PV技术的计算机处理及其在树木水分关系研究中的应用

ＰＶ技术的计算机处理及其在树木水分关系研究中的应用刘建伟,刘雅荣,王世绩（中国林业科学研究院林业研究所,北京１０００９１）ＣｏｍｐｕｔｅｒＰｒｏｃｅｓｓｉｎｇｏｆＰＶＣｕｒｖｅＡｎａｌｙｓｉｓａｎｄＩｔｓＡｐｐｌｉｃａｔｉｏｎｉｎｔｈｅＲｅｓｅａｒｃ...     

Genomic insights into selection for heterozygous alleles and woody traits in Populus tomentosa

Heterozygous alleles are widespread in outcrossing and clonally propagated woody plants. The variation in heterozygosity that underlies population adaptive evolution and phenotypic variation, however, remains largely unknown. Here, we describe a de novo chromosome-level genome assembly of Populus tomentosa, an economic and ecologically important native tree in northern China. By resequencing 302 natural accessions, we determined that the South subpopulation (Pop_S) encompasses the ancestral strains of P. tomentosa, while the Northwest subpopulation (Pop_NW) and Northeast subpopulation (Pop_NE) experienced different selection pressures during population evolution, resulting in significant population differentiation and a decrease in the extent of heterozygosity. Analysis of heterozygous selective sweep regions (HSSR) suggested that selection for lower heterozygosity contributed to the local adaptation of P. tomentosa by dwindling gene expression and genetic load in the Pop_NW and Pop_NE subpopulations. Genome-wide association studies (GWAS) revealed that 88 single nucleotide polymorphisms (SNPs) within 63 genes are associated with nine wood composition traits. Among them, the selection for the homozygous AA allele in PtoARF8 is associated with reductions in cellulose and hemicellulose contents by attenuating PtoARF8 expression, and the increase in lignin content is attributable to the selection for decreases in exon heterozygosity in PtoLOX3 during adaptive evolution of natural populations. This study provides novel insights into allelic variations in heterozygosity associated with adaptive evolution of P. tomentosa in response to the local environment and identifies a series of key genes for wood component traits, thereby facilitating genomic-based breeding of important traits in perennial woody plants.     

The genetic resolution of juvenile canopy structure and function in a three-generation pedigree of Populus

 A genetic approach to the understanding of tree architecture is to cross trees of contrasting features and to study their segregating F₂ progenies. For this purpose, members of a 3-generation pedigree, combining Populus trichocarpa, P. deltoides, and their F₁ and F₂ offspring, were grown side by side in a clonally replicated plantation. At 2 and 3 years of growth, tree architecture was analyzed at the stem, branch, and leaf levels. In all generations, proleptic branches were more numerous, longer, and had more and larger leaves than sylleptics initiated in the same year. The analysis of variance revealed significant genotypic effects on growth, branch and leaf biometrics in the F₂ family, with broad-sense heritabilities (H²) ranging from 0.50 to 0.80 for most traits. For branch and leaf traits, the H² values were found to vary among branch types and crown positions. In year 2, the degree of genetic control was stronger for sylleptics than proleptics and for upper than lower crown positions. These patterns were followed in year 3, except that H² values were more a function of position within crown, as a consequence of increased competition among trees. The genetic correlations between branch/leaf morphology and stem growth were also a function of branch type and crown position. Generally, traits on proleptics or at upper positions were more tightly correlated with height growth, whereas those on sylleptics or at lower positions, with basal area growth. By year 3, proleptic traits showed increased genetic correlations with both height and radial growth. The implications of these results for the construction of ideotypes are discussed. Received: 1 December 1995     

Poplar (Populus nigra L.) plants transformed with aBacillus thuringiensis toxin gene: insecticidal activity and genomic analysis

Insect-resistant poplar (Populus nigra L.) plants have been produced by infecting leaves withAgrobacterium tumefaciens strains carrying a binary vector containing different truncated forms of aBacillus thuringiensis (B.t.) toxin gene under a duplicated CaMV 35S promoter. Putative transgenic plants were propagated by cuttings at two experimental farms (in Beijing and Xinjiang, China). At 2–3 years after transformation, 17 of them were selected on the bases of insect-tolerance and good silvicultural traits, and evaluated for insect resistance, for the presence of theB.t. toxin DNA fragment (Southern blots and PCR) and for the expression of the transgene (western and northern blots). Somaclonal variation, as suggested by the appearance of permanent changes in the shape of the leaves, was also investigated with molecular tools (RFLP (restriction fragment length polymorphism), RAPD (random amplified polymorphic DNA) and microsatellite DNA).Bioassays withApochemia cineraius andLymantria dispar on the leaves of the selected clones showed different and, in some cases, high levels of insecticidal activity. The molecular analysis demonstrated integration and expression of the foreign gene. Somatic changes were correlated to extensive genomic changes and were quantified in dendrograms, in terms of genomic similarity. The analysis of control plants suggested that genomic changes were correlated to thein vitro culture step necessary forA. tumefaciens-mediated gene transfer, rather than to the integration of the foreign genes.Three transgenic clones (12, 153 and 192), selected for insect resistance, reduced morphological changes and promising silvicultural traits, are now under large-scale field evaluation in six different provinces in China.     

