Localization of Elements in Botanical Materials by Secondary Ion Mass Spectrometry

Abstract

Secondary ion mass spectrometry (SIMS) was evaluated for the distribution of selected elements in plant tissue including material grown at high levels of salinity and at toxiclevels of boron. Seedlings of Cucumis sativus, C. myrio carpus, and Pisum sativum were grown in 0.5 Hoagland’s colution culture [1] and with supplemental NaCl at 70 meq/L Na, Some cultures of P. sativum seedlings were also supplemented with 1.2% La(N0₃)₃, 0.5% H₃BO₃, or with 20 meq/L LiCl for 24 h before collection. Root segments, 0.5 cm long at 5 cm from the root tip, and leaf strips, 1 mm wide, of the control and the treated 10-day-old seedlings were fixed in 2% glutaraldehyde, dehydrated in acetone, and embedded in low viscosity epoxy resin [2]. The La, B, and Li material and their respective controls were processed by dehydration in toluene containing Al₂O₃ (acid; Brockman, activity grade 1) [3] and 0.5% dimethoxypropane (DMP) [4]. Sections 1 or 2 μm thick were mounted on 99.9999% Ag discs, 0.1 mm × 15 mm, and placed in a 60°C oven until shortly before analysis. Whole mounts of fresh leaf discs of P. sativum were mounted on Ag holders then dried at 60°C and carbon coated in a grid pattern. All other samples were uncoated. The analyses were made with a Cameca IMS 300 ion probe using a ¹⁶O₂ ⁺ primary beam having a field diameter of 250 ym. The primary beam current during observations was about 1 μA and accelerated at 10 kV. Photographs of the elemental images were taken at X100 and mass spectra were prepared at different sensitivities depending upon the elements of interest.