Leaf Senescence

Question 1

What is senescence?

Answer 1

A coordinated loss of function

Question 2

What causes senescence?

Answer 2

Typically induced by short days and long nights

Question 3

What is a critical photoperiod?

Answer 3

length of day that causes a physiological response

Question 4

How does senescence work?

Answer 4

• Promoted by low temperatures and bright light
• Affected by a drought, during the summer leaves can senesce, interrupted by frost
• As leaves senesce, nutrients (e.g nitrogen) are resorbed for storage
• Nutrients come from foliar proteins, some from chlorophyll
  Resorbed via phloem

Question 5

Describe the color change process

Answer 5

1. chlorophyll is unstable in the light, so normally constantly being replaced
2. Production of chlorophyll stops and remaining chlorophyll disappears
3. Anthocyanins allow continued functioning of the phloem during nutrient resorption

Question 6

What is the abscission zone?

Answer 6

2 layers -> pectinases digests middle lamella of top layer
Cells of lower layer expand,forcing separation
Wound is sealed with suberized cork
In angiosperms, tyloses plug the exposed vessels

Question 7

What is marcescence?

Answer 7

retention of dead organs (like when leaves die but don’t fall off)

Question 8

How is senescence mediated?

Answer 8

By plant hormones

Question 9

How is senescence promoted?

Answer 9

Low temperatures and bright lights

Question 10

What are anthocyanins?

Answer 10

Thought to act as a sunblock preventing photo-oxidative damage

Question 11

What does the accumulation of red pigments at other times of year mean?

Answer 11

Common in plants growing in high light, stressful situations