Response of photosynthesis in leaves of Sorghum bicolor×S. sudanense seedlings to phenanthrene polluted soils

In the present study, the effects of phenanthrene (Phe) polluted soils on celerity chlorophyll fluorescence kinetics parameters of Sorghum bicolor×S. sudanense seedlings were studied. The results showed that these parameters such as Fm, Fv/Fm, Fv/Fo and PIABS of the studied plants decreased with the increase of Phe concentrations which indicated that the Phe in soils inhibited the PSⅡ photochemical activities of these studied S. bicolor×S. sudanense seedlings. The study about electronic supply and transmission capacity of electronic donor side and receptor side of the PSⅡ showed that the fluorescence intensity increased and the activity of oxygen-evolving complex (OEC) decreased over 0.3 ms (K point) of OJIP curve in studied samples. Phe stressing also caused the the fluorescence intensity increasement at the J point and I point on the OJIP curve in the leaves of Phe stressed S. bicolor×S. sudanense seedlings which indicated that Phe stress reduced the electronic acceptance ability at the electronic receptor side of PSⅡ and blocked the electronic transmission from QA to QB. The optical energy absorption and distribution in leaves of S. bicolor×S. sudanense seedlings were significantly influenced by Phe stress. With the increase of Phe concentration, the ratio of optical energy absorbed by PSⅡ reaction center and used for electron transfer after QA- as well as the energy absorbed by each unit reaction center and used for electron transfer reduced in the leaves of treated S. bicolor×S. sudanense seedlings. It indicated that the proportion of optical energy captured by reaction center and used for photochemical reaction reduced and the proportion of invalid heat dissipation increased. Based on these results, it could be suggested that there were three important reasons for the reduction of PSⅡreactive center activity in leaves of S. bicolor×S. sudanense seedlings in the Phe stress soil which included the damage of OEC at electron donor side of PSⅡ, the electron transfer ability reduction at the electron acceptor side of PSⅡ and the change of the distribution and utilization of optical energy.