skip to main content


Title: How wind drives the correlation between leaf shape and mechanical properties
Abstract

From a geometrical point of view, a non-sessile leaf is composed of two parts: a large flat plate called the lamina, and a long beam called the petiole which connects the lamina to the branch/stem. While wind is exerting force (e.g. drag) on the lamina, the petiole undergoes twisting and bending motions. To survive in harsh abiotic conditions, leaves may have evolved to form in different shapes, resulting from a coupling between the lamina geometry and the petiole mechanical properties. In this study, we measure the shape of laminae from 120 simple leaf species (no leaflets). Leaves of the same species are found to be geometrically similar regardless of their size. From tensile/torsional tests, we characterize the bending rigidity (EI) and the twisting rigidity (GJ) of 15 petioles of 4 species in the Spring/Summer: Red Oak (Quercus Rubra), American Sycamore (Platanus occidentalis), Yellow Poplar (Liriodendron tulipifera), and Sugar Maple (Acer saccharum). A twist-to-bend ratioEI/GJis found to be around 4.3, within the range in previous studies conducted on similar species (EI/GJ = 2.7~8.0 reported in S. Vogel, 1992). In addition, we develop a simple energetic model to find a relation between geometrical shapes and mechanical properties (EI/GJ = 2LL/WCwhereLLis the laminar length andWCis the laminar width), verified with experimental data. Lastly, we discuss leaf’s ability to reduce stress at the stem-petiole junction by choosing certain geometry, and also present exploratory results on the effect that seasons have on the Young’s and twisting moduli.

 
more » « less
NSF-PAR ID:
10149472
Author(s) / Creator(s):
; ; ; ; ;
Publisher / Repository:
Nature Publishing Group
Date Published:
Journal Name:
Scientific Reports
Volume:
8
Issue:
1
ISSN:
2045-2322
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Agriculture is facing new challenges, with global warming modifying the survival chances for crops, and new pests on the horizon. To keep up with these challenges, gene delivery provides tools to increase crop yields. On the other hand, gene delivery also opens the door for molecular farming of pharmaceuticals in plants. However, towards increased food production and scalable molecular farming, there remain technical difficulties and regulatory hurdles to overcome. The industry-standard is transformation of plants via Agrobacterium tumefaciens , but this method is limited to certain plants, requires set up of plant growth facilities and fermentation of bacteria, and introduces lipopolysaccharides contaminants into the system. Therefore, alternate methods are needed. Mechanical inoculation and spray methods have already been discussed in the literature – and here, we compare these methods with a newly introduced petiole injection technique. Because our interest lies in the development of plant viruses as immunotherapies targeting human health as well as gene delivery vectors for agriculture applications, we turned toward tobacco mosaic virus as a model system. We studied the effectiveness of three inoculation techniques: mechanical inoculation, Silwet-77 foliar spray and petiole injections. The foliar spray method was optimized, and we used 0.03% Silwet L-77 to induce infection using either TMV or a lysine-added mutant TMV-Lys. We developed a method using a needle-laden syringe to target and inject the plant virus directly into the vasculature of the plant – we tested injection into the stem and petiole. Stem inoculation resulted in toxicity, but the petiole injection technique was established as a viable strategy. TMV and TMV-Lys were purified from single plants and pooled leaf samples – overall there was little variation between the techniques, as measured by TMV or TMV-Lys yields, highlighting the feasibility of the syringe injection technique to produce virus nanoparticles. There was variation between yields from preparation to preparation with mechanical, spray and syringe inoculation yielding 40–141 mg, 36–56 mg, 18–56 mg TMV per 100 grams of leaves. Similar yields were obtained using TMV-Lys, with 24–38 mg, 17–28, 7–36 mg TMV-Lys per 100 grams of leaves for mechanical, spray and syringe inoculation, respectively. Each method has its advantages: spray inoculation is highly scalable and therefore may find application for farming, the syringe inoculation could provide a clean, aseptic, and controlled approach for molecular farming of pharmaceuticals under good manufacturing protocols (GMP) and would even be applicable for gene delivery to plants in space. 
    more » « less
  2. Abstract

    The ability to transport water through tall stems hydraulically limits stomatal conductance (gs), thereby constraining photosynthesis and growth. However, some plants are able to minimize this height‐related decrease ings, regardless of path length. We hypothesized that kudzu (Pueraria lobata) prevents strong declines ingswith height through appreciable structural and hydraulic compensative alterations. We observed only a 12% decline in maximumgsalong 15‐m‐long stems and were able to model this empirical trend. Increasing resistance with transport distance was not compensated by increasing sapwood‐to‐leaf‐area ratio. Compensating for increasing leaf area by adjusting the driving force would require water potential reaching −1.9 MPa, far below the wilting point (−1.2 MPa). The negative effect of stem length was compensated for by decreasing petiole hydraulic resistance and by increasing stem sapwood area and water storage, with capacitive discharge representing 8–12% of the water flux. In addition, large lateral (petiole, leaves) relative to axial hydraulic resistance helped improve water flow distribution to top leaves. These results indicate thatgsof distal leaves can be similar to that of basal leaves, provided that resistance is highest in petioles, and sufficient amounts of water storage can be used to subsidize the transpiration stream.

