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971.
972.
973.
974.
Akihisa Takahashi Naoaki Shibata Shoko Nishikawa Ken Ohnishi Noriaki Ishioka Takeo Ohnishi 《Photochemical & photobiological sciences》2006,5(5):467-471
Phytoplankton such as Euglena are constantly exposed to solar light which is used for photosynthesis. Although the solar ultraviolet (UV) induces DNA damage such as cyclobutane-pyrimidine dimers (CPDs), many kinds of living organisms can repair CPDs by photoreactivation (PR) utilizing the near-UV/blue light component in sunlight. Euglena cells are known to possess such PR activity. In the present paper, the formation of CPDs induced by UV-C exposure and the photoreactivation PR repair of these CPDs by UV-A are demonstrated. To clarify the adaptive responses prior UV-B irradiation on PR activity, cells were cultured in the dark or under UV-B light. When the cells were cultured in the dark for 3 d prior to UV-C exposure, PR activity decreased. When the cells were cultured under UV-B light, however, PR activity increased. These results suggest that exposing the cells to UV-B prior to exposure to UV-C induced an adaptive response towards DNA damage caused by UV-C exposure, and this UV-C induced damage was repaired through PR activity. 相似文献
975.
976.
Geographic variation in diapause induction under constant and changing conditions in Helicoverpa armigera 总被引:1,自引:0,他引:1
Variation in the incidence of diapause in local populations of Helicoverpa armigera (Hübner) and Helicoverpa assulta (Guenée) (Lepidoptera: Noctuidae) was examined in relation to changes in photoperiod and/or temperature during the larval period. Temperate zone populations of H. assulta, a native species in temperate Japan, showed a high incidence of diapause induction when only the photoperiod was decreased during the larval period, even at favorable temperatures. This photoperiod‐dependent response may allow H. assulta to foresee the beginning of autumn well in advance in the temperate zone, where temperature conditions are severe. In contrast, temperate zone populations of H. armigera, an invasive and polyphagous species mainly distributed in the subtropics, showed a high incidence of diapause only when both photoperiod and temperature decreased, whereas subtropical populations showed a very low incidence of diapause under the same conditions. Furthermore, both temperate zone and subtropical populations of H. armigera enter diapause under constant low temperatures at short‐day photoperiod. Thus, there is geographic variation in sensitivity to diapause‐inducing stimuli (changes in photoperiod and temperature) in H. armigera. This variation may be a part of the climatic adaptation achieved by H. armigera in Japan. 相似文献
977.
Ken W. Krauss Thomas W. Doyle Robert R. Twilley Thomas J. Smith Kevin R.T. Whelan Jason K. Sullivan 《Biotropica》2005,37(1):9-15
Woody debris is abundant in hurricane‐impacted forests. With a major hurricane affecting South Florida mangroves approximately every 20 yr, carbon storage and nutrient retention may be influenced greatly by woody debris dynamics. In addition, woody debris can influence seedling regeneration in mangrove swamps by trapping propagules and enhancing seedling growth potential. Here, we report on line‐intercept woody debris surveys conducted in mangrove wetlands of South Florida 9–10 yr after the passage of Hurricane Andrew. The total volume of woody debris for all sites combined was estimated at 67 m3/ha and varied from 13 to 181 m3/ha depending upon differences in forest height, proximity to the storm, and maximum estimated wind velocities. Large volumes of woody debris were found in the eyewall region of the hurricane, with a volume of 132 m3/ha and a projected woody debris biomass of approximately 36 t/ha. Approximately half of the woody debris biomass averaged across all sites was associated as small twigs and branches (fine woody debris), since coarse woody debris >7.5 cm felled during Hurricane Andrew was fairly well decomposed. Much of the small debris is likely to be associated with post‐hurricane forest dynamics. Hurricanes are responsible for large amounts of damage to mangrove ecosystems, and components of associated downed wood may provide a relative index of disturbance for mangrove forests. Here, we suggest that a fine:coarse woody debris ratio ≤0.5 is suggestive of a recent disturbance in mangrove wetlands, although additional research is needed to corroborate such findings. 相似文献
978.
Sprouting success of shrubs after fire: height-dependent relationships for different strategies 总被引:7,自引:0,他引:7
Ken C. Hodgkinson 《Oecologia》1998,115(1-2):64-72
The sprouting success of co-occurring populations of shrub species in a temperate woodland of semi-arid Australia was investigated
and related to population survival strategies. Straw was added to 21 × 15 m plots in the woodland, burnt and the pre-fire
characteristics of shrubs were used to determine the basis for sprouting success. Species differed widely (4–94%) in sprouting
success; a high percentage of established seedlings of all species were killed by fire but survival increased with height
reaching a maximum at 25–60 cm (depending on the species). Thickness of bark at stem bases increased with height growth but
sprouting success was not related to bark thickness; sprouting success of shrubs at similar thickness varied greatly between
species. All species were able to initiate sprouts after cutting through their basal stems, so lack of active meristems was
not a limitation. Species differed in the height at which shrubs began flowering but this was always after maximum sprouting
success was reached. It is proposed that differences between individual shrubs in supply of nutrients, carbohydrates, and/or
water to activated meristems would account for patterns of in ter- and intra-specific sprouting success. The data are consistent
with recognised fire survival strategies. `Sprouters', the species relying more on sprouting than recruitment for population
persistence, maintained maximum sprouting success with height growth and gained sprouting ability along stems once they reached
1 m in height. In contrast, `non-sprouters', the species largely relying on recruitment from seed to maintain populations,
were either not able to sprout after seedling establishment or steadily lost the ability to maintain sprouts with growth beyond
60 cm and did not develop axillary buds along stems at any height.
Received: 19 July 1997 / Accepted: 8 February 1998 相似文献
979.
The effect of temperature on testicular macromolecular synthesis was studied in vitro. It was found that the DNA synthesis of testicular germ cells was temperature-sensitive whereas protein and RNA synthesis were not. This specific character of the testicular germ cells is suggested to be the primary cause of thermal inhibition of germ cell differentiation. 相似文献
980.
Marion R. Steiner Ken Somers Sheldon Steiner 《Biochemical and biophysical research communications》1974,61(2):795-801
[14C]-2 deoxy-D-glucose is incorporated into the glycolipids of both normal and transformed cells. The chromatographic pattems of [14C]-2 deoxy-D-glucose labeled lipids differ markedly in oncornavirus and herpes simplex virus-transformed cells as compared to normal and virus-infected but not transformed cells. Deoxyglucoselabeled lipids with intermediate chromatographic mobility were enriched in normal and virus-infected but not transformed cells. Studies with a murine sarcoma virus-infected cell line which is temperature-sensitive for transformation indicated that the altered chromatographic pattern of [14C]-2 deoxy-D-glucose labeled lipids was related to the expression of the transformed phenotype. 相似文献