Botany & Plant Ecology. (Abstracts-2003 Annual Meetings)‪.‬

Higher Plant Metallothionein-Like Gene Responsiveness to Cytokinin. John C. Thomas, University of Michigan-Dearborn, Department of Natural Sciences, 4901 Evergreen Road, Dearborn, MI 48128-1491; jcthomas@umd.umich.edu The biological significance of plant metallothionein-like (MT-L) genes remains uncertain. The MT-L cDNA clones pECD7, isolated from Mesembryanthemum crystallinum and pCkn16A1 from Nicotiana plumhaginifolia were used to characterize metallothionein-like mRNA expression during cytokinin treatment, copper and NaCI stress. DNA analysis suggested that both metallothionein-like cDNAs are members of small gene families. In Mesembryanthemum, copper and salt stress resulted in a 3-5 fold increase in mRNA hybridizing to pECd7. The growth regulator cytokinin was also found to greatly increase pECD7 mRNA hybridization compared to controls. Conversely, copper stress resulted in a significant loss of pCkn16A1 mRNA transcript in leaves of N. tabacum. When the Agrobacterium tumefaciens gene isopentenyl transferase (ipt) was transformed and expressed in tobacco under the control of a light inducible promoter, transgenic tobacco demonstrated greater pCkn16A1 transcript accumulation compared to nontransformed controls. Elevated pCkn16A1 mRNA concentrations may contribute to the 8-fold accumulation of copper in older leaves compared to nontransformed control plants following copper stress. Metallothionein-like protein mRNA levels and stress responsiveness may depend on endogenous cytokinin supply.