Impacts of night late frost on photosystem II components of three black poplar (Populus nigra L.) clones

It is of crucial importance to assess the performance of the photosystem II efficiency, as the most powerful system in light reactions of photosynthesis that is able to provide required electron of system by splitting water. Late frost occurred mostly in growing season and during night in early spring often results in weakness and even death of plants. Therefore, selecting tolerant varieties is one of the most efficient methods to deal with late frost. Due to high diversity and wide dispersal, poplars significantly contribute to the worldwide supply of cellulosic resources. In order to investigate the effect of night late frost on functional component of photosystem II and a number of related physiological traits, seedlings of three clones of black poplar (Populus nigra L.) were exposed to the minimum night temperature of 16, 4, 0 and –20 °C for three nights. To assess the revival potential, seedlings were further maintained in optimum temperature for 14 days. Data were analyzed using a factorial model with two factors of clone and minimum night temperature for each step of the stress and revival. Results revealed that maximum and quantum yield efficiency of photosystem II in different clones has different reduction patterns according to the efficiency of water splitting complex and plastoquinon pool (PQ). Thus, Iranian clone was concluded to be more sensitive than other clones. This difference was discussed in association with total soluble sugar, proline and chlorophyll concentration and electrolyte leakage rate of cytoplasmic membrane. In addition, the recovery process of the clones in revival period was discussed.