Investigations into the movement of glyphosate from treated to adjacent untreated plants

Transfer of glyphosate from treated to adjacent untreated plants was investigated under glasshouse conditions using wheat and Agropyron repens. When glyphosate was used at concentrations characteristic of conventional field application rates, and where shoot contact was prevented, no symptoms were observed on untreated plants. When there was shoot contact, and when glyphosate was used at 2 kg a. i./ha (10 g a. i./litre), phytotoxic effects were observed on untreated plants. At higher concentrations of glyphosate (90 or 180 g a. i./litre), typical of selective applications with ropewick or roller applicators, evidence of root transfer of herbicide was found. In pot experiments these phytotoxic effects were variable, due, perhaps, to variable amounts of root contact. Confining the roots, by growing the plants in tubes, increased the level of phytotoxicity.     

RNA silencing movement in plants

Higher eukaryotes have developed a mechanism of sequence-specific RNA degradation which is known as RNA silencing. In plants and some animals, similar to the nematode Caenorhabditis elegans, RNA silencing is a non-cell-autonomous event. Hence, silencing initiation in one or a few cells leads progressively to the sequence-specific suppression of homologous sequences in neighbouring cells in an RNA-mediated fashion. Spreading of silencing in plants occurs through plasmodesmata and results from a cell-to-cell movement of a short-range silencing signal, most probably 21-nt siRNAs (short interfering RNAs) that are produced by one of the plant Dicer enzymes. In addition, silencing spreads systemically through the phloem system of the plants, which also translocates metabolites from source to sink tissues. Unlike the short-range silencing signal, there is little known about the mediators of systemic silencing. Recent studies have revealed various and sometimes surprising genetic elements of the short-range silencing spread pathway, elucidating several aspects of the processes involved. In this review we attempt to clarify commonalities and differences between the individual silencing pathways of RNA silencing spread in plants.     

RNA silencing movement in plants

Multicellular organisms, like higher plants, need to coordinate their growth and development and to cope with environmental cues. To achieve this, various signal molecules are transported between neighboring cells and distant organs to control the fate of the recipient cells and organs. RNA silencing produces cell non-autonomous signal molecules that can move over short or long distances leading to the sequence specific silencing of a target gene in a well defined area of cells or throughout the entire plant,respectively. The nature of these signal molecules, the route of silencing spread, and the genes involved in their production, movement and reception are discussed in this review. Additionally, a short section on features of silencing spread in animal models is presented at the end of this review.     

Long-distance movement of viruses in plants

During systemic infections, plant viruses move long distances through the plant vasculature. Leaf age, the rate of plant development, plant anatomy and the direction of nutrient flow in the vasculature influence the pattern and extent of systemic spread of the virus, and, in turn, these factors are major determinants of virus resistance.     

RNA silencing movement in plants.

Higher eukaryotes have developed a mechanism of sequence-specific RNA degradation which is known as RNA silencing. In plants and some animals, similar to the nematode Caenorhabditis elegans, RNA silencing is a non-cell-autonomous event. Hence, silencing initiation in one or a few cells leads progressively to the sequence-specific suppression of homologous sequences in neighbouring cells in an RNA-mediated fashion. Spreading of silencing in plants occurs through plasmodesmata and results from a cell-to-cell movement of a short-range silencing signal, most probably 21-nt siRNAs (short interfering RNAs) that are produced by one of the plant Dicer enzymes. In addition, silencing spreads systemically through the phloem system of the plants, which also translocates metabolites from source to sink tissues. Unlike the short-range silencing signal, there is little known about the mediators of systemic silencing. Recent studies have revealed various and sometimes surprising genetic elements of the short-range silencing spread pathway, elucidating several aspects of the processes involved. In this review we attempt to clarify commonalities and differences between the individual silencing pathways of RNA silencing spread in plants.     

Nitrate movement in xylem of lucerne plants

Nitrate content in lucerne stems and leaf blades immersed by cut ends in distilled water or in KNO₃ solution increased with the increase in KNO₃ concentration and with the duration of exposure under irradiance of 100 or 230 W m^?2 PAR. The nitrate content increased from basal stem parts to apical stem parts and leaves. Nitrate was transported mainly with transpiration stream. Some flow variations occurred in stems causing time changes in nitrate content in different parts of stems.     

