荒漠植物黑沙蒿嫩枝与成熟枝内生菌群落结构差异

[背景]黑沙蒿是我国北方沙漠地区分布广泛、抗旱性能优良的固沙灌木,对稳定沙漠地区生态系统有至关重要的作用.[目的]内生菌在植物生命过程中扮演着重要角色,认识植物生长发育阶段幼嫩和成熟组织内生菌群的结构变化,对于理解菌群间的相互作用及保护宿主植物抵御生物和非生物胁迫具有积极意义.[方法]以宁夏拉巴湖林场黑沙蒿为研究对象,...     

Investigation of hydrogen peroxide formation in plants

A convenient and simple electrophoretic procedure was used to study the NAD(P)H-dependent generation of the hydrogen peroxide needed for the polymerization of coniferyl alcohol by peroxidases from the wood of Ailanthus glandulosa. The results showed that an NAD(P)H-dependent generation of hydrogen peroxide could be brought about by either: a FMN or riboflavin-dependent system; or a Mn²⁺ -dependent system. The most active system was the one incorporating Mn²⁺, followed closely by that incorporating riboflavin. In nature it appears that the method of hydrogen peroxide formation is determined by the amounts of cofactors present in the lignifying tissue. Because no quantitative data are available in the literature, further studies of the concentrations of these cofactors in the plant cell-wall are needed.     

Intervessel pit membrane thickness best explains variation in embolism resistance amongst stems of Arabidopsis thaliana accessions

Background and AimsThe ability to avoid drought-induced embolisms in the xylem is one of the essential traits for plants to survive periods of water shortage. Over the past three decades, hydraulic studies have been focusing on trees, which limits our ability to understand how herbs tolerate drought. Here we investigate the embolism resistance in inflorescence stems of four Arabidopsis thaliana accessions that differ in growth form and drought response. We assess functional traits underlying the variation in embolism resistance amongst the accessions studied using detailed anatomical observations.MethodsVulnerability to xylem embolism was evaluated via vulnerability curves using the centrifuge technique and linked with detailed anatomical observations in stems using light microscopy and transmission electron microscopy.Key ResultsThe data show significant differences in stem P_50, varying 2-fold from −1.58 MPa in the Cape Verde Island accession to −3.07 MPa in the woody soc1 ful double mutant. Out of all the anatomical traits measured, intervessel pit membrane thickness (T_PM) best explains the differences in P₅₀, as well as P₁₂ and P₈₈. The association between embolism resistance and T_PM can be functionally explained by the air-seeding hypothesis. There is no evidence that the correlation between increased woodiness and increased embolism resistance is directly related to functional aspects. However, we found that increased woodiness is strongly linked to other lignification characters, explaining why mechanical stem reinforcement is indirectly related to increased embolism resistance.ConclusionsThe woodier or more lignified accessions are more resistant to embolism than the herbaceous accessions, confirming the link between increased stem lignification and increased embolism resistance, as also observed in other lineages. Intervessel pit membrane thickness and, to a lesser extent, theoretical vessel implosion resistance and vessel wall thickness are the missing functional links between stem lignification and embolism resistance.     

云南箭竹不同年龄段假鞭的解剖学结构特征及木质化观察

该研究以云南箭竹不同年龄段的假鞭为实验材料,采用滑动切片法并利用光学显微镜观察,分析云南箭竹假鞭的解剖结构特征及其随年龄的动态变化,为假鞭结构研究提供新的解剖学数据信息。结果显示:(1)云南箭竹假鞭节间的表皮层只有1层细胞,皮下层由3～4层细胞壁加厚的纤维细胞组成,皮层一般有20～25层不规则的薄壁细胞,成熟的皮层细胞会形成皮层气道,髓实心不具髓腔。(2)云南箭竹假鞭纤维壁厚随鞭龄增加而增加,且同一年龄假鞭的内侧韧皮部面积大于外侧;纤维腔径随鞭龄增加而逐渐减小,但同一年龄假鞭内侧纤维腔径大于外侧;韧皮部的面积、维管束和导管的直径均随着鞭龄的增加而增大。(3)假鞭维管束一般不具有原生导管,外部维管通常有2个较大的后生导管,在假鞭中部及内部通常只有1个后生导管,另1个后生导管不发育或发育不全。(4)在0.5年生到2年生的云南箭竹假鞭中,被染成紫红色的木质素在纤维细胞壁、薄壁细胞壁、导管细胞壁中都有分布,且随着假鞭年龄的增加染色逐渐加深,表明云南箭竹假鞭木质素含量随着鞭龄的增长而不断增加,木质化程度随鞭龄的增长逐渐提高。     

Ascorbic acid and xylem development in trunks of the Siberian larch trees

The contents of ascorbic acid (AA) and its oxidized form, dehydroascorbic acid (DHA), were assessed as related to the tracheid differentiation in the course of early and late wood development in the Siberian larch (Larix sibirica Ldb.) trees. The samples of the cambium, cell enlargement zone and mature cells were collected at the successive developmental stages by scraping tissues off layer by layer from trunk segments of the 20-year-old trees according to anatomical and histochemical criteria. While cambium initials were rapidly dividing, the AA contents per dry weight and per cell considerably exceeded the corresponding values characteristic of the late xylem development; such difference corresponded to the higher number of early tracheids per annual ring, as compared to the late tracheids. The AA content decreased as cells enlarged. The radial growth of the early wood tracheids, as compared to the late wood tracheids, was accompanied with a threefold increase in the AA and a decline in the DHA contents. The AA/DHA ratio was in line with the early tracheid enlargement. The maximum AA content was observed at the early stage of the secondary cell wall thickening in the tracheids of early and late xylem preceding lignification. During this stage of early wood development, the DHA content exceeded sixfold the corresponding value in the late xylem; as a result, the initial rates of lignification were different in two tissues. The rate of lignification in a newly developing layer of the early xylem increased gradually and was the highest in the completely differentiated tracheids. In the late xylem, the lignification rate was at its highest at the very beginning and then declined in the course of tracheid maturation. The dissimilar patterns of lignification in the early and late xylem were primarily associated with the DHA content, which increased in the early xylem and decreased in the maturing late xylem. Thus, the AA content and its accessibility to oxidation in the growing and mature xylem cells exhibited the diverse developmental patterns in the early and late xylem: two tissues differed in the tracheid number and radial diameter as well as in the rate of lignification.Translated from Fiziologiya Rastenii, Vol. 52, No. 1, 2005, pp. 97–107.Original Russian Text Copyright © 2005 by Antonova, Chaplygina, Varaksina, Stasova.