细胞壁在植物重金属耐性中的作用

植物细胞壁主要是由多糖、蛋白质和木质素等组成的一个复合体,广泛参与植物生长发育及对各种逆境胁迫的响应,是重金属离子进入细胞质的第一道屏障。本文主要综述了植物细胞壁主要成分,包括细胞壁多糖、细胞壁蛋白质和木质素,在响应重金属胁迫反应中的作用及其参与重金属耐性的机制,以期能对植物细胞壁在重金属耐性中的作用有更深入的了解。     

Calcium Ameliorates Effects of Lead in Protonema of Funaria hygrometrica Hedw.

Two-days-old in vitro grown protonemata of Funaria hygrometrica Hedw. were treated with a mixture PbCl₂ (4 M Pb²⁺) and CaCl₂ (16 M Ca²⁺) (Ca+Pb) for 48 h. The results were compared with the control: distilled water (H₂O) and the solution of PbCl₂ (4 M Pb²⁺) (Pb). Protonemata treated with Ca+Pb were longer and contained more cells than those treated with Pb. Moreover, a lower number of cells showed apical cell deformations typical for lead toxicity: swollen tips and wall thickenings at the apex. If deformations were present they were not as extended as in Pb. In comparison with the control, however, protonemata treated with Ca+Pb were shorter, contained a lower number of cells and some apical cells in this material were altered. It can be concluded that the presence of calcium partially neutralised toxic effects of lead in Funaria hygrometrica protonemata cells.     

The role of the cell wall in the mechanism of lead and zinc tolerance in Anthoxanthum odoratum L

The respiration rate and viability of cultured cells and protoplasts isolated from two clones of Anthoxanthum odoratum tolerant to both zinc and lead were unaffected by the presence of zinc. Although intact cells were largely unaffected by the presence of lead, protoplasts isolated from cultured cells were susceptible, showing a reduced respiration rate and a high mortality. In contrast cultured cells and protoplasts of non-tolerant clones of A. odoratum were susceptible to both zinc and lead. The results provide direct evidence that in A. odoratum the cell wall is part of the mechanism of tolerance to lead, but not to zinc.     

Hypergravity stimulus enhances primary xylem development and decreases mechanical properties of secondary cell walls in inflorescence stems of Arabidopsis thaliana

BACKGROUND AND AIMS: The xylem plays an important role in strengthening plant bodies. Past studies on xylem formation in tension woods in poplar and also in clinorotated Prunus tree stems lead to the suggestion that changes in the gravitational conditions affect morphology and mechanical properties of xylem vessels. The aim of this study was to examine effects of hypergravity stimulus on morphology and development of primary xylem vessels and on mechanical properties of isolated secondary wall preparations in inflorescence stems of arabidopsis. METHODS: Morphology of primary xylem was examined under a light microscope on cross-sections of inflorescence stems of arabidopsis plants, which had been grown for 3-5 d after exposure to hypergravity at 300 g for 24 h. Extensibility of secondary cell wall preparation, isolated from inflorescence stems by enzyme digestion of primary cell wall components (mainly composed of metaxylem elements), was examined. Plants were treated with gadolinium chloride, a blocker of mechanoreceptors, to test the involvement of mechanoreceptors in the responses to hypergravity. KEY RESULTS: Number of metaxylem elements per xylem, apparent thickness of the secondary thickenings, and cross-section area of metaxylem elements in inflorescence stems increased in response to hypergravity. Gadolinium chloride suppressed the effect of hypergravity on the increase both in the thickness of secondary thickenings and in the cross-section area of metaxylem elements, while it did not suppress the effect of hypergravity on the increase in the number of metaxylem elements. Extensibility of secondary cell wall preparation decreased in response to hypergravity. Gadolinium chloride suppressed the effect of hypergravity on cell wall extensibility. CONCLUSIONS: Hypergravity stimulus promotes metaxylem development and decreases extensibility of secondary cell walls, and mechanoreceptors were suggested to be involved in these processes.     

Ecophysiology of algae living in highly acidic environments

Highly acidic environments are inhabited by acidophilic as well as acidotolerant algae. Acidophilic algae are adapted to pH values as low as 0.05 and unable to grow at neutral pH. A prerequisite for thriving at low pH is the reduction of proton influx and an increase in proton pump efficiency. In addition, algae have to cope with a limited supply of carbon dioxide for photosynthesis because of the absence of a bicarbonate pool. Therefore, some algae grow mainly in near terrestrial situations to increase the CO₂-availability or actively move within the water body into areas with high CO₂. Beside these direct effects of acidity, high concentrations of heavy metals and precipitation of nutrients cause indirect effects on the algae in many acidic environments.     

