Reef Coral Quiz 2
What is the last part of the light reaction?
ATP synthase
How does oxidative stress relate to ROS production?
Activates signaling cascades
Pathway 2 of ROS (what does it result in)
Apoptosis
Pathway 3 of ROS (what does it result in)
Apoptosis
What is partial mortality of a coral colony?
Bleached tissue must survive long enough to recover with symbionts, but sometimes tissue does not recover quickly enough and mortality occurs
How do light reactions energize dark reactions?
By reducing NADP+ to NADPH
How do damselfish farm on coral colonies and cause bleaching?
Partial mortality leads to establishment of lawns where damselfish farm and hinder recovery
What is photorespiration?
Rubisco binds oxygen instead of carbon dioxide that uses up energy but does not fix any carbon
What is one way to maintain energy balance in the cell?
Spit out energy through NPQ
What occurs during host cell apoptosis?
Disintegration of the surrounding coral cell and expels the symbiont
What is Tenacious D?
Durusdinium might just be really good at avoiding apoptosis or bleaching, not necessarily thermally tolerant
What happens if the D1 protein is damaged by thermal stress?
Electrons are still being absorbed and you get a blockage in electron flow
What is cyclic electron flow?
Electrons can fall back into the electron transport chain without being used to reduce NADP+ to NADPH. This generates ATP but does not fix carbon
How are ROSs produced?
Excess electrons reduce oxygen to create reactive oxygen species
Light reaction equation (lecture 8, slide 10)
H2O + 2NADP+ + 3ADP + Pi + 8 photons --> O2 + 2NADPH + 2H+ + 3ATP
What were Peter Glynn's findings?
High-temperature stress causes bleaching that has never really been seen before (during El Niño)
What is the best way of predicting bleaching?
How long and how severe the warm temperature anomaly is
Where do dark reactions occur in the cell?
In the stroma which is in the chloroplast
Where do light reactions occur in the cell?
In the thylakoid membranes which is in the chloroplast
How many more electrons are present on the inside of the thylakoid membrane than on the outside? Why?
- 1000 - pH is a log based scale, so a pH difference of 3 is 1000.
What is rubisco?
- A slow enzyme (only a few reactions per second) - Most abundant protein in nature - Primary rate-limiting enzyme of dark reactions
What are some ongoing work examples that we can manipulate symbionts?
- Algal symbiont manipulations at the recruit stage - Field trials testing implants into slow-growing, large colonies on local reefs to access feasibility and value
What are the main results of Kenkel et al. (2015)?
- At home sites, percentage of mass gain and host phenotypic trait measurements were highest at the home reef - At away sites, transplantation to along-shore sites resulted in the greatest reductions in mass Gian and host traits of total protein and carbohydrate - Corals showed greater mass gain at home sites than foreign sites --> due to fine-scale specialization - Local specialization poses a trade-off in ability of these controls to grow when transplanted away from their native reef site
What are the main results of Suggett and Smith (2011)?
- Bleaching can be a friend or foe - Bleaching as a friend: changing environment prompts physiological adaptation and resilience. It can allow for acclimatization like symbiont shuffling - Bleaching as a foe: can be lethal when prolonged and severe. Symbionts are also less efficient under heat stress and create ROS that damage the coral host
Low salinity bleaching
- Can inhibit enzymes of dark reactions - Damages membranes and organelles because of osmotic changes - Results in ROSs
Low temperature bleaching
- Can slow down enzymes in the dark reactions (rubisco) - Results in ROSs
Types of non-photochemical quenching (NPQ)
- Cyclic electron flow - Xanthophyll cycle - Mehler reaction - Photorespiration
What are three things that ROS damage?
- DNA - Proteins - Membranes
How does lower mucus production lead to coral bleaching?
- Fewer metazoan symbionts - Less feeding capacity - Lower disease resistance
What are three ways the host aids in mitigating bleaching?
- Fluorescent pigments, MAAs - Antioxidants, Heat Shock Proteins (HSPs) - Heterotrophic feeding
Pathway 1 of ROS (types of ROSs and what does it result in)
- High concentrations of superoxide and hydrogen peroxide - Triggers NF-kB protein that results in apoptosis (expulsion of symbiont from a symbiosome)
In what conditions are more ROSs produced in terms of symbiont density?
