THE CONSEQUENCE OF SELECTION FOR COPPER TOLERANCE ON THE UPTAKE AND ACCUMULATION OF COPPER IN MIMULUS-GUTTATUS

Previous research has shown that copper tolerance in Mimulus gurratus Fischer ex DC. is controlled by a single major gene and can be enhance d by a number of minor genes (or modifiers). Here we report the uptake of copper by three lines which all possessed the major tolerance gene but differed in the modifier genes: the major gene only (IT), the maj or gene plus increased (HT6) and decreased (LT6) modifiers. HT6 showed the highest copper tolerance and IT the lowest. Copper uptake was inv estigated at five copper concentrations and over 30 d to analyse the c oncentration of copper accumulated in roots and shoots and the partiti oning of apoplastic and symplastic root copper. Significant difference s were found for root copper concentration with the IT line accumulati ng the highest levels. Fifty-two per cent of the root copper in the IT line is symplastic and this increases to 60% in LT6 and 64% in HT6. S ignificant differences were recorded for shoot copper concentration wi th HT6 accumulating the highest and IT the lowest. At the highest exte rnal copper concentration the HT line accumulated nearly 800 mu g g(-1 ) in its shoot, approaching levels reported for copper hyperaccumulati on. (C) 1997 Annals of Botany Company.