| Effects of UV-B radiation on plants is currently one of the hottest scientific research. UV-B radiation affects plant’s growth and its synthesis of secondary metabolites. Nitrogen nutrition can reduce damage of UV-B radiation for plant’s growth, meanwhile regulate the synthesis and accumulation of secondary metabolites. Preliminary research of this paper showed that, UV-B radiation hindered growth of Dendrobium officinale Kimura et Migo and caused brown leaves, fallen leaves. This paper mainly studied how nitrogen nutrition reduce damage of UV-B radiation on growth of Dendrobium officinale Kimura et Migo, and found out in what contents of nitrogen nutrition UV-B radiation did minimal damage to Dendrobium officinale Kimura et Migo. Here are experimental methods and results:Taken Dendrobium officinale Kimura et Migo as experimental material, in UV-B radiation of 15.6μW·cm-2 which can cause damage to Dendrobium officinale Kimura et Migo, made MS medium in nitrogen nutrition level(0.552mg/L, CK)under tissue culture for reference, regulated concentration of nitrogen nutrition in medium, experiment were as below: 0.138mg/L(UV-B+N1),0.276mg/L(UV-B+N2),0.552mg/L(UV-B+CK),1.104mg/L(UV-B+N4),1.656mg/L(UV-B+N5)and 2.208mg/L(UV-B+N6). By number of sprout tillers, rate of damaged leaves, photosynthetic pigment, protection material and its related metabolic enzyme as well as protective enzyme system and active ingredient, analyzed how different nitrogen nutrition level affected growth and Active ingredient of Dendrobium officinale Kimura et Migo.(1) Rate of damaged leaves and number of sprout tillers Under UV-B radiation, rate of damaged leaves was different in different nitrogen nutrition. Damaged of Dendrobium officinale Kimura et Migo leaves was more serious with higher level nitrogen nutrition. On 16 th days’ UV-B radiation, rate of damaged leaves from higher nitrogen nutrition level to lower one were showed as below: 82.20%, 70.31%, 61.18%, 45.54%, 32.43% and 62.34%. It indicated that rate of damaged leaves in UV-B+N2 was the lowest. Besides, in early UV-B radiation, number of sprout tillers increased in UV-B+N4, UV-B+N5 and UV-B+N6 but was hindered in late radiation; but under UV-B radiation, number of sprout tillers in UV-B+N2 increased slowly.(2) Influence on content of photosynthetic pigment of Dendrobium officinale Kimura et Migo Under UV-B radiation, contents of photosynthetic pigment of UV-B+N1, UV-B+N4, UV-B+N5 and UV-B+N6 was reduced comparing with that in UV-B+CK. But content of photosynthetic pigment in UV-B+N2 changed little, it explained that Dendrobium officinale Kimura et Migo adapted to UV-B radiation.(3) Influence on antioxidant enzyme activity of Dendrobium officinale Kimura et Migo Under UV-B radiation, activity of antioxidant enzyme in UV-B+N1and UV-B+N2 improved comparing with that in UV-B+CK, but reduced in UV-B+N4, UV-B+N5 and UV-B+N6. Besides, under UV-B radiation, contents of MDA in Dendrobium officinale Kimura et Migo increased with improving nitrogen nutrition. On 16 th day’s radiation, contents of MDA in UV-B+N1, UV-B+N2, UV-B+N4, UV-B+N5 and UV-B+N6 were 126.41%, 68.82%, 146.8%, 186.83% and 203.59% of those in UV-B+CK, which illustrated that contents of MDA in Dendrobium officinale Kimura et Migo had a minimal value in UV-B+N2.(4) Influence on active ingredients of Dendrobium officinale Kimura et Migo under UV-B radiation, with improving nitrogen nutrition level, contents of polysaccharide and flavonoids reduced gradually; while reducing nitrogen nutrition made contents of polysaccharide and flavonois increase. On 16 th day’s radiation, contents of polysaccharide in UV-B+N1, UV-B+N2, UV-B+N4, UV-B+N5 and UV-B+N6 were respectively 129.75%, 184.78%, 61.04%, 28.54% and14.68% of those in UV-B+CK; contents of flavonoids in UV-B+N1, UV-B+N2, UV-B+N4, UV-B+N5 and UV-B+N6 were respectively 132.15%, 149.14%, 96.71%, 74.93% and 60.71% of those in UV-B+CK. In early UV-B radiation, contents of alkaloid of Dendrobium officinale Kimura et Migo increased significantly with rising nitrogen nutrition level; but in late radiation, contents of alkaloid of Dendrobium officinale Kimura et Migo decreased dramatically in UV-B+N5 and UV-B+N6 which were less than those in UV-B+CK. On 16 th day’s radiation, contents of alkaloid in UV-B+N1, UV-B+N2, UV-B+N4, UV-B+N5 and UV-B+N6 were respectively 17.38%, 81.63%, 86.39%, 20.01% and 12.78% of those in UV-B+CK.In all, under UV-B radiation, different nitrogen nutrition level affected growth and main active ingredient of Dendrobium officinale Kimura et Migo. Increasing concentration of nitrogen nutrition did not benefit growth of Dendrobium officinale Kimura et Migo, and made reduce plant’s main active ingredient; reducing moderately nitrogen nutrition level, like in UV-B+N2, improved contents of Polysaccharide and flavonoids in Dendrobium officinale Kimura et Migo, and benefited to reduce damage of UV-B radiation for growth of Dendrobium officinale Kimura et Migo; When concentration of nitrogen nutrition was too slow, contents of polysaccharide and flavonoids of Dendrobium officinale Kimura et Migo increased, but which hindered growth of plants. Therefore, nitrogen nutrition level of 0.276mg/L(UV-B+N2) reduces damage of UV-B radiation for Dendrobium officinale Kimura et Migo, and benefits to increase contents of polysaccharide and flavonoids of Dendrobium officinale Kimura et Migo under UV-B radiation. |
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