Photosynthetic induction in leaves of two cucumber genotypes differing in sensitivity to low-light stress

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.