# Laminar _Ulva_ Species: A Multi-Tool for Humankind?
## 3 _Ulva_ Cultivation Methods: Towards an Innovative Future?
### In Vitro  
In vitro is the expression used to study all biological process that happens in all organisms in a controlled and closed environment (inside of \"a glass\"). According to [PERSON] [106], two of the most frequent ways for plant tissue culture are by applying organogenesis, which refers to the creation of plant organs (roots or shoots) and can be performed in vitro, an can be done in seaweeds. Plants can be propagated either directly from meristens or indirectly from dedifferentiated cells known as callus. These cultures can be utilized for mass plant production through techniques like micropropagation or for the development of specific organs, such as roots in hairy root culture. Collagenis results in an amorphous mass of cells when explants are exposed to various growth regulators [107]. All plant tissue culture methods involve a sequence of steps:  
1. The plant of interest must be chosen; this is normally determined by the purpose of the study, although disease- and insect-free plants are desired; if the plant demands it, pre-treatments can be used.
2. The start of the in vitro culture necessitates the removal of tiny plant parts (explants) or the use of seeds with their surfaces sterilized.
3. The explants are then put in appropriate culture conditions and cultured for a short amount of time, with infected explants destroyed. The stages that follow differ based on the intended culture.
4. Organogenesis is the propagation phase in which explants are cultivated on suitable culture conditions for shoot or root multiplication, while in callogenesis, the callus is multiplied.
5. Callus and root cultures are grown in bioreactors, while propagated shoots are moved to root-promoting culture medium in the case of micropropagation.
6. Micropropagated plants are toughened in order to produce individual photosynthesis-capable plants. Hardening is done gradually, allowing the plants to adjust to ex vitro environments [107].  
Micropropagation is a possible cultivation technique for clonal multiplication, and it has been successfully used for tissue culture of _Ulva_ sp. [13].  
The second methodology is through axenic cultures. These are an essential tool, for example, (i) to study the chemical ecology of macroalgal-bacteria interactions, (ii) to identify (allelopathic) compounds released by the macroalgae, (iii) to research the effects of bacterial morphogenetic compounds happening in the algal growth, and (iv) to have a controlled feedstock for algal aquacultures [108]. [PERSON] et al., 2015 [41] prepared the axenic cultures in _U. linza_ by phototactic migration of freshly released gametes down a thin horizontal capillary. Under strictly sterile conditions within a laminar flow hood, movement towards a light source was induced. Sterile Pasteur pipettes equipped with 15 cm capillaries were assembled. Gametes exhibited upward movement within the pipettes, congregating at the top, where they were collected. Subsequently, they were transferred to another Pasteur pipette for further purification in the subsequent run [41]. [PERSON] 2015 includes a table with studies with _Ulva_ sp., including the methodology to prepare cultures [109].  
The third methodology is using a photobioreactor, which is the most recent method and is not yet fully developed. It may be limited to the manufacture of high-value compounds for pharmaceutical or nutraceutical purposes since it necessitates specialized infrastructure and expertise, which are costly. A study conducted by [PERSON] et al., 2017 [110] studied _Ulva compressa_ and _Ulva rigida_, which were grown for 6 months in a macroalgae photobioreactor system incorporated inside a building. _U. compressa_ grew at an average rate of 2.89-3.65% each day, but _U. rigida_ did not grow well [13].