suppress βS174F. Importance of the hinge domain [phosphate-binding loop (P-loop)/α-helixB/loop/β-sheet4, βPhe148-βGly186] as to driving rotational catalysis is discussed.     

Morphometric traits and sexual dimorphisms do not strongly differentiate populations of Zeravshan juniper (Juniperus seravschanica Kom.) in Kyrgyzstan

Intra- and among-population variations of Juniperus seravschanica were morphologically examined in eight populations originating from elevations of 1300–2200 m a.s.l. in Kyrgyzstan. Eleven traits of needles and cones were studied on 70 vouchers. In addition, height, diameter, stem form, and sex of 172 trees were recorded in the field in order to test whether male trees invest more in vegetative growth than females and if sex ratio is shaped by (limited) environmental resources. Morphological differences among populations were small, but needle length, width and thickness were statistically different. However, differences based on needle traits were independent from geographical, altitudinal and environmental distances. In sharp contrast to studies in other Juniperus species, sex ratio in J. seravschanica was strongly female biased (3.5 females : 1 male). Moreover, no correlation between the habitat conditions and the sex ratio was detected, suggesting that within the altitudinal range of this species, females occur more frequently. This has implications for sustainable use and the conservation of J. seravschanica populations. It is likely, that due to the higher investment of male individuals in vegetative growth males are more exploited than females. An average effective population size of 70% of the respective census suggests that conservation measures and non-selective logging regimes are required to allow reproduction and a natural regeneration of this species.     

Comparative studies on physiological responses to phosphorus in two phenotypes of bloom-forming <Emphasis Type="Italic">Microcystis</Emphasis>

Toxic Microcystis blooms frequently occur in eutrophic water bodies and exist in the form of colonial and unicellular cells. In order to understand the mechanism of Microcystis dominance in freshwater bodies, the physiological and biochemical responses of unicellular (4 strains) and colonial (4 strains) Microcystis strains to phosphorus (P) were comparatively studied. The two phenotype strains exhibit physiological differences mainly in terms of their response to low P concentrations. The growth of four unicellular and one small colonial Microcystis strain was significantly inhibited at a P concentration of 0.2 mg l⁻¹; however, that of the large colonial Microcystis strains was not inhibited. The results of phosphate uptake experiments conducted using P-starved cells indicated that the colonial strains had a higher affinity for low levels of P. The unicellular strains consumed more P than the colonial strains. Alkaline phosphatase activity in the unicellular strains was significantly induced by low P concentrations. Under P-limited conditions, the oxygen evolution rate, F _v/F _m, and ETR _max were lower in unicellular strains than in colonial strains. These findings may shed light on the mechanism by which colonial Microcystis strains have an advantage with regard to dominance and persistence in fluctuating P conditions. Handling editor: L. Naselli-Flores     

Leishmania donovani: dyskinetoplastid cells survive and proliferate in the presence of pyruvate and uridine but do not undergo apoptosis after treatment with camptothecin

We have shown that treatment with luteolin in leishmanial cells causes loss of mt-DNA and induces apoptosis through mitochondria dependent pathway [Sen, N., Das, B.B., Ganguly, A., Banerjee, B., Sen, T., Majumder, H.K., 2006. Leishmania donovani: intracellular ATP level regulates apoptosis-like death in luteolin induced dyskinetoplastid cells. Experimental Parasitology, in press]. Here, we report that mitochondrial DNA depleted leishmanial cells require exogenous sources of pyruvate and uridine to survive and proliferate. The presence of pyruvate and uridine in a growing media help them to produce sufficient amount of glycolytic ATP to maintain the mitochondrial membrane potential in the absence of their functional ETC. Treatment of wild type cells with CPT causes generation of ROS that leads to apoptosis. But unlike the normal cells ROS was not generated in these mt-DNA depleted cells after treatment with CPT. Taken together we have shown for the first time that dyskinetoplastid cells are auxotrophic for pyruvate and uridine and apoptosis cannot be induced in these cells in the presence of CPT. Therefore, the presence of mitochondrial DNA is absolutely necessary for the cytotoxicity of CPT in kinetoplastid parasites.