Photomorphogenesis inPhycomyces: Dependence on environmental conditions

The production of two kinds of vegetative reproductive structures, microphores and macrophores, byPhycomyces blakesleeanus Bgff. depends on plating density, ventilation, asparagine supply, and illumination. Quantitative determinations of these variables lead us to propose a new experimental system for developmental photobiology: standard plastic Petri plates containing 25 ml minimal medium are inoculated with 10⁵ viable, heat-activated spores and incubated, unpiled and unsealed, at 22° C. After 4 d microphores are counted and macrophores are weighed. Both microphorogenesis and macrophorogenesis are governed by light. Photosensitivity is a developmental phenomenon which occurs 32 to 68 h after inoculation, just before the beginning of vegetative reproduction in the dark controls. The maximum photosensitivity occurs 48 h after inoculation.     

The sensitive period for light and temperature regulation of sporangiophore development inPhycomyces

Light and temperature markedly influence sporangiophore development inPhycomyces blakesleeanus. Under normal conditions in the dark, low temperature drastically stimulates the production of dwarf sporangiophores (microphorogenesis) and inhibits that of giant sporangiophores (macrophorogenesis). These effects of low temperature could still be observed if applied only for a short period before sporangiophore initiation. Continuous white illumination strongly inhibits microphorogenesis and slightly stimulates macrophorogenesis. Short exposures to white light noticeably inhibit microphorogenesis and stimulate macrophorogenesis when given to mycelia grown for between 90 and 160 h at 14° C or 150 h or more at 10° C. These results indicate the existence in the mycelium of developmental stages for the regulation of sporangiophorogenesis by environmental signals.     

Photomorphogenesis in<Emphasis Type="Italic"> Phycomyces</Emphasis>: differential display of gene expression by PCR with arbitrary primers

The zygomycete fungus Phycomyces blakesleeanus develops two types of fruiting bodies of very different size, macrophores and microphores. Blue light stimulates macrophorogenesis and inhibits microphorogenesis. I have adapted a method based on the polymerase chain reaction with arbitrary primers to investigate the role of differential gene expression during photophorogenesis in Phycomyces. Several cDNAs for genes induced in vegetative mycelium have been observed, but only one gene induced by blue light has been detected. I have demonstrated the feasibility of this approach by the isolation of a cDNA segment for the heat-shock protein HSP100 that is induced by blue light at the onset of sporangiophore development. The heat-shock protein HSP100 is an ATP-binding protein that has the ability to disassemble protein complexes. In plants, the gene for HSP100 is induced by light. The cDNA segment for HSP100 obtained from Phycomyces is 686 bp long and the predicted amino acid sequence contains one of the ATP-binding sites.     

A mutation in Drosophila that appears to accelerate aging

The question as to the role that genes play in determining life-span is essentially unresolved. Although it is well documented that genotype influences longevity, this is no way demonstrates that life-span is genetically determined. In the present study we examine five temperature-sensitive mutations for their effect on the aging process. At the permissive temperature (22°C ), the longevity of each mutant strain is comparable to that of wild type. However, at the restrictive temperature (29°C ) the life-span of these mutants is severely curtailed. Using behavior loss as a landmark of adult physiological age, we examined each of these strains for its pattern of behavior loss relative to longevity, and compared each to a wild-type strain. In four of the mutations the pattern of behavior loss relative to longevity was severely altered at one or both temperatures. However, one strain, adl-16^tsl displayed a pattern of behavior loss that was indistinguishable from wild type at both 22°C and 29°C. At 29°C not only was the longevity decreased, the pattern of behavior loss was also compressed into a shorter time period. The compression of the pattern of behavior loss was proportional to the reduction in life-span. Thus it appears that this mutation, adl-16^tsl, may accelerate the normal aging process when placed at 29°C. The potential utility of these types of mutants for studying the aging process is discussed.     

