The Ultrastructure of Frankenia Salt Glands

The ultrastructure of the salt gland of Frankenia has been investigated.Glands were examined after treatment with distilled water andafter 4 h, 15 h, and 36 h of salt treatment. Characteristiccytoplasmic features can be correlated with each of these treatments.The results suggest that the acquisition and maintenance ofthe secreting state involves the vesiculation of endoplasmicreticulum.     

Basis of Chloride Transport in Ciliary Epithelium

The aqueous humor is formed by the bilayered ciliary epithelium. The pigmented ciliary epithelium (PE) faces the stroma and the nonpigmented ciliary epithelium (NPE) contacts the aqueous humor. Cl⁻ secretion likely limits the rate of aqueous humor formation. Many transport components underlying Cl⁻ secretion are known. Cl⁻ is taken up from the stroma into PE cells by electroneutral transporters, diffuses to the NPE cells through gap junctions and is released largely through Cl⁻ channels. Recent work suggests that significant Cl⁻ recycling occurs at both surfaces of the ciliary epithelium, providing the basis for modulation of net secretion. The PE-NPE cell couplet likely forms the fundamental unit of secretion; gap junctions within the PE and NPE cell layers are inadequate to maintain constancy of ionic composition throughout the epithelium under certain conditions. Although many hormones, drugs and signaling cascades are known to have effects, a persuasive model of the regulation of aqueous humor formation has not yet been developed. cAMP likely plays a central role, potentially both enhancing and reducing secretion by actions at both surfaces of the ciliary epithelium. Among other hormone receptors, A₃ adenosine receptors likely alter intraocular pressure by regulating NPE-cell Cl⁻ channel activity. Recently, functional evidence for the regional variation in ciliary epithelial secretion has been demonstrated; the physiologic and pathophysiologic implications of this regional variation remain to be addressed.This revised version was published online in June 2005 with a corrected cover date.     

Ultrastructural features associated with secretion in the salt glands of Frankenia grandifolia (Frankeniaceae) and Avicennia germinans (Avicenniaceae)

Using stereological procedures, a detailed analysis was made from thin section electron micrographs of secreting and nonsecreting salt glands of Frankenia grandifolia (Cham. and Schlecht) and Avicennia germinans (L.) Stem. In F. grandifolia secretory cells, vacuolar volume significantly decreased, while the volume of endoplasmic reticulum increased in secreting glands. Numerous minivacuoles were predominantly located along the periphery of secreting secretory cells, some in apparent fusion with the plasma membrane. No difference was found in mitochondrial volume in the secretory cells between secreting and nonsecreting glands. In A. germinans, there was a significant decrease in vacuolar volume in secreting secretory cells. The volume of the endoplasmic reticulum and mitochondria also increased in these cells. However, no evidence of mini-vacuolar fusion with the plasma membrane was observed. These results indicate that the physical process of secretion may differ between F. grandifolia and A. germinans; in both, however, the ultrastructural observations support the contention that specific structural parameters are correlated with the process of secretion.     

淹水对玉米叶片细胞超微结构的影响

对淹水过程中玉米（Ｚｅａ ｍａｙｓ Ｌ．）叶片细胞超微结构的变化进行连续观察。淹水２ｈ后,液泡膜发生明显内陷。淹水６ｈ后,液泡膜内陷加剧,呈极度松弛状态;叶发体被膜局部向外突出一个由单层膜包裹的泡状结构。淹水１２ｈ后,液泡膜局部破裂;叶绿体被膜破坏加剧,成为一松弛的单膜结构,同时,基质类囊体出现空泡化。淹水１８ｈ后,叶绿体的破坏进一步加剧：被膜完全消失,基质类囊体开始消化;同时,线粒体膜和核膜也开     

植物中的氯、氯通道和耐氯性

本文介绍了氯(Cl)在自然界的存在形式,Cl与植物生长发育的关系及植物对Cl-的吸收和运输机制.概述了Cl-通道和Cl-通道蛋白(CLCs)的种类与特点.探讨了不同植物对Cl-亏缺、过量的不同响应及植物耐Cl-的可能生理和分子生物学机制.     

The Physiological Basis of Genotypic Variations in Low-Oxygen Stress Tolerance in the Vegetable Sweet Potato

Russian Journal of Plant Physiology - Waterlogging caused by rainfall or improper irrigation is a serious threat that limits the growth and yield of crop plants by hypoxia stress. In the current...     

