Pulvinus

Fig63Movement of Plants

Jacaranda jasminoides (Thunb.) Sandwith (2425584978)

Pulvinus is a specialized motor organ found at the base of the leaf or leaflet in some plant species, particularly in the family Fabaceae. It plays a crucial role in leaf movement, enabling plants to adjust the orientation of their leaves in response to environmental stimuli such as light (phototropism), water (hydrotropism), and touch (thigmotropism). This adaptability helps in optimizing photosynthesis, maximizing light absorption, reducing water loss, and minimizing damage from environmental stressors.

Structure and Function

The pulvinus consists of a flexible segment of tissue that allows the leaf or leaflet to rotate or bend. It is made up of specialized motor cells that can change their turgor pressure rapidly, leading to the swelling or shrinking of the pulvinus and thus moving the leaf. This movement can be either nastic, which is non-directional and caused by internal stimuli, or tropic, which is directional and caused by external stimuli.

Phototropism

In response to light, the pulvinus can cause the leaf to orient itself to maximize light absorption. This is particularly evident in plants with solar tracking abilities, where leaves move to follow the sun across the sky, a phenomenon known as heliotropism.

Thigmotropism

The pulvinus also responds to touch or mechanical stimuli, enabling plants like the sensitive plant (Mimosa pudica) to fold their leaves inwards rapidly when touched. This is thought to deter herbivores or help reduce damage from environmental forces.

Hydrotropism

Water availability can also influence pulvinus movement, with some plants adjusting their leaf angle to reduce water loss through transpiration during dry conditions.

Ecological and Evolutionary Significance

The ability to move leaves via the pulvinus provides significant ecological advantages. By optimizing leaf orientation for photosynthesis, plants can improve their energy efficiency and growth rates. Additionally, the rapid movement in response to touch or other stimuli can protect against herbivory and physical damage.

Examples

While the pulvinus is most commonly associated with the Fabaceae family, it is also found in other plant groups. Examples include: - Mimosa pudica (Sensitive plant), known for its rapid leaf folding in response to touch. - Samanea saman (Rain tree), which closes its leaflets at night or in response to rain. - Certain species of Phaseolus (Beans), which exhibit solar tracking.

Research and Applications

Research into the mechanisms behind pulvinus movement continues to shed light on plant physiology and adaptation. Understanding these processes can have applications in agriculture, such as developing crops that can adjust their leaf orientation to cope with changing environmental conditions, potentially leading to increased yields and resilience to climate change.