Effects Of Gibberellin And Spermine On Flowering And Polyamine Synthesis Of Rhododendron Simsii

Rhododendron simsii is a world famous ornamental plant,which is widely used in landscaping.As the distribution center of Rhododendron resources in the world,R.simsii potted flowers and seedlings for landscaping in China have been growing steadily in the past 10 years.At present,cultivation measures are mainly adopted to control the florescence of R.simsii.However,the investment of cultivation measures is huge and the quality can not be guaranteed,which seriously affected the quality of flowers and resulted in huge economic losses.It has been clarified that gibberellin and polyamines are involved in regulating the florescence of plants,and besides the metabolism of polyamines changes during flowering.However,the specificity of polyamines synthesis and metabolism during senescence of R.simsii is still unclear.In this study,the R.simsii‘Zichendian'was used as the test material.The effects of exogenous GA₃?800 mg/L,1 600 mg/L,2 400 mg/L?and Spd?0.01 mmol/L,0.1mmol/L,1 mmol/L?at different concentrations on Photosynthetic characteristics,antioxidant system,endogenous nutrients and polyamines synthesis of R.simsii during flowering and florescence were observed.The results show that:?1?Spraying GA₃/Spd alone regulated the early blooming stage,increased the flowering rate,prolonged the florescence and increased the flower diameter of R.simsii.The effect was more significant in a certain concentration range of GA₃/Spd.The effect was best at 1 600 mg/L when treated with GA₃ alone.The early blooming stage was 6 days earlier than the control and florescence were 7 days longer than the control.The flower diameter and flowering rate increased by 9.82%and 11.80%,respectively,compared with the control;The effect was best at 0.1mmol/L When Spd treated alone.However,early blooming stage delayed by 8d and florescence was prolonged by 11d compared with the control.The flower diameter and flowering rate were increased by 16.38%and 8.13%,respectively.?2?The different concentration combinations had significant difference on the flowering of R.simsii with a combination of GA₃ and Spd.In a certain concentration range,the combination of GA₃ and Spd promoted the flowering of R.simsii and prolonged florescence.High concentration GA₃??1 600 mg/L?combined with low concentration Spd?0.01 mmol/L?or low concentration GA₃?800 mg/L?and high concentration Spd??0.1 mmol/L?had a significant synergistic effect on promoting flowering of R.simsii.The early blooming stage of 2 400 mg/L GA₃+0.01 mmol/L Spd treatment was 11 days earlier than that of the control,the florescence was 6 days longer than that of the control,2 days longer than that of 2 400 mg/L GA₃ alone;The early blooming stage of 800 mg/L GA₃+1 mmol/L Spd treatment was delayed by 2days,the florescence of 17 days was prolonged by 9 days,and the florescence was prolonged by 2 days compared with the control treatment alone.In general,the treatment of 2 400 mg/L GA₃+0.01 mmol/L Spd had the best effect of early flowering,and the treatment of 0.1 mmol/L Spd sprayed alone had the longest florescence.?3?Exogenous GA₃ and Spd increased anthocyanin content of petals,chlorophyll content of leaves and net photosynthetic rate?Pn?,stomatal conductance?Gs?and intercellular CO₂ concentration?Ci?during flower senescence of R.simsii.GA₃ treatments increased transpiration rate?Tr?of leaves,while Spd decreased Tr of leaves,both of which effectively alleviated the decline of chlorophyll and anthocyanin content at end flowering stage.0.1mmol/L Spd was sprayed separately,which was better than that with a combination.?4?The treatments with GA₃ and Spd reduced the MDA content of petals during flower senescence of R.simsii significantly,increased the activities of SOD,POD and CAT,and slowed down the decline of SOD at the end of flowering stage,delayed the flower senescence process and prolonged florescence effectively.The treatment of medium and high concentrations of Spd?0.1mmol/L and 1mmol/L?was better than that of the single concentration of GA₃.The mixed treatment with 800 mg/L GA₃+1mmol/L Spd was the best.The activity of SOD,POD and CAT at end flowering stage was 147.47%,56.92%and 87.74%higher than that of the control,respectively.?5?Exogenous GA₃ and Spd treatments increased the content of soluble sugar and soluble protein during flower senescence of R.simsii.Soluble sugar sprayed with1 mmol/L Spd alone had a better effect,which significantly increased the content of soluble sugar and delayed flower senescence process of R.simsii.Soluble protein had no significant difference in the treatment at squaring stage,and the treatment with the single concentration of 0.1 mmol/L Spd was better at early blooming stage and blooming stage.The treatment with 800 mg/L GA₃+1mmol/L Spd at end flowering stage showed a better effect.?6?Exogenous GA₃ and Spd significantly promoted the accumulation of endogenous polyamines in plants,and increased with the increase of exogenous GA₃and Spd concentrations.However,there was a limit value for the effect of exogenous GA₃ and Spd on the accumulation of endogenous polyamines,the concentration of exogenous GA₃ and Spd did not increase infinitely.When 2 400 mg/L GA₃ was treated with 1 mmol/L Spd,the synthesis of polyamines was inhibited.High concentration of GA₃?2 400 mg/L?and medium concentration of Spd?0.1 mmol/L?had synergistic effect on the increase of endogenous polyamines in plants.?7?The change trend of key enzymes in polyamine synthesis was consistent with those of endogenous polyamines.Both of them declined with the senescence of flowers.GA₃ and Spd treatment increased the content of polyamines and the activity of polyamine synthase during the senescence of plants,and the activity of SAMDC increased the most.It is speculated that SAMDC is an important enzyme regulating the homeostasis of polyamines in organisms.