Plant responses

Specific chemicals released by cells in response to a stimulus can act as messages. Plants rely on chemical messages for communication between different parts, allowing them to repsond to factors such as light and gravity. Plants respond to a large variety of stimuli, mostly environmental. They are sensitive to light (direction, intensity and length of exposure), gravity, water, temperature and in some cases touch and chemicals. Different parts of the same plant may react differently to the same stimulus. Plants respond to stimuli by producing or destroying chemical messages. Most of the messages are plant hormones which are produced in 1 area and then transported around the whole plant. Plant growth responses to environmental cues are known as tropisms. The main way in which plants respond to the chemicals messages is by growth. In some cases growth is stimulated whillst in other it is inhibited.

Growth is brought about by cell division, the assimilation of new material within the cells which results from the division and cell expansion which follows this assimilation. The main areas of of cell division and elongation in plants are known as the meristems. These are areas which occur just behind the tip of the root or shoot. They are also sensitve to chemial messages which make it easier for the cellulose walls to be stretched. When one side of a plant grows more than the others, the result is the bending of the shoots or roots in response to a particular stimulus.

Chlorophyll formation depends on light and day length. Without light the metabolism of a plant is severly distrupted and prolonged light deprivation causes death. Seeds of many plants will only germinate if they are exposed to light. Research has shown that red light is the most effective at stimulating germination whilst far red light actually inhibits germination. If seeds are exposed to a flash of red light they will germinate. Scientists discovered a plant pigment that reacts with different types of light which in turn affects the responses of the plant. This pigment is called phytochrome. It exists in…