Phloem flow and sugar transport in Ricinus communis L. is inhibited under anoxic conditions of shoot or roots
Peuke, A.D. ; Gessler, A. ; Trumbore, S. ; Windt, C.W. ; Homan, N. ; Gerkema, E. ; As, H. van - \ 2015
Plant, Cell & Environment 38 (2015)3. - ISSN 0140-7791 - p. 433 - 447.
carbon-isotope composition - mushrooms agaricus-bisporus - distance water transport - organic-matter - membrane-permeability - assimilate transport - plants - leaves - starch - stress
Anoxic conditions should hamper the transport of sugar in the phloem, as this is an active process. The canopy is a carbohydrate source and the roots are carbohydrate sinks.By fumigating the shoot with N2 or flooding the rhizosphere, anoxic conditions in the source or sink, respectively, were induced. Volume flow, velocity, conducting area and stationary water of the phloem were assessed by non-invasive magnetic resonance imaging (MRI) flowmetry. Carbohydrates and d13C in leaves, roots and phloem saps were determined. Following flooding, volume flow and conducting area of the phloem declined and sugar concentrations in leaves and in phloem saps slightly increased. Oligosaccharides appeared in phloem saps and after 3 d, carbon transport was reduced to 77%. Additionally, the xylem flow declined and showed finally no daily rhythm. Anoxia of the shoot resulted within minutes in a reduction of volume flow, conductive area and sucrose in the phloem sap decreased. Sugar transport dropped to below 40% by the end of the N2 treatment. However, volume flow and phloem sap sugar tended to recover during the N2 treatment. Both anoxia treatments hampered sugar transport. The flow velocity remained about constant, although phloem sap sugar concentration changed during treatments. Apparently, stored starch was remobilized under anoxia.
Flow characteristics and exchange in complex biological systems as observed by pulsed-field-gradient magnetic-resonance imaging
Homan, N. ; Venne, B.B. ; As, H. van - \ 2010
Physical Review. E, Statistical nonlinear, and soft matter physics 82 (2010)2. - ISSN 1539-3755
distance water transport - pfg nmr - porous-media - membrane-permeability - spatial correlations - self-diffusion - mri - relaxation - dispersion - sequence
Water flow through model porous media was studied in the presence of surface relaxation, internal magnetic field inhomogeneities and exchange with stagnant water pools with different relaxation behavior, demonstrating how the apparent flow parameters average velocity, volume flow and flow conducting area in these situations depend on the observation time. To investigate the water exchange process a two component biological model system consisting of water flowing through a biofilm reactor (column packed with methanogenic granular sludge beads) was used, before and after a heat treatment to introduce exchange. We show that correction of the stagnant fluid signal amplitude for relaxation at increasing observation time using the observed relaxation times reveals exchange between the two fractions in the system. Further it is demonstrated how this exchange can be quantified
Quantitative permeability imaging of plant tissues
Sibgatullin, T. ; Vergeldt, F.J. ; Gerkema, E. ; As, H. van - \ 2010
European Biophysics Journal 39 (2010)4. - ISSN 0175-7571 - p. 699 - 710.
pulsed-field gradient - time-dependent diffusion - nuclear-magnetic-resonance - water self-diffusion - membrane-permeability - pfg nmr - osmotic-stress - porous-media - yeast-cells - echo nmr
A method for mapping tissue permeability based on time-dependent diffusion measurements is presented. A pulsed field gradient sequence to measure the diffusion encoding time dependence of the diffusion coefficients based on the detection of stimulated spin echoes to enable long diffusion times is combined with a turbo spin echo sequence for fast NMR imaging (MRI). A fitting function is suggested to describe the time dependence of the apparent diffusion constant in porous (bio-)materials, even if the time range of the apparent diffusion coefficient is limited due to relaxation of the magnetization. The method is demonstrated by characterizing anisotropic cell dimensions and permeability on a subpixel level of different tissues of a carrot (Daucus carota) taproot in the radial and axial directions
Potato (Solanum tuberosum L.) tuber ageing induces changes in the proteome and antioxidants associated with the sprouting pattern
Delaplace, P. ; Fauconnier, M.L. ; Sergeant, K. ; Dierick, J.F. ; Oufir, M. ; Wal, F. van der; America, A.H.P. ; Renaut, J. ; Hausman, J.F. ; Jardin, P. du - \ 2009
Journal of Experimental Botany 60 (2009)4. - ISSN 0022-0957 - p. 1273 - 1288.
