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1.
Transgenic Japanese lawngrass (Zoysia japonica Steud.) plants regenerated from protoplasts 总被引:14,自引:0,他引:14
Transgenic Japanese lawngrass (Zoysia japonica Steud.) plants were generated by means of polyethylene glycol (PEG)-mediated direct gene transfer into protoplasts. The plasmid
pBC1 was used to deliver the hygromycin phosphotransferase (hph) and β-glucuronidase (gus) genes into protoplasts. Selection with a high concentration (400 mg/l) of hygromycin yielded a number of resistant calli
and about 400 plants were generated. Polymerase chain reaction (PCR) and Southern hybridization analyses revealed that all
of then plants tested contained introduced genes. The gus gene regulated by the maize alcohol dehydrogenase-1 (Adh 1) promoter was expressed in the leaves and roots of transgenic Japanese lawngrass plants.
Received: 13 December 1996 / Revision received: 9 June 1997 / Accepted: 2 September 1997 相似文献
2.
Deryabin A. N. Trunova T. I. Dubinina I. M. Burakhanova E. A. Sabel'nikova E. P. Krylova E. M. Romanov G. A. 《Russian Journal of Plant Physiology》2003,50(4):449-454
Tolerance to chilling was compared under in vitro conditions in potato plants (Solanum tuberosum L., cv. Désirée) transformed with a yeast-derived invertase gene under the control of the B33 class 1 tuber-specific promoter (the B33-inv plants) and potato plants transformed only with a reporter gene (the control plants). The expression of the inserted yeast invertase gene was proved by following the acid and alkaline invertase activities and sugar contents in the leaves under the optimum temperature (22°C). The total activities of acid and alkaline invertases in the B33-inv plants exceeded those in the control plants by the factors of 2–3 and 1.3, respectively. In the B33-inv plants, the activity of acid invertase twice exceeded that of the alkaline invertase, whereas the difference equaled 12% in the control plants. The contents of sucrose and glucose increased in the B33-inv plants by 21 and 13%, respectively, as compared to the control. Chilling at +3 and –1°C for 1, 3, and 6 h did not affect the rate of lipid peroxidation, as measured by the content of malonic dialdehyde (MDA) in the leaves of the genotypes under study. Only the longer exposures (24 h at +3 and –1°C and 7 days at +5°C) produced a significant decline in the MDA content in the B33-invplants, as compared to the control. Following short freezing (20 min at –9°C), the content of MDA increased by 50% in the leaves of the control plants, while in the B33-inv plants, cold-treated and control plants did not differ in the MDA content. The authors presume that the potato plants transformed with the yeast invertase gene acquire a higher tolerance to low temperatures as compared to the control plants, apparently due to the changes in sugar ratio produced by the foreign invertase. 相似文献
3.
An expression system based on the Staphylococcus aureus protein A gene (spa) was developed to allow the production and export of proteins in Lactobacillus. Plasmid shuttle vectors were constructed that carried the eZZ gene, a synthetic gene based on the Protein A gene (spa) but lacking the carboxy-terminal membrane-anchoring region. A gene fusion was created between the eZZ gene and the VD4 region
of a chlamydial major outer-membrane protein gene. Expression studies demonstrated the recognition of the spa regulatory signals by several Lactobacillus, with the recombinant protein being expressed (from 0.1 μg of EZZVD4 fusion protein per ml in L. plantarum up to 10 μg of EZZ protein per ml in L. fermentum) and exported (levels up to 20% in L. fermentum) in several Lactobacillus strains.
Received: 27 August 1996 / Received revision: 27 November 1996 / Accepted: 29 November 1996 相似文献
4.
Accumulation of trehalose increases soluble sugar contents in rice plants conferring tolerance to drought and salt stress 总被引:4,自引:0,他引:4
Mark C. F. R. Redillas Su-Hyun Park Jang Wook Lee Youn Shic Kim Jin Seo Jeong Harin Jung Seung Woon Bang Tae-Ryong Hahn Ju-Kon Kim 《Plant biotechnology reports》2012,6(1):89-96
5.
