How kelp produce blade shapes suited to different flow regimes: A new wrinkle.

Many species of macroalgae have flat, strap-like blades in habitats exposed to rapidly flowing water, but have wide, ruffled "undulate" blades at protected sites. We used the giant bull kelp, Nereocystis luetkeana, to investigate how these ecomorphological differences are produced. The undulate blades of N. luetkeana from sites with low flow remain spread out and flutter erratically in moving water, thereby not only enhancing interception of light, but also increasing drag. In contrast, strap-like blades of kelp from habitats with rapid flow collapse into streamlined bundles and flutter at low amplitude in flowing water, thus reducing both drag and interception of light. Transplant experiments in the field revealed that shape of the blade in N. luetkeana is a plastic trait. Laboratory experiments in which growing blades from different sites were subjected to tensile forces that mimicked the hydrodynamic drag experienced by blades in different flow regimes showed that change in shape is induced by mechanical stress. During growth experiments in the field and laboratory, we mapped the spatial distribution of growth in both undulate and strap-like blades to determine how these different morphologies were produced. The highest growth rates occur near the proximal ends of N. luetkeana blades of both morphologies, but the rates of transverse growth of narrow, strap-like blades are lower than those of wide, undulate blades. If rates of longitudinal growth at the edges of a blade exceed the rate of longitudinal growth along the midline of the blade, ruffles along the edges of the blade are produced by elastic buckling. In contrast, flat blades are produced when rates of longitudinal growth are similar across the width of a blade. Because ruffles are the result of elastic buckling, a compliant undulate N. luetkeana blade can easily be pushed into different configurations (e.g., the wavelengths of the ruffles along the edges of the blade can change, and the whole blade can twist into left- and right-handed helicoidal shapes), which may enhance movements of the blade in flowing water that reduce self-shading and increase mass exchange along blade surfaces.

Temporal and spatial patterns of twining force and lignification in stems of Ipomoea purpurea.

Using the TWIFOR, an electronic device for continuous, in vivo measurement of the forces exerted by twining vines, we examined the forces generated by vines growing on cylindrical poles of slender (6.35 mm) and thicker (19.05 mm) diameter. In stems of Ipomoea purpurea (L.) Roth. magnitudes of twining force (axial tensions) were, on average, less at a particular time and location on the more slender poles; while twining loads (normal force per unit length of vine) were much greater on the slender poles because of the greater curvature of the vines. Thus, the geometry of the helix formed by the vine on the pole affects the ability of the vine to maintain a frictional interaction with its support. In addition, the plant-to-plant variation in twining force was twice as great on the thicker support poles. Metaxylem and fibers developed closer to the plant apex in vines on the slender poles. On the thicker poles, a significant fraction of the maximum twining force developed during the establishment of the first gyre, before fibers were lignified, indicating that primary growth can be sufficient to establish high twining forces. On the slender poles, however, twining force increased with developmental stage until the gyre was at least 1.5 m from the apex. Thus, twining force can increase after cessation of primary growth. No simple relationship was found between the site of fiber differentiation and twining force.

Biomechanical analysis of the Rolled (RLD) leaf phenotype of maize.

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.

Effect of Water Stress on Cortical Cell Division Rates within the Apical Meristem of Primary Roots of Maize.

We characterized the effect of water stress on cell division rates within the meristem of the primary root of maize (Zea mays L.) seedlings. As usual in growth kinematics, cell number density is found by counting the number of cells per small unit length of the root; growth velocity is the rate of displacement of a cellular particle found at a given distance from the apex; and the cell flux, representing the rate at which cells are moving past a spatial point, is defined as the product of velocity and cell number density. The local cell division rate is estimated by summing the derivative of cell density with respect to time, and the derivative of the cell flux with respect to distance. Relatively long (2-h) intervals were required for time-lapse photography to resolve growth velocity within the meristem. Water stress caused meristematic cells to be longer and reduced the rates of cell division, per unit length of tissue and per cell, throughout most of the meristem. Peak cell division rate was 8.2 cells mm-1 h-1 (0.10 cells cell-1 h-1) at 0.8 mm from the apex for cells under water stress, compared with 13 cells mm-1 h-1 (0.14 cells cell-1 h-1) at 1.0 mm for controls.

Nonvascular, Symplasmic Diffusion of Sucrose Cannot Satisfy the Carbon Demands of Growth in the Primary Root Tip of Zea mays L.

