Intrinsic Fluctuations in Transpiration Induce Photorespiration to Oxidize P700 in Photosystem I

Abstract

Upon exposure to environmental stress, the primary electron donor in photosystem I (PSI), P700, is oxidized to suppress the production of reactive oxygen species that could oxidatively inactivate the function of PSI. The illumination of rice leaves with actinic light induces intrinsic fluctuations in the opening and closing of stomata, causing the net CO2 assimilation rate to fluctuate. We examined the effects of these intrinsic fluctuations on electron transport reactions. Under atmospheric O2 conditions (21 kPa), the effective quantum yield of photosystem II (PSII) (Y(II)) remained relatively high while the net CO2 assimilation rate fluctuated, which indicates the function of alternative electron flow. By contrast, under low O2 conditions (2 kPa), Y(II) fluctuated. These results suggest that photorespiration primarily drove the alternative electron flow. Photorespiration maintained the oxidation level of ferredoxin (Fd) throughout the fluctuation of the net CO2 assimilation rate. Moreover, the relative activity of photorespiration was correlated with both the oxidation level of P700 and the magnitude of the proton gradient across the thylakoid membrane in 21 kPa O2 conditions. These results show that photorespiration oxidized P700 by stimulating the proton gradient formation when CO2 assimilation was suppressed by stomatal closure.

Photosynthetic Parameters Show Specific Responses to Essential Mineral Deficiencies

“…The pmf consumption rate is equal to JgH + = gH + × pmf = kH + × Jf [5,6]; then, pmf = (kH + × Jf)/gH + = JgH + /gH + . Generally, the decrease in the net CO 2 assimilation is reflected as a decrease in Y(II), accompanied by an enhanced decrease in gH + , compared to the decreases in both (kH + × Jf) and JgH + [7,11]. The pmf subsequently increases.…”

Photosynthetic Linear Electron Flow Drives CO2 Assimilation in Maize Leaves

“…50%) was much smaller than that in g H + (ca. 85%) at 21, but not at 1 kPa O 2 ( Figure 5 B), indicating that photorespiration contributes to sustaining LEF, resulting in the H + accumulation into the thylakoid lumen ( Figure 5 A and Figure 11 ) [ 19 , 41 ]. In maize, LEF decreased almost concomitantly with g H + , different from mustard ( Figure 5 D) [ 33 ].…”

Stomatal Closure Sets in Motion Long-Term Strategies of Plant Defense Against Microbial Pathogens

“…The increase in photorespiration occurred under conditions of biotic (microbial infection) or abiotic stress (drought) (Lal et al, 1996 ; Pascual et al, 2010 ; Voss et al, 2013 ; Vo et al, 2021 ). Even fluctuations in transpiration triggered an increase in photorespiration (Furutani et al, 2020 ). The enhanced photorespiration and the associated rise in H 2 O 2 could confer disease resistance (Taler et al, 2004 ; Kubo, 2013 ; Sørhagen et al, 2013 ).…”