Global Analysis of the Genes Involved in the Thermotolerance Mechanism of Thermotolerant Acetobacter tropicalis SKU1100

Acetobacter tropicalis SKU1100 is a thermotolerant acetic acid bacterium that grows even at 42 °C, a much higher temperature than the limit for the growth of mesophilic strains. To elucidate the mechanism underlying the thermotolerance of this strain, we attempted to identify the genes essential for growth at high temperature by transposon (Tn10) mutagenesis followed by gene or genome analysis. Among the 4,000 Tn10-inserted mutants obtained, 32 exhibited a growth phenotype comparable to that of the parent strain at 30 °C but not at higher temperatures. We identified the insertion site of Tn10 on the chromosomes of all the mutant strains by TAIL (Thermal Asymmetric Interlaced)-PCR, and found 24 genes responsible for thermotolerance. The results also revealed a partial overlap between the genes required for thermotolerance and those required for acetic acid resistance. In addition, the origin and role of these thermotolerant genes are discussed.     

Vegetative regeneration on sexual organs inPhycomyces blakesleeanus

Phycomyces blakesleeanus produced an abundance of sexual organs when two mating types met on solid medium, but only about 14.7% of the sexual organs developed to the final stages. On the sexual organs showing arrested development, vegetative hyphae or dwarf sporangiophores (microphores) often regenerated. This vegetative regeneration was accelerated when the paired and looped progametangia were isolated from mycelia, when the counterparts of the progametangial cells constructing the loop were surgically incised, and whenPhycomyces was mated at high temperature (25–27°C). A leaky-carotenogenic mutant, whose sexual reaction was imperfect and arrested at an intermediate stage even when mated with the wild type, also regenerated hyphae with a high frequency on these arrested intermediate organs. The vegetative regeneration seems to result from interruption of a cell-to-cell recognition system between cells of different mating type, which is believed to be essential for the mating process of this fungus in addition to the pheromonal actions.     

Thermostability of photosynthesis in two new chlorophyllb-less rice mutants

Leaves of the two new chlorophyllb-less rice mutants VG28-1, VG30-5 and the wild type rice cv. Zhonghua 11 were subjected to temperatures 28, 36, 40, 44 and 48°C in the dark for 30 min or gradually elevated temperature from 30°C to 80°C at 0.5°C/min. The thermostability of photosynthetic apparatus was estimated by the changes in chlorophyll fluorescence parameters, photosynthetic rate and pigment content, chloroplast ultrastructure and tissue location of H₂O₂ accumulation. There were different patterns of F_o-temperature curves between the Chlb-less mutants and the wild type plant, and the temperature of F_o rising threshold was shifted 3°C lower in the Chlb-less mutants (48°C) than in the wild type (51°C). At temperature up to about 45°C, chloroplasts were swollen and thylakoid grana became misty accompanied with the complete loss of photosynthetic oxygen evolution in the two Chlb-less mutants, but chloroplast ultrastructure in the wild type showed no obvious alteration. After 55°C exposure, the disordered thylakoid and significant H₂O₂ accumulation in leaves were found in the two Chlb-less mutants, whereas in the wild type plant, less H₂O₂ was accumulated and the swollen thylakoid still maintained a certain extent of stacking. A large extent of the changes in qP, NPQ and F_v/F_m was consistent with the Pn decreasing rate in the Chlb-less mutants during high temperature treatment as compared with the wild type. The results indicated that the Chlb-less mutants showed a tendency for higher thermosensitivity, and loss of Chlb in LHC II could lead to less thermostability of PSII structure and function. Heat damage to photosynthetic apparatus might be partially attributed to the internal oxidative stress produced at severely high temperature.     

