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WHOLE PLANT AND ECOPHYSIOLOGY

A Diurnal Component to the Variation in Sieve Tube Amino Acid Content in Wheat^1,[OA]

School of Biosciences, University of Birmingham, Birmingham B15 2TT, United Kingdom (S.G., H.J.N., J.S.B., J.P.); and Centre for Analytical Bioscience, School of Pharmacy, University of Nottingham, Nottingham NG7 2RD, United Kingdom (H.-M.T., D.A.B.)

We have used high-sensitivity capillary electrophoresis coupled to a laser-induced fluorescence detection method to quantify 16 amino acids in wheat (Triticum aestivum) sieve tube (ST) samples as small as 2 nL collected by severing the stylets of feeding aphids. The sensitivity of the method was sufficient to determine a quantitative amino acid profile of individual STs without the need to bulk samples to produce larger volumes for analysis. This allowed the observation of the full range of variation that exists in individual STs. Some of the total concentrations of amino acids recorded are higher than those reported previously. The results obtained show variation in the concentrations of phenylalanine (Phe), histidine/valine (His/Val), leucine/isoleucine (Leu/Ile), arginine, asparagine, glutamine, tyrosine (Tyr), and lysine (Lys) across the ST samples. These could not be explained by plant-to-plant variation. Statistical analyses revealed five analytes (Tyr, Lys, Phe, His/Val, and Leu/Ile) that showed striking covariation in their concentrations across ST samples. A regression analysis revealed a significant relationship between the concentrations of Tyr, Lys, Phe, Leu/Ile, His/Val, asparagine, arginine, and proline and the time of collection of ST samples, with these amino acids increasing in concentration during the afternoon. This increase was confirmed to occur in individual STs by analyzing samples obtained from stylet bundles exuding for many hours. Finally, an apparent relationship between the exudation rate of ST sap and its total amino acid concentration was observed: samples containing higher total amino acid concentrations were observed to exude from the severed stylet bundles more slowly.

² Present address: Department of Biological Sciences, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Stefano Gattolin (s.gattolin{at}warwick.ac.uk).

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www.plantphysiol.org/cgi/doi/10.1104/pp.108.116079

^* Corresponding author; e-mail s.gattolin{at}warwick.ac.uk.

Received January 9, 2008; accepted April 13, 2008; published April 16, 2008.

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