西瓜小叶脉超微结构研究

用透射电子显微技术研究了西瓜叶片小叶脉,结果表明,小叶脉是由大型维管束鞘细胞包围的维管束,维管束呈现大的头部和线形的柄部,柄部是单列细胞的木质部,由维管薄壁细胞和导管分子组成;头部是韧皮部,由维管薄壁细胞、伴胞和筛管分子组成。同一小叶脉内常见有超微结构特征显著不同的两种伴胞：一种伴胞体积小,与维管束鞘细胞接触面较小或不接触,细胞内有大液泡,细胞壁上没有胞间连丝或只有少数不分枝的胞间连丝,这种伴胞为2a型;另一种伴胞体积大,通常位于韧皮部两翼,不含大液泡而含大量小泡,与维管束鞘细胞接触面较大,接触面上有大量具分枝的胞间连丝,分枝部分比未分枝部分直径小,这种伴胞为中间细胞类型。显然,西瓜是小叶脉内兼具两种类型伴胞的植物。     

Ultrastructural Basis of the Tension Increase in Sea-Urchin Eggs Prior to Cytokinesis

Cortices of sea-urchin eggs were studied by electron microscopy to identify the structure responsible for the rise in tension at the egg surface prior to cleavage. During anaphase the tension increased and fine filaments of 70–90 Å in diameter appeared in the cell cortex forming a thin mesh-work beneath the cell membrane. The meshwork spread all around the egg cortex without reference to the mitotic axis and the number of filaments seemed to increase up to telophase. Immediately before appearance of the cleavage furrow, the meshwork in the anticipated furrow region became dense. As the furrow appeared the tension began to decrease and the meshwork disappeared. In the progressing furrow region fine filaments of the same size as that of the meshwork-filament were oriented in a bundle to form a contractile ring. Treatment with cytochalasin B suppressed both the tension increase and the formation of the filamentous meshwork. These results suggest that the component filament of the meshwork is an actin microfilament, and that the tension increase at anaphase is due to formation of a meshwork of actin microfilaments from which a contractile ring is subsequently derived at late telophase.     

Some Aspects of Chloride Absorption by Bean Leaf Tissue

Rates of active chloride absorption by thin bean leaf slicesfrom 0.1 mM aqueous potassium chloride are about one-tenth ofthe rates for monovalent cation absorption by such slices andabout one-sixth of chloride absorption rates by excised beanroots. In the 2.0–5.0 mM concentration range chlorideabsorption rates of bean leaf and root tissues do not differmuch and are similar to those of monovalent cation absorptionrates.     

水稻耐光氧化和耐荫特性的生理基础

用简易、有效的人工光氧化和遮荫技术对３０个水稻（Ｏｒｙｚａ ｓａｔｉｖａ Ｌ．）种质进行筛选,鉴定出既耐光氧化又耐荫、耐光氧化不耐荫、耐荫不耐光氧化、既不耐荫又不耐光氧化等４种品种类型,并用既耐光氧化又耐荫的品种“武育粳３号”和对光氧化和遮荫均敏感的品种“香籼”进行光合特性研究。结果表明：在遮荫条件下,与对光氧化和遮荫敏感的品种“香籼”比较,“武育粳３号”的ＰＳⅡ活性差异不大,ＲｕＢｉｓＣＯ活性降     

Potassium-linked Chloride Fluxes during Rhythmic Leaf Movement of Albizzia julibrissin

Transverse sections of Albizzia pulvinules were examined with an electron microprobe to determine ion fluxes associated with turgorcontrolled leaflet movements. K⁺ and Cl⁻ concentrations are high in the flexor and low in the extensor region of closed pulvini. Both ions migrate out of the flexor and into the extensor during opening as previously described for K⁺. The distribution of these elements is significantly correlated in each phase of the rhythmic cycle examined, but only 50 to 60% of the ionic charge of potassium is balanced by chloride. This value increases to 65 to 85% if one considers only the mobile fraction of the potassium.     

Differential Tolerance of Streptomycetes to Sodium Chloride as a Taxonomic Aid

A survey was made of the NaCl tolerance of approximately 1,300 Streptomyces strains belonging to 313 species. The growth medium of the organisms was supplemented with a graded series of NaCl concentrations (4, 7, 10, and 13%). Only 1.8% of the species could not tolerate 4% NaCl; 26.9% could grow at a maximum of 4%; 49.7% could tolerate a maximum of 7%; 18.8% could grow at a maximum of 10%; and only 2.8% could tolerate 13% NaCl. In evaluating the relationships of NaCl tolerance to various taxonomic features, higher tolerance was statistically associated with the "yellow" and possibly the "white"-spored streptomycetes, whereas the "red"-spored series tended to have lesser tolerance. Higher tolerance was also indicated for spiny-spored species, as a group, than for smooth-spored forms. Likewise, nonproducers of melanin, collectively, were more NaCl tolerant than melanin-producing species. Uniformity of test responses between strains of species studied suggested the usefulness of NaCl tolerance as a taxonomic criterion.     

