Senescence
Senescence is an important program in which the function of a cell/tissue/whole plant naturally leads to its death.
Senescence involves in plant aging.
When tissues senesce they produce enzymes which can recycle the “expensive” materials and reroute the sub-units to somewhere else that growth takes place.
Overall senescence
· Occurs in the whole plant.
· Death takes place right after flower and setting.
· When the flower dies the whole plant dies too.
· Ex: Asteraceae ( Sun flower)
image via Wikipedia
Top senescence
· After the growth season the part above the ground dies remaining the underground part that can grow for several years.
· Therefore a rhizome is present.
· Ex: Weed, Grass
Deciduous senescence
· In dry seasons like winter and summer, the leaves falls and trunk remains.
· Leaves fall due to avoid the heavy transpiration occurs in the dry season.
· Ex: Deciduous plants
image via ehow.co.uk
Progressive senescence
· Older parts die due to the senescence and the new organs and tissues continue their development.
· Ex: Green trees
image via clasohm.com
As above mentioned, senescence can occur in cells as well as tissues.
Cell senescence
· Can be described according to the senescence in cell membrane and organelle level.
Senescence in cell membrane
Lipid phase change
· Plasma membrane has the fluid mosaic structure.
· This structure changes as the liquid crystalline state changes into the solid-gel state.
· Therefore the membrane gets inflexible and hard.
Degradation and preoxidation of lipids
· Lipid content gets decreased.
· It occurs as the lipid synthesis decreases and lipase content increases.
· Phospholipase, lipoxygenase, MDA and active O2 content increase.
Increase in Phospholipase activity
· Mainly the activity of Phospholipase D takes place in plants.
Biomembrane degradation and leakage
· The equilibrium of ions breaks down.
· Metabolisms get disordered.
Senescence in organelle level
· Ribosomes and RER break down.
· Chloroplasts collapse and mitochondrion cristae are swollen.
· As the vacuoles break down, all the toxics inside them is released to the cell plasma.
· Therefore the autophagy takes place and the senescence of organelles activates.
