Photosynthesis and non-photochemical excitation quenching components of chlorophyll excitation in maize and field bean during chilling at different photon flux density

Abstract

The influence of chilling (8 °C, 5 d) at two photon flux densities [PFD, L = 200 and H = 500 μmol(photon) m−2 s−1] on the gas exchange and chlorophyll fluorescence was investigated in chilling-tolerant and chilling-sensitive maize hybrids (Zea mays L., K383×K130, K185×K217) and one cultivar of field bean (Vicia faba L. minor, cv. Nadwiślanski). The net photosynthetic rate (P N) for the both studied plant species was inhibited at 8 °C. P N of both maize hybrids additionally decreased during chilling. Changes in the quantum efficiency of PS2 electron transport (ΦPS2) as a response to chilling and PFD were similar to P N. Measurements of ΦPS2/ΦCO2 ratio showed that in field bean seedlings strong alternative photochemical sinks of energy did not appear during chilling. However, the high increment in ΦPS2/ΦCO2 for maize hybrids can indicate reactions associated with chill damage generation. At 8 °C the non-photochemical quenching (NPQ) increased in all plants with chilling duration and PFD. The appearance of protective (qI,p) and damage (qI,d) components of qI and a decrease in qE (energy dependent quenching) took place. NPQ components of field bean and maize hybrids differed from each other. The amount of protective NPQ (qE + qI,p) components as part of total NPQ was higher in field bean than in maize hybrids at both PFD. On 5th day of chilling, the sum of qE and qI,p was 26.7 % of NPQ in tolerant maize hybrids and 17.6 % of NPQ in the sensitive one (averages for both PFD). The increased PFD inhibited the ability of all plants to perform protective dissipation of absorbed energy. The understanding of the genotypic variation of NPQ components in maize may have implications for the future selection of plants with a high chilling tolerance.