LIU YanWANG GuoyingLIU JunjunPENG XuexianXIE YoujuDAI JingruiGUO ShiweiZHANG Fusuo 《中国科学:生命科学英文版》1999,42(1):90-95
GutD gene, encoding a key enzyme (glucitol-6-phosphate dehydrogenase) of sugar alcohol metabolic pathway inE. coli, was transferred into maize. Results of Southern and Western blotting analysis certified that this gene had integrated and
been expressed in transgenic maize plants and their progeny. The synthesis and accumulation of sorbitol were detected in transgenic
maize plants and a preliminary nutrient solution culture experiment showed thatgutD transgenic maize plants had an increased tolerance to salt stress compared with nontransgenic ones.
Project supported by the National Natural Science Foundation of China (Grant No. 39670413) and “863” State High Technology
Development Program. 相似文献
6.
C. Liang X. Y. Zhang Y. Luo G. P. Wang Q. Zou W. Wang 《Russian Journal of Plant Physiology》2009,56(3):370-376
To investigate the physiological mechanisms of glycinebetaine (GB) involved in the improvement of salt tolerance of wheat,
three transgenic wheat (Triticum aestivum L.) lines-T1, T4, and T6-and the wild-type (WT) line Shi4185 were used. The transgenic lines were generated by introducing
the BADH gene encoding betaine aldehyde dehydrogenase, which was cloned from Atriplex hortensis L. The BADH gene induced overexpression of GB in transgenic lines. Salt stress was induced by adding 200 mM NaCl, and the osmotic adjustment
(OA), ion homeostasis, and antioxidant characteristics of wheat plants were observed. Under salt stress, the OA in the transgenic
wheat lines was significantly higher than that in WT; this may be attributed to GB itself and/or the GB-induced overaccumulation
of other osmolytes, such as free proline, soluble protein, and soluble sugar. Moreover, the transgenic lines could maintain
the lower Na+ and Cl− concentrations in their leaves by accumulating these ions in the sheaths in order to protect the leaves from ion toxicity;
however, these lines maintained a higher K+ concentration in the leaves since K+ functions as an osmolyte and maintains ion homeostasis in the leaf cells. Furthermore, the in vivo overaccumulated GB could
enhance or stabilize the activity of antioxidant enzymes that can scavenge reactive oxygen species (ROS) and mitigate oxidative
damage of biomembranes. The experimental results suggest that GB overexpression can enhance the salt tolerance of transgenic
plants by regulating ion homeostasis, enhancing OA, and scavenging ROS.
Published in Russian in Fiziologiya Rastenii, 2009, vol. 56, No. 3, pp. 410–417.
This text was submitted by the authors in English. 相似文献
7.
Tissue-specific expression of the ORF13 promoter from Agrobacterium rhizogenes 8196 was assessed throughout the development of transgenic tobacco plants using a GUS reporter gene. ORF13 exhibited high
activity in roots but with different patterns of expression. The activity of the ORF13 promoter in vascular tissues increased
from the base to the tip of the stem. The ORF13 promoter is wound inducible in a limited area adjacent to the wound site.
The time course of wound induction of ORF13 in transgenic tobacco containing an ORF13 promoter-GUS translational fusion was
similar to that previously described for genes involved in plant defense responses. A series of 5′ deletions of the ORF13
promoter fused to the β-glucuronidase gene was examined for expression in roots and leaves of transgenic plants. Cis-acting
elements that modulate quantitative expression of the transgene after wounding were detected.
Received: 11 July 1996 / Accepted: 19 November 1996 相似文献
8.
High-Level Expression of Cold-Tolerant Pyruvate, Orthophosphate Dikinase from a Genomic Clone with Site-Directed Mutations in Transgenic Maize 总被引:1,自引:0,他引:1
Shozo Ohta Yuji Ishida Satoru Usami 《Molecular breeding : new strategies in plant improvement》2006,18(1):29-38
Pyruvate, orthophosphate dikinase (PPDK) is a key enzyme in the C4 photosynthetic pathway of maize. To improve the cold tolerance of the enzyme in maize, we designed two genomic sequence-based constructs in which the carboxy-terminal region of the enzyme was modified to mimic the amino acid sequence of the cold-tolerant PPDK of Flaveria brownii (Asteraceae). A large amount of PPDK was found to have accumulated in the leaves of many of the maize plants transformed with one of these constructs – that which introduced 17 amino acid substitutions without any alteration of the exon-intron structure – although there was a wide range of variation in the amount of PPDK among the separate plants. In contrast, the production was much less in maize transformed with the second construct in which a cDNA fragment for the same carboxy-terminal region was inserted. The specific activity of PPDK in the plants transformed with the gene with the amino acid substitutions was inversely correlated with the amount of enzyme in the leaves. In addition, the activity of the cold-tolerant recombinant enzyme was judged to be regulated by the PPDK regulatory protein, similar to that of the native PPDK. The cold tolerance of PPDK in crude leaf extracts was greatly improved in plants that produced a large amount of the engineered PPDK. The photosynthetic rate at 8°C increased significantly (by 23%, p<0.05), but there was no obvious effect at higher temperatures. These results support the hypothesis that PPDK is one of the limiting factors in the C4 photosynthesis of maize under cold conditions. 相似文献
9.
