The mechanism of boron mobility in wheat and canola phloem.
Low-molecular-weight borate complexes were isolated from canola (Brassica napus) and wheat (Triticum aestivum) phloem exudates, as well as the cytoplasm of the fresh-water alga Chara corallina, and identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Phloem exudate was collected from field-grown canola inflorescence stalks by shallow incision, while wheat phloem exudate was collected by aphid stylectomy. Chara cytoplasm was collected by careful manual separation of the cell wall, vacuole, and cytosolic compartments. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry showed the presence of isotopic borate complexes, at mass-to-charge ratio of 690.22/691.22 in the canola and wheat phloem and at 300.11/301.11 in canola phloem and Chara cytoplasm. Using reference compounds, the borate complexes with mass-to-charge ratio 690.22/691.22 was identified as a bis-sucrose (Suc) borate complex in which the 4,6-hydroxyl pairs from the two alpha-glucopyranoside moieties formed an [L(2)B](-1) complex. Further investigation using liquid chromatography electrospray ionization triple quadrupole mass spectrometry analysis confirmed the presence of the bis-Suc borate complex in wheat phloem with a concentration up to 220 microm. The 300.11/301.11 complex was putatively identified as a bis-N-acetyl-serine borate complex but its concentration was below the detection limits of the liquid chromatography electrospray ionization triple quadrupole mass spectrometer so could not be quantified. The presence of borate complexes in the phloem provides a mechanistic explanation for the observed phloem boron mobility in canola and wheat and other species that transport Suc as their primary photoassimilate.
Stangoulis
James
J
School of Biological Science, Flinders University, Bedford Park, South Australia 5042, Australia. james.stangoulis@flinders.edu
Tate
Max
M
Graham
Robin
R
Bucknall
Martin
M
Palmer
Lachlan
L
Boughton
Berin
B
Reid
Robert
R
D001881:Borates / Q000737:chemistry; D001895:Boron / Q000737:chemistry*; D029688:Brassica napus / Q000737:chemistry*; D044784:Chara / Q000737:chemistry; D003593:Cytoplasm / Q000737:chemistry; D056626:Inflorescence / Q000737:chemistry; D052585:Phloem / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014908:Triticum / Q000737:chemistry*
D001881:Borates; D001895:Boron