Effects Of Ammonium And Nitrate On Plant Growth And Petal Amino Acid Biosynthesis In Petunia Mitchell

Ammonium and nitrate are the two main nitrogen forms absorbed and utilized by plants.Due to their difference in terms of energy consumption,they have different effects on the physiological and metabolic processes of plants which in turn can stimulate the growth and development of plants to various extent.So far,people rarely study the absorption specificity of ornamental plants to different forms of nitrogen leading to very limited information about their effects on plant development.In addition,the metabolism of ornamental plants has always been a hot spot in the field.At present,studies about floral primary metabolism is even less.Amino acid metabolism is an important part of primary metabolism and an important node of carbon and nitrogen metabolism interaction.Twenty essential amino acids all play key roles in plant growth and development.For example,aliphatic amino acids and aromatic amino acids are directly involved in the synthesis of nitrogen-containing secondary metabolites.Therefore,the study of amino acid metabolism in response to different forms of nitrogen can help us better understand the secondary metabolism of ornamental plants.Petunia,as one of the model plants in the field of flower fragrance and color research,is an ideal research object.In this study,Petunia Mitchell（the white flower cultivar）was used as the test material.In the hydroponic cultivation medium,NH₄NO₃was used as control and NH₄Cl（ammonium nitrogen）as well as Na NO₃（nitrate nitrogen）were used as treatments,in which the total concentration of nitrogen concentration was all set-up at 2 m M.The effects of nitrogen forms on the growth and development and petal amino acid profile of Petunia Mitchell were studied.The main conclusions of this study are as follows:1.Effects of ammonium and nitrate on phenotypes of above-ground tissues of petuniaAmmonium and nitrate significantly promoted the branches and flowering amount of petunia and affected the flower color.The number of branches in ammonium increased by40.00%,and the flowering amount increased by 54.54%.The number of branches and flowering amount of nitrate were 20.00%and 36.36%respectively.In addition,ammonium significantly increased the b*and C*of petunia petals,making the flower color yellow and higher saturation.2.Effects of ammonium and nitrate on root system and root vigor of petuniaNitrate significantly promoted the root development of petunia.The root vigor of plants treated with ammonium reached the highest value(150μg·g^-1·h^-1)after 10 days,and decreased significantly in the later stage.The root vigor level of nitrate was relatively stable at60～100μg·g^-1·h^-1which was higher than that in control.3.Effects of ammonium and nitrate on physiological characteristics of petuniaAmmonium and nitrate increased the intercellular CO₂concentration,transpiration rate and stomatal conductance.Ammonium had no effect on net photosynthetic rate,while nitrate decreased net photosynthetic rate significantly.However,all treatments had no significant effect on the fluorescence characteristics of leaves.Nitrate significantly increased the chlorophyll content.Ammonium reduced the activity of nitrate reductase in petunia leaves,but nitrate had no effect.Both ammonium and nitrate significantly increased the nitrate reductase activity in roots,and the promoted effect of ammonium was better than nitrate.Ammonium and nitrate decreased the content of NO3^--N in petunia leaves.In addition,ammonium and nitrate also reduced the content of NO3^--N in petunia roots,and the effect of ammonium was obvious.Ammonium could promote the accumulation of NH₄⁺-N in roots.4.Effects of ammonium and nitrate on nitrogen distribution in petuniaThrough ¹⁵N labeling experiment,we found that the distribution pattern of nitrogen in petunia organs was:leaf>flower>stem>root.The results showed that ammonium significantly increased the nitrogen content in flower（0.71mg per plant）,the absorption of ¹⁵N（9.80mg per plant）and the utilization rate of ¹⁵N（2.06%）,and significantly promoted the distribution of nitrogen to flower organs.It is then proposed to be the best form of organ absorption of petunia.5.Effects of ammonium and nitrate on amino acid metabolism of petunia petalsAmmonium and nitrate could cause the fluctuations in amino acid contents in petunia petals at different developmental stages which could potentially affect secondary metabolism.Ammonium could increase the content of arginine in S1 period,the content of arginine,ammonium aspartate and aspartate in S2 period,and the content of lysine,proline,glutamate and glutamine in S3 period.Nitrate promoted lysine and threonine in S1 period,arginine,phenylalanine,serine and threonine in S2 period,and lysine and proline in S3 period.