10.
H. A. Richards V. A. Rudas H. Sun J. K. McDaniel Z. Tomaszewski B. V. Conger 《Plant cell reports》2001,20(1):48-54
A dual marker plasmid comprising the reporter gene sgfp (green fluorescent protein) and the selectable bar gene (Basta tolerance) was constructed by replacing the uidA (β-glucuronidase, GUS) gene in a uidA-bar construct with sgfp. A particle inflow gun was used to propel tungsten particles coated with this plasmid into immature inflorescence-derived
embryogenic callus of switchgrass (Panicum virgatum L.). GFP was observed in leaf tissue and pollen of transgenic plants. Nearly 100 plants tolerant to Basta were obtained from
the experiments, and Southern blot hybridization confirmed the presence of both the bar and sgfp genes. Plants regenerated from in vitro cultures of transgenic plants grew on medium with 10 mg l–1 bialaphos. When the pH indicator chlorophenol red was in the medium, the transgenic plantlets changed the medium from red
to yellow. Basta tolerance was observed in T1 plants resulting from crosses between transgenic and nontransgenic control plants, indicating inheritance of the bar transgene.
Received: 11 May 2000 / Revision received: 21 August 2000 / Accepted: 22 August 2000 相似文献
11.
Xanthomonas campestris pv. campestris, the causal agent of black-rot disease of cruciferous plants, and an important industrial microbe, was able to express the
Escherichia coliβ-glucuronidase reporter gene (uidA) when fused to the E. coli lactose operon promoter on a wide-host-range plasmid vector. The gene fusion is expressed constitutively at high levels in
both complex and defined media using a wide range of carbon sources, and is not repressible by glucose or inducible by the
gratuitous lac inducer isopropyl β-d-thiogalactoside. An X. campestris campestris strain with a lesion in the clp (catabolite-repressor-like protein) locus, and containing the plac/uidA fusion, was tested for β-glucuronidase activity. We found that the expression of the plac/uidA fusion gene is dependent on the presence of catabolite-repressor-like protein, with an approximately 75% reduction of expression
in the clp -deficient mutant.
Received: 1 April 1996 / Received revision: 21 June 1996 / Accepted: 15 July 1996 相似文献
12.
Enkhchimeg Vanjildorj Tae-Woong Bae Key-Zung Riu Pil-Yong Yun Shin-Young Park Choon-Hwan Lee Soo-Young Kim Hyo-Yeon Lee 《Plant Cell, Tissue and Organ Culture》2006,87(2):109-120
Efficient procedures for regeneration and Agrobacterium-mediated transformation were established for Agrostis mongolica Roshev. and generated transgenic plants tolerant to drought and heat stresses using a regulatory gene from Arabidopsis, ABF3, which controls the ABA-dependent adaptive responses. The identification and selection of regenerable and reproducible callus type was a key factor for successful transformation. The transformation efficiency was 49.2% and gfp expression was detected in hygromycin-resistant calli and stem of putative transgenic plants. The result of Southern blot analysis showed that the ABF3 transgene was stably integrated into the genome of transgenic plants. Of the five transgenic lines analyzed, single transgene integration was observed in two lines and two copy integration was observed in three transgenic lines. Northern blot analysis confirmed that ubi::ABF3 was expressed in all transgenic lines. Transgenic plants exhibited neither growth inhibition nor visible vegetative phenotypic alternations. However, both transgenic and wild-type plants were highly sterile and did not flower during 3 years of growth period in the open field under subtropical Jeju Island climate. The stomata of the transgenic plants opened less than did stomata of the wild-type plants, and water content of the transgenic leaves remained about 3–4 fold higher than observed for wild-type leaves under drought stress. The transgenic plants showed about 2 fold higher survival rates under drought stress and about 3 fold higher survival rates under heat stress when compared to wild-type plants. Thus, overexpression of the Arabidopsis ABF3 gene results in enhancement of both drought and heat stress tolerance in Agrostis mongolica Roshev. 相似文献
13.
