In plants, the elements Fe, Zn, Mn, Cu, Ni, B, Mo and Cl are considered to be
micronutrients essential for plant growth. Micronutrient uptake systems are
intrinsically more difficult to investigate than their macronutrient
counterparts because of the low fluxes involved. Currently, the mechanism of
transport for these micronutrients has not been clearly identified, except for
Cl. In the case of the trace metal micronutrients, uptake studies point to the
presence of high and low affinity transporters with broad substrate
specificity. The kinetics of these transporters is clouded by the failure of
many investigators to consider the effects of the electrostatic nature of the
plasma membrane on cation uptake. Recent work has helped to clarify the nature
of B movement across membranes and there is now evidence of a facilitated
transport system for B, in addition to its passive permeation directly through
the membrane. The uptake of Mo is known to be induced by
NO3 and inhibited by W, but little further information
is available on how Mo enters cells. In recent years, the emphasis has shifted
from physiological studies of micronutrient uptake to molecular investigations
of transporters cloned in plants and characterized in heterologous expression
systems. There is now a substantial catalogue of transporter genes, mostly for
trace metals, whose functions in plants have yet to be clearly defined.
H+ Changes Associated with Divalent Cation Uptake by Mouse Liver Mitochondria
