Photochemical responses of cucumber (Cucumis sativus L.) plants to heat stress

Ali Doğru

doi:10.15835/nsb12410815

Abstract

In this study, photochemical responses of cucumber (Cucumis sativus L.) cultivar, ‘Beith Alpha F1’, under moderate and severe heat stress (45 °C and 55 °C, 4 hours) was studied. Chlorophyll a fluorescence measurement and the results of the JIP test indicated that severe heat stress was more drastically affected the photosynthetic activity as compared to moderate heat stress in the cotyledons of cucumber plants. Severe heat stress, for example, led to the increased level of Fo and decreased level of Fm, Fv/Fo, and Fv/Fm, suggesting remarkable photoinhibition on electron transport reactions in cucumber plants. Also, severe heat stress caused the increased level of accumulation of inactive reaction centers, resulting in a decreased amount of trapped light energy and electron transport on PSII. The enhanced values of DIo/RC and fDo in the cotyledons of cucumber plants indicated that the trapped energy cannot be used for photochemical reactions and lost as heat. Consequently, the reduction of the plastoquinone pool was partly inhibited due to the decreased yield of photochemistry. As a result, it may be concluded that severe heat stress inhibited PSII activity in several points and decreased photosynthetic yield in the cotyledons of cucumber plants.

Highlights

Rising temperature due to climate change poses a serious threat to agricultural yields worldwide (Wang et al, 2018)
In this study, chlorophyll a fluorescence measurement was used to investigate the performance of the photosynthetic apparatus in cucumber cotyledons under moderate and severe heat stress
The maximum quantum efficiency of photosystem II (PSII) in the cucumber cotyledons was not affected by moderate heat stress (45 °C), but severe heat stress (55 °C) significantly reduced Fv/Fm (Table 2)

Summary

Introduction

Rising temperature due to climate change poses a serious threat to agricultural yields worldwide (Wang et al, 2018). The growing need for food and agricultural yield losses due to global warming show that food security needs to be improved urgently (Abdelrahman et al, 2017). For this reason, it is very important to investigate the physiological, biochemical, and molecular responses of plants against heat stress. The effect of heat stress on plant metabolism varies depending on the temperature, the exposure time, and the rate of increase in temperature (Wahid et al, 2007). The exposure time of the plant must be longer for cellular damage or death to occur.

Objectives

Methods

Results

Conclusion