| MadSci Network: Cell Biology |
Yes and no. There is no scientific answer to a 'why' question: any answer I could give would be either anthropomorphic or religious in nature. Higher plants don't have centrioles because they don't need them: the microtubules' self-organizing capibilities are sufficient. Plants form a circular loop of microtubules around the future plane of division prior to prophase called the preprophase band. Also, higher plants do contain microtubule organizing centers which contain many of the same protiens found in animal centrosomes, they just don't contain the centrioles themselves. (This result is based on antibody cross-reactivity studies.)
I specify higher plants because most so-called 'lower' plants (eukaryotic algae, liverworts, mosses, etc...) do contain centrioles.
The centrosome represents the centrioles AND the pericentriolar material, an electron-dense granular substance surrounding the centriols that is believed to contain the 'seeds' (possibly gamma tubulin) for the microtubules that make up the MTOC or microtubule organizing center.
Some of my information is from Microtubules, 2nd Edition, by Pierre Dustin, Published by Springer-Verlag in 1984, other information is from Karsenti, E. and Maro, N. (1986), "Centrosomes and the spatial distribution of microtubules in animal cells.", from _Trends in Biochemical Sciences_, Vol 11: 460-463. The rest of the information is from personal communication with Trina Schroer of The Johns Hopkins University's Dept. of Biology, or from personal knowledge.