Re: Why don't onion cells have any chloroplasts

Vinh, 

Several years back I answered a similar question on this same network but, 
it was only dealing with the epidermal cells of onions. You can see this 
answer at: 
 ht
tp://www.madsci.org/posts/archives/oct2001/1002637439.Cb.r.html

Light is needed for the development of chloroplasts.  There are many types 
of plastids found in plant cells but, not all plant cells have all the 
different types of plastids.  Some plastids can contain pigments other 
than chlorophyll and are called chromoplasts and plastids that store 
starch are amyloplasts.  It is thought that all plastids arise from a pro- 
plastids. Since onion bulbs are below ground they do not get the light 
necessary for chloroplast development.  There are lots of web sites 
available that have information on this subject.  Try a google search 
using the words "chloroplasts and onions" or "onion chloroplasts".  If you 
are interested in learning more about cells, onions are a good 
experimental organism.  Onion root tips are great to study mitosis and 
meiosis and the thin membranous epidermis between the onion rings are 
perfect for observing plasmolysis.  Good luck with your studies.