Font Size

Universal Translator

Social Bookmarks

Facebook MySpace Twitter Digg Delicious Stumbleupon Google Bookmarks RSS Feed 

V. As grounded as plants PDF Print E-mail

As well grounded as plants in the material world

The wealth of the world is found in each of the kingdoms of life. It’s also tangled together across all the kingdoms . Over billions of years, the bacteria created a new cell type and the protoctists tried many different lifestyles.

Animals specialized in becoming multi-cellular. Fungi made the most of networking as both a body plan and a lifestyle. And plants? Plants managed to incorporate all of these innovations while staying grounded, spending most of their lives standing still.

More wealth in symbiosis

One of the great evolutionary powers plants use,from their very beginnings, is symbiosis. You can follow telltale traces in their genetic lineages. Building on the photosynthesis started by bacteria, some green protoctist unicells further developed solar power. Networking with fungi, plants brought this solar power out of the ocean and onto dry land.

On land, plants found more sunshine as well as more oxygen and carbon dioxide. These ingredients are essential for the higher level of photosynthesis required by plants. What is so significant about working this greater level of photosynthesis? It's part of how plants support being multi-cellular.

Managing on dry land

Plants muster every kind of creativity to meet all the material requirements of life on dry land. Each of its cells have structures unique to plants. Its cell walls are reinforced with lignin and cellulose which not only stiffen them but also protects them from drying out. Their cells specialize, creating different tissues and structures, much as animal cells collectively make different organs. Some of these plant tissues have pores which allow them to sweat excess water. Other pores, like those on a mangrove leaf, sweat salt.close up of pores on a leaf

In most plants there is a unique set of tissues which are called vascular. These consist of two types of cells, each bundled together. One is called phloem and specializes in circulating sugars around the plant. The other is xylem, transporting water and salts. This transport system, from root hairs underground to leaves at the tops of tall trees and back again, works without requiring any extra energy from the plant. It is linked with the biochemistry of photosynthesis. It’s a solar powered freight system serving huge numbers of cellular consumers. (Have a closer look at the vascular system of plants)

Supported by this energy system, in the right situation, some part of a plant is always growing. A cutting of root or stem or even a leaf, again in a favourable circumstance, will grow into a new plant. This ability of plant cells to grow and change into other types of cells and eventually into new plants is called asexual reproduction.

This same ability is what we make use of in tissue culture. New plants can be grown from small parts of plants set in broths and jellies full of nutrients.

Reinventing sex

Even though many plants have asexual reproduction as an option, most of them will still have sex. To do this means plants have to meet certain material requirements. Like animals, they have two genders and physical differences relating to whether they are male or female. Somehow different males and females must meet. Unable to travel themselves, plants have completely redefined sex acts so that these have little resemblance to most actions done by animals like us humans.

In doing so, they also redefined important ideas such as “generations” and “sexual aids”. Talking about the sex life of plants has always raised a scandal. One major episode was in the mid 1700's, when the Swedish botanist Linneaus proposed the classification system which is used in biology today. He based a lot of his system on differences in reproduction. The way he explained plant sexuality was thought to be so graphic that women were advised against studying plants.

Taking it slow

When you hear about “generations” you think of how animals reproduce: cycles of parents producing offspring who become parents themselves. But plants cycle through a different rhythm.

Plant “parents” grow special bodies, which may be specialized parts of themselves or separate plants altogether. These in turn grow the eggs or sperm. This method involving two different growths is called  “alternation of generations”. This starts with a parent form, followed by a “tween body” of one sort of another, and then offspring, which grow into the parent form again. (This diagram also explains alternation of generations)

Then there is some process by which the sperm travel to meet the eggs. bee amidst pollen in spinifex. To accomplish this, plants make sexual aids of wind, rain and most vividly, animals.

Once over lightly

Mosses and ferns, cycads and ginkos all produce sperm that can swim. They cross small distances in droplets of water to reach the stationary eggs. For the small mosses, this is a straightforward task. But for the other larger plants, this journey is much longer and relies on aids such as wind or animals.

To equip them for dry and rough travel, the plants send off their sperm in a little space craft of pollen. Pines and flowering plants also use this same packaging method.