Nonvascular, symplasmic transport of sucrose (Suc) was investigated theoretically in the primary root tip of maize (Zea mays L. cv WF9 x Mo 17) seedlings. Symplasmic diffusion has been assumed to be the mechanism of transport of Suc to cells in the root apical meristem (R.T. Giaquinta, W. Lin, N.L. Sadler, V.R. Franceschi [1983] Plant Physiol 72: 362-367), which grow apical to the end of the phloem and must build all biomass with carbon supplied from the shoot or kernel. We derived an expression for the growth-sustaining Suc flux, which is the minimum longitudinal flux that would be required to meet the carbon demands of growth in the root apical meristem. We calculated this flux from data on root growth velocity, area, and biomass density, taking into account construction and maintenance respiration and the production of mucilage by the root cap. We then calculated the conductivity of the symplasmic pathway for diffusion, from anatomical data on cellular dimensions and the frequency and dimensions of plasmodesmata, and from two estimates of the diffusive conductance of a plasmodesma, derived from independent data. Then, the concentration gradients required to drive a growth-sustaining Suc flux by diffusion alone were calculated but were found not to be physiologically reasonable. We also calculated the hydraulic conductivity of the plasmodesmatal pathway and found that mass flow of Suc solution through plasmodesmata would also be insufficient, by itself, to satisfy the carbon demands of growth. However, much of the demand for water to cause cell expansion could be met by the water unloaded from the phloem while unloading Suc to satisfy the carbon demands of growth, and the hydraulic conductivity of plasmodesmata is high enough that much of that water could move symplasmically. Either our current understanding of plasmodesmatal ultrastructure and function is flawed, or alternative transport mechanisms must exist for Suc transport to the meristem.

Kinematics and Dynamics of Sorghum (Sorghum bicolor L.) Leaf Development at Various Na/Ca Salinities (I. Elongation Growth).

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 rate). Increasing the Ca concentrations from 1 to 10 mM restored the length of the growing zone of both emerged and unemerged salinized leaves and increased the peak value of the REG rate. The beneficial effects of supplemental Ca were, however, more pronounced in leaves after their appearance above the whorl of encircling older leaf sheaths. Elevated Ca then resulted in a peak value of REG rate higher than in the salinized leaves. The peak value of unemerged leaves was not increased, although it was maintained over a longer distance. The duration of elongation growth associated with a cell during its displacement from the leaf base was longer in salinized than control leaves, despite the fact that the elongation zone was shorter in salinity. Although partially restoring the length of the elongation region, supplemental Ca had no effect on the age of cessation of growth. Elongation of a tissue element, therefore, ceased when a cellular element reached a certain age and not a specific distance from the leaf base.

Growth and Deposition of Inorganic Nutrient Elements in Developing Leaves of Zea mays L.

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 and Cl had minimal density in the leaf tips; K density was maximum in the growing region, whereas Cl density was maximum at the region of growth cessation. Ca, Mg, and P had relatively high densities at the base of the elongation zone near the node and also in the tip regions. Near the node, P and Mg densities were higher in the young, growing leaves, whereas Ca density near the node was higher in older leaves that had completed elongation. Deposition rates of all nutrients were greatest in the region of maximum elongation rate.

Axial forces and normal distributed loads in twining stems of morning glory.

In analysing the mechanics of twining, we hypothesize that contact forces are important in maintaining the twining habit of viny stems. This hypothesis is formalized with a description of the force balance in the natural coordinate system associated with the Frenet vectors attached to the 'generative helix' of the vine. The force balance indicates that, if shear forces are neglected, an axial force within the stem is balanced by a normal load distributed along the line of contact between the supporting pole and the stem. Two kinds of empirical studies were conducted to verify the importance of the putative normal load. Firstly, vine geometry was measured on and off the supporting pole. When removed from the pole, the helical stem forms a coil of smaller radius, smaller wavelength and larger torsion. Next, forces were estimated from observations of the pressure exerted by a stem twining around a water-filled balloon. Twining around a dowel 0.95 cm in diameter, a typical stem of morning glory (Pharbitis nil) sustains a tension of 100 g balanced by a normal distributed load of -30 g cm-1. Thus the twining stem puts itself into tension and uses a helical geometry to generate contact forces which are large relative to the stem weight of 40 mg cm-1.

Growth of the Maize Primary Root at Low Water Potentials : II. Role of Growth and Deposition of Hexose and Potassium in Osmotic Adjustment.

