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71.
The effects of cold treatment on the cortical microtubules (MTs) of Chaetomorpha moniligera Kjellman were investigated by immunofluorescence microscopy. Cortical MTs in Chaetomorpha thallus are arranged longitudinally. In this study, 70–75% of MTs disassembled within 4 h on ice while the others remained stable under these conditions. Reticulate background immunofluorescence, assumed to indicate the presence of a tubulin monomer, was distributed about the stable MTs. Immunofluorescence was prominent in only 50% of the cells. Tubulin polymerization was noted where the background and MT immunofluorescence was strong. New MTs grew transversely as single strings or clusters from the sides of MTs after cold treatment for 4 h and elongated with time to take on a reticulate form at 24 h. The significance of this tubulin polymerization under cold treatment is discussed.Abbreviations MT
microtubule
- MTOC
microtubule-organizing center 相似文献
72.
73.
The role of nitrogen in a simple scheme to scale up photosynthesis from leaf to canopy 总被引:12,自引:2,他引:10
A simple analytical scheme, involving the distribution of nitrogen, to scale up photosynthesis from leaf to canopy is proposed. The scheme is based on the assumption that there are two pools of nitrogen in leaves: nitrogen in photosynthetic, degradable structures (Np) and nitrogen in non-photosynthetic and non-degradable structures (Ns). The rate of photon-saturated photosynthesis, Fm, is assumed to be proportional to Np and is distributed inside the canopy similarly to photon flux density (PFD). Prior assumptions of an optimum distribution of nitrogen are not a prerequisite. Calculations made with the scheme lead to development of the hypothesis that the canopy can be treated as a ‘big leaf’ on the time scales involved in acclimation of photosynthesis to PFD. Simulations using parameters for tree species with different requirements for PFD show that shade-tolerant species may have denser canopies than sun-demanding species because of smaller amounts of non-photosynthetic structural nitrogen and/or supporting tissue in their leaves. 相似文献
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Two intertidal snails, Littorina saxatilis (Olivi, 1972) (upper eulittoral fringe/maritime zone) and Littorina obtusata (Linnaeus, 1758) (lower eulittoral) were collected from a boulder shore on Nobska Point, Cape Cod, Massachusetts, in July
and acclimated for 15–20 days at 4 ° or 21 °C. Oxygen consumption rate (Vo2) was determined for 11–15 subsamples of individuals at 4 °, 11 ° and 21 °C with silver/platinum oxygen electrodes. Multiple
factor analysis of variance (MFANOVA) of lo10 transformed values of whole animal Vo2 with log10 dry tissue weight (DTW) as a covariant revealed that increased test temperature induced a significant increase in Vo2 in both species (P<0.00001). In contrast, MFANOVA revealed that temperature acclimation did not affect Vo2 in either L. saxatilis (P= 0.35) or L. obtusata (P= 0.095). Thus, neither species displayed a capacity for the typical metabolic temperature compensation marked by an increase
in Vo2 at any one test temperature in individuals acclimated to a lower temperature that is characteristic of most ectothermic animals.
Lack of capacity for metabolic temperature acclimation has also been reported in other littorinid snail species, and may be
characteristic of the group as a whole. Lack of capacity for respiratory temperature acclimation in these two species and
other littorinids may reflect the extensive semi-diurnal temperature variation that they are exposed to in their eulittoral
and eulittoral fringe/maritime zone habitats. In these habitats, any metabolic benefits derived from longer-term temperature
compensation of metabolic rates are negated by extreme daily temperature fluctuations. Instead, littorinid species appear
to have evolved mechanisms for immediate metabolic regulation which, in L. saxatilis and L. obtusata and other littorinids, appear to centre on a unique ability for near instantaneous suppression of metabolic rate and entrance
into short-term metabolic diapause at temperatures above 20–35 °C, making typical seasonal respiratory compensation mechanisms
characteristic of most ectotherms of little adaptive value to littorinid species. 相似文献
76.
Body water content was determined on groups of Cyprinodon variegatus after sequential acclimation to ambient salinities in the range from fresh water to 100%. A multiple linear regression model applied to the data included body mass ( M ) of individuals and acclimation salinity ( S ) as independent variables, and body water content ( W ) as the dependent variable. The model that described the relationship was W (g) = 0·059 + 0·723 M (g)–0001 S (%). Converting values of body water content to percent of wet body mass produced a range of values from 74·5% in fresh water to 72·0% at 100%, only a 2·5% difference in body water content over this wide range of ambient salinities. 相似文献
77.
四个籼稻(Oryza sativa L.)品种幼苗经1℃黑暗或光照250 μm ol·m - 2·s- 1处理后,抗冷的“桂山矮选3”比不抗冷的“青华6 号”幼苗存活率高,其子代是以“桂山矮选3”为母本的比“青华6 号”为母本的存活率较高。抽穗期剑叶经光照低温处理12、24 和36 h 后,光合作用是“桂山矮选3”和以“桂山矮选3”为母本的子代比“青华6 号”和以“青华6 号”为母本的子代下降较少。呼吸作用是前者比后者在处理12 h 时有明显升高现象。荧光参数Fv/Fo和Fv/Fm比值在处理24 h 时前者比后者下降明显,但在常温下恢复则是前者比后者明显较快。自然低温(寒露风)对叶绿素荧光的影响亦有相似的规律。对水稻后代的抗冷性倾向于母本进行了讨论 相似文献
78.
Abstract Photosynthetic temperature acclimation in Carex eleocharis has been demonstrated in a previous study in which warm grown (35/15°C) plants were shown to have photosynthetic temperature optima approximately 14°C higher than cool grown (20/15°C) plants (Monson, Littlejohn & Williams, 1983). The current study examined the time course of this acclimation by determining photo-synthetic temperature optima as a function of time, of cool grown plants moved to warm growing conditions. Leaves which had developed under cool conditions were capable of an upward adjustment of 6–8°C of their optimum photosynthetic temperature within a time span of 6–14 d. For greatest photosynthetic temperature acclimation it was necessary for leaves to form and develop entirely under warm conditions. These leaves exhibited a 14–15°C upward adjustment of their optimum temperature for photosynthesis within 20–31 d since moving plants from cool to warm growing conditions. Thus, the time course of this acclimation is of short enough duration to be significant during the growing season and presumably contributes toward the ability of this species to maintain active growth during the cool and warm portions of the growing season. It is also noted that the plant with its capacity to form new leaves, has a much wider acclimation capacity than any single leaf. 相似文献
79.
80.