2.9 Secondary ion mass spectrometry (SIMS)
Roots of two-day-old plants treated with 5 μM Al for 2, 6, 24, and 72 h
were excised and fixed in 2.5% glutaraldehyde and 1.6% paraformldehyde
at 4 °C overnight, followed by 1% osmium tetroxide for 2 h. Then, the
fixed root samples were dehydrated acetone for 3 times. The root samples
were embedded in Spurr resin overnight, and polymerized at 70 °C for 24
h. Five-micrometer-thick section was cut with Leica RM2165 microtome
(Leica, Germany), and placed on the
silicon
wafer (University Wafer, USA). The element distribution in the
cross-section of different root zones was analyzed using SIMS (CAMECA,
France) according to Smart et al. (2010). The sample was pre-sputtered
with 30 nA O2+ beam for 15 min to
remove the potential contaminants on the sample surface, and ion maps of27Al of root cross-section were acquired using 300 pA
O2+ beam for 20 min, and ion map of31P was acquired using 200 pA Cs+beam for 30 min, with a resolution of 256 × 256 pixels. SIMS data was
analyzed using WinImage 2.0 (CAMECA, France).