Abstract: In order to compare the difference between maize (Zea mays L.) and wheat (Triticum aestivum L.) in response to adaptation from dark to light, the dynamics of non-photochemical quenching (q_N) were observed and analyzed during photosynthetic induction. The results showed that the dynamics of q_N could be classified into three types, which were F-form, M-form and S-form.During the dark adaptation from 15 minutes to 24 hours, wheat had F-form and M-form,while M-from and S-form were showed in maize. There was no marked difference between maize and wheat in F_v/F_m,q_p and Φ_psII,while apparent difference existed in q_N, and the time of reaching the maximum and steady-state of q_N(expressed as TqN_mtx and Tq_N, respectively),which were new parameters defined here, was markedly higher in maize leaves than in wheat leaves when tllumination occurred after dark adaptation. However, there was no apparent difference between maize and wheat in the time needed to reach the steady-state of photosynthetic rate(P_m) and stomatal conductance(G_s) under 1600 μmol·m^-2·s^-1 light intensity after dark adaptation. Meanwhile, the limitation of CO₂ supplied to leaves with plastic film sealing up the leaves in a short period(less than 30 min) had a minimal effect on the dynamics of q_N, which implied that the different dynamics did not result from the start of CO₂ assimilation or stomatal regulstion. The messurement of the typical pattern for oxidation-reduction of P₇₀₀ and the estimate of the functional pool size of intersystem electrons per reaction center supported our belief that the redox state of P₇₀₀ in PSI and the pool size of the intersystem were not the main factors that led to great differences in dynamics of q_N between maise and wheat. However, the analsis of the qN component showed that high-energy state quenching(q_E), state transitional quenching(q_T) and photoinhibitory quenching (q₁) were 55.6%, 18.5%, and 25.9% of q_N when reaching qNmex, respectively, which meant it might be q_E that resulted in the different dynsmics of q_N between maize and wheat. The results suggested that maize(C₄) might have a higher q_E to maintain the proton gradient of thylakoid than wheat (C₃) for adapting to the transition from dark to light and to initate the use of NADPH and ATP by carbon fixation during photosynthetic induction.

Key words: Maize (Zea mays L.), Wheat (Triticum aestivum L.), Photosynthesis, Non-photochemical quenching of chlorophyll fluorescence