Jerzy A. Zabkiewicz

Auxin in a seaweed extract: identification and quantitation of indole-3-acetic acid by gas chromatography-mass spectrometry

Summary Indole-3-acetic acid (IAA) has been unequivocally identified by gas chromatography-mass spectrometry in the commercial seaweed extract, Maxicrop, which is derived from the brown alga Ascophyllum nodosum Le Jol. Using a [1- 14 C]IAA internal standard to enable correction for losses during the procedure, we have estimated that one gram of the dried Maxicrop powder tested contains 6.63 ± 0.29 gg IAA.

A UNIVERSAL SPRAY DROPLET ADHESION MODEL

Initial spray droplet adhesion is a consequence of dynamic interactions of formulants within the spray droplet during flight and on impact, physical properties of the droplet, leaf surface morphology, and leaf orientation. The objective of this study was to produce a more robust universal spray droplet model using simple parameters (factors) that are easily measured. This was achieved by combining the data from two existing models for adhesion, thereby increasing the number of both species and formulations studied within one model. Plant species and formulations chosen provided a range of leaf surface characters and droplet impaction surface tensions. The velocity model was also improved in order to remove anomalies in the adhesion model. The new universal adhesion model can predict the percentage adhesion of spray droplets (ranging from 109 to 912 .m) impacting any typical leaf surface (providing that it is not excessively hairy) at velocities ranging from 1 to 3.5 m s-1. The universal adhesion model can also predict adhesion of any aqueous formulation (pure water through to emulsifiable concentrates) with dynamic surface tensions of 20 to 72 mN m-1. Overall, observed and predicted adhesion values were in good agreement, with 72% deviance explained by the new universal model.

Surface reconstruction of wheat leaf morphology from three-dimensional scanned data

Realistic virtual models of leaf surfaces are important for several applications in the plant sciences, such as modelling agrichemical spray droplet movement and spreading on the surface. In this context, the virtual surfaces are required to be smooth enough to facilitate the use of the mathematical equations that govern the motion of the droplet. Although an effective approach is to apply discrete smoothing D2-spline algorithms to reconstruct the leaf surfaces from three-dimensional scanned data, difficulties arise when dealing with wheat (Triticum aestivum L.) leaves, which tend to twist and bend. To overcome this topological difficulty, we develop a parameterisation technique that rotates and translates the original data, allowing the surface to be fitted using the discrete smoothing D2-spline methods in the new parameter space. Our algorithm uses finite element methods to represent the surface as a linear combination of compactly supported shape functions. Numerical results confirm that the parameterisation, along with the use of discrete smoothing D2-spline techniques, produces realistic virtual representations of wheat leaves.

STATISTICAL ANALYSIS TO DETERMINE THE RELATIVE IMPORTANCE OF VARIABLES INVOLVED IN FOLIAR UPTAKE

A recent study determined that mass uptake on a per unit area basis was related to the initial dose of xenobiotic applied, by an equation of the form: uptake (nmol mm-2) = a[ID]b at time t = 24 hours, where ID is the initial dose or the mass of xenobiotic applied per unit area. The current study used this relationship (nmol mm-2 uptake versus ID; termed the uptake ratio) to establish the relative importance of species, AI, AI concentration (g L-1) and surfactant to uptake. Species, AI, its concentration, and surfactant all significantly affected the uptake ratio (explaining 51% of the deviance). The percentage variance explained by each factor ranged from 8.9% (AI) to 17% (surfactant). Overall, 88% of the deviance could be explained. More useful was the analysis of the individual xenobiotics, where the models explained 83%, 85%, and 94% of the variance in uptake ratio for DOG, 2,4-D, and epoxiconazole, respectively. In all cases, species, surfactant, and AI concentration significantly affected the uptake ratio. However, there were differences in the relative importance of these factors among the xenobiotics studied. Concentration of AI increased in importance with increasing lipophilicity of AI, while species was much less important for the most lipophilic compound. Surfactant became less important with increasing lipophilicity, although it was always important. The interaction between AI concentration and species was much more important for the most polar compound, while the interaction between surfactant and species increased in importance with increasing lipophilicity.