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The ever-growing history of botany

By Anna Backhaus

When one hears the term “Botany,” names such as Linnaeus, Banks, and Humboldt first come to mind, followed by images of them chasing huge, colorful flowers through the forests of the world.

Then one could think of the impressive botanical gardens and natural history museums which house millions of collected specimens. There the flowers and leaves are neatly arranged by their taxonomic family and next to them a small plaque will feature the Latin name and a detailed description of their leaves and flowers.

This impressive classification and organization of all living things was championed by Carl Linnaeus in the 18th century, who today could be described as the godfather of classical botany. He invented the binomial system (eg Homo sapiens) which allows the classification of all living things.

But, in 1836, a new era of botany was marked by the publication of “The power of the movement of plants” by none other than Charles Darwin and his son François.

In their post, they did not describe the shape of the plants they had on hand, but rather described the reaction of plants to various stimuli. They meticulously documented the growth of seedlings, the movements of climbing plants, and the response to light, toxins, and other environmental factors, addressing questions fundamentally different from classical botany.

For Linnaeus and other classical botanists, the study of plants and stones could have been the same. The appearance of both could be studied to find their place in the taxonomic system, but neither would be subjected to behavioral studies.

Linnaeus was of course aware that plants are living objects, but he did not consider them to be as capable of sensing their surroundings as animals.

Over the centuries that followed, this view changed dramatically and we know today, in part from Darwin’s work, that plants can sense their environment, process information and use it to adapt. to their habitat.

A group of plant biologists went one step further and called the field “plant neurobiology” in the early 2000s, arguing that plants have mechanisms similar to neural networks in animals. Although this point of view is much disputed and seen as too much of a metaphor, plants do indeed have extensive capacities for deliberate movement.

Animals sense their surroundings and process this information to make informed decisions about where to run, crawl, or fly next. Likewise, a plant can change its direction of growth depending on the environment.

However, here is where one of the fundamental differences between the movement of animals and that of plants resides: Animals move through the activation of muscles. Plants lack muscles, are sessile, and can only respond to their surroundings through growth.

A suitable alternate title for Darwin’s publication might have been “The Power of Growing Plants.” And the power of growth is truly fascinating.

Plant roots and shoots can change their growth direction by 180 degrees depending on where light, gravity, and resources are signaling them to go.

Darwin’s experiments showed that plants achieve these changes in growth direction by lengthening cells on only one side of the stem or root, causing the organ to bend in the opposite direction. But apart from the unbalanced cellular expansion movement of existing cells, plants also retain the ability to develop new organs throughout their lives.

Unlike animals, plants do not complete their development during embryogenesis, but rather maintain active growth centers at the tips of their shoots and roots. These are called the shoot and root apical meristem.

Within a meristem, plants retain undifferentiated cells that are similar to human stem cells. This gives them the opportunity to develop new leaves, flowers, thorns or stems at any time. The organ that a meristem will then develop depends on the signals it receives from genetic networks responsible for organizing the meristem.

A good example of the adaptability of meristems is the development of flowers in spring.

As the days grow longer and warmer, genetic flowering signals are activated in the leaves and move to the shoot meristem. There, the flowering signal manipulates the existing genetic network, which in turn shifts from leaf initiation to flower initiation.

Understanding the connection between flowering signals and changes in cell growth patterns in the meristem is important, as most of the foods we eat have already developed into a shoot or root meristem. For example, wheat develops long stems from which hundreds of tiny grain meristems grow. While in the cruciferous meristem, human selection has altered the pattern of cell division and growth to create the various broccoli, cabbage, and shoots that we eat today.

We’re only just beginning to understand how genes can alter the fate of cells in the meristem, but we know of a handful of genes that affect the normal development of meristems. Mutations in these genes lead to the development of very oddly shaped plants, for example, tomato plants with fruits clustered together like grapes instead of spreading them out further.

However, it often remains a mystery how mutating these genes altered cell growth in the meristem. Do cells divide less or more? Are they growing faster or slower? Have they changed the direction of their growth? Today, we can ask these questions for the first time using computer tools capable of analyzing cell growth from microscopy images.

When processing images taken of the same meristem on consecutive days, programs can calculate the rate of cell growth and cell division across the meristem, as well as the direction of that growth.

Thanks to this approach, researchers can now study the rules of cell growth that give plants the power to move.

And so the field of botany has changed dramatically over the past 200 years, from describing the shape of plants, to the understanding that they can move and adapt their surrounding environment, and to the possibility now of studying the mechanisms of growth which facilitate the powerful movement of the plants.