Page 26 - Science Focus (issue 15)

If you’ve seen Marvel movies, you probably preservation, a pivotal application of callus induction
know about Baby Groot, the tree-like creature that is the production of secondar y metabolites.
has captured the hearts of millions of fans around the Secondary metabolites are organic substances that
world with his cuteness. One of his most memorable are produced by plant cells. They are not directly
moments was when he was blown into a million involved in plant development, but are medically
pieces but still made a miraculous comeback. This valuable to humans. Again, scientists need only pick
was because, a single twig fragment of himself was some cells from the plant and grow it in callus culture.
recovered and grown in a pot of soil, like a real-life The resultant cells or tissues can then be a source for
sapling. This enabled him to regrow his tree-like body extracting these important secondary metabolites.
in the film. Given that it’s a sci-fi movie, it might come By doing so, the wild populations of those rare
as a surprise to you that plants in real life can indeed medicinal plants can be left relatively undamaged
regenerate themselves from the tiniest of fragments. and conserved, while we can massively produce the
This process, already a robust technique used in secondary metabolites. One famous example of this
contemporary biology, is known as callus induction. is ginsenoside. Wild ginseng takes years to grow and
has very low yield. However, with callus induction,
To start off with, a callus refers to a ball of plant roots of ginseng plants can be cultivated from calli
cells that have not been developed into a specialized in shorter periods and ginsenoside can be extracted
cell type. Amazingly, these cells are capable of from the roots with higher yields. In addition, callus
differentiating into many different cell types given induction can also be used in conjunction with plant
the right conditions. With this knowledge in mind, transfection. To introduce specific changes to the
callus induction is easy to understand. To do so, you plant genome, scientists use Agrobacterium to deliver
take a few cells from a plant and culture it in a petri genes into plant cells. The cell regenerates completely
dish with medium containing plenty of nutrients. The into a plant, with the genetic modifications, thanks
most important of which are the plant hormones, to callus induction.
auxin and cytokinin. When these two hormones
are mixed in intermediate ratios, the cell will grow It is pretty amazing how callus
and divide, forming a ball of plant cells, the titular induction is possible to begin
callus. Afterwards, once, the callus has been grown w ith. Whi le some animals
sufficiently, it is transferred to a new culture medium. may be able to regenerate
When there is more cytokinin than auxin, the shoot d a m a g e d t i s s u e b y
growth of the callus is stimulated. Conversely, when t h e m s e l v e s l i k e t h e
there is more auxin than cytokinin, root growth is planarian flatworm with
stimulated. By altering the ratio of auxin and cytokinin, adult pluripotent stem
the callus is eventually coerced to regenerate itself cells, few others do.
from the multicellular mass of cells to a fully grown Likewise, no other man-
plant that is genetically identical to the plant from made machine can
which the original cells were taken. Thus, you have regenerate itself from
a complete clone of the original plant, just like how the tiniest of fragments,
Groot regenerates himself in a pot in the movies. making plants ver y
Indeed, in this instance, what seems made-up on the special in this regard.
silver-screen is actually completely possible. This proper ty, easily
dismissed as fiction,
On its own, callus induction isn’t very special. i n d e e d i s fa c t. W h o
But its applications are quite diverse and useful. knows, maybe some other
For one, it can be used to regenerate near-extinct phenomena we imagined in
species of flora, such as orchids, very easily. All one movies or books can one day
has to do is to pick some cells from said endangered be realized in life. All we have to
plant and make some clones of it. Besides species do is to look out for it.

References 參考資料：
[1] Callus Culture: History, Principles and Significance | Plant Tissue Culture. (2015, October 26). Retrieved from http://www.
biologydiscussion.com/plant-tissues/callus-culture/callus-culture-history-principles-and-significance-plant-tissue-culture/14597
[2] Ikeuchi, M., Sugimoto, K., & Iwase, A. (2013, September 01). Plant Callus: Mechanisms of Induction and Repression. Retrieved from http://
www.plantcell.org/content/25/9/3159
[3] Transformation 1 - Plant Tissue Culture. (n.d.). Retrieved from http://passel.unl.edu/pages/informationmodule.php?idinformationmodule
=957885612&topicorder=4&maxto=8
[4] Wagner, D., Wang, I., & Reddien, P. (2011). Clonogenic Neoblasts Are Pluripotent Adult Stem Cells That Underlie Planarian Regeneration.
Science, 332(6031), 811-816.