By Stephanie French
The other week I bumped into a friend of mine in Sainsbury’s. We were chatting away as usual when he asked me: “are plants alive?”. I thought to myself that this was just another example of how under-appreciated the Plantae kingdom is, and yes, of course, most people do know that plants are alive, but many perceive them to be boring, simple lower-life organisms.
However, this is far from the truth; land plants actually evolved after animals, and in some ways are more complex. For example, while animals can move away from poor environments, plants are forced to cope with whatever nature throws their way. They may not appear to change very much in different weather conditions, but within plants hundreds of dynamic signalling events are occurring from the cellular to the whole-plant level allowing the plant to survive in extreme environments. For example, during high light-stress, plants can move chlorophyll within their cells to more “shaded” areas, rapidly move their leaves, develop surface reflectants (pubescence), and dissipate excess heat using the xanthophylls cycle…the list goes on. Plants, unlike animals, are actually acclimating throughout their entire life cycle.
Further complexity of the plant cell can be seen just by looking down a microscope, or thinking back to the classic ‘animal cell vs plant cell’ picture present in nearly all high school biology text-books. Plants contain more organelles including, of course, chloroplasts! And, sure, animal cells can differentiate to form more complex-looking cells such as nerve cells, but plant cells can do that too (e.g. sieve-tube elements). Also, although not generally realised by most people, plants can form organs like animals too – leaves and flowers etc. are indeed organs. Do you know any animals that have chloroplasts? I think not (ok actually there are actually three but they steal the chloroplasts from plants)
And if you thought your love life was complex, for plants it is (probably) even more so. As angiosperms (flowering plants) can produce multiple stamens (male-parts) and carpels (female-parts) there is so much more potential for variation. A single flower can be male or female or hermaphrodite. On the whole plant, all flowers may be the same sex or there may be a combination of male, female or hermaphrodite flowers. Plants even have a complex mechanism called self-incompatibility, to prevent inbreeding.
When sex does occur, it is twice as good as in the animal kingdom. Double fertilization occurs whereby one sperm cell penetrates the egg cell while another penetrates a different cell called the central cell. Both these cells develop within the seed, the former forming the embryo and the later forming the endosperm, which provides nutrients to the developing plant.
In fact plants are so complex and diverse that they even confused Charles Darwin! He frequently referred to angiosperms as an ‘abominable mystery’, as he could not figure out what the most ancestral flowering plants looked like or why they diverged so rapidly. This is still disputed over by many scientists! One theory is that by using other organisms to carry their gametes, angiosperms were able exploit many niches and diverge in a short space of time.
These are just a few of the many reasons why plants deserve so much more respect than they currently receive. So much research is focussed on animals, with the possibility that it may enable future drug discoveries, which of course is great. However, plants have the potential to increase crop productivity and provide the world with renewable energy, so research on plants is equally, if not more, important.