Construction of ihpRNA Expression Vector of Sugarcane Yellow Leaf Virus CP Protein Gene and Genetic Transformation in Tabacco Differences in NH3 compensation point among tobacco (Nicotiana Tabacum L.) cultivars and its relationship with N metabolization Effects of Aminoxyacetic Acid (AOA) and 2-Aminoindan-2-phosphonic Acid (AIP) on the Activities of Some Enzymes Induced by Methyl Jasmonate in Tobacco Calli