Growth and Nutrient Uptake of Cell Suspensions of Thlaspi caerulescens and Brassica napus Treated with the Heavy Metal Zinc

Thlaspi caerulescens (Brassicaceae), known as a Zn hyperaccumulator, is able to accumulate and tolerate Zn at high concentrations in its biomass. Cell suspension cultures of Thlaspi caerulescens J et C Presl and B. napus `Westar' have been initiated to study the effect of high Zn concentrations on growth and nutrient uptake. Preliminary studies determined the optimal conditions for subculturing and maintaining cultures. Cell suspensions grew best on Murashige and Skoog medium supplemented with B5 vitamins and 1 mg 2,4-D/liter at 0.4 g/25 ml inoculation density, and with a 2-week subculture period. In an initial experiment, cell suspensions were cultured in media containing 1.96 ppm Zn (basal) or 49 ppm Zn (25x). Media and tissue samples were collected at days 0, 4, 7, 10, and 13, and their nutrient content was analyzed by ICP-AES. Thlaspi and Brassica cell suspensions grew equally well on both media. For both species, uptake patterns of Ca, K, Mg, Mn, and P were not significantly different between the two media; however, >97% of the P was taken up within 2 weeks. Zinc concentration was reduced during the first 4 days (lag phase) in the high-Zn medium, with 27% and 41% taken up by the Thlaspi and Brassica cultures, respectively. Thlaspi took up significantly less Zn than did Brassica. By day 13, Thlaspi and Brassica tissue collected from the high-Zn medium contained 10x and 32x, respectively, more Zn when compared to tissue grown on basal medium.