Natural Occurrence ofChondrostereum purpureumin Relation to Its Use as a Biological Control Agent in Canadian Forests

The incidence of natural fructification ofChondrostereum purpureumwas estimated quantitatively on southern Vancouver Island during two winter seasons in randomly located 1000-m²plots and compared with potential added fructification that might occur as a result of using the fungus to control stump-sprouting of hardwood weeds in young forest stands. Fructification was surveyed in forests as well as in urban or agricultural areas by estimating the surface areas of woody substrates covered with basidiocarps. In addition to random plots, estimates were made also in locations where the fungus would be expected to occur (woodpiles, silvicultural thinnings, and killed trees). Basidiocarps were found throughout the area in various types of forest cover as well as in urban or agricultural situations. The amount of added fructification through the use of the fungus as a biological control agent was determined from inoculated plots as well as from calculated stump-surface areas developed from published stand-density data. Added fructification was multiplied by a factor representing the maximum biological control frequency in order to compare added fructification with natural fructification values. From the various calculations, it was determined that the added fructification ofC. purpureumis of the same order of magnitude as naturally occurring levels or even lower. In addition, there is a distinct geographical separation between predominantly forestry and predominantly settled areas where fruit and ornamental trees are cultivated. Accordingly, it was concluded that using the fungus as a biological control agent in forestry is not likely to pose a significant threat to fruit growing and commercial forests.     

Photomorphogenesis and canopy dynamics. Phytochrome-mediated proximity perception accounts for the growth dynamics of canopies of Populus trichocarpa × deltoides'Beaupré'

The phytochrome family of signal-transducing photoreceptors provides plants with the capacity to perceive variations in the relative fluxes of red (R) and far-red (FR) radiation. This capacity has been proposed to be of ecological value in the perception of the proximity of neighbouring plants and the consequent induction of shade avoidance responses. The work reported here has evaluated this potential by determining quantitatively the effect of neighbour proximity on the growth of canopies of Populus trichocarpa×deltoides‘Beaupré’ trees, and relating the measured variables to the long-term vectoral radiation quality inside each canopy. The spectral distribution of radiation inside four canopies of Populus trichocarpa×deltoides‘Beaupre’ of different densities was monitored throughout the growing season. Spectral distributions inside the canopies were measured in 10° wedges at different heights and angles. The results are presented as PFD over 400–700 nm (PFD400–700) and PFD over 400–800 nm (PFD400–700). Results are also presented for the calculated phytochrome photoequilibrium (Pfr/P) and red:far-red ratio (R:FR). Data are presented as in-canopy angular and height profiles, and as diurnal and seasonal variations. PFD_400–700 and Pfr/P were found to be reduced inside each canopy, the reduction being greatest in the most dense canopy, and least in the most open canopy. At any height within each canopy, calculated Pfr/P decreased linearly with time throughout the growing season, until leaf senescence began. The reduction was greater in the denser canopies and was found to be similar for three consecutive field seasons. Linear relationships were found between plant stem growth rate, plant spacing and Pfr/P calculated from radiation propagated approximately horizontally within the canopies. The findings support the role of phytochrome in proximity perception in the natural environment and provide a quantitative basis for investigating the competitive interactions between plants growing in dense stands. The hypothesis is proposed that the dynamics of developing or regenerating canopies can be accounted for on the basis of phytochrome-mediated perception of the proximity of neighbouring plants.     