Studies of the Physiological and Genetic Basis of Acid Tolerance in Rhizobium leguminosarum biovar trifolii

Acid-tolerant Rhizobium leguminosarum biovar trifolii ANU1173 was able to grow on laboratory media at a pH as low as 4.5. Transposon Tn5 mutagenesis was used to isolate mutants of strain ANU1173, which were unable to grow on media at a pH of less than 4.8. The acid-tolerant strain ANU1173 maintained a near-neutral intracellular pH when the external pH was as low as 4.5. In contrast, the acid-sensitive mutants AS25 and AS28 derived from ANU1173 had an acidic intracellular pH when the external pH was less than 5.5. The acid-sensitive R. leguminosarum biovar trifolii ANU794, which was comparatively more sensitive to low pH than mutants AS25 and AS28, showed a more acidic internal pH than the two mutants when the three strains were exposed to medium buffered at a pH of less than 5.5. The two acid-sensitive mutants had an increased membrane permeability to protons but did not change their proton extrusion activities. However, the acid-sensitive strain ANU794 exhibited both a higher membrane permeability to protons and a lower proton extrusion activity compared with the acid-tolerant strain ANU1173. DNA hybridization analysis showed that mutants AS25 and AS28 carried a single copy of Tn5 located in 13.7-kb (AS25) and 10.0-kb (AS28) EcoRI DNA fragments. The wild-type DNA sequences spanning the mutation sites of mutants AS25 and AS28 were cloned from genomic DNA of strain ANU1173. Transfer of these wild-type DNA sequences into corresponding Tn5-induced acid-sensitive mutants, respectively, restored the mutants to their acid tolerance phenotypes. Mapping studies showed that the AS25 locus was mapped to a 5.6-kb EcoRI-BamHI megaplasmid DNA fragment, whilst the AS28 locus was located in an 8.7-kb BglII chromosomal DNA fragment.     

Salt Tolerance in the Triticeae: Salinity-induced Changes in the Leaf Solute Composition of Some Perennial Triticeae

Changes in the leaf solute composition of a number of perennialTriticeae in response to salinity are described. There was variationboth within and between species in the extent of Na and Cl accumulationin the leaves. In almost all cases leaf nitrate concentrationsdecreased substantially and orthophosphate concentrations increasedin response to salinity. There was no overall decrease in arange of soluble nitrogen-containing compounds nor in totalnitrogen. In Thinopyrum scirpeum there was an inverse relationshipbetween proline and glycinebetaine contents of different tissues,with proline levels higher in older leaves. Concentrations ofboth compounds were higher in salt-stressed plants. Key words: Triticeae, salinity, leaf solute composition     

Leaf Abscission in Soybean: Cytochemical and Ultrastructural Changes following Benzylaminopurine Treatment

6-benzylaminopurine (BAP) delays leaf abscission of soybeanGlycine max (L.) Merr. Abscission of the distal pulvinus ofprimary leaves was induced in 12-d-old seedlings or explantsby removal of the leaf blade. BAP applied to the cut end ofthe pulvinus following leaf blade removal delayed abscission.Discoloration of the pulvinus occurred before abscission commencedand the number of grana in chloroplasts within cortical parenchymacells of the pulvinus decreased over time following leaf bladeremoval. BAP prevented discoloration of pulvinus tissues anda decrease in grana number. Starch grains within amyloplastsof cells of the starch sheath in the pulvinus disappeared followingleaf blade removal, whereas starch accumulated within the abscissionzone prior to abscission. BAP prevented this apparent redistributionof starch and instead promoted an increase in starch withinplastids of cortical parenchyma cells of the pulvinus. Duringthe abscission process, cells within the separation layer enlargedand their nuclei and nucleoli became more evident prior to theirseparation from one another. Cell separation resulted from breakdownof middle lamellae and partial degradation of primary cell walls.Cycloheximide applied directly to the external surface of theabscission zone inhibited abscission in a similar way to theBAP treatment. These results suggest that BAP prevents abscissionby altering patterns of starch distribution in the pulvinusand abscission zone and by inhibiting the synthesis of proteinsthat typically appear de novo in induced abscission zone tissues. Key words: Benzylaminopurine, BAP, Soybean, Pulvinus, Abscission, amyloplast.     

The Role of Pigmentation, Ultraviolet Radiation Tolerance, and Leaf Colonization Strategies in the Epiphytic Survival of Phyllosphere Bacteria

Phenotypic mechanisms that enhance bacterial UVR survival typically include pigmentation and DNA repair mechanisms which provide protection from UVA and UVB wavelengths, respectively. In this study, we examined the contribution of pigmentation to field survival in Clavibacter michiganensis and evaluated differences in population dynamics and leaf colonization strategies. Two C. michiganensis pigment-deficient mutants were significantly reduced in UVA radiation survival in vitro; one of these mutants also exhibited reduced field populations on peanut when compared to the wild-type strain over the course of replicate 25-day experiments. The UVR-tolerant C. michiganensis strains G7.1 and G11.1 maintained larger epiphytic field populations on peanut compared to the UVR-sensitive C. michiganensis T5.1. Epiphytic field populations of C. michiganensis utilized the strategy of solar UVR avoidance during leaf colonization resulting in increased strain survival on leaves after UVC irradiation. These results further demonstrate the importance of UVR tolerance in the ability of bacterial strains to maintain population size in the phyllosphere. However, an examination of several bacterial species from the peanut phyllosphere and a collection of environmental Pseudomonas spp. revealed that sensitivity to UVA and UVC radiation was correlated in some but not all of these bacteria. These results underscore a need to further understand the biological effects of different solar wavelength groups on microbial ecology.