Brassicaceae (Cruciferae) Family,Plant Biotechnology,and Phytoremediation

Plants represent a natural environmentally safe way to clean or remediate contaminated sites. Members of the Brassicaceae or Cruciferae plant family have a key role in phytoremediation technology. Many wild crucifer species are known to hyperaccumulate heavy metals and possess genes for resistance or tolerance to the toxic effects of a wide range of metals. Metal uptake, sensitivity, and sequestration have been studied extensively in Arabidopsis thaliana, and a number of heavy metal-sensitive and ion-accumulating mutants have been identified. This species is a likely source of genes for phytoremediation. Within the Brassicaceae, Brassica and other crop species are likely candidates for phytoremediation. There is a wealth of information on the agronomics of the economically important members and biomass production can be extensive. Many of these species are well adapted to a range of environmental conditions. Some species are tolerant to high levels of heavy metals, and there is the potential to select superior genotypes for phytoremediation. They are well suited to genetic manipulation and in vitro culture techniques and are attractive candidates for the introduction of genes aimed at phytoremediation. Biotechnology and molecular biology are valuable tools for studies of metal accumulation and tolerance in hyperaccumulating species and for the transfer of relevant genes into crucifer species suitable for phytoremediation. The purpose of this article is to review the potential use of both wild and cultivated members of the Brassicaceae in phytoremediation.     

Metal ligands in micronutrient acquisition and homeostasis

Acquisition and homeostasis of micronutrients such as iron (Fe) and zinc (Zn) pose specific challenges. Poor solubility and high reactivity require controlled synthesis and supply of ligands to complex these metals extracellularly and intracellularly. Cytosolic labile pools represent only a minute fraction of the total cellular content. Several low‐molecular‐weight ligands are known in plants, including sulfur ligands (cysteine and peptides), nitrogen/oxygen ligands (S‐adenosyl‐l ‐methionine‐derived molecules and histidine), and oxygen ligands (phenolics and organic acids). Some ligands are secreted into the extracellular space and influence the phytoavailability of metal ions. A second principal function is the intracellular buffering of micronutrients as well as the facilitation of long‐distance transport in xylem and phloem. Furthermore, low‐molecular‐weight ligands are involved in the storage of metals, predominantly in vacuoles. A detailed molecular understanding is hampered by technical limitations, in particular the difficulty to detect and quantify cellular metal–ligand complexes. More, but still too little, is known about ligand synthesis and the transport across membranes, either with or without a complexed metal. Metal ligands have an immediate impact on human well‐being. Engineering metal ligand synthesis and distribution in crops has tremendous potential to improve the nutritional quality of food and to tackle major human health risks.     

灵芝转录因子AreA的生物学功能

AreA作为丝状真菌氮代谢中的关键转录因子,在真菌响应外界氮源、生长发育、次级代谢及抗逆过程中发挥了重要作用。本研究通过生物信息学比对分析,获得了灵芝AreA的全长序列,研究了AreA对菌丝生长、抵御细胞壁胁迫以及次级代谢的影响,AreA编码蛋白的C末端含有保守的GATA型锌指结构域,与其他担子菌中AreA的亲缘关系较近。通过qRT-PCR分析发现,外界氮源浓度的变化能够影响AreA的转录水平。在低氮源浓度条件下,AreA的转录水平显著高于氮源丰富的条件。利用前期构建的AreA沉默转化子研究发现,沉默AreA后菌株生长速率显著低于野生菌株,约下降70%;且AreA沉默菌株菌丝比野生菌株蓬松。细胞壁的组成成分检测发现,AreA沉默菌株的葡聚糖和几丁质含量比野生菌株（WT）和转入空载沉默质粒的菌株（CK）分别下降约65%和40%-60%。随后检测了对细胞壁胁迫的耐受性,结果发现AreA沉默转化子对刚果红和SDS极为敏感,几乎不能生长。在AreA沉默菌株中,灵芝三萜的含量相比于对照菌株下降了约23%。研究结果表明灵芝AreA能够响应环境中的氮源浓度,并且在灵芝的生长发育、次级代谢以及抵御细胞壁胁迫中发挥了重要作用。     

