Table 1 Identity and percent composition of Se species in shoot tissue of SMT over-producingA. thalianaline smt2-9.

Se species	峰#	t_R(min)	m/z	μmol g^-1dry weight	% of extractable shoot Se
¹Selenite	nd	nd	nd	0.16	3
²MeSeCys	1	4.75	167 (M+H-NH₃)⁺	0.71	12
²MeSeCys	2	6.25	167 (M+H-NH₃)⁺	1.68	31
²Unidentified	3	8.75	nd	0.27	5
³γGluMeSeCys	4	7.5	313 (M+H)⁺	1.16	26
³Unidentified	5	10.5	nd	0.37	6
³Unaccounted	-	-	-	-	17

¹Calculated using XAS data.²Mobile phase water-methanol (99:1, v/v) 0.1% HFBA.³Mobile phase water-methanol (99:1, v/v) 0.1% TFA. HPLC fractions (0.5 – 1.0 ml) were collected and analyzed for total Se by ICP-MS. Replicate chromatography was also performed using HPLC-ESI-MS to confirm the identity of the compounds in the Se containing peaks. The various Se compounds were quantified based on their Se content. Chromatography and mass spectroscopy data shown in Figure2.