Cellular and molecular basis of plant responses to drought, salinity and heavy metals
The distribution and accumulation of solutes in plants depends on the activity of precisely regulated transport processes at the cellular level. These can play an important role in plant responses to environmental stress. We are investigating the molecular basis of plant adaptations to drought, salinity and metals. Much of our work focuses on solute accumulation in the cell vacuole, since this provides the most important storage compartment for osmotically active and potentially cytotoxic ions.
One system studied as a paradigm for regulation of vacuolar solute transport is malic-acid accumulation in plants showing crassulacean acid metabolism (CAM). This process is energized by a vacuolar H+-ATPase (V-ATPase), which drives the influx of malate ions across the tonoplast through a malate-selective ion channel. A combination of approaches has been used to study the mechanism of both malate influx and efflux, as well as the metabolic characteristics of CAM induction during leaf development. In halophytic CAM plants, such as Mesembryanthemum crystallinum, CAM is environmentally regulated, and cell vacuoles can accumulate sodium chloride to concentrations in excess of 1.0 M. We have been studying the transport of both Na+ and Cl- using ion-sensitive fluorescent probes and the patch-clamp technique, as well as the transcriptional regulation of genes encoding the V-ATPase.
Our other major research effort is in the study of "metal-hyperaccumulator plants". These are extremely metal-tolerant plants that accumulate exceptional concentrations of transition metals in their leaves (for example, more than 3 % by dry biomass of nickel or zinc). We are investigating the cellular and molecular basis of this phenomenon to improve our understanding of metal-ion homeostasis in plant cells. Further, it is possible that such plants may aid in the clean-up of contaminated soils through the process of phytoremediation. However, many soils are polluted with mixtures of both organic and inorganic contaminants, and the implications of this for the bioremediation process are being investigated.