Lipoxygenase in singlet oxygen generation as a response to wounding: in vivo imaging in Arabidopsis thaliana

Abstract

Wounding, one of the most intensive stresses influencing plants ontogeny and lifespan, can be induced by herbivory as well as by physical factors. Reactive oxygen species play indispensable role both in the local and systemic defense reactions which enable “reprogramming” of metabolic pathways to set new boundaries and physiological equilibrium suitable for survival. In our current study, we provide experimental evidence on the formation of singlet oxygen (1O2) after wounding of Arabidopsis leaves. It is shown that 1O2 is formed by triplet-triplet energy transfer from triplet carbonyls to molecular oxygen. Using lipoxygenase inhibitor catechol, it is demonstrated that lipid peroxidation is initiated by lipoxygenase. Suppression of 1O2 formation in lox2 mutant which lacks chloroplast lipoxygenase indicates that lipoxygenase localized in chloroplast is predominantly responsible for 1O2 formation. Interestingly, 1O2 formation is solely restricted to chloroplasts localized at the wounding site. Data presented in this study might provide novel insight into wound-induced signaling in the local defense reaction.

Singlet Oxygen Plays an Essential Role in the Root’s Response to Osmotic Stress

“…However, it is important to keep in mind that elimination of singlet oxygen specifically by the scavenger His was also potent in reducing cell death. Interestingly, wounded leaves were shown to produce singlet oxygen that was diminished in the lipoxygenase mutant lox2 (Prasad et al, 2017). As shown here, the inhibition of the PEG responses by the reversible inhibitor of lipoxygenase, SHAM, is consistent with this result.…”

Oxygen and ROS in Photosynthesis

“…Autooxidation of PQH 2 is one possible mechanism (Figure 4 [61]. The equilibrium constant for Reaction (116) was estimated to be 10 −9.2 [301], which shows that the formation of PQH • via Reaction (116) is negligible. Thus, the apparent rate of O 2…”

“…The forward and reverse second-order rate constants for the formation of O2 •− by PQ •− (Reaction (31)) are kforward ~ 10 8 M −1 s −1 and kreverse ~ 7 × 10 7 M −1 s −1 [61]. The equilibrium constant for Reaction (116) was estimated to be 10 −9.2 [301], which shows that the formation of PQH • via Reaction (116) is negligible. Thus, the apparent rate of O2 •− production in the PQ pool is determined by the rate of PQ •− appearance, rate of O2 •− production via reaction of O2 with PQ •− (Reaction (31)) and the rate of O2 •− removal from the equilibrium Reaction (31).…”

“…The lack of FLU, a nuclear-encoded chloroplast protein that plays a key role during the negative feedback control of Chl biosynthesis, leads to the accumulation of protochlorophyllide in plastids and, consequently, to photosensitized generation of 1 O 2 [115]. It has been recently shown that lipoxygenase localized in the chloroplast is responsible for 1 O 2 formation [116]. Lipoxygenase initiates lipid oxidation to corresponding lipid peroxides, which decompose to lipid peroxyl radicals (LOO • ).…”

“…These rates were calculated assuming that PQH 2 oxidation by O 2 is a second-order chemical reaction and the oxidation of PQH 2 occurs in the volume of thylakoid membrane. The steady-state concentration of PQ •− inside the thylakoid membrane produced via reaction (116) can be estimated to be about 10 −8 M. The following values were used in the calculations: amount of photoactive PQ, 14 × 10 −3 mol PQ (mol Chl) −1 [248]; volume of thylakoid membrane, 4.6 × 10 −6 L (mg Chl) −1 [304]; molar mass of Chl, 894 g mol −1 [304]; the equilibrium constant for reaction (116) was taken as 10 −10 ; and the ratio of PQ and PQH 2 was taken as 1/9. If O 2 •− is very rapidly removed and therefore Reaction (31) [252].…”