Wendy Silk - Academia.edu (original) (raw)

Papers by Wendy Silk

Primary plant root growth occurs in the 10 mm root tip segment. Primary growth is characterized b... more Primary plant root growth occurs in the 10 mm root tip segment. Primary growth is characterized by longitudinal cells expansion that uses water to stretch the rigid cell walls. Silk and Wagner (1980) provided an osmotic root growth model to describe the water potential necessary to sustain this process. The osmotic model assumes that the growth zone is hydraulically isolated from the rest of the root, with all water necessary for growth coming from the surrounding soil. Unfortunately the radial water potential gradient suggested by the osmotic model results cannot be verified empirically. We have expanded upon the original theory to create a threedimensional model with the addition of leakypipe point sources in the growth zone. The point source root growth theory is based on the discovery of protophloem structures extending into the growth zone (Gould, et al. 2004). It is our conjecture that these structures are acting as pipes for water to be pushed down into the growth zone fro...

Groundwater nitrate pollution poses a serious challenge in regions with intensively managed agric... more Groundwater nitrate pollution poses a serious challenge in regions with intensively managed agricultural systems. Therefore, it is important to develop crop management practices that limit nitrate transport past the root zone. In California, leaching can be significant during winter months, when the soil typically is left fallow and precipitation is highest. In some systems, winter cover crops have been shown to reduce leaching by incorporating nitrate into biomass and/or altering water movement through the soil. In an ongoing field study, we aim to quantify nitrate leaching during the rainy season and assess the effectiveness of two commonly grown cover crop species, triticale (x Triticosecale) and bell bean (Vicia faba). The two cover crops generate contrasting root systems: triticale has a fibrous root system while bell bean produces a taproot system. Furthermore, bell bean nodules fix N late in the season. The two cover crops were grown separately and fallow fields served as a c...

In the first year of the project we have characterized saturated soil shear strength in fallow so... more In the first year of the project we have characterized saturated soil shear strength in fallow soil (controls) and in soil planted with Avena fatua as a function of several key variables: depth from soil surface, plant developmental stage, and soil compression. Root tensile strength was measured as a function of distance from the root apex in well-watered and water-stressed roots. Root growth analysis revealed the spatial pattern of expansion producing the root elongation in the soil. Root architecture was characterized to correlate with the soil shear strength measurements. We addressed management implications by networking with Andrew Simon and

Environmental Pollution, 2011

The large uptake of Cu from nanoparticulate CuO suspension into duckweed tissue causes the toxici... more The large uptake of Cu from nanoparticulate CuO suspension into duckweed tissue causes the toxicity of CuO-NP to be equivalent to about four times the soluble Cu in the NP suspension.

Mechanics of Swelling, 1992

If swelling is defined as water uptake leading to an increase in volume, then growth of plants mu... more If swelling is defined as water uptake leading to an increase in volume, then growth of plants must be considered an ecologically important swelling process. The irreversible expansion of plant cells is thought to involve an osmotically driven uptake of water and concomitant yielding of the cellulosic cell wall under turgor pressure. For my contribution to this symposium, I emphasize analysis of plant growth in continuum mechanical terms. I will review some experimental and theoretical work on kinematics of growth of maize roots and the underlying biophysics. Topics include description of the growth field, the water potential field which sustains the observed growth pattern, and the distributions (within the growing region) of osmotically active species and some rheological properties. This article is related to others in the symposium. I am relying on the presentation of L. Boersma for a review of the structure and water relations of the plant cell. Mechanical aspects of plant growth are addressed by J. Passioura who describes some intriguing empirical results showing plant elongation rate as a function of applied pressure. And J. Nakielski generalizes the one-dimensional growth analysis to a two-dimensional tensorial treatment using a natural coordinate system to describe apical growth.

Environmental and Experimental Botany, 1989

... Pergamon Press plc ON THE CURVING AND TWINING OF STEMS WENDY KUHN SILK Department of Land, Ai... more ... Pergamon Press plc ON THE CURVING AND TWINING OF STEMS WENDY KUHN SILK Department of Land, Air, and Water Resources, University of California, Davis, CA 95615, USA (Received ... I was led to this subject by an interesting, but short paper by Professor Asa Gray . . ...

Journal of Experimental Botany

This article comments on: Rivière M, Corre Y, Peaucelle A, Derr J, Douady S. 2020. The hook shape... more This article comments on: Rivière M, Corre Y, Peaucelle A, Derr J, Douady S. 2020. The hook shape of growing leaves results from an active regulatory process. Journal of Experimental Botany 71, 6408–6417.

