chloroplast ultrastructure

[samuelmain]

Hello everybody,
Could you have a look to the picture attached, and tell me what you think about it? This is a transmission electron micrograph of Arabidopsis (Columbia0 ecotype) 14-days-old cotyledons. Is this chloroplast senescing? Is this a chromoplast, or anoter kind of plastid? Or is it a regular healthy chloroplast?
Thank you very much for your help,
best regards,
... and happy new year!
Samuel

[MrMistery]

hard to tell from one picture, but here is my opinion as a non-experienced student:
it is a chloroplast, because that structure looks like a lamellar system. It resembles a little with a picture i once saw of a chloroplast grown in a medium without light. It is definitely not a normal mature chroloplast, because it lacks grana. See that chloroplast in the right bottom corner? That is a normal one. Honestly there is not much i can tell you, except that it is an abnormal chloroplast. Sorry...

[samuelmain]

OK, thanks for your opinion, and i agree with you.
And as it's hard to tell with one picture, here is a second one, representing a whole cell containing many of those strange plastids.
And to finish, is the bottom-right corner plastid really normal? I thought that regular thylacoids were darker than the background stroma... (here it is the converse).
What do you think?

best regards *

[MrMistery]

well it looks normal to me. The thylacoids do look darker, at least i see them that way. I may be excessively tired right now. And also note the beautiful orderly structure.
As for your second picture: sorry nothing more to add. I prefer to remain silent than to say something stupid.
But do let me know if you find out the answer