Multiple generation effects of high temperature on the development and fecundity of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B

Insects are ectotherms and their ability to resist temperature stress is limited. The immediate effects of sub‐lethal heat stress on insects are well documented, but longer‐term effects of such stresses are rarely reported. In this study, survival, development and reproduction of the whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B, were compared over five consecutive generations at 27, 31 and 35 °C and for one generation at 37 °C. Both temperature and generation significantly affected the fitness of the whitefly. These impacts were more dramatic with increasing generations and temperatures. Among the experimental temperatures, the most favorable for development and reproduction were 27 °C and 31 °C. At 27 °C, survival, development and fecundity were all stable over these five generations. At 31 °C, immature survival rate was the highest in the fifth generation, but female fecundities decreased in the fourth and fifth generations. At 35 °C, egg hatching rate, immature survival rate and female fecundity decreased significantly in the fourth and fifth generations. At 37 °C, survival of B. tabaci was not adversely affected, but female fecundity at 37 °C was less than 10% of that at 27 °C or 31 °C. These results demonstrate that the lethal high temperature for B. tabaci is over 37 °C, and the whitefly population continued expanding in the five generations at 35 °C. The ability of B. tabaci biotype B to survive high temperature stress will play an important role in its population extension under global warming.     

Determination of temperature sensitive stages for sexual differentiation of the gonads in embryos of the turtle,Emys orbicularis

In order to determine the temperature sensitive stages for sexual differentiation of the gonads in Emys orbicularis, eggs of this turtle were shifted at different stages of embryonic development from the male-producing temperature of 25°C to the female-producing temperature of 30°C and reciprocally. Based on the series of developmental stages described by Yntema (′68) for Chelydra serpentina, temperature begins to influence sexual differentiation of Emys orbicularis at stage 16, a stage in which the gonads are still histologically undifferentiated. Its action lasts over the first steps of histological differentiation of the gonads. The minimal exposure at 25°C required for male differentiation of all individuals extends from stage 16 to somewhat before stage 21. For 100% female differentiation, incubation at 30°C must be longer, from stage 16 to somewhat before stage 22. Shorter exposures at 25°C or 30°C during these periods result in different percentages of males, females, and intersexes. Our results show that there is a critical stage (stage 16) which is the same for both male and female differentiation of the gonads. The thermosensensitive periods are rather long, corresponding to 11–12 days at 25°C and 30°C.     

Comparison of dependence of growth and sexual reproduction ofChlamydomonas geitleri on temperature and irradiance

Dependence of the growth of this alga culture on temperature displays a wide interval of temperatures (from 4 °C to 30 °C) and the dependence of the sexual reproduction only a narrow one (from 18 °C to 25 °C). The optimum temperatures for both the processes are not so different (round 23 °C). Dependence of both the processes on irradiance displays a wide interval of irradiances in both eases (from 4 W m^t-2 to 80 W m^t-2 PhAR and higher). The optimum irradiances for these processes are very different (approx. 50 W m^t-2 PhAR for the growth and approx. 10 W m^t-2 PhAR for the sexual reproduction) under the experimental conditions used.     

Genome-wide identification of neuropeptides and their receptor genes in Bemisia tabaci and their transcript accumulation change in response to temperature stresses

Insect neuropeptides play an important role in regulating physiological functions such as growth,development,behavior and reproduction.We identified temperaturesensitive neuropeptides and receptor genes of the cotton whitefly,Bemisia tabaci.We identified 38 neuropeptide precursor genes and 35 neuropeptide receptors and constructed a phylogenetic tree using additional data from other insects.As temperature adaptability enables B.tabaci to colonize a diversity of habitats,we performed quantitative polymerase chain reaction with two temperature stresses(low=4℃ and high=40℃)to screen for temperature-sensitive neuropeptides.We found many neuropeptides and receptors that may be involved in the temperature adaptability of B.tabaci.This study is the first to identify B.tabaci neuropeptides and their receptors,and it will help to reveal the roles of neuropeptides in temperature adaptation of B.tabaci.     

