Teaching resources. Movement of macromolecules in plant cells through plasmodesmata.
(25/95)
Plasmodesmata are intercellular organelles in plants that allow the passage of molecules between plant cells. Movement through plasmodesmata may allow transcription factors expressed in one cell to move into adjacent cells, thereby regulating gene expression non-cell autonomously. The two animations illustrate (i) movement of a protein through an individual plasmodesma and (ii) an experiment to detect the movement of the transcription factor through plasmodesmata from the L1 layer of a plant meristem into the L2 and L3 layers. These two animations would be useful in teaching plant biology or plant development or a cell biology class discussing mechanisms of intercellular transport. (+info)
An improved grafting technique for mature Arabidopsis plants demonstrates long-distance shoot-to-root transport of phytochelatins in Arabidopsis.
(26/95)
Phytochelatins (PCs) are peptides that function in heavy-metal chelation and detoxification in plants and fungi. A recent study showed that PCs have the ability to undergo long-distance transport in a root-to-shoot direction in transgenic Arabidopsis (Arabidopsis thaliana). To determine whether long-distance transport of PCs can occur in the opposite direction, from shoots to roots, the wheat (Triticum aestivum) PC synthase (TaPCS1) gene was expressed under the control of a shoot-specific promoter (CAB2) in an Arabidopsis PC-deficient mutant, cad1-3 (CAB2TaPCS1/cad1-3). Analyses demonstrated that TaPCS1 is expressed only in shoots and that CAB2TaPCS1/cad1-3 lines complement the cadmium (Cd) and arsenic metal sensitivity of cad1-3 shoots. CAB2TaPCS1/cad1-3 plants exhibited higher Cd accumulation in roots and lower Cd accumulation in shoots compared to wild type. Fluorescence HPLC coupled to mass spectrometry analyses directly detected PC2 in the roots of CAB2:TaPCS1/cad1-3 but not in cad1-3 controls, suggesting that PC2 is transported over long distances in the shoot-to-root direction. In addition, wild-type shoot tissues were grafted onto PC synthase cad1-3 atpcs2-1 double loss-of-function mutant root tissues. An Arabidopsis grafting technique for mature plants was modified to obtain an 84% success rate, significantly greater than a previous rate of approximately 11%. Fluorescence HPLC-mass spectrometry showed the presence of PC2, PC3, and PC4 in the root tissue of grafts between wild-type shoots and cad1-3 atpcs2-1 double-mutant roots, demonstrating that PCs are transported over long distances from shoots to roots in Arabidopsis. (+info)
First known image of Cucurbita in Europe, 1503-1508.
(27/95)
BACKGROUND: The genus Cucurbita (pumpkin, squash, gourd) is native to the Americas and diffused to other continents subsequent to the European contact in 1492. For many years, the earliest images of this genus in Europe that were known to cucurbit specialists were the two illustrations of C. pepo pumpkins that were published in Fuchs' De Historia Stirpium, 1542. Images of fruits of two Cucurbita species, drawn between 1515 and 1518, were recently discovered in the Villa Farnesina in Rome. FINDINGS: An even earlier image of Cucurbita exists in the prayer book, Grandes Heures d'Anne de Bretagne, illustrated by Jean Bourdichon in Touraine, France, between 1503 and 1508. This image, which shows a living branch bearing flowers and fruits, had not been examined and analysed by cucurbit specialists until now. The image is identified as depicting Cucurbita pepo subsp. texana. Unlike some of the fruits of Cucurbita depicted in the Villa Farnesina a decade later, this image does not depict an esculent and does not constitute evidence of early European contact with New World agriculture. Based on the descriptive, ecological and geographical accounts of C. pepo subsp. texana in the wild, the idea is considered that the image was based on an offspring of a plant found growing along the Gulf Coast of what is now the United States. (+info)
Extraction of features from ultrasound acoustic emissions: a tool to assess the hydraulic vulnerability of Norway spruce trunkwood?
(28/95)
The aim of this study was to assess the hydraulic vulnerability of Norway spruce (Picea abies) trunkwood by extraction of selected features of acoustic emissions (AEs) detected during dehydration of standard size samples. The hydraulic method was used as the reference method to assess the hydraulic vulnerability of trunkwood of different cambial ages. Vulnerability curves were constructed by plotting the percentage loss of conductivity vs an overpressure of compressed air. Differences in hydraulic vulnerability were very pronounced between juvenile and mature wood samples; therefore, useful AE features, such as peak amplitude, duration and relative energy, could be filtered out. The AE rates of signals clustered by amplitude and duration ranges and the AE energies differed greatly between juvenile and mature wood at identical relative water losses. Vulnerability curves could be constructed by relating the cumulated amount of relative AE energy to the relative loss of water and to xylem tension. AE testing in combination with feature extraction offers a readily automated and easy to use alternative to the hydraulic method. (+info)
Air pressure in clamp-on leaf chambers: a neglected issue in gas exchange measurements.