Photoperiodic responses of a northern and southern ecotype of black cottonwood

Photoperiod is an important signal controlling the onset of dormancy in perennial plants. Short days typically induce growth cessation, the initiation of cold acclimation, the formation of a terminal bud. bud dormancy and other adaptive responses. Photoperiodic ecotypes have evolved in many species with large latitudinal distributions. The photoperiodic responses of two northern (53°35′ and 53°50′N) and two southern (34°10′ and 40°32′N) genotypes of black cottonwood (Populus trichocarpa Torr. & Gray) were characterized by growing trees under a range of photoperiods in the greenhouse and growth chamber. Short days induced bud set in both ecotypes. resulting in trees with fewer leaves and less height growth than trees grown under long days. Short days also enhanced anthocyanin accumulation in the northern ecotype and decreased branching of the southernmost genotype. Two aspects of the photoperiodic response were evaluated for each trail: critical photoperiod. which was defined as the longest photoperiod that elicited a short-day response, and photoperiodic sensitivity, which was defined as the change in response per unit change in photoperiod. For each of the traits analyzed, the northern ecotype had a longer critical photoperiod and greater photoperiodic sensitivity than did the southern ecotype. The short critical photoperiod and reduced photoperiodic sensitivity of the southern ecotype resulted in a significant delay in bud set compared to that of the northern ecotype, even under a 9-h photoperiod. Typically, photoperiodic ecotypes have been characterized as having different critical photoperiods. Ecotypic differences in photoperiodic sensitivity, however, indicate that differences in the photoperiodic response curves cannot be completely described by the critical photoperiod alone. These results also suggest that the critical photoperiod. photoperiodic sensitivity and speed of bud set have a common physiological basis. Bud set occurred earlier hi the northern ecotype primarily because bud scale leaves were initiated earlier. For one of the northern genotypes, leaf primordia that were initialed under long days subsequently differentiated into bud scale leaves after the trees were transferred to a 9-h photoperiod. This demonstrates that primordia initiated under long days are not necessarily committed to becoming foliage leaves. The response to photoperiod did not differ appreciably between the greenhouse and growth chamber conditions that were tested.     

Molecular cloning of two tandemly arranged peroxidase genes from Populus kitakamiensis and their differential regulation in the stem

A genomic library was prepared from Populus kitakamiensis and screened with the cDNA for an anionic peroxidase from P. kitakamiensis. One genomic clone was isolated that contained two tandemly oriented genes for anionic peroxidases, prxA3a and prxA4a. Both genes consisted of four exons and three introns; the introns had consensus nucleotides, namely, GT and AG, at their 5 and 3 ends, respectively. The prxA3a and prxA4a genes encoded 347 and 343 amino acid residues, respectively, including putative signal sequences at the amino-termini. Putative promoters and polyadenylation signals were found in the flanking regions of both genes. The sequence of the coding region of prxA3a was completely identical to that of the cDNA clone pA3, whereas the sequence of the coding region of prxA4a was only 73% identical to that of the cDNA clone pA3. Northern blot analysis showed that the patterns of expression of the mRNAs that corresponded to prxA3a and prxA4a differed in stems of P. kitakamiensis.     

Factors affecting Agrobacterium tumefaciens-mediated transformation in several black poplar clones

Transient expression of the uidA reporter gene was used in preliminary experiments with two oncogenic and two disarmed Agrobacterium tumefaciens strains in order to test the efficiency of T-DNA transfer to N084 x Populus nigra and N107 x P. nigra clones. The oncogenic strain A281 pKIWI105 produced the highest average number of GUS spots per leaf disc. In order to optimize the production of transgenic plantlets from different P. nigra clones (San Giorgio, Jean Pourtet, N084 x P. nigra and N107 x P. nigra, respectively), two A. tumefaciens strains (GV2260 p35S GUS, A281pKIWI105) and bacterial concentrations (7×10⁸; 1.2×0⁹ bacteria ml^-1) were used. Following co-cultivation with A281 pKIWI105, the frequency of leaf discs producing kanamycin-resistant calli was not significantly different between the clones and bacteria concentrations used. Transformed shoots were regenerated from all clones, except for Jean Pourtet. Co-cultivation of leaf discs with GV2260 p35S GUS produced very few calli which died when transferred to selective regeneration medium. In addition, the effects of acetosyringone and leaf wounding were evaluated for the San Giorgio and Jean Pourtet clones, using the same strains. Factors which significantly affected the transformation efficiency of leaf explants were the P. nigra clone, the A. tumefaciens strain, and the presence of acetosyringone. Genetic transformation of calli and regenerated plantlets was confirmed by their ability to grow and root on Woody Plant Medium containing kanamycin, by histochemical -glucuronidase assays, and Southern blot hybridization analyses.Abbreviations BA benzyladenine - GUS -glucuronidase - IBA indolebutyric acid - MS Murashige and Skoog - NAA -naphthaleneacetic acid - nptII neomycin phosphotransferase II gene - uidA -glucuronidase gene - WPM Woody Plant Medium     

Ribulose-1, 5-bisphosphate carboxylase activity,chlorophyll and protein concentrations in differentPopulus clones

Ribulose-1,5-bisphosphate carboxylase activity (RuBPC), chlorophyll (chl) and protein (prot) concentrations and chlorophyll/protein (chl/prot) ratios were determined in five differentPopulus clones together with their maximal net CO₂ uptake rates (P_max). A classic reference clone (Populus ×euramericana “Robusta” (Dode) Guinier) was compared with four recently selected euramerican and interamerican crossings. Chl/prot ratio and RuBPC activity varied among the different clones, while chl a/chlb ratio showed only a very low coefficient of variation (1.7%) for the five clones. Poplar clone “Robusta” could be distinguished from the recent faster growing clones based on the different biochemical characteristics. A significant correlation was found between both total chl concentration and chl/prot ratio with P_max for the five clones.