- Higher proportion of thermally sensitive symbionts (Breviolum) - Higher symbiont densities
What are 5 mechanisms of symbiont loss?
- In situ degradation - Exocyctosis - Host cell detatchment - Hote cell apoptosis - Host cell necrosis
Cyanide bleaching
- Inhibits Rubisco - Results in ROSs
DCMU bleaching
- Inhibits electron transfer in PSII that blocks the plastiquinone binding site - Results in ROSs
How does ATP synthase work?
- It uses the energy from the light reactions (the proton gradient and highly acidic in the thylakoid membrane) - It funnels protons back through ATP synthase and turns ADP into ATP
What are the main results of Cunning et al. (2021)?
- Latitude and longitude did not impact coral recruitment or ED50 (phenotype did) - Reef Renewal ED50 was highest - Fish and Wildlife Service ED50 was lowest - Each nursery already contains some individuals that are thermotolerant because of their genetic differences
Explain photosynthesis with the two stages (i.e. Calvin Cycle)
- Light is powering the split of water molecules to produce oxygen and protons (H+) - Light also produces ATP and NADPH that is fed into the Calvin Cycle - The Calvin Cycle uses ATP and NADPH to spin a wheel that turns CO2 into sugar and also ADP and NADP+
What are the 8 sublethal impacts of bleaching on corals?
- Lower mucus production - Partial mortality of coral colonies - Predator concentration - Damselfish lawn expansions - Overgrowth of bleached corals by turf and macroalgae - Disease outbreaks on bleached corals - Reduced fecundity - Higher bioerosion
What are the main results of Albright et al. (2016)?
- Net calcification depressed compared to values expected for pre-industrial conditions - Alkalinity uptake = net community calcificaiton - Calcification increases when ocean chemistry is restored closer to pre-industrial conditions - Alkalinization can offset ocean acidification impacts on coral reefs
What are the main results of Dixon et al. (2015)?
- Parents from warmer location (PCB) conferred significantly higher thermotolerance to their offspring than the cooler location (OI) - PCB mom had a 5-fold increase and dad had a 2-fold increase - higher thermotolerance could be due to lack of prior stress (expression of TAGs was negatively correlated with long-term heat stress response in larvae and adults) - Heritability of coral stress-related phenotypic traits means adaptive potential from genetic variation
What happens if you end up with excess energy or can't dissipate energy quickly enough? More specifically, what can be done to combat this? (lecture 8, slide 16)
- Photochemistry - Fluorescence - Heat dissipation - Create ROS's
What are the main points of Kuffner et al. (2008)?
- Recruitment rate and percentage cover of CCA on treatment (CO2) mesocosms was lower than controls - Non-calcifying algae was higher on treatment cylinders vs. controls - CCA may be less competitive for space in high PCO2 conditions
What are positive feedbacks of losing symbionts?
- Self shading - Skeletal light amplification - The more symbionts you lose, the more remaining symbionts get hit by light
Types of Reactive Oxygen Species (ROS)
- Singlet oxygen - Superoxide - Hydrogen peroxide - Hydroxyl
What influences bleaching susceptibility?
- Symbiont identity - Symbiont density - Genotype of the coral - Coral chimerism
Name three significances of symbiont manipulation?
- Symbiont manipulations allow us to control for the effects of coral genotype - It helps us understand the spread of thermotolerant symbionts, how they influence corals, and tradeoffs - It gives us insight into corals as adaptive systems that share pools of symbionts
What are the many stressors that cause coral bleaching?
- Temperature (high or low) - Irradiance UV (high or low) - Salinity (high or low) - Herbicides - Copper - Cyanide - Oil - Sunscreen - Sediment - Dessicaiton - High CO2 - Pathogens
What is the Baker (2001) paper mainly explaining?
- The deep-water coral transplants moved to shallow water and mostly bleached within about a week and after a year, they recovered with different symbionts than what they had before in deep water - Shallow-water transplants moved to deep water didn't bleach but they were stuck with their original symbionts and died
What do protons do to pH in the cell?
- They drive pH - It is a measure of how much H+ ions are present
pH levels of thylakoid lumen and chloroplast stroma
- Thylakoid lumen: 5 - Chloroplast stroma: 8
What is the role of Symbiodiniaceae in a coral cell?
