Classification and summary of heat tolerance of Eupatorium adenophorum by OJIP using rapid chlorophyll a fluorescence kinetics curve by Handy PEA
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In the past 20 years, the rapid chlorophyll a fluorescence kinetics OJIP curve and JIP-test analysis based on the energy flow theory in biofilm have been characterized by losslessness, precision and rapidity, and have been widely used in the study of plant stress physiology. 
The OJIP curve is very sensitive to changes in various environments, such as light stress, chemicals, heat, cold, drought, heavy metal or salt stress, malnutrition, increased atmospheric CO2 or ozone, and disease growth. After the plants suffered different stresses, their OJIP curves showed different changes, while the JIP-test analysis provided quantitative analysis of the changes in the OJIP curve. Therefore, OJIP curves and JIP-test analysis can be used to analyze the effects of environmental changes on plant photosynthetic physiological processes and to screen for resistant varieties .
Eupatorium adenophorum is a global invasive species originating in Mexico. In the 1940s, E. adenophorum was introduced from Myanmar to Yunnan and has now invaded provinces such as Guangxi, Guizhou, Sichuan and Chongqing. Its invasion caused damage to local ecosystems and economic losses.
Temperature and humidity are two important ecological factors that affect the invasion and spread of Eupatorium adenophorum. The purpose of this study was to screen heat-tolerant varieties in different E. adenophorum populations, determine the effects of heat stress on the two photosystems, and explore the mechanisms for obtaining heat resistance. This helps to identify the direction of invasion and spread of Eupatorium adenophorum and assess the risk of its spread.
In this study, the OJIP curve of four Eupatorium adenophorae under heat stress was measured using the plant efficiency analyzer Handy PEA manufactured by Hansatech , UK , and the chlorophyll fluorescence parameters were analyzed in depth.
The whole plant of four E. adenophorum from South China was exposed to 40 °C, and classified into three types according to the degree of plant damage and rapid chlorophyll fluorescence kinetics: sensitive, intermediate, and tolerant. .
Performance of four Eupatorium adenophorae under heat stress
According to the analysis of JIP-test, the inhibition of oxygen release complex (OEC) and the deactivation of PS2 reaction center are the main causes of thermal damage. At moderate heat stress (<40 °C), OEC was slightly damaged but did not cause a significant K point on the OJIP curve. In severe heat stress (≥40 °C), irreversible significant damage on OEC resulted in a significant increase in K-point.
F O -F K normalization, ΔW OK and ΔW L 
F O -F P normalization and ΔW OJ
In addition, the deactivation of the PS2 reaction center, the decrease in the electron transport rate of PS2, the destruction of the PS2 antenna structure, the loss of PS2 photochemical activity, and the increase in PS1 activity also occur. Moreover, tolerant photosynthetic activity suffers less damage than intermediate and sensitive varieties.
Changes in chlorophyll fluorescence parameters
At the end of the paper, based on the extremely significant linear correlation between the thermal stress sensitive parameters PIABS and VK, the thermal sensitivity index HSI is proposed, which can be used to screen and rank the heat tolerance of different E. adenophorum varieties. The smaller the HSI, the higher the heat resistance.
The article also mentions that the heat resistance of the four E. adenophorum is significantly correlated with the extreme high temperature of the environment. This indicates that the heat resistance of E. adenophorum is derived from its adaptation to high ambient temperatures, which increases the possibility of further invasion of E. adenophorum into the tropics.
Source of this article:
Qiang S , Chen S , Ret o Jörg Strasser, et al. Classification and characteristics of heat tolerance in Ageratina adenophora populations usingfast chlorophyll a fluorescence rise OJIP[J]. Environmental &Experimental Botany, 2016, 122:126-140.
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