physiological age index - heat-shock proteins - lipid-peroxidation - oxidative stress - disulfide-isomerase - hydrogen-peroxide - seed-tubers - spectrophotometric method - membrane-permeability - superoxide-dismutase
During post-harvest storage, potato tubers age as they undergo an evolution of their physiological state influencing their sprouting pattern. In the present study, physiological and biochemical approaches were combined to provide new insights on potato (Solanum tuberosum L. cv. Desiree) tuber ageing. An increase in the physiological age index (PAI) value from 0.14 to 0.83 occurred during storage at 4 degrees C over 270 d. Using this reference frame, a proteomic approach was followed based on two-dimensional electrophoresis. In the experimental conditions of this study, a marked proteolysis of patatin occurred after the PAI reached a value of 0.6. In parallel, several glycolytic enzymes were up-regulated and cellular components influencing protein conformation and the response to stress were altered. The equilibrium between the 20S and 26S forms of the proteasome was modified, the 20S form that recycles oxidized proteins being up-regulated. Two proteins belonging to the cytoskeleton were also differentially expressed during ageing. As most of these changes are also observed in an oxidative stress context, an approach focused on antioxidant compounds and enzymes as well as oxidative damage on polyunsaturated fatty acids and proteins was conducted. All the changes observed during ageing seemed to allow the potato tubers to maintain their radical scavenging activity until the end of the storage period as no accumulation of oxidative damage was observed. These data are interpreted considering the impact of reactive oxygen species on the development and the behaviour of other plant systems undergoing ageing or senescence processes.
MRI of intact plants
As, H. van; Scheenen, T. ; Vergeldt, F.J. - \ 2009
Photosynthesis Research 102 (2009)2-3. - ISSN 0166-8595 - p. 213 - 222.
nuclear-magnetic-resonance - distance water transport - membrane-permeability - diffusion constants - spin relaxation - nmr microscopy - sap flow - photosynthesis - phloem - xylem
Nuclear magnetic resonance imaging (MRI) is a non-destructive and non-invasive technique that can be used to acquire two- or even three-dimensional images of intact plants. The information within the images can be manipulated and used to study the dynamics of plant water relations and water transport in the stem, e.g., as a function of environmental (stress) conditions. Non-spatially resolved portable NMR is becoming available to study leaf water content and distribution of water in different (sub-cellular) compartments. These parameters directly relate to stomatal water conductance, CO2 uptake, and photosynthesis. MRI applied on plants is not a straight forward extension of the methods discussed for (bio)medical MRI. This educational review explains the basic physical principles of plant MRI, with a focus on the spatial resolution, factors that determine the spatial resolution, and its unique information for applications in plant water relations that directly relate to plant photosynthetic activity
Most water in the tomato truss is imported through the xylem, not the phloem. An NMR flow imaging study
Windt, C.W. ; Gerkema, E. ; As, H. van - \ 2009
Plant Physiology 151 (2009)2. - ISSN 0032-0889 - p. 830 - 842.