(29/95)
Air pressure in leaf chambers is thought to affect gas exchange measurements through changes in partial pressure of the air components. However, other effects may come into play when homobaric leaves are measured in which internal lateral gas flow may occur. When there was no pressure difference between the leaf chamber and ambient air (DeltaP=0), it was found in previous work that lateral CO(2) diffusion could affect measurements performed with clamp-on leaf chambers. On the other hand, overpressure (DeltaP>0) in leaf chambers has been reported to minimize artefacts possibly caused by leaks in chamber sealing. In the present work, net CO(2) exchange rates (NCER) were measured under different DeltaP values (0.0-3.0 kPa) on heterobaric and homobaric leaves. In heterobaric leaves which have internal barriers for lateral gas movement, changes in DeltaP had no significant effect on NCER. For homobaric leaves, effects of DeltaP>0 on measured NCER were significant, obviously due to lateral gas flux inside the leaf mesophyll. The magnitude of the effect was largely defined by stomatal conductance; when stomata were widely open, the impact of DeltaP on measured NCER was up to 7 mumol CO(2) m(-2) s(-1) kPa(-1). Since many other factors are also involved, neither DeltaP=0 nor DeltaP>0 was found to be the 'one-size fits all' solution to avoid erroneous effects of lateral gas transport on measurements with clamp-on leaf chambers. (+info)
Ion-mediated flow changes suppressed by minimal calcium presence in xylem sap in Chrysanthemum and Prunus laurocerasus.
(30/95)
After the discovery of ion-mediated changes in xylem hydraulic resistance a few years ago, a number of research papers were published that related ion-mediated flow changes in the xylem to various aspects of whole plant functioning and evolutionary diversification of vascular cells. Ion-mediated changes in xylem hydraulic resistance are commonly quantified as the percentile change in hydraulic resistance, relative to the hydraulic resistance measured using a reference fluid, usually (ultra) pure deionized water. In this research the impact was investigated of the complete absence of all ions in deionized water compared with reference fluids containing a minimal amount of free calcium on the quantification of ion-mediated flow changes in stem segments of Chrysanthemum (Dendranthemaxgrandiflorum Tzvelev) and Prunus L. (Prunus laurocerasus L.). The addition of 10 mM KCl to deionized water significantly increased flow rate in Chrysanthemum (17-24%) and Prunus L. (16%). The addition of 1 mM CaCl(2) to the reference fluid reduced this KCl-mediated increase in flow rate to 1-2% in both species. 1 mM Ca(2+) is within the lower range of Ca(2+)-concentrations normally measured in xylem sap of many plant species, and three times lower than the original Ca(2+)-concentration measured in the xylem sap of Chrysanthemum plants used for the present measurements. The present results indicate that the complete removal of cations from the xylem fluid with deionized water causes the major part of the ion-mediated flow change previously reported in the xylem of plants. It is concluded that the use of deionized water as a reference fluid should be avoided. Earlier proposed relationships between ion-mediated changes and water flow in xylem of plants should be re-evaluated if they were based on deionized water as the reference fluid. (+info)
Quantification of cuticular permeability in genetically modified plants.
(31/95)
More and more studies on genetically modified plants are identifying parts of the genetic code with putative involvement in creating the cuticular barrier. Unfortunately, many of these studies suffer from the inadequacy of the chosen methods to quantify, in a reasonably unambiguous way, if and how the efficacy of the cuticular barrier is affected by the genetic change. A short overview of relevant findings is given and a more stringent experimental approach to quantifying effects on cuticular permeability in genetically modified plants proposed. (+info)
Temporal and spatial pattern of embolism induced by pressure collar techniques in twigs of Picea abies.
(32/95)
The pressure collar technique enables the induction of embolism in plant xylem. This artificial cavitation is based on air seeding processes which occur when specific pressure gradients between the air and water phase of the xylem are exceeded. Standard pressure collars and a new point injection technique, which builds up a local potential gradient, were used to study the time and spatial pattern of this process. On twigs of Norway spruce (Picea abies), the cross-sectional and axial pattern, and the time-course of embolism formation were analysed via conductivity and ultrasonic measurements as well as staining experiments. Furthermore, the release of air from the twig surface was studied by immersing twig sections in water. In cross-sections, embolized areas induced by the point injection technique were smaller compared with the standard collar and restricted to a circle sector. Embolism propagated from the pressure collar towards the nearest distal and proximal nodes but not further. A release of air was also observed predominantly at the internode attached to the pressure collar. Embolism rates increased within minutes and reached approximately 80% loss of conductivity after 10 min treatment with the standard collar. The size of air entry points and embolism rates correlated significantly. Embolism formation in wood therefore depends not only on vulnerability thresholds but also on the extent of air-water interfaces within the xylem and on the time of exposure to pressure gradients. These aspects and the propagation of pressure within samples are crucial for pressure collar experiments. In addition, wood architecture influences the extent and pattern of embolism caused by air seeding processes. (+info)