MAGNESIUM ANTAGONIZES POD-ZONE CALCIUM AND ZINC UPTAKE BY DEVELOPING PEANUT PODS

Abstract

Excess soil magnesium (Mg) is thought to adversely affect peanut (Arachis hypogaea L.) pod development by inhibiting calcium (Ca) uptake by peanut pods from the pod-zone. A solution culture experiment was therefore conducted to examine the effect of magnesium sulfate (MgSO₄.7H₂O) concentration (0 to1000 μM) in a simplified pod-zone solution containing (μM); ca. 101 sulfur (S), 100 Ca, 0.5 zinc (Zn), and 4 iron (Fe) on Mg and Ca absorption by developing pods in three peanut lines. There was a net Mg influx into pods from all solutions that contained Mg. The net Mg influx increased as the solution Mg concentration increased, and was accompanied by decreasing Ca influx into the pods which culminated into a net Ca efflux in the treatment with the highest solution Mg concentration (1000 μM). The pods released substantial amounts of root-absorbed potassium (K) into the pod-zone, the amount of which differed among the lines and with the Mg concentration in the pod zone. The concentration of Mg and S in the pod walls and of Mg (but not S) in the seeds increased strongly with increasing Mg and S concentration in the pod culture solution. This was accompanied by decreasing Ca and Zn concentration in the pod walls and seeds. Thus, the study provided direct evidence for the antagonism of Mg on Ca and Zn absorption from the pod-zone by developing peanut pods.

Keywords:

• calcium
• peanut pods
• magnesium
• solution culture
• zinc

ACKNOWLEDGMENTS

The study was made possible by a fellowship from the Australian Agency for International Development (now AusAID). Seeds of the two peanut cultivars used in this and related studies was kindly supplied by Mr. Alan Cruikshank, Team Leader, ACIAR Peanut Improvement Project, and Mr. Steve Magnussen of the Queensland Peanut Marketing Board.