How does it relate with the solution and solute movement through the xylem of the flower stem.
The sugars provide energy for the plant, when photosynthesis has been restricted. This slows down senescence of the cut stems.
Acids are added to slow down microbial activity in solution used for the flower. Bacteria would also consume the added sugars and block the xylem, this reducing the availability of water for your cut stems.
Thanks. I want to know about transpirational pull by flower stem and osmotic pressure exerted by vase solution with relation to the acidity (pH) and the movement across the xylem vessel. Mechanism of resultant counter forces acting.
The flowers will transpire little, but the remaining leaves will, and they will subsequently transport imported sugars to the flower.
The osmotic pressure of the sugars in the vase would be minimal and the pH does not affect the osmotic pressure at all.
The xylem delivers the sugars to the apoplasm of the leaf cells, from where the can be actively absorbed.
Does this address your questions as you wanted?
Thanks a lot. Does it mean that for the sugar to reach the petals of the flower, translocation via leaves is mandatory? On other hand, acidity (pH) influence the water uptake. How to correlate that? The plant sap itself is slightly acidic. All this for an efficient way to supply better food source to the cutflower.
The sugars will have to move in the transpiration stream. If the petals transpire significantly, they will arrive there directly. If they don't, they arrive in the leaves, from where they can be transported via the phloem to the petals. I assume there is a combination of both.
Water uptake into the cut stem is a passive process and no membranes are crossed; hence it should not be affected by the pH of the vase solution. I don't see a problem with that.
Thank you sir. Regarding pH, vase preservative are usually maintained near pH 4 in order to improve the solution uptake how to explain that? Does it means that acidity of the solution are meant only to reduce microbial infection? Also, if we put cut stems in different concentrations of sugar solution will the uptake remain same?
Indeed, the low pH is to reduce bacterial growth. The "slime" that results from bacterial growth would block the xylem and reduce uptake. The low pH is NOT important for uptake other than that, because water and solutes are taken up via the cut stem, and there is no active plant process involved at that stage; active uptake of the added sugars occurs once they have arrived in the leaves or flower.
You can increase the sugar concentration to allow more uptake, but there is no point making the solution too concentrated, as you may supply more than is actually required, and have a negative effect on vase life of the cut flower.
Which sugar?
fresh cut flower, there are a senescence process : Sucrose delay senescence and fructose and glucose induce it. So… When I was working on post-harvest I had an extensive bibliography about it…
There are a lot of biblio from the 80's about that question from memory, there was a good review from someone named Nooden. Just look for senescence + "cut flower" on scholar google you will have plenty of resources
The pull of a water molecule leaving the plant system as a result of transpiration achieves hydration of the tissues (necessary to prevent plasmolysis) and transport of dissolved substances, which in your case, sugar is of interest. This transport system relies on cohesion and adhesion of water molecules to themselves, and to the wall of the conducting vessels. These two concepts are of paramount importance to understand how plants keep turgid and adequate supply of nutrients.
Bacteria, pose a problem, they are ubiquitous, and their proliferation is exacerbated by the amount of free carbon source .. sugars. These same sugars are used in vase solutions as a carbon source for the stem. In order to control bacterial proliferation, the pH of the vase solution is dropped using a weak acid.. usually citric acid. There are other substances used as "bacteriostats" in vase solution. Halevy (http://departments.agri.huji.ac.il/horticulture/staff-eng/halevy.html) has a great series of books which go into great depths about the subject.
The other issue is the hormone ethylene...
When the complex seems impossible to grasp, go back and review the basics.
There is a species response which you should not disregard. And there is, as well, a cultivar response. So you have to be carefull before using generalizations. Which species is your concern?
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