野薄荷叶腺毛的发育形态学研究

研究了分布于我国东北部的野薄荷叶表面腺毛的结构和发育。主要腺毛有两种：多细胞盾状腺毛和弯曲单细胞头状腺毛。多细胞盾状腺毛由１个基细胞,１个柄细胞和一个由８－１２个分泌细胞构成的头部组成。单细胞头状腺毛由１个基细胞,１个柄细胞和一个分泌细胞头部构成。     

Trichome micromorphology in <Emphasis Type="Italic">Teucrium</Emphasis> (Lamiaceae) species growing in Croatia

Micromorphological investigation of the types, dimensions and distribution of characteristic trichomes in leaves and stems in Teucrium L. species (T. arduini L., T. chamaedrys L., T. flavum L., T. montanum L., T. polium L., and T. scordium L. subsp. scordioides Schreb.) distributed in Croatia was carried out as part of the taxonomical study of the genus Teucrium. Secretory types of hairs, peltate and capitate hairs were observed on the epidermis of stems and leaves of all investigated species. Non-secretory, acicular hairs were almost completely lacking on stems of T. scordium subsp. scordioides. Flagelliform hairs were not found in T. flavum and T. polium. Cladose hairs were present only in T. polium. The largest micromorphological variability was established between wild and cultivated samples of T. arduini and T. scordium subsp. scordioides, while cultivated and wild specimens of T. polium were almost identical. Differences were primarily observed in trichome dimensions and much less in micromorphological features.     

AtEXO70A1, a member of a family of putative exocyst subunits specifically expanded in land plants, is important for polar growth and plant development

The exocyst is a hetero-oligomeric protein complex involved in exocytosis and has been extensively studied in yeast and animal cells. Evidence is now accumulating that the exocyst is also present in plants. Bioinformatic analysis of genes encoding plant homologs of the exocyst subunit, Exo70, revealed that three Exo70 subgroups are evolutionarily conserved among angiosperms, lycophytes and mosses. Arabidopsis and rice contain 22 and approximately 39 EXO70 genes, respectively, which can be classified into nine clusters considered to be ancient in angiosperms (one has been lost in Arabidopsis). We characterized two independent T-DNA insertional mutants of the AtEXO70A1 gene (exo70A1-1 and exo70A1-2). Heterozygous EXO70A1/exo70A1 plants appear to be normal and segregate in a 1:2:1 ratio, suggesting that neither male nor female gametophytes are affected by the EXO70A1 disruption. However, both exo70A1-1 and exo70A1-2 homozygotes exhibit an array of phenotypic defects. The polar growth of root hairs and stigmatic papillae is disturbed. Organs are generally smaller, plants show a loss of apical dominance and indeterminate growth where instead of floral meristems new lateral inflorescences are initiated in a reiterative manner. Both exo70A1 mutants have dramatically reduced fertility. These results suggest that the putative exocyst subunit EXO70A1 is involved in cell and organ morphogenesis.     

Root hairs are the most important root trait for rhizosheath formation of barley (Hordeum vulgare), maize (Zea mays) and Lotus japonicus (Gifu)

Background and AimsRhizosheaths are defined as the soil adhering to the root system after it is extracted from the ground. Root hairs and mucilage (root exudates) are key root traits involved in rhizosheath formation, but to better understand the mechanisms involved their relative contributions should be distinguished.MethodsThe ability of three species [barley (Hordeum vulgare), maize (Zea mays) and Lotus japonicus (Gifu)] to form a rhizosheath in a sandy loam soil was compared with that of their root-hairless mutants [bald root barley (brb), maize root hairless 3 (rth3) and root hairless 1 (Ljrhl1)]. Root hair traits (length and density) of wild-type (WT) barley and maize were compared along with exudate adhesiveness of both barley and maize genotypes. Furthermore, root hair traits and exudate adhesiveness from different root types (axile versus lateral) were compared within the cereal species.Key ResultsPer unit root length, rhizosheath size diminished in the order of barley > L. japonicus > maize in WT plants. Root hairs significantly increased rhizosheath formation of all species (3.9-, 3.2- and 1.8-fold for barley, L. japonicus and maize, respectively) but there was no consistent genotypic effect on exudate adhesiveness in the cereals. While brb exudates were more and rth3 exudates were less adhesive than their respective WTs, maize rth3 bound more soil than barley brb. Although both maize genotypes produced significantly more adhesive exudate than the barley genotypes, root hair development of WT barley was more extensive than that of WT maize. Thus, the greater density of longer root hairs in WT barley bound more soil than WT maize. Root type did not seem to affect rhizosheath formation, unless these types differed in root length.ConclusionsWhen root hairs were present, greater root hair development better facilitated rhizosheath formation than root exudate adhesiveness. However, when root hairs were absent root exudate adhesiveness was a more dominant trait.     

Development and persistence of sandsheaths of Lyginia barbata (Restionaceae): relation to root structural development and longevity

Background and Aims

Strongly coherent sandsheaths that envelop perennial roots of many monocotyledonous species of arid environments have been described for over a century. This study, for the first time, details the roles played by the structural development of the subtending roots in the formation and persistence of the sheaths.

Methods

The structural development of root tissues associated with persistent sandsheaths was studied in Lyginia barbata, native to the Western Australian sand plains. Cryo-scanning electron microscopy CSEM, optical microscopy and specific staining methods were applied to fresh, field material. The role of root hairs was clarified by monitoring sheath development in roots separated from the sand profile by fine mesh.

