JOURNAL OF NANJING FORESTRY UNIVERSITY ›› 2023, Vol. 47 ›› Issue (4): 103-113.doi: 10.12302/j.issn.1000-2006.202108034

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Effects of 1-MCP pretreatment on photosynthetic characteristics and related gene expression of rhododendron seedlings under heat stress

WANG Lulu(), GENG Xingmin(), HUAN Zhiqun, XU Shida, ZHAO Hui   

  1. College of Landscape Architecture, Nanjing Forestry University, Nanjing 210037, China
  • Received:2021-08-19 Revised:2021-11-29 Online:2023-07-30 Published:2023-07-20

Abstract:

【Objective】 Our goals are to reveal regulatory mechanisms of ethylene on the heat tolerance of rhododendron seedlings, and to examine the effects of ethylene receptor inhibitor 1-MCP pretreatment on the heat tolerance and the photosynthetic system of rhododendron seedlings under high temperature stress.【Method】Two Rhododendron cultivars with different heat resistance were used to analyze the effects of 1-MCP pretreatment on the heat damage index, photosynthetic pigment content, photosynthetic gas exchange parameters and chlorophyll fluorescence parameters of rhododendron leaves under high temperature stress. Furthermore, the transcriptome data of ‘Hong Yue’ were used to analyze the transcriptional regulation of 1-MCP pretreatment and high temperature stress on the related photosynthetic pathway genes.【Results】High temperature stress reduced net photosynthetic rate (Pn), photosynthetic pigment content, fluorescence maximum (Fm), potential photochemical activity (Fv/Fo) and maximal photochemical efficiency (Fv/Fm), whereas it increased fluorescence origin (Fo) in the two Rhododendron cultivars. However, the change ranges of these indexes were smaller in ‘Yanzhi Mi’ than in ‘Hong Yue’. The pretreatment with appropriate concentrations of 1-MCP slowed down the decline of chlorophyll content under high temperature stress, maintained the stability of relevant indexes of photosynthetic system of rhododendron leaves, alleviated the damage of photosynthetic apparatus induced by heat stress, and reduced the degree of photoinhibition. Changes of the parameters of the PSⅡ reaction center activity showed that the absorption flux per reaction center (ABS/RC) increased significantly in the leaves of the two Rhododendron cultivars, while the rate of electron transport flux of the photosystem Ⅱ reaction center (ETo/RC) decreased under high temperature stress. The quantum yield of light energy absorption, capture and electron transfer per unit area decreased significantly, suggesting that the electron transfer of the PSⅡ was blocked. The pretreatment with appropriate concentrations of 1-MCP slowed down the decline of electron transport (ETo/CSm), absorption (ABS/CSm), trapping (TRo/CSm) in the PSⅡ cross-section of the two Rhododendron cultivars. The pretreatment also alleviated the overreduction of electron transfer chain by increasing electron transfer per unit reaction center and the obstruction of electron transfer in the PSⅡ reaction center under high temperature stress. The transcriptional data analysis of ‘Hong Yue’ showed that the expression of all 30 DEGs related to the photosynthetic pathway, except the psbA, were down-regulated under high temperature stress, while 1-MCP pretreatment alleviated the decline of transcription levels of genes related to the photosynthetic pathway to a certain extent, but the variation trend was not significant.【Conclusion】 High temperature stress inhibits the photosynthetic efficiency of rhododendron leaves, and Rhododendron cultivars with high heat-resistant may maintain the stability of photosynthetic system under high temperature stress. The pretreatment with appropriate concentrations of 1-MCP can effectively improve the photosynthetic capacity of rhododendron leaves and alleviate the symptoms of heat stress.

Key words: rhododendron, heat stress, 1-MCP, photosynthesis

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