Taylor Made: A little plant science
Just as gravity has a role in human growth, it is also a factor in plant growth. Plants exhibit geotropism, meaning their growth orients in response to the earth’s gravitational pull. The root system demonstrates positive geotropism, growing toward the pull. Some models for root system growth have been made using fractal pattern techniques.
Plant root systems have two basic forms. Taproot systems have one primary root from which many smaller roots, called lateral roots, grow. Fibrous systems are made of a dense mass of adventitious roots, roots that all develop from the stem instead of other roots. Some plants use a combination of both systems.
Taproot systems provide a strong anchor that helps to prevent stalks from being blown over as well as stabilize plants that grow in shifting soils. Some taproots can store reserves of starches and sugars for the plant to use to promote stalk and seed development. Two examples of these taproots are carrots and sugar beets. In contrast, the geometry of fibrous systems causes them to have more surface area than taproot systems of similar size, which is a factor in nutrient and water intake. Fibrous systems are also able to absorb water from the surface very quickly.
Branches demonstrate negative geotropism through the use of an anti-gravitropic offset mechanism (AGO). Plants with branches that grow at a smaller angle with respect to the horizontal have a stronger AGO, while those that grow closer to vertical have a weaker AGO. This mechanism also operates in root systems. The AGO is essentially powered by a plant hormone called auxin.
Crop physiologists study variables that control plant growth, looking at how plants respond to changes in their environment. One area of study is how to manipulate auxin, which can change the nature of the root system growth to improve how a crop responds to a certain environment. For example, crops sown in soils that contain the majority of nutrients near the surface could be altered to have shallow, outward-growing roots in order to maximize nutrient use. Manipulation could also be done in leaves and branches for the similar purpose of boosting efficiency or yield.
Unlike animal cells, each plant cell is able to duplicate all parts of the plant, making it possible to grow identical plants from one parent plant. For example, a stalk of aloe cut from a well-established aloe plant can be planted to grow another aloe plant.
Fun fact: Groups of aspen trees are connected by one root system, making them clones that will all change color at the same time (see top photo, above).