Leaf-type ferredoxin-NADP(H) oxidoreductase, encoded by AtLFNR1 gene in Arabidopsis, extensively exists in chloroplast stroma and thylakoids and is responsible for the reduction of NADP + to NADPH in PSI. To investigate the relationship between the characteristics of chlorophyll a fluorescence transients OJIP and the function of AtLFNR1 protein, the fluorescence rise kinetics OJIP curves of AtLFNR1 mutant leaves were determined. It is observed that AtLFNR1 mutant has a lower level of variable fluorescence intensity relative to wild type, especially the J-step and the IP-phase. The JIP-test analysis suggests that the loss of AtLFNR1 function decreases clearly the oxidation rate of plastocyanin as well as PSI reaction center, damages slightly PSII antenna size and pigment assemblies, but stimulates distinctly the photosynthetic activity of PSII. Such multiple effects contribute to the change of shape characteristics of the OJIP transient curve in AtLFNR1 mutant.
Alamethicin (AMT) is a linear antimicrobial peptide isolated from fungi Trichoderma viride. To date, the mode of action of AMT in plant cells remains unknown. Our experimental results indicate that AMT causes leaf lesion attributed to its multiple effects on PSII. AMT decreases the O2 evolution rate of PSII. Based on chlorophyll fluorescence data, similar to the classical herbicide diuron, AMT interrupts PSII electron transfer beyond QA at the acceptor side, leading to the inactivation of the PSII reaction centers. Additionally, AMT decreases chlorophyll content and destroys the architecture of PSII pigment assemblies. However, AMT does not affect the oxygen-evolving complex at the donor side of PSII. Thus, it is concluded that AMT is a natural photosynthetic inhibitor with several action sites in PSII.Additional key words: bioherbicide; chlorophyll a fluorescence; leaf lesion; natural product. transport rate; FV/FM -maximum quantum yield of PSII photochemistry; OEC -oxygen-evolving complex; qP -photochemistry quenching coefficient; RCs -reaction centers; ROSreactive oxygen species; TAP -Tris-acetate-phosphate; TR0 -trapping flux.
Photooxidative damage to the needle leaves of evergreen trees results from the absorption of excess excitation energy. Efficient dissipation of this energy is essential to prevent photodamage. In this study, we determined the fluorescence transients, absorption spectra, chlorophyll contents, chlorophyll a/b ratios, and relative membrane permeabilities of needle leaves of Pinus koraiensis, Pinus tabulaeformis, and Pinus armandi in both cold winter and summer. We observed a dramatic decrease in the maximum fluorescence (F
m) and substantial absorption of light energy in winter leaves of all three species. The F
m decline was not correlated with a decrease in light absorption or with changes in chlorophyll content and chlorophyll a/b ratio. The results suggested that the winter leaves dissipated a large amount of excess energy as heat. Because the cold winter leaves had lost normal physiological function, the heat dissipation depended solely on changes in the photosystem II supercomplex rather than the xanthophyll cycle. These findings imply that more attention should be paid to heat dissipation via changes in the photosystem complex structure during the growing season.
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