Photobiology is the scientific study of the beneficial and harmful interactions oflight (technically,non-ionizing radiation) in livingorganisms.[1] The field includes the study of photophysics, photochemistry,photosynthesis,photomorphogenesis,visual processing,circadian rhythms, photomovement,bioluminescence, andultraviolet radiation effects.[2]
The division betweenionizing radiation and non-ionizing radiation is typically considered to be a photon energy greater than 10 eV,[3] which approximately corresponds to both the first ionization energy of oxygen, and the ionization energy of hydrogen at about 14 eV.[4]
Whenphotons come into contact with molecules, these molecules can absorb the energy in photons and become excited. Then they can react with molecules around them and stimulate "photochemical" and "photophysical" changes of molecular structures.[1]
This area of Photobiology focuses on the physical interactions of light and matter. When molecules absorb photons that matches their energy requirements they promote a valence electron from a ground state to an excited state and they become a lot more reactive. This is an extremely fast process, but very important for different processes.[5]
Source:[6]
This area of Photobiology studies the reactivity of a molecule when it absorbs energy that comes from light. It also studies what happens with this energy, it could be given off as heat or fluorescence so the molecule goes back to ground state.
There are 3 basiclaws of photochemistry:
Plant growth and development is highly dependent onlight.Photosynthesis is one of the most important biochemical processes for life on earth and its possible only due to the ability of plants to use energy from photons and convert it into molecules such asNADPH andATP, to then fixcarbon dioxide and make it into sugars that plants can use for their growth and development.[7] But photosynthesis is not the only plant process driven by light, other processes such asphotomorphology and plantphotoperiod are extremely important for regulation of vegetative and reproductive growth as well as production of plantsecondary metabolites.[8]
Photosynthesis is defined as a series of biochemical reactions that phototrophic cells perform to transform light energy to chemical energy and store it in carbon-carbon bonds ofcarbohydrates.[9] As it is widely known, this process happens inside of thechloroplast of photosynthetic plant cells where light absorbingpigments can be found embedded in the membranes of structures calledthylakoids.[9] There are 2 main pigments present in thePhotosystems ofhigher plants:chlorophyll (a or b) andcarotenes.[7] These pigments are organized to maximize the light reception and transfer, and they absorb specificwavelengths to broaden the amount of light that can be captured and used for photo-redox reactions.[7]
Due to the limited amount of pigments in plant photosynthetic cells, there is a limited range of wavelengths that plants can use to perform photosynthesis. This range is called "Photosynthetically Active Radiation (PAR)". This range is almost the same as the human visible spectrum and it extends in wavelengths from approximately 400-700 nm.[10] PAR is measured in μmol s−1m−2 and it measures the rate and intensity of radiant light in terms of micro-moles per unit of surface area and time that plants can use for photosynthesis.[11]
Photobiologically Active Radiation (PBAR) is a range of light energy beyond and includingPAR. Photobiological Photon Flux (PBF) is the metric used to measure PBAR.
This process refers to the development of the morphology of plants which is light-mediated and controlled by 5 distinct photoreceptors: UVR8, Cryptochrome, Phototropin, Phytochrome r and Phytochrome fr.[12] Light can control morphogenic processes such as leaf size and shoot elongation.
Different wavelengths of light produce different changes in plants.[13] Red to Far Red light for example, regulates stem growth and straightening of the seedling shoots that are coming out of the ground.[14] Some studies also claim that red and far red light increases the rooting mass of tomatoes[15] as well as the rooting percentage of grape plants.[16] On the other hand, blue and UV light regulate the germination and elongation of the plant as well as other physiological processes such as stomatal control[17] and responses to environmental stress.[18] Finally, green light was thought not to be available to plants due to the lack of pigments that would absorb this light. However, in 2004 it was found that green light can influence stomatal activity, stem elongation of young plants and leaf expansion.[19]
These compounds are chemicals that plants produce as part of their biochemical processes and help them perform certain functions as well as protect themselves from different environmental factors. In this case, some metabolites such as anthocyanins, flavonoids, and carotenes, can accumulate in plant tissues to protect them from UV radiation and very high light intensity[20]
| Internal rhythms |  | |
|---|---|---|
| External cycles | ||
| Fields | ||
| See also | ||
| International | |
|---|---|
| National | |
| Other | |