Use of transgenic plants to measure insect herbivore movement

Use of ingested transgenic corn tissue as a marker for measuring movement of adult Diabrotica virgifera virgifera (LeConte) (Coleoptera: Chrysomelidae; western corn rootworm) was investigated. Laboratory observations of beetles feeding on corn foliage, pollen, silks, or soybean foliage provided background on feeding patterns. The interval between food consumption and its appearance in feces (gut passage time) ranged from 102.7 +/- 11 min for soybean foliage to 56.7 +/- 2.9 min for corn silks. In a laboratory assay, protein expression tests identified the presence of Cry3Bb1 protein inside 50% of adult D. virgifera for up to 16 h after they had last consumed Cry3Bb1 protein-expressing corn silks from 'YieldGard Rootworm' corn plants (Monsanto Co.). Cry3Bb1 protein could not be detected by 32 h postfeeding. The proportion of Cry3Bb1 protein-positive beetles declined linearly with increasing time since feeding on 'YieldGard Rootworm' tissue. Approximately 20% of adult D. virgifera collected near 'YieldGard Rootworm' corn plots tested positive for Cry3Bb1 protein, indicating 'YieldGard Rootworm' tissue consumption within the last 16-32 h. Based on a 16- to 32-h postfeeding detection interval for Cry3Bb1 protein and the distance between 'YieldGard Rootworm' sources and sites where Cry3Bb1-positive insects were collected, 85.3% of males and females moved < or = 4.6-9.1 m/d through R2-R3 stage corn. Among Cry3Bb1-positive adults that left corn and were captured in an adjacent soybean field, 86.4% of males and 93.1% of females moved < or = 4.6-9.1 m/d through soybean. Detection of transgenic plant tissues in mobile insect herbivores is a novel application of biotechnology to the study of insect movement.     

Glucose movement into rat interine fluid

The uterine horns of anaesthetized rats were cannulated and 2.5 ml 0.9% NaCl at 37 degrees C were recirculated for up to 90 min. Glucose appeared in the medium, reaching a concentration of approximately 1 mM. Various aspects of the transport process were examined, and it is suggested that the glucose is mainly derived from the plasma, and probably enters the uterine lumen by a process involving facilitated diffusion.     

Solute flux into parasitic plants

Parasitic plants form intimate contacts with host tissue in order to gain access to host solutes. There are a variety of cell types within the host which parasitic plants could access to extract solutes. Depending on the degree to which the parasite has embraced the parasitic lifestyle, the extent of solute flux and the pathways used to transfer solutes from host to parasite will vary. To date, a variety of experimental approaches argue for diversity in the mechanisms and the routes by which parasites accumulate host solutes. Contact between host and parasite ranges from direct lumen-to-lumen links between host and parasite xylem and continuity between the sieve elements of host and parasite, to the involvement of transfer cells between host and parasite. Progress has been slow since Solms-Laubach distinguished types of parasitic plants that fed from host phloem or xylem in 1867, but advances in clearly delineating the pathways that link host and parasite should now be possible using fluorescent proteins expressed and restricted to particular cell types of the host. This will initially necessitate using Arabidopsis, but should allow the types of connection, i.e. symplasmic or apoplasmic, to be determined and then the identification of parasite transporters responsible for solute flux.     

Integrating individual movement behaviour into dispersal functions

Dispersal functions are an important tool for integrating dispersal into complex models of population and metapopulation dynamics. Most approaches in the literature are very simple, with the dispersal functions containing only one or two parameters which summarise all the effects of movement behaviour as for example different movement patterns or different perceptual abilities. The summarising nature of these parameters makes assessing the effect of one particular behavioural aspect difficult. We present a way of integrating movement behavioural parameters into a particular dispersal function in a simple way. Using a spatial individual-based simulation model for simulating different movement behaviours, we derive fitting functions for the functional relationship between the parameters of the dispersal function and several details of movement behaviour. This is done for three different movement patterns (loops, Archimedean spirals, random walk). Additionally, we provide measures which characterise the shape of the dispersal function and are interpretable in terms of landscape connectivity. This allows an ecological interpretation of the relationships found.