Changes in apple leaf and fruit peel photosystem-II photochemistry under high light conditions

Changes in apple leaf and fruit peel photosystem-II (PSII) photochemical processes were investigated under field high light conditions (1800 µmol m^-2 s^-1) in North Patagonia.
This was done to increase understanding of its susceptibility to photooxidative damage.
Leaves and fruits growing exposed (E), non-exposed (NE), and suddenly-exposed (SE) to high solar radiation were picked 110 days after full bloom (DAFB). Chlorophyll content (Chl), chlorophyll a fluorescence transient (OJIP), and membrane peroxidative damage were evaluated.
Total Chl decreased 26.6 and 20.6% with high light exposure in E and SE fruits respectively, while in E leaves Chl was decreased by 24.2% with respect to NE leaves.
Chl a minimum fluorescence (F_o) decreased in E fruits.
While maximum fluorescence (F_m), maximum quantum yield of PSII (F_v/F_m), and performance index on absorption basis (PI_abs) decreased in E and SE fruits and leaves.
Amount of active PSII reactive centers per cross-section (RC/CS) increased in E fruits, while absorption flux (ABS/CS), trapped energy flux (TRo/CS), electron transport flux (ETo/CS), and reduction of end acceptors at PSI electron acceptor side per cross-section (REo/CS) were reduced.
Dissipated energy flux (DIo/CS) increased in SE fruits.
In leaves, only REo/CS and DIo/CS increased at E and SE conditions.
Compared to NE, membrane peroxidative damage increased 21.4 and 11.7% in leaves and 74.8 and 87.9% in fruits at E and SE conditions respectively.
In conclusion, a reduction in PSII photochemistry was observed in fruits at E and SE conditions.
SE conditions seem to be more damaging to the fruits than to the leaves.

I International Apple Symposium

V. Blackhall, G.A. Orioli, M.G. Colavita

high light stress, JIP-test, chlorophyll a fluorescence transient, photooxidative damage, fruit sunburn

https://doi.org/10.17660/ActaHortic.2019.1261.12