Liu Peng Yang Y. S. Xu Gendi Guo Shuiliang Zheng Xiaobin Wang Min 《Frontiers of Biology in China》2006,1(3):295-302
Different plants have physiological responses under Al stress, but there is no systematic study to examine physiological responses
of herbaceous plants under Al stress. The aim of this study is to investigate the effect of Al on physiological characteristics
of four herbaceous plants, which distributed in red soil area in South China, and to analyze the differences in physiological
responses to Al stress between the four herbaceous plants. Four herbaceous plants (Pharbitis nil, Cassia occidentlis, Echinochloa colonum and Aeschynomene indica) were used, and the seed germination percentage, the contents of chlorophyll, proline, and malondialdehyde (MDA), membrane
permeability (MP), soluble sugar, and activities of peroxides (POD) and catalase (CAT) in leaves under five Al3+ treatments (0, 80, 400, 2 000, and 10 000 mg/L) were assayed with the sand culture method. The results showed remarkable
effects of Al3+ on physiological characteristics of these four herbaceous plants. The seeds of all the four species could not germinate at
10 000 mg/L, and the growth of all plants were retarded under the 2 000 mg/L Al3+ treatment. Compared with the control, 2 000 mg/L Al3+ significantly (P < 0.05) reduced the contents of chlorophyll a and chlorophyll a + b, and increased the contents of MDA and MP. The content
of proline increased very significantly (P < 0.01) and activities of POD and CAT were depressed. The contents of MDA and MP in leaves of P. nil and A. indica decreased, and the activities of POD and CAT in leaves of the two plants increased under 80 mg/L and 400 mg/L. However, the
changes in C. occidentlis leaves were opposite to those of the above two plants. The changes in leaves of E. colonum were similar to those of P. nil and A. indica at 80 mg/L, but were opposite to those at 400 mg/L Al3+. It is suggested that plants with higher activities of POD and CAT, more contents of chlorophyll and proline, and lower contents
of MDA and MP consequently improve the tolerance to Al stress under low and middle Al treatments.
__________
Translated from Acta Phytoecologica Sinica, 2005, 29(4): 644–651 [译自: 植物生态学报, 2005, 29(4): 644–651] 相似文献
14.
《Molecular & general genetics : MGG》1998,258(1-2):1-8
Asr is a family of genes that maps to chromosome 4 of tomato. Asr2, a recently reported member of this family, is believed to be regulated by abscisic acid (ABA), stress and ripening. A genomic
Asr2 clone has been fully sequenced, and candidate upstream regulatory elements have been identified. To prove that the promoter
region is functional in vivo, we fused it upstream of the β-glucuronidase (GUS) reporter gene. The resulting chimeric gene
fusion was used for transient expression assays in papaya embryogenic calli and leaves. In addition, the same construct was
used to produce transgenic tomato, papaya, tobacco, and potato plants. Asr2 upstream sequences showed promoter function in all of these systems. Under the experimental conditions tested, ABA stimulated
GUS expression in papaya and tobacco, but not in tomato and potato systems.
Received: 24 March 1997 / Accepted: 26 November 1997 相似文献
15.
L. N. Hansen E. D. Earle 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,94(8):1078-1085
Somatic Hybrids between Sinapis alba and rapid-cycling Brassica oleracea were generated for transferring of resistance to Alternaria brassicae to B. oleracea. A. brassicae causes the significant disease black spot in cruciferous crops. A total of 27 plants were regenerated from protoplast fusion
using 0, 5, 10, 20 and 30 krad γ-irradiation of the resistance donor and iodoacetate treatment of B. oleracea. All plants showed intermediate morphology with partially divided leaves and some trichomes on stems and leaves. Flow cytometry
and banding patterns of the enzymes leucine amino peptidase (LAP) and phosphoglucose isomerase (PGI) confirmed the hybrid
status of the regenerated plants. Some of the plants obtained from cuttings from the somatic hybrids showed a resistance to
A. brassicae that was similar to that found in S. alba. The flowers of the somatic hybrids had reduced anthers with little pollen production.
