Abstract: In order to investigate the effects of chilling stress and subsequent recovery on photosystem II(PSII) reaction centers and acceptor side of PSII in tomato, a controlled experiment was conducted in artificial climate chamber of Jinggangshan University. Tomato (Solanum lycopersicum L. cv Zhongshu No.4) with 6-leaf stage was used for this experiment. Two treatments employed were: (1) control(CK): seedlings were cultured in artificial climate chamber with temperature range approximately 18−28℃, photosynthetic photo flux density (PPFD) approximately 600μmolm−2s−1, 12h photoperiod. (2) Chilling(CL): seedlings were transferred at the beginning of the photoperiod(7：00) to artificial climate box(ZRY-YY1000, Ningbo, China) with a 12h photoperiod and 200μmolm−2s−1 PPFD and temperature of 8℃. The CL treatment lasted 4 days and the plants were transferred at the beginning of the photoperiod(7：00) to the artificial climate chamber at normal temperature for 4 days. Throughout the experiment, chlorophyll fluorescence transient was examined in the youngest developmental leaf under chilling stress and subsequent recovery periods. The results showed that chilling reduced the photochemical efficiency and photosynthetic performance of PSII in tomato leaves, and induced photoinhibition. Chilling decreased the numbers of active PSII reaction centers per cross section(RC/CS) and the efficiency that a trapped electron can move further ahead of QA−(Ψo). Chilling also decreased the specific energy fluxes per cross section for absorption (ABS/CS), trapping(TRo/CS), electron transport(ETo/CS), and the quantum yield of electron transport beyond QA−(φEo), which suggested that chilling inhibited the photosynthetic electron transportation. At the same time, chilling also initiated defense mechanism: first, chilling induced the reversible inactivation of PSII reaction center and promoting heat dissipation to decrease of the absorption and transportation of light energy, and reduction the accumulation of excess excitation energy. Soon afterwards, chilling increased the capacity of PQ in the PSII receptor side to prevent the accumulation of excess excitation energy in PSII. In this study, chilling mainly inhibited PSII activity, but had little effect on PSI. The absorption of light energy by antenna pigment and the capture of light energy by PSII reaction centers were easier to recover than electron transfer, and high light would aggravate the degree of photoinhibition at the early stage of recovery.

Key words: Solanum lycopersicum L., Chilling, Photoinhibition, Chlorophyll fluorescence transient