Primary roots of maize (Zea mays L. cv WF9 x Mo17) seedlings growing in vermiculite at various water potentials exhibited substantial osmotic adjustment in the growing region. We have assessed quantitatively whether the osmotic adjustment was attributable to increased net solute deposition rates or to slower rates of water deposition associated with reduced volume expansion. Spatial distributions of total osmotica, soluble carbohydrates, potassium, and water were combined with published growth velocity distributions to calculate deposition rate profiles using the continuity equation. Low water potentials had no effect on the rate of total osmoticum deposition per unit length close to the apex, and caused decreased deposition rates in basal regions. However, rates of water deposition decreased more than osmoticum deposition. Consequently, osmoticum deposition rates per unit water volume were increased near the apex and osmotic potentials were lower throughout the growing region. Because the stressed roots were thinner, osmotic adjustment occurred without osmoticum accumulation per unit length. The effects of low water potential on hexose deposition were similar to those for total osmotica, and hexose made a major contribution to the osmotic adjustment in middle and basal regions. In contrast, potassium deposition decreased at low water potentials in close parallel with water deposition, and increases in potassium concentration were small. The results show that growth of the maize primary root at low water potentials involves a complex pattern of morphogenic and metabolic events. Although osmotic adjustment is largely the result of a greater inhibition of volume expansion and water deposition than solute deposition, the contrasting behavior of hexose and potassium deposition indicates that the adjustment is a highly regulated process.

Effects of low water potential on cortical cell length in growing regions of maize roots.

Roots growing under low water potential commonly exhibit a marked decrease in growth rate and in diameter. Using median longitudinal sections of fixed maize (Zea mays L. cv WF9 x Mo 17) seedling roots, we investigated the cellular basis for these effects. Cortical cells in the shortened elongation zone of water stressed roots were longer than cortical cells in the comparable location of well-watered roots. Nearly twofold differences in cell length were seen in the region 2 to 4 millimeters behind the root apex. The shortened growth zone, however, leads to a final mean cortical cell length approximately 30% shorter in the stressed roots. These differences were present regardless of the age of the control roots. These data, and the slower growth rate seen in water-stressed roots, suggest that the water deficit causes a significant reduction in the rate of cell supply to the cortical cell files.

Growth Patterns Inferred from Anatomical Records : Empirical Tests Using Longisections of Roots of Zea mays L.

Our objective was to test whether accurate growth analyses can be obtained from anatomical records and some mathematical formulas. Roots of Zea mays L. were grown at one of two temperatures (19 degrees C or 29 degrees C) and were prepared with standard techniques for light microscopy. Positions of cell walls were digitized from micrographs. The digitized data were averaged and smoothed and used in formulas to estimate growth trajectories, Z(t), velocities, v(z), and strain rates, r(z), where Z(t) is the location occupied by the cellular particle at time t; and v(z) and r(z) are, respectively, the fields of growth velocity and strain rate. The relationships tested are: for Z(t), t = n * c; v(z) = l(z) * f; and r(z) = f * ( partial differential/ partial differentialz (l(z))). In the formulas, n represents the number of cells between the origin and the position Z(t); l(z) is local cell length; the constant c, named the ;cellochron,' denotes the time for successive cells to pass a spatial point distal to the meristem; l(z) is local cell length, and f is cell flux. Growth trajectories and velocity fields from the anatomical method are in good agreement with earlier analyses based on marking experiments at the two different temperatures. Growth strain rate fields show an unexpected oscillation which may be due to numerical artifacts or to a real oscillation in cell production rate.

Effect of temperature on spatial and temporal aspects of growth in the primary maize root.

In the range 16 to 29 degrees C, increases in temperature caused large (two-to threefold) increases in growth velocity, growth strain rate, and biomass deposition rate in primary roots of maize, Zea mays L. Temperature had small effects on root diameter, fresh weight density, and dry weight density, and negligible effects on length of the growth zone and growth strain at particular positions.

Growth of the maize primary root at low water potentials : I. Spatial distribution of expansive growth.

Seedlings of maize (Zea mays L. cv WF9 x Mo 17) were grown in vermiculite at various water potentials. The primary root continued slow rates of elongation at water potentials which completely inhibited shoot growth. To gain an increased understanding of the root growth response, we examined the spatial distribution of growth at various water potentials. Time lapse photography of the growth of marked roots revealed that inhibition of root elongation at low water potentials was not explained by a proportional decrease in growth along the length of the growing zone. Instead, longitudinal growth was insensitive to water potentials as low as - 1.6 megapascal close to the root apex, but was inhibited increasingly in more basal locations such that the length of the growing zone decreased progressively as the water potential decreased. Cessation of longitudinal growth occurred in tissue of approximately the same age regardless of spatial location or water status, however. Roots growing at low water potentials were also thinner, and analysis revealed that radial growth rates were decreased throughout the elongation zone, resulting in greatly decreased rates of volume expansion.

Spatial distributions of potassium, solutes, and their deposition rates in the growth zone of the primary corn root.

Densities of osmoticum and potassium were measured as a function of distance from the tip of the primary root of Zea mays L. (cv WF9 x mo17). Millimeter segments were excised and analyzed for osmotic potential by a miniaturized freezing point depression technique, and for potassium by flame spectrophotometry. Local deposition rates were estimated from the continuity equation with values for density and growth velocity. Osmotic potential was uniform, -0.73 +/- 0.05 megapascals, throughout the growth zone of well-watered roots. Osmoticum deposition rate was 260 muosmoles per gram fresh weight per hour. Potassium density fell from 117 micromoles per gram in the first mm region to 48 micromoles per gram at the base of the growth zone. Potassium deposition rates had a maximum of 29 micromoles per gram per hour at 3.5 millimeters from the tip and were positive (i.e. potassium was being added to the tissue) until 8 millimeters from the tip. The results are discussed in terms of ion relations of the growing zone and growth physics.

