This post belong to my search for explanation of extreme longevity of Siscia Lemon fruits.
Googling for "lemon fruit regreening" gives interesting links. The most amasing and totaly unexpected is that one of authors mentioned there, Nikola Ljubesic, was born just a few kilometers from my location. World is small, indeed.

"Chromoplasts - the last stages in plastid development" by N. Ljubesic, M. Wrischer and Z. Devidé, 1991.:
http://www.ncbi.nlm.nih.gov/pubmed/1814407

"...
Concluding remarks
The various physiological functions of the chromoplasts are just
beginning to be understood. Recent investigations have further
revealed that chromoplasts are organelles with an active metabolism
leading to the accumulation of various pigments (carotenoids)
and to the formation of special structures that contain the pigments.
The correlation between these structures and their chemical
constituents (pigments) is not always clear.
...
A large variety of pigment-containing structures exists even in
one and the same chromoplast. Some of these structures are
transient, being present only in unripe chromoplasts. In most ripe
and senescent chromoplasts plastoglobules are the prevailing
inclusions, which bear, in addition to lipids, various carotenoids.
Chromoplasts are usually the last step in plastid development,
which finishes with their senescence and death. There are however
many objects for which a reversible transformation leading back to
chloroplasts is confirmed. Factors which correlate these processes
are still not well understood, since intensive biochemical and
genetic investigations on chromoplasts have been started only in
the last few years..."

Now hunting article:
Ljubesic, N., 1984: "Structural and functional changes of plastids during yellowing and regreening of lemon fruits. Acta Bot. Croat. 43: 25-30."

My hunt for above mentioned article resulted in:

Dr. sc. Nikola Ljubešić (right) and his brother Ivica in visit, 2011-09-06:



The tree is Siscia Lemon hosted by Poncirus Trifoliata "Siscia".

Talking about visits, forum member Sylvain, 2011-08-14:



Sorry for so many sticks around.

Love the fact that at 50 years old the trees are doing so well in containers and still at a manageable size.

The oldest container grown citrus tree that I am personally aware of is now 122 years old. It is a Sour Orange tree. This tree might not be the oldest container tree, but it is the oldest, that I personally know of. - Millet (460-)

SeaHorse_Fanatic,
Easy-To-Grow seems to be one of the characteristics of this tree.
Just impression for now, to be more precise on it much more work has to be done.

Millet,
122 y means constant care through several generations,
is that tree owned by a family or an institution ?

It's always nice to put a face to those who contribute so much to this forum. Thank you, Ivica, and all the others who contribute so much.

Ivica, the 122 year old container Sour Orange tree is growing at the Catholic Monastery of Our Lady of The Rosary in Summit, New Jersey, USA. Presently the tree is under the care of a Nun named Sister Mary Catharine. The tree is a rooted cutting that was taken from the famous Sour Orange tree that Saint Dominic planted in the year 1200 at Saint Sabina Convent in Rome, and is still alive today. The rooted cutting tree came to the USA in 1889 when the order opened a new monastery in New Jersey, and has been under the care of the Dominican nuns ever since. Any of our members who might be interested in the history of the mother tree, they can read about it in the book "The Citrus Industry" Vol. 1 pages 45 & 46. - Millet (460-)

This whole thread has been a joy to follow. Thank you Ivica!

Jrb, Gotro17 you are so kind. Thank You.

Millet,
Yes, I can recall that now. At the time I was following the topic "Mainly for Millet"
link

Any updates Ivica ?

Short report on taste test performed mid February:

All volunteers are females: one daughter, wife, sister, neighbour.
I made slices of 3 homegrown fruits: Siscia , Meyer and Lisbon lemon,
and gave them 3 stacks of slices to taste and tell which one is the best.
They did not know which stack belongs to which variety.

Result: All agreed that Siscia lemon fruit tastes the best.

Note about fruits:
All fruits were result of flowering in May last year. Meyer fruit was over-ripen,
other two were not fully ripe.

Main updates will follow here:
link

Amazing !!!

Wonder which treasures still are hidden and wait to be revielded ...

Just what me wonders is that you think green seeds belong to Mandarins.

I saw thousands of Mandarin seeds and none was green.
Just all KUMQUAT seeds are green.

Sanguinello, thanks.
Those green seeds are still a mystery.
I saw no difference between seedlings of those and seedlings of 'regular' seeds - seedlings of both type were lemons.

You are very welcome !

There is no difference.

The seeds inside the Cumquats are green, but if you put them outside they turn to normal seeds within few minutes.

As it was said before, also the seeds of overripe citrus get green, but only after germinated.