LOCALIZATION OF NICKEL IN EPIDERMAL SUBSIDIARY CELLS OF LEAVES OF THLASPI-MONTANUM VAR SISKIYOUENSE (BRASSICACEAE) USING ENERGY-DISPERSIVE X-RAY-MICROANALYSIS

Thlaspi montanum var. siskiyouense occurs as an endemic on serpentine soils in southwestern Oregon, U.S.A. The leaves accumulate nickel at l evels up to 3% dry mass. To determine if nickel was localized in parti cular cells or tissues, leaves were prepared for scanning electron mic roscopy and energy-dispersive X-ray microanalysis by first soaking the leaves in dimethylglyoxime to precipitate nickel. Leaves were then fi xed in glutaraldehyde, dehydrated, and critical-point dried. Spectra o f leaves of T. montanum var. siskiyouense showed accumulation of nicke l, calcium, potassium, and phosphorus. On X-ray maps of the upper and lower epidermis, nickel was localized in the subsidiary cells that sur round guard cells but not in guard cells or in other more elongate epi dermal cells.