Key Results and Conclusions

The formation of the sheaths depends entirely on the numerous living root hairs which extend into the sand and track closely around individual grains enmeshing, by approx. 12 cm from the root tip, a volume of sand more than 14 times that of the subtending root. The longevity of the perennial sheaths depends on the subsequent development of the root hairs and of the epidermis and cortex. Before dying, the root hairs develop cellulosic walls approx. 3 µm thick, incrusted with ferulic acid and lignin, which persist for the life of the sheath. The dead hairs remain in place fused to a persistent platform of sclerified epidermis and outer cortex. The mature cortex comprises this platform, a wide, sclerified inner rim and a lysigenous central region – all dead tissue. We propose that the sandsheath/root hair/epidermis/cortex complex is a structural unit facilitating water and nutrient uptake while the tissues are alive, recycling scarce phosphorus during senescence, and forming, when dead, a persistent essential structure for maintenance of a functional stele in the perennial Lyginia roots.     

Leaf micromorphology and leaf glandular hair ontogeny of Myoporum bontioides A. Gray

Myoporum bontioides A. Gray (Myoporaceae), a red list plant in Japan, is restricted to only a few East Asian countries like China, Japan and Taiwan, associated to some true mangroves. The leaf is isolateral and has a thick cuticle; stomata are anomocytic, sunken and have a beak‐shaped cuticular outgrowth at the inner and outer side of the stomatal pore (ledges); profuse glandular hairs are scattered on both leaf surfaces of young leaves. The mesophyll is compact with palisade and spongy parenchyma cells in the young stage, but at maturity profuse intercellular spaces can be observed. Secretory ducts occur in young leaves. Pear‐shaped glandular hairs protrude from the epidermal layer. Hair primordia are well distinct by their larger size and undergo divisions to produce two laterally placed basal cells, two stalk cells and four radiating terminal cells. The cuticle layers of the terminal cells are often separated from the cell wall to form a space, in which ions accumulate for excretion. Inner walls of the basal cells are connected with the mesophyll. Though ontogeny and structure of glandular hairs have resemblance to typical mangroves, considering leaf micromorphology, this plant is better termed as “mangrove associate” instead of “true mangrove”. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

SNARE VTI13 plays a unique role in endosomal trafficking pathways associated with the vacuole and is essential for cell wall organization and root hair growth in arabidopsis

Background and Aims

Root hairs are responsible for water and nutrient uptake from the soil and their growth is responsive to biotic and abiotic changes in their environment. Root hair expansion is a polarized process requiring secretory and endosomal pathways that deliver and recycle plasma membrane and cell wall material to the growing root hair tip. In this paper, the role of VTI13 (AT3G29100), a member of the VTI vesicular soluble NSF attachment receptor (SNARE) gene family in Arabidopsis thaliana, in root hair growth is described.

Methods

Genetic analysis and complementation of the vti13 root hair phenotypes of Arabidopsis thaliana were first used to assess the role of VTI13 in root hair growth. Transgenic lines expressing a green fluorescent protein (GFP)–VTI13 construct were used to characterize the intracellular localization of VTI13 in root hairs using confocal microscopy and immunotransmission electron microscopy.

Key Results

VTI13 was characterized and genetic analysis used to show that its function is required for root hair growth. Expression of a GFP–VTI13 fusion in the vti13 mutant background was shown to complement the vti13 root hair phenotype. GFP–VTI13 localized to both the vacuole membrane and a mobile endosomal compartment. The function of VTI13 was also required for the localization of SYP41 to the trans-Golgi network. Immunohistochemical analysis indicated that cell wall organization is altered in vti13 root hairs and root epidermal cells.

Conclusions

These results show that VTI13 plays a unique role in endosomal trafficking pathways associated with the vacuole within root hairs and is essential for the maintenance of cell wall organization and root hair growth in arabidopsis.     

Chemosensory control of pollen ingestion in the hoverfly Eristalis tenax by labellar taste hairs

The labellar gustatory system of the dronefly Eristalis tenax L. (Syrphidae; Diptera) that enables the fly to discriminate between pollen and nectar is investigated, and the triggering of pollen ingestion is examined. In behavioural preference tests, exhaustively extracted pollen of the sunflower Helianthus annuus is consumed in smaller amounts than untreated pollen, indicating that water-soluble substances are important for acceptance. Dry pollen is preferred over moist pollen in which the grains stick together, suggesting that mechanical properties of the pollen also play a role in its sensory assessment. Electrophysiological studies of the labellar taste hairs reveal that aqueous extracts of pollen (2% w/v) stimulate the salt receptor cell, but not the sugar receptor cell. The response of the water receptor cell remains the same as to pure water (or standard electrolyte, 10 mmol · l⁻¹ KCl). Of the 20 amino acids tested, the salt cell is sensitive only to proline in a submillimolar range. Behavioural experiments support the electrophysiological findings. When KCl is applied at concentrations eliciting salt-cell spike frequencies equal to those produced by pollen extract (which is often accepted), the water receptor cell is inhibited and a pronounced rejection behaviour occurs. This rejection of concentrated salt solution in Eristalis is therefore mainly mediated by the inhibition of the water cell. Accepted: 27 November 1999