Variation of Wheat Root Exudates under Aluminum Stress

Abstract

The wheat (Triticum aestivum L.) cultivar Yangzhou 158 was used as a reference. The wheat root exudates were collected using a hydroponic mode. The changes of the electrolytes, H+, sugar, organic acids, amino acids, and secondary metabolites in wheat root exudates induced by aluminum (Al) were studied. The research results show that Al stress affects wheat root exudation. The secreted electrolytes and sugar increase with the increasing of the external Al3+ concentration. The total amount of secreted amino acids has a specific correlation with the external Al3+ concentration. At first, the amino acids secrete normally, but when Al3+ concentration is over 10 mg.L-1, the amino acid constitution varies obviously. Under Al stress, some original secondary metabolites disappear gradually, and other new secondary metabolites release simultaneously. Increasing the external Al3+ concentration gradually stimulates the exudation of organic acids. The organic acid levels in the wheat root zone increase in response to Al treatments. Active Al ions are accumulated in wheat roots. This Al-dependent variation in wheat root exudates suggests a specific Al-induced response of the wheat.

Methods of plant root exudates analysis: a review

“…min −1 , or a Bio-rad HPX-87 column, with 0.005 M H 2 SO 4 following at a rate o 0.5 mL. min −1 at ambient temperature as the solvent (UV detection at 210 nm) or mobile phase 0.005 M H 2 SO 4 , 0.5 mL.min −1 , 50 ºC, wavelength 210 nm were used for separation of organic acids (Schwab et al, 1983;Gransee and Wittenmayer, 2000;Wang et al, 2006); basic compounds were separated a er precolumn derivatization with o-phtaldialdehyde (OPA) reagent on a RP select-B (Merck, Darmstadt), 250 mm × 4 mm, particle size 4 μm, gradient elution with 1 M TBAH in MeOH/MeCN/water 7.5:50: 442.5  7.5:350:142.5 (m/m/m), fl ux rate 1.0 mL.min −1 (Gransee and Wittenmayer, 2000). Nardi et al (2002Nardi et al ( , 2005 used anionic fraction of root exudates to be separated by HPLC on an Aminex column (HPX 87 H -Biorad) with 6 mM H 2 SO 4 as mobile phase and detection at 210 nm.…”

“…Sometimes, for analysis of amino acids was used Amino Acids analyzer -column elution with sodium citrate buff ers (Schwab et al, 1983;Bacilio-Jiménez et al. 2003;Wang et al, 2006). Paynel et al (2001) measured amino acids in root exudates using HPLC as o-phthaldialdehyde derivatives on a C-18 column using Gold system 8.0.…”

“…Kravchenko et al (1993; measured tryptophane in root exudates using HPLC with LiCrosorb RP-18 reversed phase column, which was eluted with solution containing 13.7% acetonitrile and 0.22% acetic acid in water. Wang et al (2006) separated and quantifi ed sugars in root exudates using in HPLC with an RI x 4 detector and Sugar-pak 1. P/N 85188 column (temperature 85 ºC, mobile phase Milli-Q water, 0.6 mL.min.…”

“…Total soluble sugar content was also determined by colorimetric procedure using sulphonated -naphthol (Denvor, 1950). For measurement of total sugars Wang et al (2006) hydrolyzed concentrated root exudates with H 2 SO 4 under vacuum at 110 ºC; a er cooling, fi ltration, drying and dissolution in 0.005 M H 2 SO 4 , the total sugars were separated and quantifi ed using HPLC. Total amino acids were assessed e.g.…”

“…Total amino acids were assessed e.g. by colorimetric procedure using ninhydrin (Spies, 1957); sample of root exudates before analysis by HPLC or amino acid analyzer can also be hydrolysed (Bacilio-Jiménez et al, 2003;Wang et al, 2006) e.g. by 6 M HCl under vacuum at 110 ºC and with a drop of phenol to avoid degradation of tyrosine residues as reported by Bacilio-Jiménez et al (2003).…”