Changes in arginine and nitric oxide levels in Malus hupehensis Rehd. seedlings during plant development

Changes in arginine, arginase, nitric oxide (NO), nitric oxide synthase (NOS) levels in roots, stems, leaves and cotyledons of Malus hupehensis Rehd. seedlings, which are related to plant growth and development, were investigated. The results showed that the levels of arginine and arginase were the highest in cotyledons, which decreased slowly during plant development, followed by leaves and stems, with roots being the lowest. In cotyledons, NO and NOS levels reached the highest after 5 days of growth, then decreased quickly after 8 days of growth. Among roots, stems and leaves, the highest levels of NO and NOS existed in stems and reached the highest after 11 days of growth, coinciding with the rapid elongation of stems, while those of roots were the lowest and reached the highest after 8 days of growth, coinciding with the rapid elongation of primary roots. NO and NOS levels in leaves reached the highest after 17 days of growth, coinciding with the rapid expansion of leaves. It is concluded that NO is mainly located in actively growing tissues, suggesting its possible roles in plant growth and development in Malus hupehensis Rehd. seedlings and cotyledon arginine might be one of the important nitrogen reserve that is required for the early development of the seedlings.