- Thylakoid membrane composition - D1 protein damage vs. repair rate
How do light reactions and dark reactions relate to each other?
Light reactions produce ATP and NADPH that the Calvin Cycle uses to produce sugar from carbon dioxide from the atmosphere. The Calvin Cycle then produces NADP+ and ADP and P for the light reaction to use to produce ATP and NADPH and so on.
Photosynthesis stages
Light-dependent reactions and light-independent (dark) reactions
What are three things we are learning from symbiont manipulations?
- You have to bleach the corals first in order to get rid of their existing symbionts if you want them to gain different symbionts - We can use "stress hardening" through controlled bleaching and recovery - You can manipulate a coral by using tissue plugs with introduced symbionts controlled by the environment
What exactly is happening in the Calvin Cycle?
1. 3 molecules of CO2 are taken up by rubisco and turns it into 3-PGA 2. ATP and NADPH energizes the dark reactions and reduces 3-PGA into GA3P 3. One of those 6 molecules of GA3P comes off 4. The 5 molecules of Ga3P regenerates rubisco 5. Rubisco regenerates the 5, 3-carbon molecules into 3, 5-carbon molecules of RuBP
What are the three stages of the Calvin Cycle? (lecture 8, slide 12)
1. Carbon fixation 2. Reduction of 3-PGA 3. Regeneration of Ribulose-1,5-bisphosphate (RuBP)
What is the bleaching cascade?
1. Damage to the photosynthetic machinery 2. Excess excitation energy 3. Production of ROS 4. Cellular signaling cascade involving reactive nitrogen species 5. Bleaching
Three steps of NOAA's Degree Heating Weeks calculation
1. Establish the baseline high temperature for cell of interest 2. Define what constitutes an anomalously warm temperature for week i 3. Calculate cumulative anomalies (total thermal stress)
Explain how light reactions work
1. Light enters Photosystem II and is funneled into a receptor molecule 2. Water is split into oxygen and a proton (H+) 3. Electrons are passed into plastoquinone that transports it through the membrane and exports it into the lumen 4. The electron energy passes through the plastocyanin and into Photosystem I 5. Light enters PSI and a new energy state is funneled through ferredoxin and is used to turn NADP plus a proton into NADPH 6. ATP synthase
Explain the Calvin Cycle (lecture 8, slide 11)
1. Takes ATP and NADPH from the light reactions and is fed into the Calvin Cycle 2. The Calvin Cycle spins its wheel once and takes out one CO2 molecule 3. After 3 spins of the wheel it is turned into a 3-carbon sugar molecule 4. the ATP and NADPH is turned back into NADP+, ADP, and a P (end)
What is the bleaching threshold?
1°C above the MMM
What does the Calvin cycle produce?
A 3-carbon sugar
What happens when the thylakoid membrane is damaged by thermal stress?
A broken membrane means that light is still being harvested but not producing ATP, so dark reactions cannot proceed but still evolve O2 and create ROSs
What is the principle cause of mass coral bleaching and mortality?
Sustained high temperatures
When did we first understand that mass bleaching was a result of heat stress?
The 1982-1983 El Niño Oscillation in tea tropical eastern Pacific (Indonesia, Galapagos, Panama)
What is the xanthophyll cycle?
The interchange between diatoxanthin and diadinoxanthin that uses up energy
Stroma
The intracellular space between the thylakoid membranes
Grana
The stacks of the thylakoid membranes
How does thermal stress cause damage in the cell?
Thermal stress can damage the D1 protein in PSII, thylakoid membrane, it can inactivate rubisco, and cause disfunction of carbon transfer by disrupting carbonic anhydrase
Did Pocillopora in American Samoa grow faster or slower in warm pools than cool pools despite having more Durusinium symbionts? What does this mean?
They grew faster in the warm pools. This means that tradeoffs are environmentally dependent.
Light reaction main summary
They have taken two photons and split water, generated NADPH and ATP
What do Degree Heating Weeks calculate?
They predict bleaching from sea surface temperature (SST)
How does bleaching occur in a coral?
Through an imbalance of energy flow in the cell (excess incoming energy or decreased ability to process energy and get rid of it)
How is an imbalance of energy created in the cell?
Through too much energy coming in or not enough energy being used for photochemistry or NPQ
What is the mehlar reaction?
Water produces oxygen that is used as an electron that produces ROS and then water