重金属诱导拟南芥原生质体DNA损伤的单细胞凝胶电泳检测

以拟南芥原生质体为实验体系,研究不同浓度的3种重金属离子对拟南芥原生质体的毒性和DNA损伤的差异。结果表明,用1-5mmol·L^-1的Zn^2＋、Cd^2＋和Cu^2＋分别处理的拟南芥原生质体,2小时内活力逐渐下降,并表现出明显的浓度依赖性：与相同浓度的Cd^2＋和Cu^2＋相比,Zn^2＋对拟南芥原生质体活力的影响程度较小,表现出较低的毒性。单细胞凝胶电泳检测发现,用0．1-0．8mmol·L^-1的Zn^2＋、Cd^2＋和Cu^2＋分别处理拟南芥原生质体30分钟,以OTM值表示的原生质体DNA损伤量随重金属离子浓度的增加而递增：相同浓度（0．5mmol·L^-1）的3种重金属离子相比,Zn^2＋对原生质体的遗传毒性明显低于Cu^2＋和Cd^2＋。综合原生质体活力和DNA损伤的单细胞凝胶电泳检测结果,发现ZnO^2＋对拟南芥原生质体的遗传毒性较低,而CdO^2＋和Cu^2＋的遗传毒性较高。本研究建立的拟南芥原生质体实验体系,结合运用单细胞凝胶电泳技术,能够快速、灵敏地检测重金属对植物细胞的遗传毒性。     

Structural Changes in Radish Seedlings Exposed to Cadmium

Radish (Raphanus sativus L. cv. Redondo Vermelho) seedlings were analysed by light and scanning electron microscopy to characterize the structural changes caused by the exposure to 0.5 or 1.0 mM cadmium chloride for 24, 48 and 72 h. The analyses showed changes in the anatomical and morphological characteristics of roots, stems and leaves of two-week-old seedlings. In all tissues, pressure potential was decreased. Premature death with the disintegration of the epidermis and an increase in the number of root hairs was observed in roots exposed to Cd. The stem of seedlings exposed to Cd exhibited more cells layers in the cambial region. The main effects observed in leaves in response to Cd were stomatal closure, lack of cell wall thickening and alterations in the shape of the chloroplasts. It is suggested that the structural changes observed in seedlings treated with Cd were mainly caused by a Cd-induced decrease in water uptake.     

拟南芥AtGA3OX1和AtGA3OX2基因影响茎秆次生细胞壁增厚的分子机理

赤霉素不仅对植物的种子萌发、叶片伸展和开花结果有重要的影响, 而且在茎秆的发育过程中扮演关键的角色。它的生物合成受到多种酶的调控, 其中赤霉素3-氧化酶(GA3OX)是关键的限速酶, 备受重视。拟南芥AtGA3OX 基因由4个成员组成, 其中A3OX1 和 AtGA3OX2 基因在茎中超量表达, 可能与茎的发育有关。目前, 尚未见到AtGA3OX1、AtGA3OX2基因调控次生细胞壁增厚的报道。文章以拟南芥AtGA3OX1 和 AtGA3OX2 基因双突变体atga3ox1atga3ox2为材料, 系统研究了AtGA3OX1和AtGA3OX2 基因对次生细胞壁的影响。结果表明：同时突变 AtGA3OX1和AtGA3OX2基因不仅显著抑制了茎秆次生细胞壁纤维细胞的增厚(对导管细胞没有影响), 而且也明显降低了次生细胞壁3个组分(纤维素、半纤维素和木质素)的含量。利用实时荧光定量PCR (qRT-PCR) 进一步分析次生细胞壁3个组分生物合成基因及相关的转录因子的表达情况, 结果显示这些基因在双突变体中均受到显著影响, 表明拟南芥AtGA3OX1和 AtGA3OX2 基因可能是通过调控这些转录因子进而调控了次生细胞壁的加厚。研究结果为基因工程调控拟南芥AtGA3OX1、AtGA3OX2 基因(或其他物种同源基因), 进而增强粮食作物抗倒伏性和提高能源植物纤维生物质量提供了理论依据。     

Critical analysis of protein signaling networks involved in the regulation of plant secondary metabolism: focus on anthocyanins

Anthocyanin biosynthesis in Arabidopsis is a convenient and relatively simple model for investigating the basic principles of secondary metabolism regulation. In recent years, many publications have described links between anthocyanin biosynthesis and general defense reactions in plants as well as photomorphogenesis and hormonal signaling. These relationships are complex, and they cannot be understood intuitively. Upon observing the lacuna in the Arabidopsis interactome (an interaction map of the factors involved in the regulation of Arabidopsis secondary metabolism is not available), we attempted to connect various cellular processes that affect anthocyanin biosynthesis. In this review, we revealed the main signaling protein modules that regulate anthocyanin biosynthesis. To our knowledge, this is the first reconstruction of a network of proteins involved in plant secondary metabolism.