Effects of temperature on the adults and progeny of the predaceous mite Lasioseius japonicus (Acari: Blattisociidae) fed on the cereal mite Tyrophagus putrescentiae (Acari: Acaridae)

The predatory mite Lasioseius japonicus Ehara is a newly recorded species in China that has been shown to have great potential as a biological control agent. The species is a soil-dwelling mite that is known to prey on various pests including economically important mites, fungus gnats and other terricolous arthropods. Considering that temperature is one of the most important factors affecting the population dynamics of arthropods, the development, survival and reproduction of L. japonicus were evaluated under indoor conditions at seven temperatures: 19, 22, 25, 28, 31, 34 and 37 °C, at 75% relative humidity and L0:D24 h photoperiod. The mites were fed on the cereal mite Tyrophagus putrescentiae (Schrank) and the data were analyzed using the two-sex life table. The results demonstrated that L. japonicus could complete their development and reproduce at temperatures between 19 and 34 °C, but were unsuccessful at 37 °C. Increasing temperature shortened the development time of the pre-adult stage and the average generation time (T). The life table parameters indicated that at temperatures from 22 to 31 °C the development rate and reproduction of L. japonicus were highest: at 22, 25, 28 and 31 °C the net reproduction rate (R₀) was 55.5, 61.6, 61.2 and 59.0, respectively, and the average fecundity rate (F) was 81.7, 88.0, 102.0 and 86.8, respectively. The maximum values of intrinsic population growth rate (r) (0.341) and finite rate of increase (λ) (1.407) occurred at 31 °C.

     

Bionomics of a polyphagous predator:Orius laevigatus (Het.: Anthocoridae)

The main characteristics of the imaginal and preimaginal development and the reproduction ofOrius laevigatus were studied at 15, 20, 25 and 30°C. Temperature greatly influences the developmental and reproductive biology of this species. The lowest developmental threshold is 10,6°C. Reproduction is greatly reduced at 15°C relative to the higher temperatures tested. O. laevigatus is well adapted to relatively high temperature conditions. The best development and reproduction rates are observed between 20 and 30°C with a theoretical optimum at 26°C.

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Résumé Les principales caractéristiques du développement pré-imaginal et imaginal ainsi que la reproduction d'Orius laevigatus sont étudiées à des températures de 15, 20, 25 et 30°C. La température influence considérablement le développement embryonnaire et post-embryoannaire de cette espèce. Le zéro théorique de développement se situe à 10,5°C. Les capacités reproductrices sont fortement perturbées à des températures inférieures à 15°C. Les résultats montrent queO. laevigatus est une espèce adaptée à des conditions thermiques relativement élevées. C'est entre 20 et 30°C, avec un optimum de 26°C, que s'expriment le mieux les capacités de développement et de reproduction de ce prédateur.

     

Genetic control of the cell division cycle in the fission yeast Schizosaccharomyces pombe

Summary Twenty seven recessive temperature sensitive mutants have been isolated in Schizosaccharomyces pombe which are unable to complete the cell division cycle at the restrictive temperature. These mutants define 14 unlinked genes which are involved in DNA synthesis, nuclear division and cell plate formation. The products from most of these genes complete their function just before the cell cycle event in which they are involved. Physiological characterisation of the mutants has shown that DNA synthesis and nuclear division form a cycle of mutually dependent events which can operate in the absence of cell plate formation. Cell plate formation itself is usually dependent upon the completion of nuclear division.     

Life history parameters for Nesidiocoris tenuis (Reuter) (Het., Miridae) under different temperature regimes

The development time for eggs and nymphs and female fertility were determined for Nesidiocoris tenuis Reuter (Het., Miridae: Dicyphini) at 15, 20, 25, 30, 35 and 40 ± 1°C, using tomato, Solanum esculentum (Miller), as substrate and eggs of Ephestia kuehniella Zeller as substitute prey. At 40°C, N. tenuis was unable to develop and barely reproduced. Egg development ranged from 30.8 days at 15°C to 6.3 days at 35°C. The cumulative thermal requirements for the eggs were 148.6 degree days (°d) and the lower thermal threshold, 10.3°C. The duration of the nymphal instar decreased from 55.9 days at 15°C to 8.6 days at 35°C. The thermal constant for the nymphs was 182.3 °d and the lower thermal threshold 11.7°C. No nymphs survived at 40°C, and the highest mortalities were at extreme temperatures (15 and 35°C). Female and male weights were influenced significantly by temperature. The fertility of N. tenuis females was reduced greatly at 15 and 40°C. The highest fertility during an observation period of 18 days following female emergence (79.5–60.0 nymphs per female) was within the temperature range of 20 to 35°C. Fertility was related directly to female weight and temperature (r² = 0.932). Based on development, reproduction data and thermal requirements, the optimum temperature range for N. tenuis was established as being between 20 and 30°C. Overall, N. tenuis is the most thermophilous of all dicyphines from vegetable crops in the Mediterranean area studied so far.     

