长三角及邻近地区138种草本植物DNA C-值测定及其生物学意义

为了评估DNA C-值和基因组大小(genome size)在植物入侵性评估中的价值,应用流式细胞仪测定了长三角及邻近地区138种草本植物的核DNA含量,其中111种为首次报道。在此基础上比较了不同植物类群这两个值的差异,特别是入侵性与非入侵性植物这两个值的差异。结果表明:(1)138种草本植物平均DNA C-值为1.55 pg,最大者是最小者的37.17倍。127个类群平均基因组大小为1.08 pg,最大者是最小者的34.11倍;(2)统计了菊科(Asteraceae)、禾本科(Poaceae)、石竹科(Caryophyllaceae)、十字花科(Brassicaceae)、玄参科(Scrophulariaceae)、蓼科(Polygonaceae)、唇形科(Labiatae)和伞形科(Umbelliferae)的DNA C-值和基因组大小,发现禾本科植物的这两个值显著地大于其他7个科(P0.01)。单子叶的DNA C-值和基因组极显著地大于双子叶植物(P0.01);(3)杂草比非杂草具有更低的DNA C-值(P0.01)和基因组大小(P0.001);与DNA C-值相比,基因组大小在这两个类群之间的差异更为明显(P0.001),这种现象也体现在菊科植物中。随着基因组(X1)和DNA C-值(X2)由大变小,植物的杂草性(入侵性,Y)由弱变强,两者关系分别符合:Y=2.2334-1.2847 ln(X1)(r=0.4612,P0.01)和Y=2.4421-0.7234 ln(X2)(r=0.2522,P0.01),DNA C-值和基因组大小可以作为植物入侵性评估的一个指标;(4)多倍体杂草的基因组极明显地小于二倍体杂草(P0.01),前者为后者的0.63倍。在非杂草中,多倍体基因组比二倍体的略小,前者仅为后者的0.84倍,差异不显著(P0.5)。菊科植物中多倍体杂草的基因组也显著地小于二倍体杂草(P0.1)。基因组变小和多倍体化相结合,进一步增强了植物的入侵性。在多倍体植物入侵性评估中,基因组大小比DNA C-值更有价值。

DNA C-values of 138 herbaceous species and their biological significance

The DNA C-value is an important biological concept and it has been used in many areas of biological research. The C-value can be used as an index for evaluating angiosperm invasiveness. However, it is still uncertain how the DNA C-value influences plant invasiveness because there is a paucity of systematic experiments that test all the important aspects of this question. There is also a lack of data that identify the relationships between DNA C-value and invasiveness using invaders and non-invaders from the same genus or family. Therefore, expanding the database of plant DNA C-values is important for elucidating the mechanism by which the DNA C-value influences plant invasiveness. Using a cytometry method, we determined the DNA C-values for 138 herbaceous species collected from the Yangtze River Delta and its neighboring area. Among these species, 111 were newly reported. According to related literature and the plants'' distributions in artificial habitats, we also evaluated the weediness of these 138 species, and classified them using five grades: 0, 1, 2, 3, and 4. Based on these data, we calculated the genome sizes of 127 species with known ploidy levels and compared the differences in the two nuclear values (DNA C-value and genome size) between families, monocots and dicots, polypoid and diploid species, and invasive and non-invasive groups. The results showed that: (1) The average DNA C-value of the 138 herbaceous species was 1.55 pg, with the maximum 37.17 times greater than the minimum. The average genome size of the 127 species with known ploidy was 1.08 pg, with the maximum 34.11 times greater than the minimum;(2) We compared the average DNA C-value/genome size (pg) among Poaceae (2.6803/1.2436), Asteraceae (1.7007/1.2436), Caryophyllaceae (1.1612/1.1842), Brassicaceae (0.9165/0.8029), Scrophulariaceae (0.9164/0.6314), Polygonaceae (1.0003/0.7064), Labiatae (0.7990/0.7164), and Umbelliferae (0.7259/0.7259), and found that these two values in Poaceae were significantly higher than in those in the other seven families (P < 0.01). Additionally, the two values in monocots were significantly higher than those in dicots;(3) The average DNA C-value of weeds was significantly lower than that of non-weeds (P < 0.01), while the difference in genome sizes between the two groups was more significant than that of the DNA C-values (P < 0.001). A similar situation was found for Asteraceae. With the decrease of genome size (x₁) and DNA C-value (x₂) in the focal plants, their weediness (or invasiveness, y) increased, following y=2.2334-1.2847ln(x₁) (r=0.4612, P < 0.01) and y=2.4421-0.7234ln(x₂) (r=0.2522, P < 0.01). We suggest that the DNA C-value and genome size could be used as indicators to evaluate plant invasiveness and;(4) The genome sizes of polyploid weeds were significantly lower than those of diploid weeds (P < 0.01), with the former 0.63 times greater than the latter. The genome size of non-weedy polyploid plants was not significantly lower than that of diploid plants (P > 0.5). In Asteraceae weeds, the genome sizes for polyploids were significantly lower than those for diploids (P < 0.1). Our analyses showed that genome downsizing with polyploidy enhances plant invasiveness. In the evaluation of polyploid plant invasiveness, knowing the genome size is more valuable than knowing the DNA C-value. The expansion of the plant DNA C-values database is also useful for comprehensively understanding the variation of plant DNA C-values among different taxa, and it has possible uses in taxonomic, systematic, ecological, and evolutionary studies.