long-distance signalling

Question 1

What are the primary modes of long-distance signaling in plants?

Answer 1

• Hormones
• Nutrients
• Gases (oxygen and carbon dioxide)
• Metabolites (e.g., sugars)
• RNA and proteins

Question 2

How does abscisic acid (ABA) function in long-distance signaling?

Answer 2

• ABA is synthesized in roots under water stress and transported to leaves via the xylem to induce stomatal closure.
• Split root experiments and ABA radiolabelling show that ABA and conjugates move through the symplast and apoplast, with transport via the xylem being rate-limiting.

Question 3

How does auxin function in long-distance signaling?

Answer 3

• Auxin is produced in the apex and moves to the base of the plant, playing a crucial role in gravitropism.
• The flow of auxin and calcium ions to the lower side of horizontal roots inhibits cell elongation, causing roots to grow downward.

Question 4

How does nutrient feedback regulate signaling between shoots and roots?

Answer 4

• Nitrate uptake is feedback-regulated based on internal nitrogen levels.
• NH4+, glutamine, and other amino acids may mediate feedback inhibition of nitrate transporters in roots.
• Hormones, peptides, proteins, and RNA likely play a role in this signaling.

Question 5

How does oxygen function in long-distance signaling in plants?

Answer 5

• Oxygen is vital for ATP production. Depletion in roots triggers a reduced metabolism in leaves and oxygen transport to roots.
• Ethylene plays a role in oxygen signaling, and plants can adapt to hypoxia by inducing enzymes for ethanol fermentation.

Question 6

What is the role of carbon dioxide (CO2) in long-distance signaling?

Answer 6

• CO2 affects stomatal movement and stomatal density.
• High CO2 concentrations decrease stomatal density and interact with sugar signaling pathways.
• Jasmonic acid signaling regulates stomatal density in response to elevated CO2.

Question 7

How do sugars function in long-distance signaling in plants?

Answer 7

• Sugars such as sucrose and glucose are key signaling molecules for growth and flowering.
• Sucrose regulates flowering and gene expression, while glucose interacts with hormones and stress responses.
• Trehalose affects root elongation, starch accumulation, and photosynthesis.

Question 8

How do RNA and proteins contribute to long-distance signaling?

Answer 8

• Proteins and RNA move through plasmodesmata (PD), membrane-lined pores between cells.
• Large proteins (>50 kDa) and messenger RNA can cross PD.
• Movement proteins can dilate PD, enhancing protein and RNA transport.
• RNA movement has been observed in the phloem.

Question 9

How does long-distance signaling coordinate plant responses?

Answer 9

• It enables coordinated growth, development, metabolism, and environmental responses across different plant parts.
• This is facilitated by signaling molecules such as hormones, gases, sugars, and RNA/proteins.