Plant responses to internal and external signals

What do most responses from plants involve?

Since they are stationary, most responses involve growth and development

What are signals?

Something that conveys information

• usually information external to the cell that comes from the plants environment or internal to the plant, such as hormones

what occurs when a plant receives information?

1. The signal is received (reception)

2. the signal is then transferred and amplified (transduction)

3. Then the signal activates a cellular response

The signal transduction pathway

1. Reception: the signal is detected by a receptor, causing the receptor proteins to change shape in response to specific stimuli (signals)

2. Transduction: the change in the receptors conformation activates second messengers

   1. sometimes the reception of one signal can activate multiple secondary messengers (which is amplification)

3. Response: The second messengers activate one or more response proteins, leading to regulation of one or more cellular activities

where are receptor proteins usually located?

Usually embedded in the cell membrane but sometimes in the cytoplasm

what are some common second messengers?

Ca (2+) and GMP

what do plants use for communication between different parts of the plant?

They use chemicals, which are often produced in response to external signals

How are chemical signals transported in plants? (What is the system they are transported through)

They are transported quickly through the xylem and phloem vascular tissue within the plant

• these signals are transported through the vascular system

what is a hormone?

A signaling molecule that is produced in low concentrations in one part of the body and transported to other parts

why are hormones referred to as plant growth regulators?

They typically impact changes in how the plant grows, such as in cell division, elongation, and differentiation

what do hormones do to target cells and tissues?

they bind to specific receptors and trigger responses

what are the four main plant hormones (focused specifically in this chapter)?

• Auxin

• Cytokinins

• Abscisic Acid

• Ethylene

What is Auxin?

They are important hormones for plant tropism and controls spatial organization of plants

• was the first plant hormone to be discovered

what is tropism?

the growth toward or away from stimulus

what does Auxin promote?

Elongation of plant cells, such as differential elongation (different sides of stem)

Where is Auxin produced and then transported to?

Primarily in the tips of roots and shoots, then transported mostly to other cells where action is usually initiated or through phloem

What does more auxin equal to in a plant?

Equals to more apical dominance, resulting in axillary buds not developing and promotes new leaf growth

How did Charles Darwin experiment on plant elongation? (What were the results?)

He removed the tip from plants and covered the tips of other plants using an opaque cap, a transparent cap, and a opaque shield over the curvature of a plant

• Plants with the tips removed and with an opaque cap on resulted in no tropism occurring

• However, plants with a transparent cap and a opaque shield over the curvature was seen bending and being able to detect the sunlight

what did charles darwin conclude from his results on plant elongation?

He concluded that the tips of plants were able to sense sunlight

How did Boysen-Jensen experiment on plant elongation? (what did it result?)

He separated the tip of one plant with an impermeable barrier and another with a permeable barrier

• The plant tip with the impermeable barrier resulted in no tropism occurring

• however the plant tip with the permeable barrier resulted in the tip bending

what is the process of how Auxin causes cell elongation to occur?

1. The auxin binds to a receptor and stimulates a proton pump

2. activating expansins to loosen the cell walls and encouraging more water intake

3. resulting in an increase in turgor pressure and wall plasticity, causing cell elongation to happen

What does auxin alter?

Gene expression to sustain growth

what if there is only cytokinin and no auxin?

The cells in a plant will grow larger but wont divide

what if there is cytokinin and auxin present?

The cells in a plant will divide

what if there is an equal amount of cytokinin and auxin

the plant cells will be undifferentiated

what if there’s more auxin than cytokinin?

the auxin will suppress axillary bud growth

what if there’s more cytokinin than auxin?

the cytokinin will promote axillary bud growth