vapor-pressure deficit - membrane-permeability - transpiration flows - biological tissues - ricinus-communis - grape berries - fruit-growth - sap flow - transport - plants
In this study, we demonstrate nuclear magnetic resonance flow imaging of xylem and phloem transport toward a developing tomato (Solanum lycopersicum) truss. During an 8-week period of growth, we measured phloem and xylem fluxes in the truss stalk, aiming to distinguish the contributions of the two transport tissues and draw up a balance between influx and efflux. It is commonly estimated that about 90% of the water reaches the fruit by the phloem and the remaining 10% by the xylem. The xylem is thought to become dysfunctional at an early stage of fruit development. However, our results do not corroborate these findings. On the contrary, we found that xylem transport into the truss remained functional throughout the 8 weeks of growth. During that time, at least 75% of the net influx into the fruit occurred through the external xylem and about 25% via the perimedullary region, which contains both phloem and xylem. About one-half of the net influx was lost due to evaporation. Halfway through truss development, a xylem backflow appeared. As the truss matured, the percentage of xylem water that circulated into the truss and out again increased in comparison with the net uptake, but no net loss of water from the truss was observed. The circulation of xylem water continued even after the fruits and pedicels were removed. This indicates that neither of them was involved in generating or conducting the circulation of sap. Only when the main axis of the peduncle was cut back did the circulation stop
Aquaporins of the PIP2 class are required for efficient anther dehiscence in tobacco
Bots, M.L. ; Vergeldt, F.J. ; Wolters-Arts, M. ; Weterings, K. ; As, H. van; Mariani, C. - \ 2005
Plant Physiology 137 (2005)3. - ISSN 0032-0889 - p. 1049 - 1056.
jasmonic acid biosynthesis - membrane-permeability - arabidopsis-thaliana - brassica-oleracea - channel proteins - gene-expression - osmotic-stress - male-sterility - water - plants
Several processes during sexual reproduction in higher plants involve the movement of water between cells or tissues. Before flower anthesis, anther and pollen dehydration takes place before the release of mature pollen at dehiscence. Aquaporins represent a class of proteins that mediates the movement of water over cellular membranes. Aquaporins of the plasmamembrane PIP2 family are expressed in tobacco (Nicotiana tabacum) anthers and may therefore be involved in the movement of water in this organ. To gain more insight into the role these proteins may play in this process, we have analyzed their localization using immunolocalizations and generated plants displaying RNA interference of PIP2 aquaporins. Our results indicate that PIP2 protein expression is modulated during anther development. Furthermore, in tobacco PIP2 RNA interference plants, anther dehydration was slower, and dehiscence occurred later when compared with control plants. Together, our results suggest that aquaporins of the PIP2 class are required for efficient anther dehydration prior to dehiscence.
Theoretical prediction of 'optimal' freezing programmes
Woelders, H. ; Chaveiro, A. - \ 2004
Cryobiology 49 (2004)3. - ISSN 0011-2240 - p. 258 - 271.
intracellular ice formation - glycerol concentration - membrane-permeability - water permeability - spermatozoa frozen - cooling velocity - bull spermatozoa - sperm - cells - injury
We have developed a quantitative description of the osmotic behaviour of cells during freezing without a presupposed value of the cooling rate. Instead, at all times the intracellular supercooling is maximised provided that it does not exceed a predetermined value 'p' (e.g., 2°C). This should preclude intracellular ice formation, but also ensures that the osmotic gradient and the CPA concentration gradient are limited, as well as the gradient driven transmembrane fluxes of water and CPA. Using the condition of a constant level of supercooling of p°C, equations can be derived to generate non-linear cooling curves in which at all times the cooling rate is maximised (to minimise slow cooling damage), while preventing conditions that could lead to fast cooling damage. Simulations of the osmotic events during freezing, and prediction of the 'optimal' freezing curve can be performed provided that values are available for the membrane permeability coefficients for water (L p) and cryoprotectant (Ps), and their respective activation energies, the initial intracellular osmotically active aqueous volume, and the membrane surface area. Simulations are shown, both with and without permeant solute, to demonstrate how the predicted 'optimal' freezing curve is affected by medium composition, and by membrane permeability and osmotic cell characteristics.