Received : 9 May 1996 / Accepted : 15 November 1996 相似文献
16.
Subbiyan Maruthasalam Yi Lun Liu Ching Mei Sun Pei Ying Chen Chih Wen Yu Pei Fang Lee Chin Ho Lin 《Plant cell reports》2010,29(9):1035-1048
Scientific evidences in the literature have shown that plants treated exogenously with micromole concentration of hydrogen
peroxide (H2O2) acquire abiotic stress tolerance potential, without substantial disturbances in the endogenous H2O2 pool. In this study, we enhanced the endogenous H2O2 content of tobacco (Nicotiana tabaccum L. cv. SR1) plants by the constitutive expression of a glucose oxidase (GO; EC 1.1.3.4) gene of Aspergillus niger and studied their cold tolerance level. Stable integration and expression of GO gene in the transgenic (T0–T2) tobacco lines were ascertained by molecular and biochemical tests. Production of functionally competent GO in transgenic
plants was confirmed by the elevated levels of H2O2 in the transformed tissues. When three homozygous transgenic lines were exposed to different chilling temperatures for 12 h,
the electrolyte conductivity was significantly lower in GO-expressing tobacco plants than the control plants; in particular, chilling protection was more prominent at −1°C. In addition,
most transgenic lines recovered within a week when returned to normal culture conditions after −1°C–12 h cold stress. However,
control plants displayed symptoms of chilling injuries such as necrosis of shoot tip, shoots and leaves, consequently plant
death. The protective effect realized in the transgenic plants was comparable to cold-acclimatized wild tobacco. The chilling
tolerance of transgenic lines was found associated, at least in part, with elevated levels of total antioxidant content, CAT
and APX activities. Based on our findings, we predict that the transgenic expression of GO may be deployed to improve cold tolerance potential of higher plants. 相似文献
17.
Sugar accumulation,photosynthesis and growth of two indica rice varieties in response to salt stress 总被引:1,自引:0,他引:1
S. Cha-um A. Charoenpanich S. Roytrakul C. Kirdmanee 《Acta Physiologiae Plantarum》2009,31(3):477-486
Sugar, a final product of photosynthesis, is reported to be involved in the defense mechanisms of plants against abiotic stresses
such as salinity, water deficiency, extreme temperature and mineral toxicity. Elements involved in photosynthesis, sugar content,
water oxidation, net photosynthetic rate, activity of enzyme and gene expression have therefore been studied in Homjan (HJ),
salt-tolerant, and Pathumthani 1 (PT1), salt-sensitive, varieties of rice. Fructose-1,6-biphosphatase (FBP) and fructokinase (FK) genes were rapidly expressed in HJ rice when exposed to salt stress for 1–6 h and to a greater degree than in PT1 rice.
An increase in FBP enzyme activity was found in both roots and leaves of the salt-tolerant variety after exposure to salt
stress. A high level of sugar and a delay in chlorophyll degradation were found in salt-tolerant rice. The total sugar content
in leaf and root tissues of salt-tolerant rice was 2.47 and 2.85 times higher, respectively, than in the salt-sensitive variety.
Meanwhile, less chlorophyll degradation was detected. Salt stress may promote sugar accumulation, thus preventing the degradation
of chlorophyll. Water oxidation by the light reaction of photosynthesis in the salt-tolerant variety was greater than that
in the salt-sensitive variety, indicated by a high maximum quantum yield of PSII (F
v/F
m) and quantum efficiency of PSII (ΦPSII) with low nonphotochemical quenching (NPQ), leading to a high net photosynthetic rate. In addition, the overall growth performances
in the salt-tolerant variety were higher than those in the salt-sensitive variety. The FBP gene expression and enzyme activity, sugar accumulation, pigment stabilization, water oxidation and net photosynthetic rate
parameters in HJ rice should be further investigated as multivariate salt-tolerant indices for the classification of salt
tolerance in rice breeding programs. 相似文献
18.
