Acclimation 2 Flashcards
Stress-induced production of ROS
Reactive oxygen species are produced in high quantities:
In chloroplasts under high light, especially if combined with water stress and/or cold
In peroxisomes under drought and heat stress
In mitochondria under heat and cold stress
ROS scavenging
Superoxide dismutase (produced more to handle more superoxide)
Catalyses the dismutation of superoxide into hydrogen peroxide
O2.- + O2.- + 2 H+ → H2O2 + O2
to limit the formation of hydroxyl radicals through the Haber-Weiss reaction
O2- + H2O2 –> O2 + OH + OH-
Present in most cellular compartments
Different forms in different compartments, relying on a variety of metals (Cu/Zn, Mn, Fe)
Catalase
Converts hydrogen peroxide into water
H2O2 + H2O2 → O2 + 2 H2O
Present mostly in peroxisomes and other small organelles
Low affinity for hydrogen peroxide: efficient under high [H2O2]
No need for reducing power
photorespiration in peroxisomes. it can handle a lot of hyderogen peroxide
Ascorbate glutathione cycle
Converts hydrogen peroxide into water
Requires reducing power provided by NAD(P)H
High affinity for hydrogen peroxide: efficient under low [H2O2]
in chloroplast in cytoplasm and in mitochondria
uses ascorbate acid gets rid of hydrogen peroxide. Limited amount of it though.
Gets rid of more H2O2
Stress-induced production of ROS in chloroplasts
Mehler reaction
The water-water cycle
Specific to chloroplasts (stroma)
Integrated into photosynthesis
Allows electron flow without accumulation of ROS even when NADP+ limiting
also uses ascorbic acid this has a thylakoid ascorbate peroxidase. instead of using reducign power fom nADH you use reducing power of extra electrons going through??
allows electron flow without the need of NADH(whhich could eb limiting) reduces extra electrons.
its called water water cycle becasue …
source embedded in light cycle reaction
handles H2O2 production in stroma of chloroplasts
ROS detoxification
Peroxiredoxins reduce peroxides (e.g. in lipids, proteins and DNA) into alcohols and H2O2 into water; they are found in most cellular compartments.
Reductants (electron donors) regenerating the active peroxiredoxin include NAD(P)H, thioredoxins and glutaredoxins.
Acclimation to light: leaf movement
Plants displaying paraheliotropism can make their leaves more vertical so that they receive less light and avoid photoinhibition. This behaviour is mostly found in legumes.
Opening and folding leaves of Bauhinia tenuiflora
Acclimation to light: chloroplast movement
Chloroplasts can move to areas of the cell with limited irradiation under high light conditions.
Chloroplasts movement under varying light intensity could depend on the relocation of actin filaments around the chloroplast. (they hide under each other. makes leaf lighter green if more light)
Acclimation to light: non-photochemical quenching
how is it induced?
What does low lumen pH trigger?
What are PsbS proteins?
high light situations may arise vey quickly e.g when clouds move quickly.
Non-photochemical quenching (NPQ) (excitation by heat) can be induced in a matter of seconds or minutes by the acidification of the thylakoid lumen.
Protons accumulate in the lumen under excess light due to proton pumping and reduced use of proton by the ATPase.
Under excess light, violaxanthin epoxidase is activated by low lumen pH and converts violaxanthin to antheraxanthin and zeaxanthin, both of which can dissipate chlorophyll excitation heat. part of xanthines?? which are yellowish pigments
Low lumen pH also triggers changes in the conformation of light harvesting complex (LHC) proteins that promotes de-excitation (quenching) of chlorophylls through the xanthophylls.
The PsbS proteins acts like a pH sensor that initiates the changes in antenna organisation.
???
Acclimation to light: photosystem II repair
D1 repair cycle occurs at all light levels, but under excess light, it speeds up and relies on a pool of replacement D1. The repair machinery (including FtsH) can be damaged by ROS. ROS scavenging is therefore essential to PSII repair.
D needs to be repares 60-8- times more than other ???
Acclimation to cold
Cold acclimation (= hardening) occurs when plants experience chilling temperatures. It involves cellular changes that will limit frost induced damages.
Cold acclimation includes general water stress and oxidative acclimations, as well as more specific changes.
Acclimation to cold: change in membrane composition
During cold acclimation, lipids prone to forming hexagonal II phases decrease, while lipids stabilising bilayer configuration increase in chloroplast and plasma membranes.
Changes in plasma membrane lipid composition after four weeks at 2°C
Changes in membrane lipid composition depend on species.
Acclimation to cold: increase in membrane lipid unsaturation
An increase in lipid unsaturation counterbalances the increase in membrane rigidity due to low temperatures. More unsaturated phosphatidylcholine reduces the risk of expansion-induced lysis.
Acclimations to wind
Strategies:
Reduce wind strain (drag) by decreasing the surface offered to the wind (avoidance)
-Decrease stem/trunk growth rate
-Leaf/branch shedding
-Reconfiguration: temporary or permanent
-Leaf rolling/re-orientation (adaptation?)
Increase resistance to breakage (tolerance)
-Thicker/reinforced stem/trunk
-(woody ≠ non woody plants)
-Flexible petioles and branches
-Flexure wood
Increase anchorage
-Higher root to shoot ratio
