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Photosynthetic Efficiencies of LEDs: Results of Short …

Photosynthesis - Wikipedia

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In NASA-speak: ECLSS Environmental Control And Life Support System

Xanthophylls (oxygenated carotenoids) are also found in zooxanthellae. Two xanthophylls (diadinoxanthin and diatoxanthin) play an important role in protecting symbiotic algae and coral hosts from excessive light energy. When light energy is sufficient enough to effect pH changes within the photosynthetic apparatus of zooxanthellae, diadinoxanthin is converted to diatoxanthin. This conversion shunts light energy away from photosynthesis. In darkness, the process reverses, and diatoxanthin becomes diadinoxanthin. Note that these xanthophylls both absorb some violet but most strongly blue wavelengths at ~450 - 490nm. See Figure 28.

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*Chlorophyll A; A type of chlorophyll that is the most common photosynthetic organisms predominant in all higher plants, red & green algae higher plants, red & green algae. It is best at absorbing wavelength in the 400-450 nm & 650-700 nm

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*Chlorophyll B; The chlorophyll that occurs only in plants & green algae. It functions as a light harvesting chlorophyll pigment that pass on the light excitation to chlorophyll a. It absorbs well at wavelength of 450-500 nm & 600-650 nm

Since many photosynthetic organisms live where light in higher spectrums of PAS such as 600nm & higher penetrate less if at all (in particular algae, zooxanthellae, & cynaobacteria), many have adapted to ways to still harvest this light energy.
These organisms use Phycobilisomes which are light harvesting antennae of photosystem II (Chlorophyll synthesis in the Photosynthic Action Spectrum-PAS).

This is another concept to consider that we do not know all the "mechanisms" that drive it.
Basically photoinhibition is the damage to the light harvesting reactions of the photosynthetic capacity of a vascular plant, algae, or cyanobacterium by excess light energy trapped by the chloroplast.
This process can occur in in all organisms capable of oxygenic photosynthesis. In both plants & cyanobacteria, blue light causes photoinhibition more efficiently than other wavelengths of visible light, although it has been demonstrated the red light can cause photoinhibition as well.

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Plant Biology (59) 89-113, 2008.


2
CO fixation
2
Absorption
Heat (Fast)
E
2
E
1
E
0
Fluorescence
What's wrong with this picture for chlorophyll?
Fluorescence is one of three major quenchers of excitation energy
Heat
Photochemistry
PSII quenches fluorescence (takes energy from chlorophyll) when the Q site is oxidized
Fluorescence and PSII
When it is oxidized it is ready to receive an electron and is "open"
When it is reduced it can't receive an electron and it is "closed"
A
PSII quenching
PSII
Photosystem II can be closed due to downstream backup or damage
Photosystem I is an excellent quencher, so all the fluorescence observed comes from PSII
Decoding quenching
Fluorescence
Heat
Photochemistry
How can we use fluorescence to understand heat dissipation and photochemistry?
DCMU
Heat (nonphotochemical, NPQ) quenching changes
photochemical
non-photochemical (heat)
DCMU to resolve quenching
Only works in algae
Hard to probe a living system when you kill it
Saturation pulses to decode quenching
Heat (NPQ)
Photochemistry
Use rapid, saturating flashes of light to fully reduce Q and resolve photochemical quenching and NPQ
Fluorescence
A
One way to maximally reduce Q ...
A
Requires "pulse-amplitude modulated fluorometry" (PAM) to separate background fluorescence from chlorophyll fluorescence
Fluorescence quenching analysis using modulated fluorescence
DOB
In the dark Q maximally oxidized and PSII is maximally open
Fluorescence is at a minimum because there is little NPQ and PSII quenches efficiently
Weak non-actinic measuring light
A
Fluorescence yield when PSII is fully closed
Actinic light turned on
PSII close
NPQ increases
Far-red opens PSII
Fluorescence in action
Wasteful (but protective) heat dissipation
Light use efficiencies
Maximum quantum efficiency
Measured on dark-adapted leaves
Healthy leaves ~0.82
Decreases with stress and damage
Maximum quantum efficiency
Operating quantum efficiency
Photon to electron efficiency
What can this be used for?
Linear electron flux
Linear electron flux
Most energy in the light goes to photosynthesis
Two electrons reduce one NADPH
Two NADPH are needed to reduce one CO
Can we estimate gas exchange from fluorescence?
2
Yes, for C4 at least...
What about C3?
Have to account for NADPH demand of photorespiration
Can be done with leaf models of photosynthesis
Requires some assumptions, but is possible
Can be used to estimate mesophyll conductance
Poll Time!
Getting Good measurements
Who will be/has been using a LiCor 6400 to do fluorescence?
Read the manual
Refer to Licor Fluorometer manual for more information.

Implications of these tests:

This controlled test has aquatic implications, as photosynthesis is the same whether it be a terrestrial plant, a freshwater aquatic plant, or symbiotic zooanthellic algae found in corals.
The main difference would be that light energy is quickly absorbed by water, especially red light waves and many modern high-end LED fixtures such as an EcoTech Radion, AI Sol Vega Blue, ZetLight ZT 6600, AAP Fiji Blue, AAP Ocean Blue NP, and AAP Reef White 2000 produce the light energy for deeper aquarium water penetration more comparable to the popular 20k "Radium" Metal Halides.

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Last Word Archive | New Scientist

Those molecules initiate photosynthesis by trapping photons. Chlorophyll is called a and, as it sits in its “,” it only absorbs wavelengths of light that . The wavelengths that plant chlorophyll does absorb well are in the green range, which is why plants are green. Some photosynthetic bacteria absorb green light, so , and there are many similar variations among bacteria. Those initial higher electron orbits from photon capture are not stable and would soon collapse back to their lower levels and emit light again, defeating the process, but in the electron is stripped from the capturing molecule and put into another molecule with a more stable orbit. That pathway of carrying the electron that got “excited” by the captured photon is called an . Separating protons from electrons via chemical reactions, and then using their resultant electrical potential to drive mechanical processes, is how life works.

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