Nickel in plants: I. Uptake kinetics using intact soybean seedlings

Area of Science:

• Plant Physiology
• Environmental Science
• Biochemistry

Background:

• Nickel (Ni2+) is an essential micronutrient for plants, but its uptake mechanisms and interactions with other essential cations are not fully understood.
• Soybean (Glycine max) is a globally important crop, making its nutrient uptake dynamics critical for agricultural productivity and soil health.

Purpose of the Study:

• To investigate the concentration-dependent absorption kinetics of Ni(2+) in soybean plants.
• To explore the interactions between Ni(2+) and various nutrient cations (Cu(2+), Zn(2+), Fe(2+), Co(2+)) during plant uptake.
• To elucidate the transport mechanisms and identify potential carrier sites involved in Ni(2+) absorption.

Main Methods:

• Investigated Ni(2+) absorption in 21-day-old soybean plants across a concentration range of 0.02 to 100 µM.
• Applied Michaelis-Menten kinetics to analyze uptake isotherms and determine kinetic constants (K(m), K(i)).
• Conducted competition kinetic studies using various nutrient cations to assess their inhibitory effects on Ni(2+) absorption.

Main Results:

• Observed multiple absorption isotherms for Ni(2+), each conforming to Michaelis-Menten kinetics.
• Identified competitive inhibition of Ni(2+) uptake by Cu(2+) and Zn(2+), indicating shared carrier sites.
• Quantified kinetic constants (K(m) and K(i)) for Ni(2+) and its interactions with Cu(2+) and Zn(2+).
• Observed inhibition by Fe(2+) and Co(2+) but did not fully resolve the inhibition mechanism using classical kinetics.

Conclusions:

• Soybean plants exhibit complex, multi-site mechanisms for Ni(2+) absorption.
• Cu(2+) and Zn(2+) compete with Ni(2+) for the same transport sites, impacting nickel bioavailability.
• Further research is needed to fully understand the inhibitory mechanisms of Fe(2+) and Co(2+) on Ni(2+) uptake.