Hi Leelavathy,
Please see the similar discussion on RG:
https://www.researchgate.net/post/Why_is_MS_half_strength_used_during_rooting
Hi Leelavanthy,
1. I attach a paper for you. In Discussion section, they listed at least 8 research results which showed the beneficial effect of a reduced culture-medium strength on the in vitro initiation of roots from different plant species (see yellow highlights).
2. In the paper, they also pointed out that "The effect of the medium strength could be possibly associated with particular components of the culture medium". They gave an example: "Castiglione et al. observed a radical reduction in the number and length of roots induced from white poplar (Populus alba) cultures when zinc concentration in the culture medium was increased."
Just by using logic we can make an "intelligent guess" by saying when explant produces callus it produces lots of mass, just need more nutrients. Now, when just rooting it doesn't need so much...
@ Luis,
Also, probably the individual plants can start to make their own food.
Half strength medium may induce a stress that helps to initiate rooting in plants cultured in vitro.
Just to give the plant a stress so that it will thrive itself for intake of nutrients and thus will result in good root elongation and lateral spread too.
Definitions
In vitro culture
Plant in vitro cultures are plant explant cultures, on a synthetic medium, in sterile conditions, in a controlled environment and in reduced space (Def. from Technivit).
Explants: part of the plant, from all the aerial part to isolated cells, as parts of leaves, of roots, seeds and buds.
Synthetic medium: it is generally composed by the following elements: water,mineral salts (macro and micro-elements), plant hormones , vitamins, sugar, and for solid medium: a gelling agent, most commonly agar-agar. The medium has to be adapted according to the plant species and of the researched effect (multiplication, growing, root production, etc).
Sterile conditions: the culture medium, rich in sugar, highly favours bacteria and fungus development and thus it is important to work with sterile material. Explants have to be disinfected too. They are soaked for some minutes to half an hour, according to the explants, in a mixture of water and bleach. Handlings are carried out under an horizontal laminar flow workstation. The filtered air is propelled in the direction of the worker. In this way, the contaminated air in the room can't penetrate under the workstation.
Controlled environnement: temperature, light intensity and photo period are regulated.
Reduced space: plants are maintained at a small size in glass containers. Those are arranged on shelves in culture rooms (= controlled environment).
Belgium is the second producer of plants by in vitro culture (50 millions plants par year).
In vitro micropropagation constitutes in many cases the most efficient multiplication way, on a large scale, for some plant species.
Introduction of explants in in vitro culture
Plants, or their seeds, are the hosts of various bacteria and fungus. It is necessary, in order to cultivate them on a sterile medium rich in sugar, to disinfect their surfaces.
Parts of a plant, or seeds, are soaked in a mixture of water, bleach and detergent for ten to thirty minutes.
Then, the work has to be done in sterile conditions, under an horizontal laminar flow workstation. According with the plant, parts of leaves (vegetative reproduction, adventitious budding) or axillary buds are cut and these explants are placed in individual jars, or alternatively seeds are sowed.
Multiplication
In in vitro culture, plants are multiplicated by cloning the plants themselves. In such manner, we can obtain a large number of specimens identical to each other and to the specimen introduced in vitro at the beginning of the process. For multiplication, thevegetative reproduction capacity of plants is used. To control this vegetative multiplication, plant hormones, particularly cytokinins, are used.
Multiplication by axillary buds.
Multiplication by adventitious buds.
On the left, Dianthus before and after a multiplication stage by axillary buds development and above, Butterwort leaf before and after a multiplication stage by adventious buds development.
The reintroduction of plants into"natural environment"
Rooting
By in vitro culture, the multiplication of stems with leaves is obtain. To obtain complete plants, those stems have to develop roots. This phase can be carried out by placing the stems in a medium with auxine (plant hormones).
On the right, a rosette plant, a sundew, before and after the rooting stage.
Acclimatisation
When stems are rooted, plants can be acclimatised , meaning they get rehabituated to living in normal conditions. The gel the plants have grown in is cleaned off the roots and the plants are transplanted in an adequate substrate (peat, soil,..). Plants are maintained in a confined environment so they can adapt progressively to drier air and to light intensity and temperature variations.
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