Motile plant cell body: a "bug" within a "cage"

Analysis of the cytoskeleton in morphogenetically active plant cells allows us to propose a unified concept for the structural organization of eukaryotic cells. Their cytoarchitecture is determined by two principal structural complexes: nucleus-microtubule-based cell bodies ("bugs") and plasma-membrane-F-actin-based cell periphery complexes ("cages"). There are dynamic interactions between each of these entities in response to extracellular and intracellular signals. In the case of the cell body, these signals determine its polarization, rotation and migration. Interactions between cell body and cell periphery complexes determine cell growth polarity and morphogenesis throughout the eukaryotic kingdom.     

"Florigen ": an intriguing concept of plant biology.

"Florigen" is the name that Mikhail Chailakhyan coined in 1937 for the putative hormone regulating flowering. At this concept, plant physiologists arrived following early research concerning the effects of temperature and day length on the transition from vegetative to reproductive stages of plants. The existence of florigen was postulated on the experimental backgrounds involving i) the response of plants to inductive conditions; ii) transmission of a flowering stimulus by grafting; iii) extraction of this stimulus from induced plants. This experimental results showed the existence of florigen at least as concept because they always failed to offer the experimental evidence of its chemical existence. The myth of florigen persisted as long as the end of the Seventies, when physiologists began to consider flowering as a complex process in which various classes of hormones might variously interplay.     

Agrobacterium-mediated plant transformation: the biology behind the "gene-jockeying" tool.

Agrobacterium tumefaciens and related Agrobacterium species have been known as plant pathogens since the beginning of the 20th century. However, only in the past two decades has the ability of Agrobacterium to transfer DNA to plant cells been harnessed for the purposes of plant genetic engineering. Since the initial reports in the early 1980s using Agrobacterium to generate transgenic plants, scientists have attempted to improve this "natural genetic engineer" for biotechnology purposes. Some of these modifications have resulted in extending the host range of the bacterium to economically important crop species. However, in most instances, major improvements involved alterations in plant tissue culture transformation and regeneration conditions rather than manipulation of bacterial or host genes. Agrobacterium-mediated plant transformation is a highly complex and evolved process involving genetic determinants of both the bacterium and the host plant cell. In this article, I review some of the basic biology concerned with Agrobacterium-mediated genetic transformation. Knowledge of fundamental biological principles embracing both the host and the pathogen have been and will continue to be key to extending the utility of Agrobacterium for genetic engineering purposes.     

Amyloid-like aggregates of a plant protein: a case of a sweet-tasting protein, monellin.

We report here a novel case of amyloid-like aggregation of a plant protein. A sweet-tasting protein, monellin, experiences an irreversible heat denaturation at pH 2.5 and 85 degrees C. Addition of 100 mM NaCl couples this process with protein aggregation. The aggregates were structured as regular fibers with approximately 10 nm width and capable of binding to Congo red, similarly to well-known amyloid fibrils. The amyloid-like aggregation process was also successfully monitored with a calorimetric method. This work supports the universality of the amyloid-like aggregation, not restricted to some special categories of protein.     

Consolidation of cytoskeleton during plant spindle formation. II. "Fused spindles"

Three mechanisms of fused spindle formation in meiosis of Solanacea have been described: 1) approach of daughter nuclei at prophase II; 2) fusion of perinuclear cytoskeleton systems at prophase II; 3) approach and fusion of prometaphase chaotic figures at prometaphase II. The process of fusion spindle formation appears to be complex and including several steps.     

Organismal view of a plant and a plant cell.

Cell walls are at the basis of a structural, four-dimensional framework of plant form and growth time. Recent rapid progress of cell wall research has led to the situation where the old, long-lasting juxtaposition: "living" protoplast--"dead" cell wall, had to be dropped. Various attempts of re-interpretation cast, however, some doubts over the very nature of plant cell and the status of the walls within such a cell. Following a comparison of exocellular matrices of plants and animals, their position in relation to cells and organisms is analysed. A multitude of perspectives of the biological organisation of living beings is presented with particular attention paid to the cellular and organismal theories. Basic tenets and resulting corollaries of both theories are compared, and evolutionary and developmental implications are considered. Based on these data, "The Plant Body"--an organismal concept of plants and plant cells is described.     

Functional markers and a 'systemic strategy': convergency between plant breeding, plant nutrition and molecular biology.

Research perspectives towards sustainable plant production through plant breeding on abiotic stress tolerance require interdisciplinary competence. The present paper wants to strengthen awareness of important activities or current insights in plant breeding, plant nutrition and molecular biology to facilitate approximation of the disciplines and to direct efforts in molecular biology early in development towards application. As a consequence of recent discussion on appropriate approaches in systems biology towards crop improvement, a global 'systemic strategy' is presented to identify functional marker candidates for abiotic stress tolerance more efficiently.     

"Whistleblowing": a health issue.

