Exogenous spermidine maintains the chloroplast structure of cucumber seedlings and inhibits the degradation of photosynthetic protein complexes under high-temperature stress
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Cucumbers (Cucumis sativus L.) are thermophilic horticulture crop but do not tolerate high temperature. The photosynthesis of cucumber under high temperature is highly susceptible to damage. To study the physiological mechanism of exogenous spermidine (Spd) on cucumber photosynthesis under heat stress, the sensitive cucumber cultivar ‘Jinchun no. 2’ was grown in substrate culture at a high temperature in an artificial climate box and treated with 1.0 mmol L−1 Spd under high-temperature stress (42/32 °C). The results showed that exogenous Spd alleviated the photosynthetic damage caused by heat shock, added the chlorophyll content and maintained the chloroplast structures relatively intact. Western blotting analysis showed that exogenous Spd inhibited the degradation of photosynthetic proteins, slowed the dissociation of the protein complexes, and maintained the stability of light-harvesting complexes (LHCs) in cucumber leaves under high-temperature stress. Twenty-two differentially expressed thylakoid membrane proteins involved in different photosynthetic processes were successfully authenticated by sodium dodecyl sulphate (SDS)-urea-PAGE and Blue native-polyacrylamide gel electrophoresis (BN-PAGE). The results showed that exogenous Spd regulated the expression of photosynthetic and bursal somatic membrane proteins, which resulted in adaptive changes under high-temperature stress at the transcriptional and translational levels, inhibited the degradation of thylakoid membrane proteins in cucumber leaves, and maintained the stable structure of the thylakoid membrane. Collectively, these results suggested that exogenous Spd alleviated high temperature-induced photosynthesis damage by improving the expression and synthesis of thylakoid membrane proteins, mitigating the dissociation of LHCII–Chl and thylakoid membrane protein complexes and maintaining the integrity and functional stability of the photosynthetic organ structure.
KeywordsChloroplast ultrastructure Cucumis sativus L. High-temperature stress Spermidine Thylakoid membrane proteins
- 2-D BN/SDS-PAGE
Two-dimensional blue-native/SDS–polyacrylamide gel electrophoresis
Blue native-polyacrylamide gel electrophoresis
- Cyt b6/f
Light-harvesting complex II
Light-harvesting chlorophyll a/b binding protein
Photosynthetic photon flux density
Sodium dodecyl sulphate
Sodium dodecyl sulphate–polyacrylamide gel electrophoresis
This work was financially supported by the National Natural Science Foundation of China (Nos. 31471869, 31401919, and 31272209), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PDPA), the China Agriculture Research System (CARS-25-C-03) and the Research Fund for the Doctoral Program of Higher Education (20130097120015).
Compliance with ethical standards
Conflict of interest
The authors have no conflicts of interest to declare.
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