LeNRT1.1 Improves Nitrate Uptake in Grafted Tomato Plants under High Nitrogen Demand

Area of Science:

• Plant Physiology
• Agricultural Science
• Molecular Biology

Background:

• Grafting is common in tomato cultivation for enhanced plant vigor.
• Grafted plants exhibit increased nitrogen (N) uptake, but the underlying mechanisms are unclear.
• Investigating N uptake requires understanding root plasma membrane transporter functions.

Purpose of the Study:

• To determine if increased N uptake in grafted tomatoes is due to low- or high-affinity root transporters.
• To compare nitrate transporter expression and activity in grafted versus ungrafted tomato plants under varying radiation levels.

Main Methods:

• Assessed expression of nitrate transporters (LeNRT1.1-2.3) in root plasma membranes.
• Measured Michaelis-Menten kinetics (Vmax, Km), root respiration, and nitrate reductase activity.
• Compared grafted, homografted, and ungrafted plants under different light intensities.

Main Results:

• Nitrate uptake primarily mediated by LeNRT1.1 and LeNRT1.2 in all plant types.
• Vigorous rootstocks showed similar LeNRT1.1/LeNRT1.2 expression under high N demand.
• Ungrafted plants exhibited higher LeNRT1.2 expression under high N demand.
• No significant differences in uptake capacity (Vmax), root respiration, or nitrate assimilation were observed.

Conclusions:

• Increased N uptake in grafted tomatoes is not linked to enhanced transporter capacity or activity.
• Differential expression of LeNRT1.2 in ungrafted plants suggests alternative regulatory mechanisms.
• Root plasma membrane transporters function similarly across grafted and ungrafted tomatoes regarding capacity and respiration.