化感胁迫诱导植物细胞损伤研究进展

化感胁迫(allelochemical stress)是指一种植物通过淋溶、挥发、根系分泌和残株腐解等途径释放化学物质,对另一种植物(包括微生物)产生直接或间接的伤害作用。有害化感物质对受体植物具有显著的细胞毒性,影响根边缘细胞的形成过程和活性,改变细胞壁和细胞膜的特性,破坏细胞内部结构,干扰细胞有丝分裂过程和基因表达模式;此外,化感胁迫往往伴随着氧化胁迫,受体植物细胞活性氧(ROS)水平升高,膜脂过氧化程度加剧,抗氧化系统被破坏,ROS影响与凋亡相关的信号调控过程,引起细胞大量死亡。因此,化感胁迫诱导的氧化胁迫可能是引起细胞凋亡的原因之一。阐明化感胁迫介导的氧化损伤和细胞损伤的相互关系以及根边缘细胞对化感胁迫的响应机制,是今后研究化感作用机制的一个方向。

Advance in allelochemical stress induced damage to plant cells

Allelopathy is a common phenomenon in nature and can be defined as any direct or indirect effects of one plant on the other one (including microbes) through the release of plant produced secondary products (allelochemicals) into the environment by ways of leaching, volatilization, root exudation, and decomposition of residues. When the effect of the allelochemicals is to inhibit the growth and development of receptors, it is considered as a biotic stress called allelochemical stress. The allelochemical can result in the obvious cytotoxicity to receptor plants, affect the generation and survival of root border cells, a population of viable cells that are attached to the root apex in a one-cell layer in a manner similar to that of white blood cells functioning in the defense. Allelochemical-treated cells exhibit irregular arrangement and shape, and altered the structure of cell walls, plasma membrane, and certain organelles including mitochondria, chloroplasts, Golgi apparatus, vacuoles, etc. The allelochemical also has genotoxicity to receptor plants by interfering with DNA replication, cell division, and gene expression pattern. Chromosomal abnormalities, such as the break, lag, and conglutination of chromosomes, formation of micronucleus and nuclear buds and chromosomal bridges and rings, and three pole divisions was often observed. As a resultant, the mitotic index was significantly reduced in cells exposed to allelochemicals. The allelochemical causes the changes of DNA molecular marker genotype (DNA chain type) in terms of variation in band intensity, or the loss of bands and appearance of new bands. The gene expression pattern in allelochemical-treated plants is changed and different genes are up-regulated, down-regulated, transient-expressed, or continuous-expressed, respectively. Furthermore, allelochemical treatment enhances the production of reactive oxygen species (ROS), the toxic metabolic products in plants and other aerobic organisms. However, the activities of ROS scavenging enzymes such as catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) are decreased. Such imbalance results in the oxidative stress, which is regarded as a common phenomenon caused by allelochemical stress. The enhanced production of ROS leads to the peroxidation of lipid and damages to macromolecules such as proteins, nucleic acids and lipids. As a resultant, the membrane permeability and the content of malondialdehyde (MDA) are increased. The increased level of ROS can also be the signal to activate the relevant signaling cascade and ultimately to trigger genome-wide changes in gene expression. As a resultant, the apoptosis is induced and the cellular injury and plant growth inhibition are observed in receptor plants. Oxidative stress induced by allelochemical treatment might be a cause of apoptosis in receptor plants. In conclusion, allelochemical stress interferes with the defensive function of root border cells, induces cell damage, genetic damage, and oxidative damage of receptor plant cells. Elucidation of the relevance between the cell damage and oxidative damage induced and the mechanism of the response of root border cells to allelochemical stress would be expected to be a trend in the future to reveal allelopathic mechanisms.