Jinlei Shi Yingping Cao Xiaorong Fan Min Li Yaofeng Wang Feng Ming 《Molecular breeding : new strategies in plant improvement》2012,29(3):743-757
A full-length cDNA clone of OsFAD2, which encodes a Δ-12 fatty acid desaturase, the key enzyme for the conversion of oleic acid (18:1) into linoleic acid (18:2),
was isolated from rice (Oryza sativa ssp. japonica) leaves. The deduced amino acid sequence of OsFAD2 displayed three histidine boxes characteristic of all membrane-bound desaturases, and possessed a C-terminal signal for endoplasmic
reticulum retention. Phylogenetic analysis showed that OsFAD2 is grouped within plant housekeeping FAD2 sequences. Expression analysis by real-time PCR showed that the gene is expressed
in all tissues of rice tested, including root, seed, stem, and leaf. In situ hybridization showed that OsFAD2 mRNA accumulated in leaf mesophyll cells and in root epidermis cells when exposed to 15°C for 4 days in dark conditions.
When OsFAD2 was expressed in Saccharomyces cerevisiae, the cells could convert oleic acid to linoleic acid, which wild-type yeast cells cannot do, suggesting that the isolated
gene encoded a functional FAD2 enzyme. Heterologous expression of OsFAD2 enhanced the yeast cells’ cold tolerance capacity compared to wild-type yeast. OsFAD2 was also shown to be a highly active desaturase when expressed in Xenopus oocytes. In addition, when the OsFAD2 gene was transferred into an Arabidopsis thaliana
fad2-1 mutant, it effectively restored wild-type fatty acid composition and growth characteristics. Stress tolerance and light regulatory
elements were identified in the predicted promoter of the OsFAD2 gene. Exogenously supplied hormone affected the level of FAD2 mRNA accumulation, accompanied by a change of content of di-unsaturated fatty acid species in rice leaves. Furthermore, OsFAD2 enhanced tolerance to low temperature when overexpressed in rice at the vegetative stage. More importantly, the 35S::OsFAD2
plants showed significantly enhanced cold tolerance at the reproductive stage, increasing grain yield by 46% over controls
in the greenhouse under cold conditions. These results indicated that OsFAD2 is involved in fatty acid desaturation and maintenance
of the membrane lipids balance in cells, and could improve the tolerance of yeast and rice to low temperature stress. 相似文献
19.
A new class of recessive Arabidopsis mutants, designated cristal (cri ) has been isolated which display several abnormalities reminiscent of hyperhydric symptoms. These characteristics include
translucent and wrinkled cotyledons and leaves, abnormal chloroplast organization, a reduced amount of chlorophyll, a reduced
dry weight and a decreased number of palisade cells in the leaves accompanied by an increase of intercellular space, and therefore
give a vitreous appearance to the aerial part. The phenotype is also dependent on the culture medium water potential. The
cri1 gene was mapped on chromosome 4 close to the DHS1 marker.
Received: 5 August 1996 / Accepted: 11 December 1996 相似文献
20.
The use of higher plants as the basis for a biological life support system that regenerates the atmosphere, purifies water, and produces food has been proposed for long duration space missions. The objective of these experiments was to determine what effects microgravity (μg) had on chloroplast development, carbohydrate metabolism and gene expression in developing leaves of Triticum aestivum L. cv. USU Apogee. Gravity naive wheat plants were sampled from a series of seven 21-day experiments conducted during Increment IV of the International Space Station. These samples were fixed in either 3% glutaraldehyde or RNAlater™ or frozen at −25°C for subsequent analysis. In addition, leaf samples were collected from 24- and 14-day-old plants during the mission that were returned to Earth for analysis. Plants grown under identical light, temperature, relative humidity, photoperiod, CO2, and planting density were used as ground controls. At the morphological level, there was little difference in the development of cells of wheat under μg conditions. Leaves developed in μg have thinner cross-sectional area than the 1 g grown plants. Ultrastructurally, the chloroplasts of μg grown plants were more ovoid than those developed at 1 g, and the thylakoid membranes had a trend to greater packing density. No differences were observed in the starch, soluble sugar, or lignin content of the leaves grown in μg or 1 g conditions. Furthermore, no differences in gene expression were detected leaf samples collected at μg from 24-day-old leaves, suggesting that the spaceflight environment had minimal impact on wheat metabolism.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. 相似文献