Nitrite reduction system in barley roots: existence of an electron carrier operating in an electron-transport sequence from glucose-6-phosphate to nitrite reductase

Abstract

An electron carrier that can be substitutes for ferredoxin in a cytochrome c reduction system has been identified in extracts prepared from the roots of barley (Hordeum vulgare L. cv. Daisen-gold) seedlings. The root electron carrier (REC) had a red color and was able to transport electrons from a NADPH-regenerating system (glucose-6-phosphate, NADP, and glucose-6-phosphate dehydrogenase) to cytochrome c in a reaction catalyzed by ferredoxin-NADP reductase (EC 1.6.7.1) from spinach leaves. It had absorption maxima at 412 and 467 nm, and the absorption peak at 412 nm shifted to 419 nm upon reduction with dithionite. REC could transport electrons from dithionite to nitrite reductase (EC 1.7.7.1) purified from the same roots, and also operated as an electron transporter in the presence of spinach leaf ferredoxin-NADP reductase from glucose-6-phosphate to the nitrite reductase system, which is considered to be the in vivo nitrite-reduction system in the roots. REC could not be distinguished from spinach leaf ferredoxin in the transport of electrons from either dithionite or the NADPH-regenerating system to nitrite reductase.

Key Words:

• barley root
• ferredoxin-like electron carrier
• Hordeum (nitrite reduction)
• nitrite reduction