植物也會患癌症嗎？
蘇韋霖
By Raphaella So
This article may be useful as supplementary reading for biology classes, based
on the DSE syallbus.
根據生物科文憑試課程剛要，本文或可作為有用的補充讀物。
Can
Plants
develop cancer? This is an easy question to
ask, but the answer is more convoluted than one
might imagine. In the 90s, two related articles
were published in close succession: “Why don’t
plants get cancer?” and “Plants can get cancer”.
The first article argued that plants could tolerate
abnormal cell division (which is what cancer is) by
incorporating the extra cells into other development
to prevent these cells from forming tumours [1].
The second article conveys a conflicting opinion.
It proposed the notion that plants that develop
cancer may appear otherwise normal but are
harbouring cancer internally. However, “plant
cancer” may not refer to the same thing as cancers
in mammalian animals, because the symptoms of
plant cancer are manifested differently [2]. Years
later, scientists continue to contribute to this debate
[3].
In animal cel ls, mutations in two t ypes of
genes can cause the formation of tumours: proto-
oncogenes and tumour suppressor genes. The
former facilitates normal cell division by coding
for proteins that regulate the process. Certain
mutations, however, transform the gene into
an oncogene and cause the cell to synthesise
a lot more protein products than required. An
overabundance of cell division promoting proteins
in turn leads to continuous cell proliferation and
results in tumour formation. During normal cell
division, another group of genes, the tumour
suppressors, act as guards at different checkpoints
and prevent abnormal or uncontrolled cell division.
At the DNA damage checkpoint, for example,
relevant tumour suppressors would not allow the
cell to enter mitosis until all the damaged DNA has
been repaired. Mutations can render the tumor
suppressor genes ineffective, allowing damaged
DNA to be passed onto the daughter cells. This
process results in the accumulation of even more
mutations, causing uncontrolled cell division.
Moreover, if the genes that help anchor the cells
to their normal locations are mutated, the tumour
can then spread to other parts of the body by
metastasis.
L i ke i n an ima l ce l l s , mutat i ons i n p roto -
oncogenes and tumour suppressors can occur in
plants. However, except in certain hybrid species,
these mutations are rarely oncogenic. Interestingly,
the most frequent cause of plant tumours is due
to pathogenic infection [3]. Certain species of
bacteria can transfer DNA into the plant cell
nucleus and alter the signalling of plant growth
hormones. Fungal pathogens can also promote cell
proliferation by affecting these hormones. However,
they transfer proteins instead of DNA into the plant
cell. While some viruses can also act through
Can
PLANTS
develop CANCER?