Upon landing, the hatch opens and the sperm makes another voyage to the egg. If the sperm can now swim to an egg, well and good. This works for ferns, cycads and ginkos. Otherwise, as in the case of pines and flowering plants, the pollen must grow a tube down into the egg case. The sperm then uses the tunnel to complete the journey to the egg. (Try this diagram showing  a model flower and pollination)

Setting up the next generation

In each case the fertilized egg is now an embryo ready to grow. Mosses and ferns release their embryos as plant “spores” with no food supply. moss capsules holding spores

But the other plants equip their embryos very well. This supply of sugars and starch, together with the embryo inside a protective coat, make up seeds.

For example, look at the female part of the spinifex plant on the Byron Bay beach dunes. It has a special catcher for pollen, which leads to the ovary where the embryo develops (left side of picture below). All around are spikes, which will form a tumbleweed. When the seed is "ripe", the tumbleweed takes off across the sand. When it stops drifting, the new plant starts to grow.
ovary/seed, spinifex plant

Seeds, such as beans and grains, are a popular food item with many kinds of animals. So are fruits, which are essentially seeds, wrapped up with tasty packaging.

With the help of your microbes in your gut, you are likely completely digesting most seeds. But not every animal digestive tract does this. The guts of birds and fruit bats often don’t. They end up either excreting or spitting out seeds far and wide as they forage. In this way, the animals also help set up each seed with extra nutrition and a fresh location for its growth.

How weird is that

The many ways that plants influence animals is a powerful process often quite difficult to figure out. There are thousands of examples. Many are still being understood. One of the latest relationships explained is the one between an Australian cycad and small insects called thrips.cycad, Byron Bay Australia

The male cycad grows a cone full of pollen. The thrips come to eat the pollen. But twice each day, the plant changes its metabolism and the cone starts to stink. It also heats up, reaching 38 degrees Celsius (100 degrees Fahrenheit).

This drives away the small thrips, still covered with pollen. They take shelter deep in cone of a nearby female cycad. The cone has many hidden crevices which are cooler and smell more attractive. While there, they shed pollen in the hidden crevices, fertilizing the eggs.

Later in the day, the male cone loses its stink and cools off. Their new odour attracts thrips back again. (To see the exact species of plant and animal involved, see this article.)

Other kingdom interactions

The other kingdoms are also deeply involved with plants, for both better and worse. Again, cycads illustrate the ups and downs of these relationships.

Sometimes a fungus will kill off the plant. Other times the leaves can look as if they are covered with black soot. This soot is a fungus which grows not on the plant itself but on the sweet sap dripping from a colony of aphids on a tree above it.

And if you cut open the small coralline roots of a cycad, inside you will find a blue green layer of cells. bluegreen bacteria in cycad rootletThese are cyanobacteria, (also called blue-green bacteria) which, at some stage in the growth of the cycad, are incorporated into its tissue. That cyanobacteria is the original bacteria group that developed photosynthesis in the first place.

Living in a material world

As with every kingdom, the creativity of plants is seen not only in their many relationships but also in their materialism. Although they are rooted in one place, their embryos spread far and wide either shifted by animals or on the wind.

They get what they need to power their lives from soil and sunshine. In turn, they produce pollen, leaves, bark, flowers, fruits, nuts and seeds, all of which attract the attention of other kingdoms.

This might look like some spendthrift abundance. But it is actually something else altogether. Certainly, all the production is for their own survival and reproduction. But given the mutualistic way of the world, it also acts as an integral resource for the local tangle of life. Changing the plants of an area can change the surrounding communities, often right across all the kingdoms.

And if all that produced by plants wasn’t enough, they also create and release fragrances and scents. Of course, some of these are especially to influence animals. But some are not noticed by animals at all. They appear to be coded messages sent to neighbouring plants.

We don’t quite understand most of these messages. However, some of them seem to announce insect invasions or grazing by other animals. When the neighbouring plants get this message, they brace themselves by producing biochemical repellents.

It’s worth remembering – and repeating to everyone else –

To be as well grounded as plants in the material world: how do YOU do that?

We welcome your comments. We’d love to hear from you.

In your day to day life, how are YOU grounded in nature?

If you want to READ MORE by Mary Gardner about plants and related topics check out the following stories

From eBook 1 Byron Orchid, After 'Sorry', Auxins

From eBook 2 Phenology, Nature Strip, Nitrogen (sundews)

From eBook 3 Sheoaks, Pandanus, Wallum

Try the FREE SAMPLER ebook by Mary Gardner

To READ MORE ONLINE about plants check the cool links and blogs on this website.