title: Thermotolerance of apple tree leaves probed by chlorophyll a fluorescence and modulated 820 nm reflection during seasonal shift.
abstract: During the seasonal shift from June to August, air temperatures increase. To explore how apple trees improve their thermotolerance during this shift, we examined the photochemical reaction capacity of apple tree leaves by simultaneous measurement of prompt chlorophyll fluorescence, delayed chlorophyll fluorescence, and modulated 820 nm reflection at varying temperatures. It was found that the reaction centers and antennae of photosystem II (PSII) and photosystem I (PSI), the donor side of PSII, the electron transfer capacity from QA to QB, and the reoxidation capacity of plastoquinol were all sensitive to heat stress, particularly in June. As the season shifted, apple tree leaves improved in thermotolerance. Interestingly, the acclimation to seasonal shift enhanced the thermotolerance of PSII and PSI reaction centers more than that of their antennae, and the activity of PSII more than that of PSI. This may be a strategy for plant adaptation to changes in environmental temperatures. In addition, results from prompt and delayed fluorescence, as well as modulated 820 nm reflection corroborate each other. We suggest that the simultaneous measurement of the three independent signals may provide more information on thermal acclimation mechanisms of photochemical reactions in plant leaves.
authors: State Key Laboratory of Crop Stress Biology for Arid Areas, College of Horticulture, Northwest A&F University, Yangling, Shaanxi 712100, China.
authors: Ying
authors: Y
authors: Duan
authors: State Key Laboratory of Crop Stress Biology for Arid Areas, College of Horticulture, Northwest A&F University, Yangling, Shaanxi 712100, China.
authors: Mengxia
authors: M
authors: Zhang
authors: State Key Laboratory of Crop Stress Biology for Arid Areas, College of Horticulture, Northwest A&F University, Yangling, Shaanxi 712100, China.
authors: Jin
authors: J
authors: Gao
authors: State Key Laboratory of Crop Stress Biology for Arid Areas, College of Horticulture, Northwest A&F University, Yangling, Shaanxi 712100, China. Electronic address: Lipm@nwsuaf.edu.cn.
authors: Pengmin
authors: P
authors: Li
authors: Department of Biophysics and Radiobiology, Faculty of Biology, St. Kliment Ohridski University of Sofia, 8 Dr. Tzankov Blvd., 1164 Sofia, Bulgaria.
authors: Vasilij
authors: V
authors: Goltsev
authors: State Key Laboratory of Crop Stress Biology for Arid Areas, College of Horticulture, Northwest A&F University, Yangling, Shaanxi 712100, China.
authors: Fengwang
authors: F
authors: Ma
mesh_terms: D000064:Acclimatization; D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism*; D000077194:Chlorophyll A; D007700:Kinetics; D027845:Malus / Q000378:metabolism / Q000502:physiology*; D018515:Plant Leaves / Q000378:metabolism / Q000502:physiology*; D012621:Seasons; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D002734:Chlorophyll; D002245:Carbon Dioxide; D000077194:Chlorophyll A
keywords: Apple tree leaves; Delayed chlorophyll fluorescence; Photochemical reactions; Prompt chlorophyll fluorescence; Seasonal shift; Thermotolerance