Nitrate reduction in tendrils of semi-leafless pea

Area of Science:

• Plant physiology
• Genetics
• Biochemistry

Background:

• The recessive gene 'af' in Pisum sativum L. modifies leaf morphology, replacing leaflets with tendrils.
• Previous research suggested tendrils support plant growth via carbon metabolism, but their role in nitrogen metabolism was unexplored.

Purpose of the Study:

• To investigate the nitrate reduction capacity of tendrils in the semi-leafless Pisum sativum L. 'Solara' variety.
• To compare the nitrate reductase activity and activation state of tendrils with traditional flat leaf structures.

Main Methods:

• Enzyme assays to determine maximum nitrate reductase activity (EC 1.6.6.1) on a protein basis.
• Measurement of nitrate reductase activation state in tendrils and flat leaf structures.
• Calculation of tendril contribution to overall plant nitrate reduction using in vitro and in vivo measurements.

Main Results:

• Tendrils exhibited significantly lower maximum nitrate reductase activity per protein compared to flat leaf structures.
• Nitrate reductase activation state was significantly higher in tendrils (70%) than in flat leaf structures.
• Tendrils contributed up to 25% to the plant's total nitrate reduction, with higher values from in vivo measurements.

Conclusions:

• Despite lower maximum activity, tendrils play a crucial role in nitrogen assimilation in semi-leafless pea varieties due to their high nitrate reductase activation.
• The findings provide insights into the physiological and metabolic contributions of tendrils beyond carbon metabolism.
• Results are discussed in the context of nitrate, magnesium, carbohydrate, amino acid, and adenylate levels within tendrils.