Characterization of photosynthetic electron transport chain in bioenergy crop Jerusalem artichoke (Helianthus tuberosus L.) under heat stress for sustainable cultivation.

摘要

In order to explore the response of photosynthetic electron transport chain to heat stress, chlorophyll a fluorescence and modulated 820 nm reflection transients were examined in the leaves of Jerusalem artichoke (Helianthus tuberosus L.). J step was elevated at 43 degrees C, suggesting that electron transport beyond primary quinone electron acceptor of photosystem II (Q_A) was inhibited. I step was elevated at 45 degrees C due to the lowered plastoquinol re-oxidation rate. Significant decrease in the Q_A reducing reaction centers per photosystem II (PSII) antenna chlorophyll and marked increase in relative variable fluorescence intensity at 300 micro s also occurred at 45 degrees C, indicating that the electron transport chain from PSII donor side to Q_A was injured. Overall, the fragment between Q_A and plastoquinol is the most susceptible to heat in the electron transport chain before photosystem I (PSI). The maximal photochemical capacity of PSI was not affected by heat stress even at 48 degrees C, and the interaction between PSII and PSI become unbalanced, when temperature rose to 45 degrees C. At 45 degrees C, prolonged PSI oxidation occurred in the expanding leaves because of the inhibited electron donation from PSII, however, PSI oxidation amplitude decreased in the expanded leaves. We infer that electron transport chain of PSI acceptor side is more sensitive to heat stress than the chain before PSI in the expanded leaves. Therefore, electrons in PSI reaction center could not be efficiently drained to the downstream at high temperature, and then PSI oxidation was blocked.