51 research outputs found
Digital microscopy: A useful technique for measuring root elongation in solution
Decreased root elongation and rupture of outer cells, major effects of soluble aluminum (Al), may be studied using digital microscopy with little interference by the experimental technique. Single roots of 3-d-old mungbean (Vigna radiata L.) or soybean (Glycine max (L.) Merr.) seedlings were marked with activated charcoal particles and grown for ca. 2 h in 500 mL 1 mM CaCl solution at pH 6, followed by the imposition of an Al treatment. A digital image at 25-time magnification was recorded every 5 min for up to 7 h. Examination of the digital images showed that Al exerted its rhizotoxic effects rapidly (ca. 20-50 min) by reducing cell expansion in the elongation zone. Rupture of epidermal and outer cortical cells occurred later (after≥4 h) and closer to the root tip. Digital microscopy has a number of inherent benefits and problems, but is overall a valuable technique that may find wide use in studies on root growth
Strategies in a metallophyte species to cope with manganese excess
The effect of exposure to high Mn concentration
was studied in a metallophyte species, Erica
andevalensis, using hydroponic cultures with a range
of Mn concentrations (0.06, 100, 300, 500, and
700 mg L-1). At harvest, biomass production, element
uptake, and biochemical indicators of metal
stress (leaf pigments, organic acids, amino acids,
phenols, and activities of catalase, peroxidase, superoxide
dismutase) were determined in leaves and roots.
Increasing Mn concentrations led to a decrease in
biomass accumulation, and tip leaves chlorosis was
the only toxicity symptom detected. In a similar way,
photosynthetic pigments (chlorophylls a and b, and
carotenoids) were affected by high Mn levels. Among
organic acids, malate and oxalate contents in roots
showed a significant increase at the highest Mn
concentration, while in leaves, Mn led to an increasing
trend in citrate and malate contents. An increase of Mn also induced an increase in superoxide dismutase
activity in roots and catalase activity in leaves. As
well, significant changes in free amino acids were
induced by Mn concentrations higher than
300 mg L-1, especially in roots. No significant
changes in phenolic compounds were observed in
the leaves, but root phenolics were significantly
increased by increasing Mn concentrations in treatments.
When Fe supply was increased 10 and 20 times
(7–14 mg Fe L-1 as Fe-EDDHA) in the nutrient
solutions at the highest Mn concentration
(700 mg Mn L-1), it led to significant increases in
photosynthetic pigments and biomass accumulation.
Manganese was mostly accumulated in the roots, and
the species was essentially a Mn excluder. However,
considering the high leaf Mn concentration recorded
without toxicity symptoms, E. andevalensis might be
rated as a Mn-tolerant speciesinfo:eu-repo/semantics/publishedVersio
Competitive sorption reactions between phosphorus and organic matter in soil: a review
The incorporation of organic matter (OM) in soils that are able to rapidly sorb applied phosphorus (P) fertiliser reportedly increases P availability to plants. This effect has commonly been ascribed to competition between the decomposition products of OM and P for soil sorption sites resulting in increased soil solution P concentrations. The evidence for competitive inhibition of P sorption by dissolved organic carbon compounds, derived from the breakdown of OM, includes studies on the competition between P and (i) low molecular weight organic acids (LOAs), (ii) humic and fulvic acids, and (iii) OM leachates in soils with a high P sorption capacity. These studies, however, have often used LOAs at 1–100 mm, concentrations much higher than those in soils (generall
Do Decomposing Organic Matter Residues Reduce Phosphorus Sorption in Highly Weathered Soils?
Many studies have shown a reduction in P sorption in highly weathered soils when organic matter (OM) is applied, suggesting competition between OM decomposition products and P for sorption sites. However, such studies seldom consider the P released from the added OM. To delineate the effects of OM addition on P availability through sorption competition and P addition, water leachate from incubated soybean (SB) [Glycine max (L.) Merr.] and Rhodes grass (RG) (Chloris gayana Kunth cv. Callide) was used in competitive P sorption studies both undiluted and after acidification (i.e., the fulvic acid [FA] component). Addition of two rates (0.2 and 2 mL) of SB leachate to an Oxisol significantly increased P sorption at the higher rate, while a similar trend was observed following RG leachate addition at the same rates. Extending the range of highly weathered soils examined (two Oxisols, an Ultisol, and an acidic Vertisol) resulted in no observed decrease in P sorption following addition of OM leachate. Surprisingly, SB leachate transiently increased P sorption in the two Oxisol soils. Addition of the FA component of the leachates resulted in a transient
A role for pectin in the control of cell expansion
Uptake of nutrients and water depends on the growth of roots through elongation of individual cells near the. root tip. Many of the numerous components of Type I primary cell walls, those of dicotyledons and monocotyledons other than grasses (Poaceae), have been determined, and many hypotheses have been proposed for the control of cell expansion. This important aspect of plant growth still needs elucidation, however. A model is proposed in which pectin, which occurs as a calcium (Ca) pectate gel between the load-bearing cellulose microfibrils and xyloglucan (XG) chains, controls the rate at which cells expand. It is considered that the increasing tension generated by the expanding cell is transmitted to interlocked XG chains and cellulose microfibrils. The resulting deformation of the embedded Ca pectate gel elicits the excretion of protons from the cytoplasm, possibly via compounds such as cell wall-associated kinases, that weakens the Ca pectate gel, permitting slippage of XG molecules through the action of expansin. Further slippage is prevented by deformation of the pectic gel, proton diffusion, and the transfer of residual tension to adjacent XG chains. Evidence for this model is based on the effects of pH, Ca, and aluminum (Al) on root elongation and on the reactions of these cations with Ca pectate. This model allows for genetic selection of plants and adaptation of individual plants to root environmental conditions
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