Experimental determination of Philodendron melinonii and Arabidopsis thaliana tissue microstructure and geometric modeling via finite-edge centroidal Voronoi tessellation.

Plant petioles and stems are hierarchical cellular structures, displaying structural features defined at multiple length scales. One or more of the intermediate hierarchical levels consists of tissues, in which the cellular distribution is quasirandom. The current work focuses on the realistic modeling of plant tissue microstructures. The finite-edge centroidal Voronoi tessellation (FECVT) is here introduced to overcome the drawbacks of the semi-infinite edges of a typical Voronoi model. FECVT can generate a realistic model of a tissue microstructure, which might have finite edges at its border, be defined by a boundary contour of any shape, and include complex heterogeneity and cellular gradients. The centroid-based Voronoi tessellation is applied to model the microstructure of the Philodendron melinonii petiole and the Arabidopsis thaliana stem, which both display intense cellular gradients. FECVT coupled with a digital image processing algorithm is implemented to capture the nonperiodic microstructures of plant tissues. The results obtained via this method satisfactorily obey the geometric, statistical, and topological laws of naturally evolved cellular solids. The predicted models are also validated by experimental data.

In the heat of the night--alternative pathway respiration drives thermogenesis in Philodendron bipinnatifidum.

• Philodendron bipinnatifidum inflorescences heat up to 42 °C and thermoregulate. We investigated whether they generate heat via the cytochrome oxidase pathway uncoupled by uncoupling proteins (pUCPs), or the alternative oxidase (AOX). • Contribution of AOX and pUCPs to heating in fertile (FM) and sterile (SM) male florets was determined using a combination of oxygen isotope discrimination, protein and substrate analyses. • Both FM and SM florets thermoregulated independently for up to 30 h ex planta. In both floret types, AOX contributed > 90% of respiratory flux during peak heating. The AOX protein increased fivefold with the onset of thermogenesis in both floret types, whereas pUCP remained low throughout development. These data indicate that AOX is primarily responsible for heating, despite FM and SM florets potentially using different substrates, carbohydrates or lipids, respectively. Measurements of discrimination between O2 isotopes in strongly respiring SM florets were affected by diffusion; however, this diffusional limitation was largely overcome using elevated O2. • The first in vivo respiratory flux measurements in an arum show AOX contributes the bulk of heating in P. bipinnatifidum. Fine-scale regulation of AOX activity is post-translational. We also demonstrate that elevated O2 can aid measurement of respiratory pathway fluxes in dense tissues.