title: [Responses of primary photochemical reactions in apple fruit peel to the changes of incident PFD and air temperature in sunny days].
abstract: Taking Malus domestica Borkh as test object, this paper studied the primary photochemical reactions and xanthophyll cycle in its fruit peel in response to the diurnal changes of incident photon flux density (PFD) and air temperature in sunny days. With the increase of PFD and air temperature in a daily cycle, a severe photo-inhibition of the primary photochemical reactions in M. domestica fruit peel occurred from 12:00 to 14:00. The relative variable fluorescence at 300 micros of chlorophyll a fluorescence transient (Wk) did not change significantly through the day, which indicated that the activity of oxygen evolving complex (OEC) was not damaged by strong light and high temperature. However, the efficiency that a trapped exciton moved an electron into the electron transport chain beyond QA(-) (Psio) was reduced from 12:00 to 14:00, indicating that the acceptor side of PS II in apple fruit peel was damaged. Strong light decreased the density of PS II reaction centers per excited cross-section (RC/CS), which induced the increase of the energy absorption per active reaction center (ABS/RC). However, the excited energy was not able to be efficiently used via photochemical reaction (TRo/RC), resulting in an increase in non-photochemical energy dissipation per active reaction center (DIo/RC). Along with the appearance of photo-inhibition, the de-epoxidation level of xanthophyll pigment pool (PRI) increased markedly, showing that the xanthophyll cycle in fruit peel was enhanced by strong light to dissipate excess excitation energy to prevent photosynthetic apparatus from further damage. Both strong light and high temperature enhanced the photo-inhibition in apple fruit peel, and the effect of strong light was significantly more prominent than that of high temperature during a day.
authors.affiliation: Shandong Institute of Pomology, Tai'an 271000, Shandong, China. sunshan03@163.com
authors.forename: Shan
authors.initials: S
authors.lastname: Sun
authors.forename: Li-Tao
authors.initials: LT
authors.lastname: Zhang
authors.forename: Hui-Yuan
authors.initials: HY
authors.lastname: Gao
authors.forename: Huai-Rui
authors.initials: HR
authors.lastname: Shu
authors.forename: Lai-Ping
authors.initials: LP
authors.lastname: Wang
mesh_terms: D005638:Fruit / Q000378:metabolism / Q000528:radiation effects*; D006358:Hot Temperature; D027845:Malus / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D055668:Photochemical Processes / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism / Q000528:radiation effects*; D013472:Sunlight
chemical_list: D045332:Photosystem II Protein Complex