Arginine metabolism in roots and leaves of apple (Malus domestica Borkh.): The tissue-specific formation of both nitric oxide and polyamines

In addition to serving as an important nitrogen reserve, l-Arginine participates in various physiological processes in plants. In plants, like in animals, nitric oxide (NO) is synthesized through nitric oxide synthase (NOS) pathway, while polyamines (PAs) are through arginine decarboxylase (ADC) and/or arginase-ornithine decarboxylase (ODC) pathway in arginine metabolism. In this study, arginine metabolism in fine roots and leaves of different development stages (white roots, brown roots, young leaves and mature leaves) were investigated, using potted 3-year-old apple plants. The results showed that different pathways in arginine metabolism are positively correlated, producing polyamines and nitric oxide in a tissue-specific manner. Higher levels of arginine, polyamines and nitric oxide, as well as arginase, ADC, ODC and NOS activities exist in roots than in leaves. White roots and young leaves exhibit higher levels of arginine metabolism than brown roots and mature leaves, respectively. As both polyamines and nitric oxide are multifunctional molecules involved in plant development and stress response, it is possible to conclude that the unique physiological roles of l-Arginine in plants might be associated with the coordinated biosynthesis of both polyamines and nitric oxide via arginine metabolism.