Biology of Agistemus olivi,a new predator of eriophyid mites infesting olive trees in Egypt

Life history and prey consumption of the predatory stigmaeid mite Agistemus olivi Romeih, as affected by feeding on the motile stages of the olive bud mite Aceria oleae Nalepa and the olive rust mite Tegolophus hassani Keifer (Acari : Eriophyidae), has been studied for the first time at different temperatures and 70–75% r.h. A greater capability was shown for consuming the olive bud mite than the olive rust mite and the former prey relatively induced more fecundity. The rise of different temperatures from 20°C to 25°C and 30°C shortened development and increased reproduction and prey consumption. The maximum reproduction (6.92 and 6.08 eggs ♀ day) was recorded at the higher temperature, while the minimum reproduction (1.50 and 1.30 eggs ♀ day) was observed for A. oleae and T. hassani, respectively.     

Control of Saccharomyces cerevisiae 2microN DNA replication by cell division cycle genes that control nuclear DNA replication.

The replication of the 2 μm DNA of Saccharomyces cerevisiae has been examined in cell division cycle (cdc) mutants. The 2 μm DNA does not replicate at the restrictive temperature in cells bearing the cdc28, cdc4, and cdc7 mutations which prevent passage of cells from the G1 phase into S phase. Plasmid replication also is prevented in a mating-type cells by α factor, a mating hormone which prevents cells from completing an event early in G1 phase. The 2 μm DNA ceases replication at 36 °C in a mutant harboring the cdc8 mutation, a defect in the elongation reactions of nuclear DNA replication. Plasmid replication continues at the restrictive temperature for approximately one generation in a cdc13 mutant defective in nuclear division. These results show that 2 μm DNA replication is controlled by the same genes that control the initiation and completion of nuclear DNA replication.     

Subfossil chydorid (Cladocera, Chydoridae) ephippia as paleoenvironmental proxies: evidence from boreal and subarctic lakes in Finland

Chydorids (Cladocera, Chydoridae) have two reproductive strategies: asexual reproduction that prevails during favorable environmental conditions and sexual reproduction that is induced by environmental stimuli associated with seasonal or aperiodic environmental stresses. These modes of reproduction can be recognized in the subfossil sedimentary records as parthenogenetic shells of females (asexual reproduction) and by ephippia (sexual reproduction). We studied the interrelations between subfossil chydorid ephippia and environmental variables by analyzing surface sediment samples obtained from 76 Finnish lakes across a latitudinal gradient (60–70°N). The results showed that the total chydorid ephippia (TCE) increases along the climate gradient from ~2 to 3% in the south to ~25% in the north and suggested a significant dependence (r ~ −0.8, P < 0.001) with several climate factors, especially that of mean July air temperature. We used this relationship to create a model for reconstructing past mean July air temperatures. A linear regression of the log₁₀ transformed TCE as a single independent variable explained 76% (SE ± 0.76°C) of the variance of the observed mean July air temperatures. Accordingly, we propose that this novel tool may be highly suitable for reconstructing paleotemperatures in cold-temperate environments.     

A selection procedure for obtaining conditional gametogenic mutants using a photosynthetically incompetent strain of Chlamydomonas reinhardi

Summary A new selection procedure has been developed for the isolation of temperature sensitive gametogenic mutants in Chlamydomonas reinhardi. This technique makes use of pet-10-1, a mutant strain incapable of photosynthetic electron transport, and the redox dye, methyl viologen. Two mutants found by this method are discussed. The first, gam-4, does not agglutinate at 35°, whereas the second, gam-5, is capable of sexual agglutination, but not of zygote formation at the restrictive temperature. Both mutants appear to be inherited in a Mendelian fashion and are expressed in mating type (+) and mating type (-).