Postanthesis nitrate assimilation in winter wheat : in situ flag leaf reduction

Area of Science:

• Plant Physiology
• Agricultural Science
• Biochemistry

Background:

• Wheat (Triticum aestivum L.) utilizes soil nitrate (NO(3)(-)) and internal nitrogen (N) reserves for kernel development.
• Vegetative wheat tissues possess nitrate reductase activity, but direct measurement of in situ nitrate utilization within the shoot has been limited.

Purpose of the Study:

• To investigate the in situ assimilation and partitioning of nitrate (NO(3)(-)) in winter wheat (Triticum aestivum L.) after anthesis.
• To quantify the contribution of different vegetative organs to the nitrogen supply for developing kernels.

Main Methods:

• (15)N-labeled nitrate (NO(3)(-)) was injected into the penultimate internode of wheat plants at 7 days after anthesis.
• Heat girdling was used to block phloem export from the flag leaf in treated plants, while controls were not girdled.
• The assimilation and partitioning of (15)N were tracked over a 5-day period post-injection.

Main Results:

• The flag leaf was estimated to contribute 37% of the total reduced (15)N excess in the injected shoot.
• The lower shoot contributed 18% to the total reduced (15)N excess.
• The peduncle and spike together accounted for 45% of the total reduced (15)N excess.

Conclusions:

• Wheat flag leaves play a significant role in assimilating and partitioning nitrate (NO(3)(-)) for kernel development.
• Both vegetative tissues and the developing spike contribute to nitrogen assimilation and supply during grain filling in wheat.
• Understanding these N partitioning dynamics is crucial for optimizing nitrogen use efficiency in wheat production.