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Question
Read the following statements (I - II) related to explants and state whether the following statements are true (T) or false (F).
I - The cells of the explant are always meristematic in nature.
II - The cells of an explant may sometimes undergo dedifferentiation when put into the culture medium.
III- An explant develops into an unorganized mass of undifferentiated cells.
Read the following statements (I - II) related to explants and state whether the following statements are true (T) or false (F).
I - The cells of the explant are always meristematic in nature.
II - The cells of an explant may sometimes undergo dedifferentiation when put into the culture medium.
III- An explant develops into an unorganized mass of undifferentiated cells.
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Solution
The correct option is A I - F, II - T, III - T
An explant is any plant part, tissue or organ that is grown or cultured in a sterile culture medium under controlled environmental conditions via the process of tissue culture.
The explant can be any plant part such as a root, shoot, tissue or organ. Meristematic tissues (actively dividing plant cells responsible for growth) are found only in the growing plant parts such as root or shoot tips or in the lateral cambium (found in vascular bundles or cortex of the plant). Only explants extracted from these parts will have meristematic cells.
Figure : Meristem culture
Any explant extracted from other structural parts of the plant, (leaves, twigs, etc,) will contain permanent tissues (tissues having specialised functions and no cell division capacity) and not meristematic cells. Hence statement I is false.
When an explant is asceptically inoculated into a sterile culture media, it starts growing by active mitotic cellular divisions. The culture media contains necessary nutrients and plant growth hormones to support this growth.
The presence of intermediate concentration of growth hormones auxin and cytokinin, induces the permanent tissues present in the explant to lose their specialisation and become meristematic (dedifferentiate). If explant is composed of meristematic tissues then this step is not needed. So statement II is True.
Figure : Dedifferentiation in explant under the influence of hormones
The de-differentiated cells or meristematic cells actively divide to give rise to an unorganised mass of undifferentiated cells known as the callus. The cells of the callus are totipotent in nature, that means they can differentiate into any cell type and give rise to an entire organism. Hence statement III is True.
Figure : Callus
An explant is any plant part, tissue or organ that is grown or cultured in a sterile culture medium under controlled environmental conditions via the process of tissue culture.
The explant can be any plant part such as a root, shoot, tissue or organ. Meristematic tissues (actively dividing plant cells responsible for growth) are found only in the growing plant parts such as root or shoot tips or in the lateral cambium (found in vascular bundles or cortex of the plant). Only explants extracted from these parts will have meristematic cells.
Figure : Meristem cultureAny explant extracted from other structural parts of the plant, (leaves, twigs, etc,) will contain permanent tissues (tissues having specialised functions and no cell division capacity) and not meristematic cells. Hence statement I is false.
When an explant is asceptically inoculated into a sterile culture media, it starts growing by active mitotic cellular divisions. The culture media contains necessary nutrients and plant growth hormones to support this growth.
The presence of intermediate concentration of growth hormones auxin and cytokinin, induces the permanent tissues present in the explant to lose their specialisation and become meristematic (dedifferentiate). If explant is composed of meristematic tissues then this step is not needed. So statement II is True.
Figure : Dedifferentiation in explant under the influence of hormonesThe de-differentiated cells or meristematic cells actively divide to give rise to an unorganised mass of undifferentiated cells known as the callus. The cells of the callus are totipotent in nature, that means they can differentiate into any cell type and give rise to an entire organism. Hence statement III is True.
Figure : CallusSuggest Corrections
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