Influence Factors Against Polysaccharide Accumulation And Sucrose Metabolism Of Dendrobium Officinale

Polysaccharide is the main active constituent of Dendrobium officinale and also an important evaluating index for its quality.Monosaccharides,components of Dendrobium polysaccharides,are usually decomposed or derived from sucrose,therefore the accumulation of polysaccharides is directly correlated to the sucrose metabolism.Plant growth conditions and the exogenous additives such as hormones and metal ions normally have the impacts on the accumulation of plant polysaccharides and sucrose metabolism and regulate the different sugar levels and a variety of physiological functions in plants.In this study,the sugar contents and 4 sucrose enzymetic activities of SPS,SS,AI and NI in stems and leaves of Dendrobium officinale seedlings were investigated to study the influencing factors and working machanisms on Dendrobium polysaccharides accumulation and sucrose metabolism through the treatments of plant growth conditions of temperature,illumination,pH and the exogenous additives including Ca²⁺,Mn²⁺,NaCl and ABA on Dendrobium officinale seedlings.The main results are listed as follows:Different effects on the sugar contents and the enzymetic activities of 4 sucrose metabolic enzymes in stems and leaves of Dendrobium officinale seedlings were presented under the different treatments of temperature,illumination and pH:（1）Within the certain range of temperatures,the higher the temperature was,the higher the activities of SPS were produced.The higher activities of SS,AI and NI were presented at 25°C.Furthermore,the SPS activity was significantly positive correlated with sucrose contents（R=0.816）and the AI activity was significantly positive correlated with polysaccharides（R=0.811）and extremely significant positive correlated with glucose contents（R=0.903）respectively.The sucrose,polysaccharide and glucose contents reached the highest at 25℃.（2）Under the different light intensities,the activities of SPS and SS in the leaves were significantly higher than those in the stems,SPS was the main enzyme in sucrose synthesis and had a significant positive correlation with sucrose content（R=0.896）.SS was significantly correlated with polysaccharide（R=0.833）,indicating that SS was mainly involved in the sucrose decomposition.The activities of SPS and SS were reached the highest level,and the contents of sucrose and polysaccharide were reached a significant level under the light intensity of 3500 lx.（3）Different pH values produced greater effects on AI activities,pH5 was more favorableto the AI catalytic activities,The higher pH was,the more inhibiting effects were produced,the higher activities of SPS,SS,NI were reached at pH7.Both SPS and SS affected the synthesis of sucrose,AI and NI worked on the accumulation of glucose and polysaccharides,in which the functions of AI were more significant than NI.pH7 was more favorable to the accumulation of sucrose,polysaccharide and glucose in Dendrobium officinale.The effects of different exogenous additives on sugar contents and sucrose metabolic enzyme activities of Dendrobium officinale were observed in different degrees.（1）The exogenous addition of Ca²⁺not only enhanced the sucrose storage,but also promoted the activities of sucrose metabolic enzymes and the transport of sucrose into the sugar storeroom.At the Ca²⁺concentration of 4.5mmol·L^-1,the higher activities of 4 sucrose metabolic enzymes were produced and the more sucrose and polysaccharides were accumulated.The accumulation of sucrose was significantly affected by SPS,whereas AI significantly affected the accumulation of polysaccharides and glucose.（2）The exogenous addition of Mn²⁺significantly enhanced the activities of SPS and AI,improved the sucrose synthesis in leaves and increasedsugar contents in the storage.At the Mn²⁺concentration of 1.0mmol·L^-1,the maximum activities of both SPS and AI were reached and the soluble sugar contents wereincreased significantly.（3）The exogenous addition NaCl of different concentrations increased significantly the catalytic activity of invertase and promoted the accumulation of glucose.Although SS and SPS activities were increased,but the differences were not significant.At the certain concentration range of NaCl,the sugar contentswere increased greatly and the adversity stresseswere decreased.At the NaCl concentration of 50 mmol·L^-1,the sugar contents of Dendrobium officinale were reached the highest in order to satisfy the requirements of high energy and enhance the resistant ability to adverse environments.（4）The exogenous addition of ABA at different concentrations could promote the catalytic activities of SS and invertase to a certain extent,significantly affect the sugar accumulation of Dendrobium officinale,but produce the inhibitory effect to SPS.Sucrose content was significantly positive correlated with SS and SPS.Atthe ABA concentration of 60 umol·L^-1,the higher activities of SS and invertase were presented,and the sugar accumulation in Dendrobium officinalewas reached a significant level.In terms of polysaccharide accumulation and sucrose metabolism in Dendrobium officinale,the results showed that 25℃,3500 lx and pH7 were the optimum growth conditions,Ca²⁺4.5mmol·L^-1,Mn²⁺1.0mmol·L^-1,NaCl 50 mmol·L^-11 and ABA 60umol·L^-1were the best treatment concentration for each exogenous additive respectively.The sucrose metabolic enzymes activities were the highest,the ability of resisting adverse environment was the strongest,and the sugar accumulation of Dendrobium officinale was the most favorable under these conditions.These factors changed the direction of sucrose accumulation or decomposition by affecting the activities of sucrose metabolic enzymes in Dendrobium officinale to meet the material and energy needs of plant growth and development and maintain the balance of cell osmotic potential.These results can provide the basis for further study and regulation of polysaccharides and sucrose metabolism of Dendrobium officinale.