Identifying sucrose as a signal for nitrate uptake by wheat roots

Some sugars supplied directly to roots can stimulate nitrate uptake by wheat (Triticum aestivum L.) roots. To identify a signaling molecule, we compared the response of net nitrate influx to sugar supply. A method with a high time resolution (minutes) enabled to make a comparison. A signaling sugar should cause a faster and greater response than other compounds. Among nine sugars and mannitol tested, sucrose alone caused an immediate active stimulation of net nitrate influx. Glucose, fructose, and raffinose caused weak responses with a lag. Other carbohydrates had no effect. Sucrose behaves as a specific signal for nitrate uptake, which has long been supposed but not supported experimentally.