Response of Garden Pea to Nickel Toxicity

Abstract

Hydroponically-grown Pisum sativum plants were sensitive to Ni²⁺ (100–1000 µmol/L). Lower Ni²⁺ concentration (25 µmol/L) stimulated general growth up to 20 d. Nickel (Ni)-free plants showed nodulation (average 27 per plant), but the frequency went down to 82% even in 100 µmol/L Ni²⁺. The Ni²⁺ concentration, when raised to 200 or 300 µmol/L, inhibited nodulation completely. The Ni²⁺ accumulation in P. sativum was concentration- and time-dependent. External Ni²⁺ concentration (200 or 300 µmol/L) contributed cation buildup of 34 µg g⁻¹ dw, average. The root/shoot share of Ni²⁺ was invariably 60 : 40 indicating that 40% of Ni²⁺ accumulated gets translocated to foliar parts. Proline biosynthesis in plants was promoted by 3.36-fold. A 40:60 root/shoot share of this amino acid infers that it is synthesized primarily in foliar parts and can be adopted as a reliable metal-stress indicator. The Ni²⁺ load invariably lowered thiol biosynthesis in P. sativum with the exception of a 1.14-fold stimulation by the lowest Ni²⁺ dose (25 µmol/L) during the first 5 d. However, plants failed to sustain this stimulation any longer as the level paralleled the Ni-free control during subsequent growth. Urease activity increased to a maximum of 24.7 µmol g⁻¹ dw during 20 d although it declined to 22.4 units at the end of the experiment (30 d). The marginal stimulation of urease by Ni²⁺ can be arranged as 100 > 25 > 0 > 200 > 300 µmol/L. Pisum sativum roots even at the seedling stage, had double the amount of urease as shoots. It is suggested that this may primarily be to facilitate the plant assimilation of urea from the ambient environment.

Keywords:

• Pisum sativum
• Proline
• Nickel
• Thiol
• Urease

Acknowledgments

This work was supported by a grant from the Ministry of Environment and Forests, Government of India (Grant No. 19/30/95-RE dt. 24 August, 1998).