Plant cells: Plastids:
As previously mentioned, plastids are doubled membraned 'sac-like' organelles, generally involved in either the manufacture or storage of food.
They include chloroplasts, chromoplasts and leucoplasts
All develop from proplastids: simple, generally colorless undifferentiated plastids..
Number: may range from a few in algae to 75-125 in angiosperm cells.
Note: the outer membrane derived from the ER is made up of 30% protein and 70% lipid while the inner membrane is composed of 0% protein and 40% lipids like bacteria
Note: DNA material is circular, with no histones; 20-100 per chloroplast
Grana = stack of thylakoids ( 2-100 thylakoids per grana) with 40-60 grana per cell
Stroma colorless fluid rich in enzymes.
a. photosynthesis thus they contain chlorophyll, carotenoids in the thylakoids
b. as they contain ribosomes, they are involved in amino acid and protein sythesis.This is not surprising considering the enzyme RUBP involved in photosynthesis can make up 50% of the total protein in a leaf extract analysis.
*What is also critical to note here is their size: 2/3 the size of eukaryotes and the fact they are inhibited by the antibiotic erythromycin. What are the potential implications here? combine this fact with those given above on the differences between the inner and out membranes...
Endosymbiotic theory stipulates that a prochlorophyta ( precursor of the BG's) was incorporated into a larger cell
Progressive evolution stipulates that a BG 'blobed' into the cell and was surrounded
c. Not only can they produce aa's, but also fatty acids. Why?
d. they can store starch, but only temporarily....again why?
e. they also can synthesize RNA and together with CH-DNA are involved in the production of new chloroplasts and pigments
Chromoplasts are found commonly in flowers and fruits.
They contain yellow, orange and or red pigments... carotenoids
Function? they convey information or serve as attractants. In fruits, these colors signal that the fruit is ripe ( as is the embryo), starches have converted to sugars and the bond that holds the cells together digesting to produce a softer texture. Most organisms recognize that 'green' means hold off.
They also serve as attractants and identifiers... a fast moving potential pollinator has little time to site a flower.. the brighter, the more distinguishable, the more likely it will be visited. In some cases, the flower will change color to signal it has already been pollinated and nectar is no longer available.
Leucoplasts are non-pigmented plastids involved in either synthesis or storage
Amyloplasts: starch production
Elaioplasts: oil production
Proteoplasts: develop into specialized plastids as need arises....