Surface tension and viscosity of axenic maize and lupin root mucilages

Abstract

SUMMARYIn many plants, mucilage permeates the interface between root and soil, yet little is known about its physical properties or its infiuence on the physical properties of the rhizosphere. Mucilage was collected from 3-4-d-old, axenically-grown maize {Zea mays L. cv. Freya) and lupin {Lupinus angustifolius L. cv. Merrit) seedlings. Surface tension and viscosity were measured over a range of mucilage hydration, and neutral sugar analyses of the hydrolysed mucilages were obtained by gas chromatography. Surface tension of both maize and lupin mucilage was reduced to ~ 48 mN m"^ at total solute concentrations > 0-7 mg mr\ indicating the presence of powerful surfactants. Mucilage viscosity increased with increasing solute concentration and decreasing temperature. At a total solute concentration of 07 mg mr\ the viscosity of maize mucilage at 20 °C w^as 2-1 mPa s (approx. double that of pure water), increasing to 3-3 mPa s at 5 °C. Both maize and lupin mucilage showed viscoelastic behaviour. The major component of maize mucilage was found to be glucose, but in lupin it was fucose.The surface tension and viscosity results support the idea that mucilage plays a major role in the maintenance of root-soil contact in drying soils. As surface tension decreases, the ability of the mucilage to w^et the surrounding soil particles becomes greater. Also, as viscosity and elasticity increase, the resistance to movement of any soil particles in contact with the mucilage increases, a degree of stabilization of the rhizosphere structure is achieved and hydraulic continuity is maintained. It is unclear whether the surfactant is actively secreted by the root or is present simply as a result of leakage from root cells.

Plant roots release phospholipid surfactants that modify the physical and chemical properties of soil

“…Capillary rise (typically ranging between 25 and 45 mm) was measured at 20 ° C with a travelling microscope using the equilibrium position of the receding meniscus (Read & Gregory, 1997). Individual measurements are accurate to ± 1 mN m − 1 .…”

“…In a previous study, Read & Gregory (1997) measured the surface tension of mucilage collected from the roots of 3-4-d-old, axenically grown maize (Zea mays L. cv. Freya) and lupin (Lupinus angustifolius L. cv.…”

Plant exudates improve the mechanical conditions for root penetration through compacted soils

“…These have found a large impact of plant exudates on soil physical behaviour, which varies between plant species, seeds and roots. Exudates are often more viscous and have a lower surface tension than water (Read and Gregory 1997). This will have a large impact on the capacity of plants to capture water from soils.…”

Physical changes in the rhizosphere and their significance for plant-soil interactions

“…We have been conducting experiments to determine whether mucilage possesses physical properties consistent with the role of maintaining root-soil contact in a dynamic rhizosphere where fluctuations in water content are influenced by the plant. Read and Gregory (1997) found that the surface tension of maize mucilage decreased by up to 40% and its viscosity by 50% as solute concentration increased (Fig. 1).…”