冷冻液温和季节对鼠尾过冷点的影响

为研究动物对寒冷的适应性,将鼠尾置于冷液浸冻,发现在一定条件下鼠尾组织可发生过冷现象。实验表明,鼠尾组织的过冷点和冷冻液温有关,同一季节冷冻液温越低过冷点越高;而不同季节相同冷冻条件下,冬季鼠尾组织的过冷点明显低于春季。 动物肢体组织的过冷特性是动物的抗寒冷特性,它和组织自身的物理化学性质有关。理沦证明,过冷度(△T)和表面张力(O)、摩尔质量(M),冰点(Ti)、密度(p)、摩尔凝固热(△H)及冰胚临界半径(rk)有关,其关系式为△T=26MTi/p△Hrk.     

Structural features are as important as sequence homologies inDrosophila heat shock gene upstream regions

Summary Pelham has shown that theDrosophila hsp 70 gene is not transcribed under heat shock conditions unless a given upstream region is present. Davidson et al. have recently compiled a list of sequences homologous to this region in otherDrosophila heat shock genes. They proposed that a set of unlinked genes, such as the heat shock genes, could be coordinately induced through an interaction in cis with a common regulatory molecule. That this interaction involves structural elements is suggested by the fact that these upstream regions share inverted repeats as well as areas of Z-DNA potential. Furthermore, using the Calladine-Dickerson rules for local helical parameters, we show that these regions share structural homology. This is significant because the presence of regions homologous to a derived consensus sequence does not necessarily imply structural similarity. Therefore, we suggest that these structural features are at least as important as the sequence homologies in enabling the heat shock response.     

Heat treatment of ripening apples: Differential effects on physiology and biochemistry

Apples ( Malus domestica Borkh.) were heated for 4 days at 38°C immediately after harvest and then placed at 20°C for 7–10 days. Protein synthesis, ethylene production and fruit softening were reversibly inhibited by the heat treatment. Fruit respiration, membrane permeability and chlorophyll degradation in the fruit peel were enhanced during the treatment. The heat-treated apples ripened normally but more slowly than untreated apple We hypothesize that heat treatment differentially affects processes which normally increase simultaneously during fruit ripening, by inhibiting those processes which require tie novo protein synthesis and enhancing those that do not.     

Genetic analysis of risk in clonal populations of forest trees

Summary A major concern arising from the culture of clonally propagated crops of forest trees is risk of catastrophic loss due to an agent or event not anticipated at the time of population establishment. Since danger of such a catastrophe depends to some degree on the genetic variability within clonal mixtures, attention has been focused on the number of clones needed to keep the risk of catastrophic loss below specified levels. In this paper, we describe a genetical analysis of susceptibility to a destructive agent and the effect that frequency of genes for susceptibility have on the number of clones needed to effectively manage this risk. As a part of the analysis, parameters representing the minimum unacceptable mortality rates in plantations () and acceptable levels of risk () are defined, and their effects on the number of single-pair matings needed for the production of clonal stock are evaluated. Dominance and recessive gene action models for a single two-allele genetic locus are investigated. Probabilities for plantation failure are functions of the gene frequency for the allele conferring susceptibility. These functions converge to zero for allele frequencies less than but to one for frequencies greater than or equal to . This convergence is periodic rather than monotonie, since probabilities for plantation failure increase rather than decrease over restricted ranges of increasing numbers of clones. Recessive and dominance gene actions are found to have different effects on the minimum number of clones needed to attain acceptable risk levels. For conditions in which substantial numbers of clones are required, selecting multiple clones per mating is an effective method for reducing the number of matings necessary to achieve acceptable risks.Paper No. 12480 of the Journal Series of the North Carolina Agriculture Research Service, Raleigh, NC 27695-7643, USA     

Heat shock proteins induce pores in membranes

Human heat shock protein (hsp) 70 and bacterial protein groEL promote leakage of calcein from liposomes induced by human serum albumin signal peptide, byS. aureus toxin or by diphtheria toxin. Hsp 70 and groEL, as well as two mycobacterial homologues hsp 71 and hsp 65, induce ion conducting pores across planar lipid bilayers at low or neutral pH. It is concluded that hsp induce pores in membranes and that this may contribute to their action within cells.     

