L14 - Ripening and Senescence Flashcards
Ripening:
- Definition
- Changes that happen
- When does it take place
Ripening: Biochemical and structural changes that make the fruit attractive for us (animals) to eat (and distribute the seeds)
● Changes in color»_space; attractiveness
● Volatile production»_space; aroma
● Softening»_space; texture, juiciness
● Changes in nutrient composition»_space; taste
● Ripening may take place plant attached, or after harvest
Takes place both when attached to plant or after harvest
Dependent on the temperature
Climacteric fruits
Climacteric: ethylene plays an important role in the ripening. Often an increase in respiration is observed
So fruits that can be harvested and ripened off the plant. Fruits undergo significant physiological changes.
Large increase in sugar during ripening because they have starch
Non climacteric fruits
Fruits that are not capable of continuing the ripening process (physiological changes) once removed from the plant
No increase in sugar content
Decrease in respiration after harvest
Changes in firmness, external color and aroma
List of Climacteric/Non climacteric fruit
Slides 4-5
Color change. Example in fruits
The chlorophyll is broken down and other compounds may be produced during ripening
• Tomato: lycopene produced
• Banana: the yellow compounds
were already there
• Apple: anthocyanin
produced
Avocado: specific anthocyanins produced (cyanidine-3-O glucoside)
Mango flesh :
carotenoids produced
Mango peel : anthocyanin produced
Firmness loss, softening
Cell walls loosen due to the action of several
enzymes (e.g. cellulase , pectate lyase , pectin
methyl esterase, poly galacturonase , glucosidase, xylosidase, expansin, XET) -> Fruit softens
Cell wall properties determine the textural features of the product (Crunchy, mealy, juicy)
Nutritional changes during ripening
In many (but not all) fruit (apple, mango, banana, pear, ..), starch (or another carbohydrate storage form) is converted into sugar (sweet) and/or acids are broken down (may also be converted into sugar.
In some products (strawberry) sucrose is converted into gl+fr which may make the fruit more sweet
Several enzymes are involved. Sugars may stimulate respiration (ATP production)
Starch and ripening
Note that starch is a poly glucose molecule: many conversions take place during ripening
Amount of starch = ripeness indicator
Volatiles and ripening
Volatiles produced during breakdown of:
- Protein
- Fatty acids
- Phenolic compounds
- Carotenoids
- Amino acids
Volatile production reflects the ongoing ripening processes
Senescence or Aging. What is it?
An ordered process that leads to the death of a cell, not just an accidental event. Programmed Cell Death
Senescence is an active process which is slowed down at lower temperature
Ethylene may stimulate the process
PCD types in animals
Apoptosis:
Cell contents of dying cell is degraded in other cells (type 1)
Autophagic cell death: Large scale autophagy (self eating) prior to or during cell death (type 2)
Programmed necrosis: No self eating, no degradation of cell contents in other cells. Swelling and breakdown of cell membrane (type 3)
All forms of programmed cell death may be accompanied
by “apoptotic features”
More about apoptosis
Most cells die in an ordered way showing recognizable morphological features
Apoptotic bodies are taken up and content is degraded in lysosome (vacuole) of other (living) cell
Morphological features of Autophagic PCD
Large scale autophagy is observed ( Cytoplasmic components
are degraded in lytic compartments of the same cell)
Also some of the apoptosis features are observed
It is not clear if autophagy is the reason that the cell dies
It may be that when all components have been eaten, the cell enters the apoptotic pathway
Necrosis
Happens in response to severe stress
Gives rise to inflammatory response
The process can be non programmed, but also be executed in a controlled way (called programmed necrosis, type 3)
Senescence: General information
Cells die in an ordered way, they follow a program
Often, at first most cell content is degraded in the
vacuole ( may also include essential vitamins
Degradation products are redistributed and re used
The type of cell death observed during over ripening and
senescence in fruit, leaves and flowers is most similar the animal Autophagic Cell Death (self eating)
In plants this type of cell death has now been termed Vacuolar Cell Death