Journal of Experimental Botany, 1994

The equations and experimental methods are reviewed for calculating solute deposition rates and f... more The equations and experimental methods are reviewed for calculating solute deposition rates and fluxes an growing parts of roots. Then the expression for the growth-sustaining sucrose flux in the meristem is presented and evaluated to show the sucrose flux required to produce the empirically observed biomass deposition rate in primary maize roots. Two independent methods (one based on dye transport measurements and the second based on Stokes radii) are used to estimate the symplasmic conductivity for diffusion. The concentration gradients required to drive a growth-sustaining symplasmic diffusion of sucrose are found to be physiologically unreasonable. Either our current understanding of plasmodesmatal ultrastructure is flawed, or alternative mechanisms must exist for sucrose transport to the meristem.

J Plant Growth Regul, 2000

Books in Soils, Plants, and the Environment, 2002

The distribution of both water and nutrients in the root-zone can be highly non-uniform. The shap... more The distribution of both water and nutrients in the root-zone can be highly non-uniform. The shape of the wetted soil volume under micro-irrigation and the spatial distribution of soil water, and nitrate concentrations are dependent on many factors, including soil layering, hydraulic properties, emitter discharge rates, spacing, and their placement (above or below the soil surface), irrigation quantity and frequency, crop water uptake rates, etc. In general, root development in micro-irrigated field is constrained to the soil volume wetted by the irrigation water, with root length density decreasing with depth, whereas plants can quickly adapt their spatial pattern of water and nutrient uptake in response to irrigation water application distribution. Also, roots can adjust their uptake patterns, thereby compensating for local stress conditions by enhanced or preferential uptake in other regions of the rooting zone with less stressful conditions. A better understanding of the interac...

Plant physiology, 1992

Spatial distributions of growth and of the concentration of some inorganic nutrient elements were... more Spatial distributions of growth and of the concentration of some inorganic nutrient elements were analyzed in developing leaves of maize (Zea mays L.). Growth was analyzed by pinprick experiments with numerical analysis to characterize fields of velocity and relative elemental elongation rate. Inductively coupled plasma and atomic emission spectroscopy were used to measure nutrients extracted from segments of leaf tissue collected by position. Leaves 7 and 8, both elongating 3 millimeters per hour had maximum relative elemental growth rates of 0.06 to 0.08 millimeters per hour with maximum rates 20 to 50 millimeters from the node and cessation of growth by 90 millimeters from the node. Spatial distribution of dry weight density revealed that the rate of biomass deposition was maximum in the most rapidly expanding region and continued beyond the elongation zone. The nutrient elements K, Cl, Ca, Mg, and P showed different distribution patterns of ion density (on a dry weight basis). K...

Plant physiology, 1993

In many salt-sensitive species, elevated concentrations of Ca in the root growth media ameliorate... more In many salt-sensitive species, elevated concentrations of Ca in the root growth media ameliorate part of the shoot growth reduction caused by NaCl stress. The physiological mechanisms by which Ca exerts protective effects on leaf growth are still not understood. Understanding growth inhibition caused by a stress necessitates locating the leaf expansion region and quantifying the profile of the growth reduction. This will enable comparisons and correlations with spatial gradients of probable physiologically inhibiting factors. In this work we applied the methods of growth kinematics to analyze the effects of elevated Ca concentrations on the spatial and temporal distributions of growth within the intercalary expanding region of salinized sorghum (Sorghum bicolor [L.] Moench, cv NK 265) leaves. NaCl (100 mM) caused a decrease in leaf elongation rate by shortening the leaf growing zone by 20%, as well as reducing the peak value of the longitudinal relative elemental growth rate (REG r...

The pleiotropic effects of the Rld1-O/+ mutation of Zea mays (Poaceae) on leaf phenotype include ... more The pleiotropic effects of the Rld1-O/+ mutation of Zea mays (Poaceae) on leaf phenotype include a suppression of normal transverse unrolling, a reversed top/bottom epidermal polarity, and an apparently straighter longitudinal shape. According to engineering shell theory, there might be mechanical coupling between transverse and longitudinal habit, i.e., the leaf rolling itself might produce the longitudinal straightening. We tested this possibility with quantitative curvature measurements and mechanical uncoupling experiments. The contributions of elastic bending under self weight, mechanical coupling, and rest state of leaf parts to the longitudinal and transverse habit were assessed in Rld1-O/+ mutants and a population of sibling +/+ segregants. Elastic bending and curvature coupling are shown to be relatively unimportant. The Rld1-O/+ mutation is shown to alter not only the unrolling process, but also the developmental longitudinal curving in the growing leaf, leading to a straighter midrib and a rolled lamina. The Rld1-O/+ mutant is thus a suitable model to study the relation between tissue polarity and differential curvature development in the maize leaf. Since on the abaxial side of the leaf, more abundant sclerenchyma is found in +/+ than in Rld1-O/+, a gradient in sclerification may contribute to the development of midrib curvature.