Welcome to JAAN's science class!!

Big hi to all of you! I'm an undergraduate following a Bsc in bioscience. Trust me I know the feeling of surfing around the net for ages and getting nothing in return! Or getting something worthless for the time we spent surfing. So I started this blog adding the science stuff I have noted which I think might help someone in their home work. Ok then enjoy!

12 August 2011

Plant senescence in brief


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.

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