Microcalorimetric investigations on human leukemia cells--Molt 4

Heat production by leukemia cells Molt 4, growing in suspensions with 1 and 3 x 10(5) cells/ml for 4 days, was studied by microcalorimetry. Heat production rates were related to cell growth, glucose consumption, lactate production and cellular ATP-content. The results show that the time course of heat dissipation is dependent on initial cell number. However, observed thermal power maxima were fairly identical in all experiments. Heat production rates per cell were similar during the initial phase of the study independently of initial cell number, while higher cell densities resulted in significantly lower rate of heat production. Glycolytic conversion of glucose into lactate is nearly stoichiometric. Our results indicate a relationship between heat production and amounts of glucose and lactate in the medium. ATP concentration in cells decreased after 24 hours of culture.     

Arabidopsis: Sensitivity of growth to high temperature

Arabidopsis thaliana seedlings as measured by an electrolyte leakage assay, have been found to be extremely sensitive to high temperature stress as compared to a high temperature tolerant variety (Tracy) of soybean. Over 50% ion leakage occurred in Arabidopsis leaves during a 15-minute exposure to 50°C, indicating a heat killing time of less than 15 minutes. In contrast, the heat killing time for soybean at 50°C was over five times longer. When soybean or Arabidopsis seedlings in culture plates were exposed to 37°C for 2 hours and then returned to 23°C, they suffered no apparent short-term or long-term damage. Soybean seedlings given a 42°C, treatment for 2 hours also showed no damage. Arabidopsis seedlings after a 42°C treatment for 2 hours showed no apparent immediate damage, but 48 hours after return to 23°C severe damage symptoms were visible and after 96 hours all the seedlings were dead. Both soybean and Arabidopsis seedlings synthesize heat shock proteins (hsps) when exposed to 42°C for 2 hours. The hsps synthesized are of similar molecular weights, although the relative abundances of the different size classes are very different in the two plants. Even though hsps are produced in Arabidopsis seedlings after a 2 hour exposure to 42°C their presence is not sufficient for the seedlings to recover from the effects of rhe heat shock when returned to 23°C. Our results show that Arabidopsis has a heat sensitive genotype. This along with its other characteristics should make it a good model system in which to assay in transgenic plants, the functions of homologous and heterologous genes that might be candidates for determining heat tolerance in plants.     

Localization of constitutive heat shock proteins in developing ascidians

Heat shock proteins (HSP) are a group of highly conserved proteins that regulate protein folding and ameliorate the effects of environmental stress. In the present study, the question of whether or not ascidian oocytes, embryos and larvae constitutively synthesize HSP was studied using HSP 60 and HSP 70 antibodies. Developmental stages obtained from Boltenia villosa, Cnemidocarpa finmarkiensis, Styela montereyensis and Corella willmeriana were examined for HSP using indirect immunocytochemistry. Myoplasm in oocytes and unfertilized eggs reacted with HSP 60 and 70 antibodies. HSP signals dramatically moved into the vegetal egg cytoplasm during ooplasmic segregation and colocalized with the myoplasm. In cleavage-stage embryos, HSP signals were partitioned with the myoplasm into muscle progenitor blastomeres and HSP signals were evident in the tail muscle cells of larvae. Immunoblots of proteins extracted from oocytes, eggs, embryos and larvae indicate that anti-HSP 60 recognizes a single band having an estimated molecular weight of 60 kDa. Egg centrifugation experiments suggest that most of the ascidian myoplasmic HSP are mitochondrial proteins. These results raise an intriguing possibility that mitochondria associated with the myoplasm perform biochemical functions that are unique to the embryonic muscle cell lineage.