Search

Here, we developed a method for measuring the in vivo redox state of the plastoquinone (PQ) pool in the cyanobacteria Synechocystis sp. PCC 6803. Cells were illuminated on a glass fiber filter, PQ was extracted with ethyl acetate and determined with HPLC. Control samples with fully oxidized and reduced photoactive PQ pool were prepared by far‐red and high light treatments, respectively, or by blocking the photosynthetic electron transfer chemically before or after PQ in moderate light. The photoactive pool comprised 50% of total PQ. We find that the PQ pool of cyanobacteria behaves under light treatments qualitatively similarly as in plant chloroplasts, is less reduced during growth under high than under ambient CO2 and remains partly reduced in darkness. [ABSTRACT FROM AUTHOR]

Plants survive periods of unfavourable conditions with the help of sensory mechanisms that respond to reactive oxygen species (ROS) as signalling molecules in different cellular compartments. We have previously demonstrated that protein phosphatase 2A (PP2A) impacts on organellar cross-talk and associated pathogenesis responses in A rabidopsis thaliana. This was evidenced by drastically enhanced pathogenesis responses and cell death in cat2 pp2a-b′γ double mutants, deficient in the main peroxisomal antioxidant enzyme CATALASE 2 and PP2A regulatory subunit B′ γ (PP2A-B′ γ). In the present paper, we explored the impacts of PP2A-B′ γ and a highly similar regulatory subunit PP2A-B′ ζ in growth regulation and light stress tolerance in Arabidopsis. PP2A - B ′γ and PP2A - B ′ζ display high promoter activities in rapidly growing tissues and are required for optimal growth under favourable conditions. Upon acclimation to a combination of high light, elevated temperature and reduced availability of water, however, pp2a-b′γζ double mutants grow similarly to the wild type and show enhanced tolerance against photo-oxidative stress. We conclude that by controlling ROS homeostasis and signalling, PP2A-B′ γ and PP2A-B′ ζ may direct acclimation strategies upon environmental perturbations, hence acting as important determinants of defence responses and light acclimation in plants. [ABSTRACT FROM AUTHOR]

Plastoquinol (PQH 2 -9) and plastoquinone (PQ-9) mediate photosynthetic electron transfer. We isolated PQH 2 -9 from thylakoid membranes, purified it with HPLC, subjected the purified PQH 2 -9 to singlet oxygen ( 1 O 2 ) and analyzed the products. The main reaction of 1 O 2 with PQH 2 -9 in methanol was found to result in formation of PQ-9 and H 2 O 2 , and the amount of H 2 O 2 produced was essentially the same as the amount of oxidized PQH 2 -9. Formation of H 2 O 2 in the reaction between 1 O 2 and PQH 2 -9 may be an important source of H 2 O 2 within the lipophilic thylakoid membrane. [ABSTRACT FROM AUTHOR]

Instead of red anthocyanins, birches synthesise colourless (to human eye), UV-absorbing flavonols during autumn senescence. To test if flavonols protect against insects, and if leaves with high or low amounts of flavonols differ in their photosynthetic functions, aphid-free and aphid-infested green and senescing birch leaves were collected from outdoor-grown trees and analysed. Photosynthetic parameters were greatly affected by the leaf chlorophyll content (i.e. the phase of senescence). Photochemical quenching and the amount of functional Photosystem I decreased linearly with chlorophyll content, while FV/FM (Photosystem II functionality) decreased strongly only at the end of senescence. Non-photochemical quenching of excitation energy (NPQ) increased towards the end of senescence. However, no significant differences in the total flavonol amounts, nor in individual flavonol species, were found between aphid-free and aphid-infested leaves, suggesting that flavonols play no role in defence against aphid herbivory. Interestingly, both green and senescing leaves with a high flavonol content showed low FV/FM values. High flavonol content slowed down PSII photoinhibition and improved recovery, but only in green leaves. Previously, we proposed that anthocyanins provide an additional sink for photosynthates at the nitrogen resorption phase during autumn senescence, and the present data may suggest that flavonol synthesis plays a similar role., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Plants survive periods of unfavourable conditions with the help of sensory mechanisms that respond to reactive oxygen species (ROS) as signalling molecules in different cellular compartments. We have previously demonstrated that protein phosphatase 2A (PP2A) impacts on organellar cross-talk and associated pathogenesis responses in Arabidopsis thaliana. This was evidenced by drastically enhanced pathogenesis responses and cell death in cat2 pp2a-b'γ double mutants, deficient in the main peroxisomal antioxidant enzyme CATALASE 2 and PP2A regulatory subunit B'γ (PP2A-B'γ). In the present paper, we explored the impacts of PP2A-B'γ and a highly similar regulatory subunit PP2A-B'ζ in growth regulation and light stress tolerance in Arabidopsis. PP2A-B'γ and PP2A-B'ζ display high promoter activities in rapidly growing tissues and are required for optimal growth under favourable conditions. Upon acclimation to a combination of high light, elevated temperature and reduced availability of water, however, pp2a-b'γζ double mutants grow similarly to the wild type and show enhanced tolerance against photo-oxidative stress. We conclude that by controlling ROS homeostasis and signalling, PP2A-B'γ and PP2A-B'ζ may direct acclimation strategies upon environmental perturbations, hence acting as important determinants of defence responses and light acclimation in plants., (© 2015 John Wiley & Sons Ltd.)

Plants form volatile oxylipins and related compounds under stress. Some of them are important flavor chemicals and give big impact on the flavor quality of food made from plant materials. They are also involved in defense responses of plants against pathogens and herbivores. Furthermore, in some instances, they cause harmful effects on plants themselves. Because of these significances of volatile oxylipins and related compounds, demands to perform comprehensive analyses of these compounds are increasing. In this chapter, we describe the simple but efficient procedures to reveal profiles of volatile oxylipins and related compounds by using HPLC and GC-MS. They are simple and can be performed in biochemical laboratories equipped with common facilities.