Uronide Deposition Rates in the Primary Root of Zea mays.

The spatial distribution of the rate of deposition of uronic acids in the elongation zone of Zea mays L. Crow WF9 x Mo 17 was determined using the continuity equation with experimentally determined values for uronide density and growth velocity. In spatial terms, the uronide deposition rate has a maximum of 0.4 micrograms per millimeter per hour at s = 3.5 mm (i.e., at the location 3.5 mm from the root tip) and decreases to 0.1 mg mm(-1) h(-1) by s = 10 mm. In terms of a material tissue element, a tissue segment located initially from s = 2.0 to s = 2.1 mm has 0.14 mug of uronic acids and increases in both length and uronic acid content until it is 0.9 mm long and has 0.7 mug of uronide when its center is at s = 10 mm. Simulations of radioactive labeling experiments show that 15 min is the appropriate time scale for pulse determinations of deposition rate profiles in a rapidly growing corn root.

Mechanical properties of the rice panicle.

Curvature, bending moment, and second moment of stem cross-sectional area were evaluated from photographic data and used to compute flexural rigidity and Young's modulus in the panicle rachis of rice, Oryza sativa L. ;M-101.' Flexural rigidity C, and its components E, Young's modulus, and I, the moment of inertia of the area about the neutral axis, were evaluated 1.5 cm (tip), 9.5 cm (mid), and 16.5 cm (base) from the tip of the panicle rachis. In dynes per square centimeter, C increases from 1.1 x 10(3) near the tip to 1.09 x 10(4) in the middle to 5.35 x 10(4) in the basal region of the rachis. Of the components of C, the I changes have the larger effect, increasing from 2.12 x 10(-7) centimeters(4) near the tip to 8.21 x 10(-7) centimeters(4) in mid regions to 6.0 x 10(-6) centimeters(4) in the basal regions. Young's modulus increases from 4.8 x 10(9) dynes per square centimeter near the tip to 1.4 x 10(10) dynes per square centimeter in mid regions then falls to 7.4 x 10(9) dynes per square centimeter near the base of the main stem. Values of Young's modulus from Instron experiments were in satisfactory agreement with values calculated from the beam bending equation. Flexural rigidity in the curved region of the panicle proved independent of panicle load, indicating that the dissected panicle rachis behaves in some respects as a tapered loaded beam.

Protein and nitrate content of lemna sp. As a function of developmental stage and incubation temperature.

Lemna protein per frond and per root increases with developmental stage until plants are at least two generations old. Protein per frond, per root, and per unit dry weight is greater in plants grown at 23.9 C than at 18.3 C. More protein is found in fronds than in roots, and more nitrate occurs in roots than in fronds. Nitrate per root increases with developmental stage and is higher (per root) in plants grown at 23.9 C than in those grown at 18.3 C. The distribution of generations within a growing population is constant for at least eight doubling times. Whether populations multiply slowly at 15.6 C or more rapidly at 23.9 C, fronds which have not yet produced progeny form 62% of the population; fronds which are one generation old form 24% of the population; and fronds which are two generations old form 9% of the population.

Growth-sustaining Water Potential Distributions in the Primary Corn Root: A NONCOMPARTMENTED CONTINUUM MODEL.

An equation is derived from transport theory to relate local growth rate to local water potential in an expanding tissue. For a noncompartmented continuum model, the relative elemental growth rate (L) equals the divergence of the tensor product of hydraulic conductivity (K) and the gradient of water potential, psi, i.e. L = big dn tri, open * [K . big dn tri, open psi]. This equation is solved numerically using published values of L and K to show the water potential distribution which can sustain the observed growth pattern in the primary root of Zea mays L. The water potential required to sustain growth decreases from the outside to the inside of the root, and the longitudinal profile shows most negative values near the location of the highest growth rate. A cell originally located near the apex experiences a loss and then a gain in water potential as it is displaced through the growth zone.THE APPROACH DIFFERS FROM PREVIOUS FORMULATIONS IN TWO RESPECTS: the assumption of spatial heterogeneity in growth rate, and the solution for spatial (site-specific) rather than material (cell-specific) values of water potential. The role of air spaces and of components (wall and possibly cytoplasm) of the water-conducting pathway which do not accumulate water remains to be clarified; and, as in earlier work, the most uncertain aspects of the analysis are probably the values for hydraulic conductivity.