     
    more » « less
  3. Abstract

    Soft fiber‐reinforced polymers (FRPs), consisting of rubbery matrices and rigid fabrics, are widely utilized in industry because they possess high specific strength in tension while allowing flexural deformation under bending or twisting. Nevertheless, existing soft FRPs are relatively weak against crack propagation due to interfacial delamination, which substantially increases their risk of failure during use. In this work, a class of soft FRPs that possess high specific strength while simultaneously showing extraordinary crack resistance are developed. The strategy is to synthesize tough viscoelastic matrices from acrylate monomers in the presence of woven fabrics, which generates soft composites with a strong interface and interlocking structure. Such composites exhibit fracture energy,Γ, of up to 2500 kJ m−2, exceeding the toughest existing materials. Experimental elucidation shows that the fracture energy obeys a simple relation,Γ = W · lT, whereWis the volume‐weighted average of work of extension at fracture of the two components andlTis the force transfer length that scales with the square root of fiber/matrix modulus ratio. SuperiorΓis achieved through a combination of extraordinarily largelT(10–100 mm), resulting from the extremely high fiber/matrix modulus ratios (104–105), and the maximized energy dissipation density,W. The elucidated quantitative relationship provides guidance toward the design of extremely tough soft composites.

     
    more » « less
  4. Abstract

    Earth system models (ESMs) rely on the calculation of canopy conductance in land surface models (LSMs) to quantify the partitioning of land surface energy, water, andCO2fluxes. This is achieved by scaling stomatal conductance,gw, determined from physiological models developed for leaves. Traditionally, models forgwhave been semi‐empirical, combining physiological functions with empirically determined calibration constants. More recently, optimization theory has been applied to modelgwinLSMs under the premise that it has a stronger grounding in physiological theory and might ultimately lead to improved predictive accuracy. However, this premise has not been thoroughly tested. Using original field data from contrasting forest systems, we compare a widely used empirical type and a more recently developed optimization‐typegwmodel, termedBBandMED, respectively. Overall, we find no difference between the two models when used to simulategwfrom photosynthesis data, or leaf gas exchange from a coupled photosynthesis‐conductance model, or gross primary productivity and evapotranspiration for aFLUXNETtower site with theCLM5 communityLSM. Field measurements reveal that the key fitted parameters forBBandMED,g1Bandg1M,exhibit strong species specificity in magnitude and sensitivity toCO2, andCLM5 simulations reveal that failure to include this sensitivity can result in significant overestimates of evapotranspiration for high‐CO2scenarios. Further, we show thatg1Bandg1Mcan be determined from meanci/ca(ratio of leaf intercellular to ambientCO2concentration). Applying this relationship withci/cavalues derived from a leaf δ13C database, we obtain a global distribution ofg1Bandg1M, and these values correlate significantly with mean annual precipitation. This provides a new methodology for global parameterization of theBBandMEDmodels inLSMs, tied directly to leaf physiology but unconstrained by spatial boundaries separating designated biomes or plant functional types.

     
    more » « less
  5. Melzer, Rainer (Ed.)
    Abstract The juvenile-to-adult phase transition during vegetative development is a critical decision point in a plant’s life cycle. This transition is mediated by a decline in levels of miR156/157 and an increase in the activities of its direct targets, SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) proteins. In Arabidopsis, the juvenile-to-adult transition is characterized by an increase in the length to width ratio of the leaf blade (a change in the distal region of a leaf), but what mediates this change in lamina shape is not known. Here, we show that ectopic expression of SPL9 and SPL13 produces enlarged and elongated leaves, resembling leaves from the blade-on-petiole1 (bop1) bop2 double mutant. The expression of BOP1/BOP2 is down-regulated in successive leaves, correlating with the amount of miR156 and antagonistic to the expression of SPL9 and SPL13 in leaves. SPL9 and SPL13 bind to the promoters of BOP1/BOP2 directly to repress their expression, resulting in delayed establishment of proliferative regions in leaves, which promotes more blade outgrowth (the distal region of a leaf) and suppresses petiole development (the proximal region of a leaf). Our results reveal a mechanism for leaf development along the proximal–distal axis, a heteroblastic character between juvenile leaves and adult leaves. 
    more » « less