Handbook of Plant and Crop Physiology

16

Mineral Nutrient Transport in Plants

Benjamin Jacoby and Nava Moran

The Hebrew University of Jerusalem, Rehovot, Israel

337

I. INTRODUCTION

This chapter deals with the absorption and accumulation of mineral nutrient ions by plant cells and with
their primary translocation in the plant. The permeability of the phospholipid bilayer of biological mem-
branes to mineral ions is very low. Transport proteins—carriers and channels—embedded in the phos-
pholipid bilayer facilitate the transport of mineral ions across the membranes.
Plant cells accumulate all essential mineral ions to higher concentrations than those present in their
environment (Table 1). This accumulation is selective, as evidenced by the different accumulation ratios
of the ions shown in Table 1. Some questions that arise are:

How is passage through the impermeable lipid bilayer accomplished?

How is accumulation against the concentration gradient accomplished?

How is metabolic energy coupled to such transport?

What is the mechanism of selectivity?

How is vectorial transport accomplished?

These questions are dealt with in the sections that follow.

II. DEFINITIONS

At the outset, let us define some basic terms used in this chapter.

Electrochemical potential of solute j—
j(J mol^1 ): This is the Gibbs free energy [1] of the solute j:


j

*j2.3RTlogajzjFP
V (1)

whereRis the gas constant (8.314 J mol^1 ),Tis temperature in kelvin, ajis the chemical activity

ofj(aj
jcj, where (^) jis the activity coefficient and cjthe chemical concentration of j),zjis the
electrical charge (ionic charge) of j, Fis the Faraday constant (9.649 10^4 J mol^1 V^1 ),is the
electrical potential (V), Pis the pressure in excess of atmospheric pressure (MPa), V
is the partial
molal volume of j(m^3 mol^1 ), and 
*jis the electrochemical potential of jin the standard state (a

1.0,
0,P
0).