34 research outputs found
Sticky mucilages and exudates of plants: putative microenvironmental design elements with biotechnological value
Plants produce a wide array of secretions both above- and belowground. Known as mucilages or exudates, they are secreted by seeds, roots, leaves and stems and fulfil a variety of functions including adhesion, protection, nutrient acquisition or infection. Mucilages are generally polysaccharide-rich and often occur in the form of viscelastic gels and in many cases have adhesive properties. In some cases, progress is being made in understanding the structure-function relations of mucilages such as for the secretions that allow growing ivy to attach to substrates and the biosynthesis and secretion of the mucilage compounds of the Arabidopsis seed coat. Work is just beginning in understanding root mucilage and the proposed adhesive polymers involved in the formation of rhizosheaths at root surfaces and for the secretions involved in host plant infection by parasitic plants. In this article, we summarize knowledge on plant exudates and mucilages within the concept of their functions in microenvironmental design, focusing especially on their bioadhesive functions and the molecules responsible for them. We draw attention to areas of future knowledge need, including the microstructure of mucilages and their compositional and regulatory dynamics. This article is protected by copyright. All rights reserved
Fast X-Ray Fluorescence Microtomography of Hydrated Biological Samples
Metals and metalloids play a key role in plant and other biological systems as some of them are essential to living organisms and all can be toxic at high concentrations. It is therefore important to understand how they are accumulated, complexed and transported within plants. In situ imaging of metal distribution at physiological relevant concentrations in highly hydrated biological systems is technically challenging. In the case of roots, this is mainly due to the possibility of artifacts arising during sample preparation such as cross sectioning. Synchrotron x-ray fluorescence microtomography has been used to obtain virtual cross sections of elemental distributions. However, traditionally this technique requires long data acquisition times. This has prohibited its application to highly hydrated biological samples which suffer both radiation damage and dehydration during extended analysis. However, recent advances in fast detectors coupled with powerful data acquisition approaches and suitable sample preparation methods can circumvent this problem. We demonstrate the heightened potential of this technique by imaging the distribution of nickel and zinc in hydrated plant roots. Although 3D tomography was still impeded by radiation damage, we successfully collected 2D tomograms of hydrated plant roots exposed to environmentally relevant metal concentrations for short periods of time. To our knowledge, this is the first published example of the possibilities offered by a new generation of fast fluorescence detectors to investigate metal and metalloid distribution in radiation-sensitive, biological samples
Analysis of nickel concentration profiles around the roots of the hyperaccumulator plant Berkheya coddii using MRI and numerical simulations
Abstract Investigations of soil-root interactions are
hampered by the difficult experimental accessibility of
the rhizosphere. Here we show the potential of Magnetic
Resonance Imaging (MRI) as a non-destructive measurement
technique in combination with numerical
modelling to study the dynamics of the spatial distribution
of dissolved nickel (Ni2+) around the roots of the
nickel hyperaccumulator plant Berkheya coddii. Special
rhizoboxes were used in which a root monolayer
had been grown, separated from an adjacent inert glass
bead packing by a nylon membrane. After applying a
Ni2+ solution of 10 mg l−1, the rhizobox was imaged
repeatedly using MRI. The obtained temporal sequence
of 2-dimensional Ni2+ maps in the vicinity of
the roots showed that Ni2+ concentrations increased
towards the root plane, revealing an accumulation
pattern. Numerical modelling supported the Ni2+
distributions to result from advective water flow
towards the root plane, driven by transpiration, and
diffusion of Ni2+ tending to eliminate the concentration
gradient. With the model, we could study how the
accumulation pattern of Ni2+ in the root zone transforms
into a depletion pattern depending on transpiration
rate, solute uptake rate, and Ni2+ concentration in
solution
Cropland soil–plant systems control production and consumption of methane and nitrous oxide and their emissions to the atmosphere
Iron (Fe) speciation in xylem sap by XANES at a high brilliant synchrotron X-ray source: opportunities and limitations
The development of highly brilliant synchrotron facilities all around the world is opening the way to new research in biological sciences including speciation studies of trace elements in plants. In this paper, for the first time, iron (Fe) speciation in xylem sap has been assessed by X-ray absorption near-edge structure (XANES) spectroscopy at the highly brilliant synchrotron PETRA III, beamline P06. Both standard organic Fe-complexes and xylem sap samples of Fe-deficient tomato plants were analyzed. The high photon flux provided by this X-ray synchrotron source allows on one side to obtain good XANES spectra in a reasonable amount of time (approx. 15 min for 200 eV scan) at low Fe concentrations (sub parts-per-million), while on the other hand may cause radiation damage to the sample, despite the sample being cooled by a stream of liquid nitrogen vapor. Standard Fe-complexes such as Fe(III)-succinate, Fe(III)-α-ketoglutarate, and Fe(III)-nicotianamine are somehow degraded when irradiated with synchrotron X-rays and Fe(III) can undergo photoreduction. Degradation of the organic molecules was assessed by HPLC-UV/Vis analyses on the same samples investigated by X-ray absorption spectroscopy (XAS). Fe speciation in xylem sap samples revealed Fe(III) to be complexed by citrate and acetate. Nevertheless, artifacts created by radiation damage cannot be excluded. The use of highly brilliant synchrotrons as X-ray sources for XAS analyses can dramatically increase the sensitivity of the technique for trace elements thus allowing their speciation in xylem sap. However, great attention must be paid to radiation damage, which can lead to biased results
Delimiting soil chemistry thresholds for nickel hyperaccumulator plants in Sabah (Malaysia)
Nickel hyperaccumulator plants have been the focus of considerable research because of their unique ecophysiological characteristics that can be exploited in phytomining technology. Comparatively little research has focussed on the soil chemistry of tropical nickel hyperaccumulator plants to date. This study aimed to elucidate whether the soil chemistry associated with nickel hyperaccumulator plants has distinctive characteristics that could be indicative of specific edaphic requirements. The soil chemistry associated with 18 different nickel hyperaccumulator plant species occurring in Sabah (Malaysia) was compared with local ultramafic soils where nickel hyperaccumulator plants were absent. The results showed that nickel hyperaccumulators in the study area were restricted to circum-neutral soils with relatively high phytoavailable calcium, magnesium and nickel concentrations. There appeared to be a ‘threshold response’ for the presence of nickel hyperaccumulator plants at >20 μg g−1 carboxylic-extractable nickel or >630 μg g−1 total nickel, and >pH 6.3 thereby delimiting their edaphic range. Two (not mutually exclusive) hypotheses were proposed to explain nickel hyperaccumulation on these soils: (1) hyperaccumulators excrete large amounts of root exudates thereby increasing nickel phytoavailability through intense rhizosphere mineral weathering; and (2) hyperaccumulators have extremely high nickel uptake efficiency thereby severely depleting nickel and stimulating re-supply of Ni from diffusion from labile Ni pools. It was concluded that since there was an association with soils with highly labile nickel pools, the available evidence primarily supports hypothesis (2