In vivo nitrate reductase activity in dark- and light-grown sugarcane callus

Area of Science:

• Plant Physiology
• Biochemistry
• Enzymology

Background:

• Nitrate reductase is a key enzyme in nitrogen assimilation in plants.
• Environmental factors like light can influence enzyme activity.
• Understanding enzyme kinetics and cofactor dependency is crucial for plant metabolism.

Purpose of the Study:

• To investigate the in vivo nitrate reductase activity in sugarcane callus under different light conditions.
• To determine the effect of NADH supplementation on nitrate reductase activity.
• To compare NADH penetration and enzyme response in callus versus leaf tissues.

Main Methods:

• Assay of in vivo nitrate reductase activity in dark- and light-grown sugarcane callus.
• Supplementation of reaction systems with NADH (0.3 mM).
• Kinetic analysis of NADH dependence (Michaelian kinetics).
• NADH penetration studies in callus and leaf tissues.

Main Results:

• Dark-grown callus showed over threefold higher nitrate reductase activity than light-grown callus.
• NADH increased in vivo nitrate reductase activity by over twofold in both dark- and light-grown callus.
• Apparent Km values for NADH were 0.083 mM (dark) and 0.20 mM (light).
• NADH did not affect activity in green sugarcane leaves; NADH penetration was observed in callus but not in leaf discs.

Conclusions:

• Light significantly impacts nitrate reductase activity in sugarcane callus.
• NADH is a critical cofactor for nitrate reductase in sugarcane callus, with differential kinetics based on light exposure.
• Differential NADH penetration explains the varied response between sugarcane callus and leaf tissues.