OBJECTIVE--To examine the response of organizations to "whistleblowing" and the effects on individual whistleblowers. DESIGN--Questionnaire survey of whistleblowers who contacted Whistleblowers Australia after its publicity campaign. SETTING--Australia. SUBJECTS--25 men and 10 women from various occupations who had exposed corruption or danger to the public, or both, from a few months to over 20 years before. RESULTS--All subjects in this non-random sample had suffered adverse consequences. For 29 victimization had started immediately after their first, internal, complaint. Only 17 approached the media. Victimization at work was extensive: dismissal (eight subjects), demotion (10), and resignation or early retirement because of ill health related to victimization (10) were common. Only 10 had a full time job. Long term relationships broke up in seven cases, and 60 of the 77 children of 30 subjects were adversely affected. Twenty nine subjects had a mean of 5.3 stress related symptoms initially, with a mean of 3.6 still present. Fifteen were prescribed long term treatment with drugs which they had not been prescribed before. Seventeen had considered suicide. Income had been reduced by three quarters or more for 14 subjects. Total financial loss was estimated in hundreds of thousands of Australian dollars in 17. Whistleblowers received little or no help from statutory authorities and only a modest amount from workmates. In most cases the corruption and malpractice continued unchanged. CONCLUSION--Although whistleblowing is important in protecting society, the typical organisational response causes severe and longlasting health, financial, and personal problems for whistleblowers and their families.     

Micropropagation of a medicinal plant, Plantago major L.

An efficient micropropagation protocol was developed for an important medicinal plant, Plantago major L. For this purpose, it is recommended to culture shoot-tips on modified MS medium [412.5 mg dm-3 NH4NO3 and 340 mg dm-3 KH2PO4] supplemented with 50 g dm-3 glucose and 0.5 μM 6-benzylaminopurine. Maximum rooting frequency was obtained at 1 μM naphthaleneacetic acid. This revised version was published online in August 2006 with corrections to the Cover Date.     

Import, targeting, and processing of a plant polyphenol oxidase.

A tomato (Lycopersicon esculentum L.) gene encoding a precursor of polyphenol oxidase (PPO) was transcribed and translated in vitro. The import, targeting, and processing of the [35S]methionine-labeled precursor protein (pPPO) were studied in isolated chloroplasts. The protein was routed to the thylakoid lumen in two steps. The 67-kD precursor was first imported into the stroma in an ATP-dependent step. It was processed to a 62-kD intermediate by a stromal peptidase. Translocation into the lumen was light dependent and involved processing of the 62-kD to the 59-kD mature form. The mature polypeptide was soluble in the lumen and not bound to thylakoids. This two-step targeting pattern was observed in plastids from a variety of plants including pea (Pisum sativum L.), tomato, and maize (Zea mays L.). The ratio between the intermediate and mature forms observed depended on the plant species, leaf age, growth conditions, and illumination regime to which the plants had been subjected. Cu2+ was not required for pPPO import or processing. Furthermore, low concentrations of Cu2+ (1-5 microM) markedly inhibited the first import step. Tentoxin specifically inhibited pPPO import, leaving the precursor bound to the envelope membrane. The two-step routing of pPPO into chloroplasts, typical of thylakoid lumen proteins, is consistent with the two-domain structure of the transit peptide and appears to be a feature of all plant PPO genes isolated so far. No evidence was found for unorthodox routing mechanisms, which have been suggested to be involved in the import of plant PPOs. The two-step routing may account for some of the multiplicity of PPO observed in vivo.     

Properties of "diplophage": a lipid-containing bacteriophage.

We describe the purification and properties of Dp-1, a bacteriophage isolated from Diplococcus pneumoniae. The phage was sensitive to the organic solvents deoxycholate and Sarkosyl, and its infectivity was reduced by treatment with phospholipase C. Electron microscopy indicated the presence of a double-layered coat around the phage particles. Purified phage preparations contained lipid amounting to about 8.5% of the dry weight of the phage, and thin-layer chromatography resolved the lipids into four components. The phage had a buoyant density in CsCl of 1.47 g/cm3, and a sedimentation constant in 0.1 M NaCl of 313S. Analysis in acrylamide gel electrophoresis indicated the presence of three major proteins. Dp-1 DNA shows a density of 1.681 g/cm3. Neutralizing antisera against the phage have a low potency (K less than 120/min).     

Campylobacter enteritis: a "new" disease.

By selective culture campylobacters (C jejuni and C coli) were isolated from the faeces of 57 (7-1%) out of 803 unselected patients with diarrhoea; none were isolated from 194 people who had not got diarrhoea. Specific agglutinins were found in the sera of 31 out of 38 patients with campylobacter enteritis and 10 of them had a rising titre. Half the patients were aged 15 to 44 years, but the incidence was highest in young children. All the patients with campylobacters had a distinctive clinical illness with severe abdominal pain. Campylobacters are a relatively unrecognised cause of acute enteritis, but these findings suggest that they may be a common cause. Spread of infection was observed within 12 out of 29 households, and in these cases children were usually implicated. Several patients were apparently infected from chickens, both live and dressed, and poultry may be the primary source of the organism. In two cases dogs with diarrhoea were found to be infected with strains indistinguishable from their human contacts. Ten patients acquired their infections while travelling abroad.