Pisum sativum is more commonly known as the pea
plant. These plants are well known for growing peas in pods which are the plant’s
fruit. This is an important crop now grown in many parts of the world. It is
thought that peas were first domesticated in the area of modern day Greece,
Turkey and Syria. Despite now being a commonly eaten vegetable, when peas were
first introduced to France in the 1600s they were described as a luxurious
delicacy. Peas were also vital to the discovery of modern genetics as Gregor
Mendel used simple characteristics, such as shape and colour of the pea seeds,
to understand inheritance.
The roots of
the pea plant have developed from one primary root, which grows downwards more or less straight. From this primary root,
a large number of secondary (or lateral) roots have branched to fill the pot.
How do roots
know in which direction to grow? A process called positive gravitropism directs
root growth downwards into the soil. The primary root has a strong positive
gravitropism which makes it grow down more or less vertically. Lateral roots
have a less strong positive gravitropism, so that they grow downwards but also
sideways. This allows the plant roots to explore the soil for anchorage,
nutrients, and water.
In the ageotropum pea mutant, positive gravitropism
does not work. Without gravitropism as the main force for an ordered root
(system) structure, the roots are growing randomly through the soil.
