Growing up as a plant

Have you ever planted a seed in the ground and watched it grow? If you find it tough growing up, imagine what it’s like as a plant. The process behind it all is photosynthesis, and our survival depends upon it.

The building blocks of plant growth Photosynthesis (foe-toe-SIN-thuh-sys) is the way that plants use energy from the Sun to make their own food using carbon dioxide from the air and water from the ground. The energy that plants absorb from sunlight is used to trigger a chemical reaction. The reaction turns water and carbon dioxide into sugar and oxygen. The sugar eventually gets turned into plant fibre, while the oxygen is released into the air.

Our life depends upon it Professor Susanne von Caemmerer from the Australian National University specialises in the form and function of plants: in other words, what they look like and what they do. “Photosynthesis is universal,” she says. “All terrestrial [land-based] plants do it, and that’s what makes our life possible.” The oxygen we breathe comes from photosynthesis that has been going on for thousands of millions of years.

Knowing better Photosynthesis doesn’t happen the same way in all environments. This year, it’s time to celebrate our understanding of a type of photosynthesis best suited to hot and dry places. It’s known as C4 photosynthesis.

Fifty years ago, two Australian scientists – Dr Hal Hatch and Dr Roger Slack – were the first in the world to understand the details of the C4 chemical reaction. They found that sugar cane used a different process to photosynthesise than other plants they knew about. Since then, scientists have found that lots of other plants use C4 photosynthesis too.

Plants that handle the heat Plants that use C4 photosynthesis can use less water and deal with heat better than their cold weather cousins. They do this by managing the carbon dioxide in their cells differently to other plants. This ability makes it much easier for C4 plants to survive in places like north Queensland, where a lot of sugar cane is grown.

C4 photosynthesis first came about around 40 million years ago, when the carbon dioxide level in the atmosphere dropped to what it is today. Plants started to evolve to deal with the change. Since then, more than 70 different kinds of plants have evolved this C4 photosynthesis mechanism.

“The transition to C4 is mind-bogglingly difficult, so the fact that it happened 70 times is quite incredible,” says Hal.

Food for thought Photosynthesis of all kinds is an important process for researchers to understand, because all our food ultimately comes from plants. C4 plants make up more than 30 per cent of the worldwide food supply, including crops such as corn and sorghum. Australia has lots of C4 grass species, such as kangaroo grass and lovegrass.

Looking a little bit deeper, we see that many plants do things in their own distinct way. But no matter where they live or how they get their energy, remember that it’s plants that make it possible for us to breathe and eat, and therefore survive.

This short article was originally published in the October 2016 issue of the Double Helix Magazine, an Australian children’s science magazine.

This year is the 50th anniversary of the discovery of the C4 photosynthetic pathway, and I was lucky enough to talk to Hal Hatch, one of the discovers, about it. The parallel evolution of this cell mechanism in 70 distinct species is incredible, because as he puts, it is “mind-bogglingly difficult.”

Susanne von Caemmerer is part of a team trying to do just that, artificially convert a plant from C3 to C4. Their aim is rice, a plant that could grow in far more places, far more efficiently, if it’s photosynthetic pathway was a bit different. Their huge ambition is amazing, and the potential is tremendous.


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