The scientific behind How orchid flowers keep growing even after the buds open?

[Halloamey]

The science behind how orchid flowers keep growing even after the buds open?

Recently we have had many posts with gorgeous vandaeceous blooms. Everyone noted and mentioned a particular characteristic about these flowers. The flowers keep growing in size even after buds open.



How does this happen? Why does it happen? And does it happen in other orchids or even other plants?? These are all the questions I will try to answer in this article.

All the floral organs are ultimately made up of neatly arranged and organized cells.



The microscopic images are from a Phalaenopsis flower and by Brian Johnston from Canada.
(http://www.microscopy-uk.org.uk/mag/artnov07/bj-orchid.html]Microscopy-UK Micscape Microscopy and Microscopes Magazine[/url])

The ‘growth’ we observe is very different from say the normal growth of leaves, roots or developing buds. Growth can be defined as the increase in mass (weight) and volume (size) which also corresponds to the increase in the number of cells. We have all studied mitosis in various details at some or the other point in our academic lives. Basically growth occurs by the multiplication of the cells termed as mitosis. Here is a diagrammatic representation of all the stages in Mitosis to brush up.



In essence a cell enlarges in size, duplicates its DNA, and then divides into two sister cells each with an identical copy of the original DNA. This goes on until the desired growth is achieved.What is important to note is that cell division or mitosis cannot control the shape and size, these have to be regulated my plant hormones and organ identity genes that organize these cells into proper structures. Mitosis can only increase mass and volume, it cannot give the necessary shape without the help from hormones and other factors.





From Both the above images you can see that on duplication it is impossible for the cells to organise into the same square shape as that of the original group of cells, so along with growth in size, there is change of organisation and shape.
This is essentially what happens during tissue culture when cells are allowed to multiply to form callus. Callus is a mass of multiplying cells which is unorganized, i.e. lacking arrangement in the form of organs like roots, leaves, etc. Shown here is an image of tobacco callus from Wikipedia.




Another important aspect is that this organization and division can only occur in meristematic cells. Meristimatic cells are the precursor for all cells. After division and organization by the hormones and regulatory genes the cells differentiate into cells that are meant and programmed for a particular function, in doing so they lose their meristimatic identity. It is just like young students out of school, they can decide pretty much whatever they want to do and study in their lives, but once they choose a path of say medical studies, they can only become a doctor, not an engineer.
When an orchid bud opens, it essentially is completely developed, all the structures are organized, there are petals, column etc and there is no unorganized meristimatic tissue that can multiply and yet orchid flowers grow in terms of mass and volume without losing the integrity of their organization and shape, how is that even possible?