The Effects Of Drought Stress And Rewatering On The Physiology And Secondary Metabolites Of Dendrobium Candidum

Dendrobium moniliforme is the plant in orchid dendrobium.It has small flowers with pure and beautiful color.And it has a longish florescence which is often used for cut flowers and potted flowers.In addition,it is a drought-tolerant crop and it is a precious herbal and widely used as food and health care medicine.Therefore,Dendrobium moniliforme has great market potential.Now,there are only researches in extraction process of polysaccharide,the active ingredients,pharmacological effects and tissue culture of Dendrobium moniliforme.As a plant with relatively high medicinal value,there are few reports on alkaloids of Dendrobium moniliforme and there is almost no report on flavonoids content of it.At the same time,there is no research about the water utilization in Dendrobium moniliforme.For reasonable use of Dendrobium moniliforme,find the most suitable irrigation methods,play the economic benefits and we know that the drought stress can affect the growth and secondary metabolites of plants,and the re-water operation has compensation function.So,it adopts the artificial water control in different soil water content in this research,and making the Dendrobium moniliforme under different drought stress and the re-water conditions to investigate the physiological condition and secondary metabolites contents.The experimental materials are three-year-old plants of Dendrobium moniliforme.Dendrobium moniliforme was grown in four kinds of drought intensity and was exposed for 20 days,then gave it a re-water operation in different stages(day 0,5,10,15,20).At every point in time,it has a determination in physiological indexes of Dendrobium moniliforme,including these indicators:leaf water content,total chlorophyll content,carotenoid content,catalase activity,peroxidase activity,soluble sugar content,soluble protein content and malondialdehyde content.Besides,it also has a determination in secondary metabolites contents of Dendrobium moniliforme,including these indicators:polysaccharide content,total flavonoids content and total alkaloid content.Significant difference was found in this study by using SPSS software for data analysis,get the following conclusion:1.The effect of leaf water content in Dendrobium moniliforme under drought stress and re-watering.It can endure drought stress within a certain scope to the influence of its leaf water content.Under the three drought gradients,the leaf water content of Dendrobium moniliformewith the extension of processing time,the water content of leaves had a descending trend.After re-watering,The mild drought stress group of Dendrobium moniliforme was catabatic from the drought stress,but it did not return to normal levels.When there is a re-water opereation to moderate drought stress group of Dendrobium moniliforme,it was catabatic from the drought stress,but it was worse than the Dendrobium moniliforme under mild drought stress.When there is a re-water opereation to severe drought stress group of Dendrobium moniliforme,the leaf water content can't ease during the whole experiment.2.The effect of photosynthetic pigment content in Dendrobium moniliforme under drought stress and re-watering.At a certain range,it can improve the total chlorophyll content of Dendrobium moniliforme under drought stress,but the carotenoid content was increased slightly at the early stage of the drought stress,and it was lower than the control group at the late stage of drought stress.After re-watering for 24 hours,the total chlorophyll content was increased at the early stage of mild drought stress and it was increased at the late stage of the mild and severe drought stress.Along with the drought degree aggravating,the impact on the total chlorophyll content could not be recovered.Under the three drought gradients,the carotenoid content of Dendrobium moniliforme was higher than the control group at early and middle stage.3.The effect of respiration in Dendrobium moniliforme under drought stress and re-watering.The POD activity of Dendrobium moniliforme showed a trend of decrease after an increase under mild and moderate drought stress,and it was lower than the control group at the late stage.The POD activity of Dendrobium moniliforme showed a trend of increase after a decrease under severe drought stress,and it was higher than the control group at the late stage.At the early stage of the mild drought stress,it has a strong activity in the CAT activity of Dendrobium moniliforme.Along with the drought degree aggravating and the extension of processing time,the CAT activity of Dendrobium moniliforme was decreased.After re-watering,the POD activity of Dendrobium moniliforme was increased at some time under the mild and moderate drought stress,and it was significantly increased under severe drought stress.Also,the CAT activity of Dendrobium moniliforme was increased under mild drought stress after re-watering.4.The effect of organic substance metabolism in Dendrobium moniliforme under drought stress and re-watering.Under the three drought gradients,the soluble sugar content of Dendrobium moniliforme was higher than the control group.But,along with the drought degree aggravating,the soluble sugar content of Dendrobium moniliforme was decreased gradually,and it showed a trend of decrease under severe drought stress.Besides,the appropriate intensity of drought was conducive to the accumulation of protein in Dendrobium moniliforme.After re-watering,the soluble sugar content of Dendrobium moniliforme was increased under some drought gradients,but it was decreased when the drought gradients were too strong.Besides,the soluble protein content of Dendrobium moniliforme was increased under mild and moderate drought stress after re-watering.5.The effect of adversity physiological index in Dendrobium moniliforme under drought stress and re-watering.Under mild drought stress,the cell membrane of Dendrobium moniliforme was damaged at early stage,but it has adapted to the drought environment at the late stage,so there was no obvious damage to the cell membrane of Dendrobium moniliforme.The cell membrane of Dendrobium moniliforme was under different stage of damage under the moderate and the severe drought stress,and it led to the decrease of the activity of protective enzyme system.Besides,under severe drought stress,the cell membrane was severely damaged,and it produced more malondialdehyde.When there was a re-water operation to the severe drought stress,it could not ease the damage in Dendrobium moniliforme.And it was conducive to the recovery of the protective enzyme activity only under mild and moderate drought stress after re-watering in Dendrobium moniliforme.6.The effect of secondary metabolites in Dendrobium moniliforme under drought stress and re-watering.At the early stage of the experiment,the mild drought stress was conducive to the accumulation of the polysaccharide content in Dendrobium moniliforme.At the late stage of the experiment,the severe drought stress was conducive to the accumulation of the polysaccharide content in Dendrobium moniliforme.At the early stage of the experiment,the moderate drought stress was conducive to the accumulation of the total flavonoids content in Dendrobium moniliforme.At the middle and the late stage of the experiment,the mild drought stress was conducive to the accumulation of the total flavonoids content in Dendrobium moniliforme.At the early stage of the mild and moderate drought stress,it was conducive to the accumulation of the total alkaloids content in Dendrobium moniliforme.With the increase of intensity and the extension of processing time,it was not conducive to the accumulation of the total alkaloids content in Dendrobium moniliforme.After re-watering,it was conducive to the accumulation of polysaccharide content in Dendrobium moniliforme under mild drought stress and the early stage of the moderate drought stress.And it was conducive to the accumulation of polysaccharide content in Dendrobium moniliforme under severe drought stress after re-watering,and it could get a maximum at the end of the severe drought stress after re-watering.After re-watering,it was conducive to the accumulation of total flavonoids content in Dendrobium moniliforme under mild drought stress.Besides,after re-watering,it was conducive to the accumulation of total alkaloids content in Dendrobium moniliforme under the early stage of the mild and the moderate drought stress.