2Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, 119334 Moscow, Russia
3Moscow Secondary School 261, 121108 Moscow, Russia
4Lomonosov Moscow State University, Faculty of Biology, 119991 Moscow, Russia
5Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, 127276 Moscow, Russia
* To whom correspondence should be addressed.
Received June 15, 2016; Revision received September 7, 2016
The kinetics of irradiation-induced changes in leaf optical transparence (ΔT) and non-photochemical quenching (NPQ) of chlorophyll fluorescence in Tradescantia fluminensis and T. sillamontana leaves adapted to different irradiance in nature was analyzed. Characteristic times of a photoinduced increase and a dark decline of ΔT in these species were 12 and 20 min, respectively. The ΔT was not confirmed to be the main contributor to the observed middle phase of NPQ relaxation kinetics (τ = 10-28 min). Comparison of rate of photoinduced increase in ΔT and photosystem II quantum yield recovery showed that the former did not affect the tolerance of the photosynthetic apparatus (PSA) to irradiances up to 150 µmol PAR·m–2·s–1. Irradiance tolerance correlated with the rate of “apparent NPQ” induction. Considering that the induction of apparent NPQ involves processes significantly faster than ΔT, we suggest that the photoprotective mechanism induction rate is crucial for tolerance of the PSA to moderate irradiance during the initial stage of light acclimation (first several minutes upon the onset of illumination).
KEY WORDS: Tradescantia, excessive light stress, leaf optical transparence, chlorophyll fluorescence