Photosynthetic response to low sink demand after fruit removal in relation to photoinhibition and photoprotection in peach
trees
Wei Duan (1), Pei G. Fan (1), Li J. Wang (1), Wei D. Li (1), Shu T. Yan (1) and Shao H. Li (1, 2)
1. Institute of Botany, The Chinese Academy of Sciences, 100093 Beijing, P.R. China / 2. Corresponding author () / Received February 14, 2007; accepted April 4, 2007; published online October 15, 2007
Summary
Diurnal variations in photosynthesis, chlorophyll fluorescence, xanthophyll cycle, antioxidant enzymes and antioxidant metabolism
in leaves in response to low sink demand caused by fruit removal (–fruit) were studied in ‘Zaojiubao’ peach (Prunus persica (L.) Batch) trees during the final stage of rapid fruit growth. Compared with the retained fruit treatment (+fruit), the
–fruit treatment resulted in a significantly lower photosynthetic rate, stomatal conductance and transpiration rate, but generally
higher internal CO2 concentration, leaf-to-air vapor pressure difference and leaf temperature. The low photosynthetic rate in the –fruit trees
paralleled reductions in maximal efficiency of photosystem II (PSII) photochemistry and carboxylation efficiency. The midday
depression in photosynthetic rate in response to low sink demand resulting from fruit removal was mainly caused by non-stomatal
limitation. Fruit removal resulted in lower quantum efficiency of PSII as a result of both a decrease in the efficiency of
excitation capture by open PSII reaction centers and an increase in closure of PSII reaction centers. Both xanthophyll-dependent
thermal dissipation and the antioxidant system were up-regulated providing protection from photo-oxidative damage to leaves
during low sink demand. Compared with the leaves of +fruit trees, leaves of –fruit trees had a larger xanthophyll cycle pool
size and a higher de-epoxidation state, as well as significantly higher activities of antioxidant enzymes, including superoxide
dismutase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase and a higher
reduction state of ascorbate and glutathione. However, the –fruit treatment resulted in higher hydrogen peroxide and malondialdehyde
concentrations compared with the +fruit treatment, indicating photo-oxidative damage.