Ageing increases the sensitivity of neem (Azadirachta indica) seeds to imbibitional stress
Neya, O. ; Golovina, E.A. ; Nijsse, J. ; Hoekstra, F.A. - \ 2004
Seed Science Research 14 (2004)2. - ISSN 0960-2585 - p. 205 - 217.
storage behavior - membrane-permeability - desiccation tolerance
Imbibitional stress was imposed on neem (Azadirachta indica) seeds by letting them soak for 1 h in water at unfavourable, low temperatures before further incubation at 30degreesC. Sensitivity to low imbibition temperatures increased with a decrease in seed moisture content (MC). To investigate a possible involvement of seed age in the extent of imbibitional damage, initially high-quality seed lots that differed in storage history (10 weeks versus 10 months) were examined at 4 and 7% (fresh weight basis). After 10 months of storage, the 7% MC seeds had become sensitive to imbibitional stress. Further drying (1 week) to 4% MC affected aged seeds more than non-aged seeds. Barrier properties of cellular membranes in axes excised after 1 d of rehydration were estimated using a spin-probe technique. The proportion of cells with intact membranes increased with increasing imbibition temperature. For each temperature tested, there were more cells with leaky membranes after 10 months than after 10 weeks of dry storage. Localization of embryo cells displaying loss of turgor and abnormal cellular structure was accomplished using cryo-planing, followed by cryo-scanning electron microscopy. Inspection of the cryo-planed surfaces confirmed that imbibitional damage was temperature dependent, occurring at the periphery. Ageing increased the number of imbibitionally damaged, peripheral cell layers. Germination was estimated to fail when less than 70% of axis cells were alive. We conclude that ageing increases the sensitivity to imbibitional stress. Both the fast ageing and the sensitivity to imbibitional stress might explain the apparent controversies about neem seed desiccation tolerance and storage behaviour.
Homotypic interactions of the infectious bursal disease virus proteins VP3, pVP2, VP4, and VP5: mapping of the interacting domains
Tacken, M.G.J. ; Beuken, P.A. van den; Peeters, B.P.H. ; Thomas, A.A.M. ; Rottier, P.J.M. ; Boot, H.J. - \ 2003
Virology 312 (2003)2. - ISSN 0042-6822 - p. 306 - 319.
dependent rna-polymerase - double-stranded-rna - escherichia-coli-cells - nonstructural proteins - membrane-permeability - maturation process - cleavage sites - expression - poliovirus - yeast
Infectious bursal disease virus (IBDV), a nonenveloped double-stranded RNA virus of chicken, encodes five proteins. Of these, the RNA-dependent RNA polymerase (VP1) is specified by the smaller genome segment, while the large segment directs synthesis of a nonstructural protein (VP5) and a structural protein precursor from which the capsid proteins pVP2 and VP3 as well as the viral protease VP4 are derived. Using the recently redefined processing sites of the precursor, we have reevaluated the homotypic interactions of the viral proteins using the yeast two-hybrid system. Except for VP1, which interacted weakly, all proteins appeared to self-associate strongly. Using a deletion mutagenesis approach, we subsequently mapped the interacting domains in these polypeptides, where possible confirming the observations made in the two-hybrid system by performing coimmunoprecipitation analyses of tagged protein constructs coexpressed in avian culture cells. The results revealed that pVP2 possesses multiple interaction domains, consistent with available structural information about this external capsid protein. VP3¿VP3 interactions were mapped to the amino-terminal part of the polypeptide. Interestingly, this domain is distinct from two other interaction domains occurring in this internal capsid protein: while binding to VP1 has been mapped to the carboxy-terminal end of the protein, interaction with the genomic dsRNA segments has been suggested to occur just upstream thereof. No interaction sites could be assigned to the VP4 protein; any deletion applied abolished its self-association. Finally, one interaction domain was detected in the central, most hydrophobic region of VP5, supporting the idea that this virulence determinant may function as a membrane pore-forming protein in infected cells