MadSci Network: Cell Biology

Re: What are the functions of plastids?

Date: Sun Nov 12 00:21:27 2000
Posted By: Maggie Guo, Grad student, Plant Physiology and Molecular Biology Program, Dept.of Plant Biology, UIUC
Area of science: Cell Biology
ID: 973478102.Cb


Plastids are plant organelles which have diverse functions include 
photosynthesis, gravity perception, and biogenesis of micro- and 
macromolecules. All kinds of plastids develop from proplastids, which are 
small bodies found in plants growing in dark as well as in the light. 

Leucoplast is the general name for colorless plastids, which are usually 
found in root and dark-adapted plants. Some leucoplasts contain proteins or 
starch, performing storage function. Leucoplasts may also take part in 
gravity perception, but I didn't find reference on mechanism of this function. 

Chloroplast is the location of photosynthesis, as I think youve already known. 
Chromoplast are considered derived from chloroplast, but may arise from 
less differentiated plastids. Chromoplast is the location of forming 
carotenoid pigments such as carotene or lycopene. Chromoplast can be found 
in flower, fruit, and leaves in stress or senescence. In flower, carotenoid 
pigment enables the forming of different color, which can attract insects. 
Also, chromoplast carotenoids are known to accumulate in green tissues 
experiencing stress conditions, and studies indicate that they provide 
efficient protection against oxidative stress. For example, it is shown 
that oxidative stress is a potent driving force for the expression of 
carotenoid biosynthetic genes during the chloroplast to chromoplast 
transition. This is very important for plants. Being immobile and because of 
oxygenic photosynthesis, plants have the highest internal oxygen 
concentrations of any other organism. The concentration of molecular oxygen 
in plant leaf cells is 250 M, which is higher than the concentration of 0.1 
M found in mammalian mitochondria. It has been estimated that 1% of the 
oxygen consumed by plants is diverted into active oxygen.  As a consequence, 
plant cells have developed some nonenzymatic and enzymatic mechanisms for 
scavenging this toxic component. Neutralization by carotenoids is example of 
nonenzymatic mechanisms.


Florence Bouvier, Ralph A. Backhaus, and Bilal Camara: 
Induction and Control of Chromoplast-specific Carotenoid Genes by Oxidative 
Stress J. Biol. Chem. 1998 273: 30651-30659

Anatomy of Seed Plants, 2nd Edition, Katherine Esau, 1976, John Wiley and 
sons publishers.

Plant Physiology, Fourth Editio, Salisbury & Ross, 1991, Wadsworth 

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