Abstract

Low light is one of the most important stress factors affecting cucumber production in China greenhouse. Two cucumber genotypes (Cucumis sativus L.), Deltastar with low light-tolerance and Jinyan No. 2 with low light-sensitivity were used to study the response of gas exchange, chlorophyll fluorescence, stomatal opening and ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) activity to low light during photosynthetic induction. In this experiment, cucumber plants were exposed to 75 to 100 μmol·m^-2·s^-1 (control light 500 to 550 μmol·m^-2·s^-1) at 25 or 17°C (day/night) for 20 days. Photosynthetic induction was determined during cultivation after pre-dark 14 to 16 h. The results showed that there were stomatal and non-stomatal limitations (biochemical limitation) during induction of leaf photosynthesis. However, the biochemical limitation played a primary role in the early stage, but the stomatal limitation was predominant in the later stage during the whole photosynthetic induction. The time of net photosynthetic rate (P_N), stomatal conductance (g_s), actual photosystem II efficiency (Ф_PSII), linear electron transport rate (J) and non-photochemical quenching (NPQ) to reach maximal levels (steady-state) of cucumber leaves acclimated to low-light displayed longer induction process when compared with that under control light condition. Moreover, Jinyan No. 2, the low light-sensitive genotype, showed a longer start time of photosynthesis (STP), lower P_N, Ф_PSII, degree of stomatal opening and Rubisco activation state, as well as higher NPQ than those of Deltastar.

Key words: Cucumis sativus, low light, photosynthetic induction, chlorophyll a fluorescence, Rubisco, stomata.

Abbreviation

Chl, Chlorophyll; C_i, intercellular CO₂ concentration; CT, the control level light; F_o, minimal fluorescence in dark-adapted state; F_m, maximum fluorescence in dark-adapted state; F_v, maximum variable fluorescence in dark-adapted state (=F_m-F_o); F_v / F_m, maximum quantum yield of photosystem II photochemistry; F_s, steady-state fluorescence under irradiance; F_m′, maximum fluorescence in light-adapted state; F_v′, maximum variable fluorescence in light-adapted state (=F_m′-F_o′); g_s, stomatal conductance; J, the linear electron transport rate; LL, low light; L_s, stomata limitation value; NPQ, non-photochemical quenching; P_N, net photosynthetic rate; PPFD, photosynthetic photon flux density;PSII, photosystem II; Ð¤_PSII, the actual photosystem II efficiency under irradiance;Rubisco, ribulose-1, 5-bisphosphate carboxylase/oxygenase; RuBP, ribulose-1,5-bisphosphate; STP, starting time of photosynthesis.