Please use this identifier to cite or link to this item: https://hdl.handle.net/2440/79250
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Type: Journal article
Title: Improved techniques for measurement of nanolitre volumes of phloem exudate from aphid stylectomy
Author: Palmer, L.
Palmer, L.
Pritchard, J.
Graham, R.
Stangoulis, J.
Citation: Plant Methods, 2013; 9(1):1-18
Publisher: BioMed Central Ltd.
Issue Date: 2013
ISSN: 1746-4811
1746-4811
Statement of
Responsibility: 
Lachlan J Palmer, Lyndon T Palmer, Jeremy Pritchard, Robin D Graham and James CR Stangoulis
Abstract: Background: When conducting aphid stylectomy, measuring accurate rates of phloem exudation is difficult because the volumes collected are in the nanolitre (nl) range. In a new method, exudate volume was calculated from optical measurement of droplet diameter as it forms on the tip of a severed aphid stylet. Evaporation was shown to decrease the accuracy of the measurement but was countered with the addition of water-saturated mineral oil. Volume measurements by optical estimation of the volume of a sphere suspended in oil was affected by the curvature of the oil surface. In contrast, measuring the exudate volume from optical measurement of droplet-diameter as formed on the tip of a severed aphid stylet, removes any inaccuracies due to oil surface curvature. A modified technique is proposed for measuring exudate volumes without oil by estimating the flow rate from photo-sequences of the collection period; a correction for evaporation is applied later. Results: A change in oil volume of ±1.75% from an optimum volume of 285 μl had a statistically significant effect on droplet measurement, under or over-estimating droplet volume due to optical effects caused by the oil surface. Using microscope image capture and measurement software, a modified method for measuring phloem volume in air was developed, by reducing air exposure during measurement to approximately 5 s for each measurement. Phloem volumes were measured using both techniques with measurements in air being on average 19.9 nl less (SD 18.87, p<0.001) than those made in oil, and there was a strong linear relationship (R2=0.942) between the techniques. This linear relationship enabled the development of a correction equation with no significant difference at the 5% level between corrected volumes and actual volumes measured under oil. Conclusions: This study showed that oil has a significant role in countering evaporation but oil volume must be carefully optimised for optical measurement of droplets to ensure measurement accuracy. A linear correction factor was generated to correct the volumes measured in air for loss due to evaporation and the method provides for a much simpler alternative to previous approaches for measuring exudation rates and volumes from a cut aphid stylet.
Keywords: Aphid stylectomy
Exudate
Phloem
Volume measurement
Rights: © 2013 Palmer et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
DOI: 10.1186/1746-4811-9-18
Published version: http://dx.doi.org/10.1186/1746-4811-9-18
Appears in Collections:Agriculture, Food and Wine publications
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