In some species of plants the stigmas are ready for pollination, after blooming flower, and some species of plants the stigmas are ready for pollination before the opening of a flower - still in the bud
Nadine is correct. As the stigma becomes receptive the papillae in the surface extend and look glassy due to the exudates on the surface.
For example when crossing Arabidopsis, emasculate flowers when stigma is first visible through the sepals about 24 hours later you should see that the papillae have extended and they are receptive.
I'm going to disagree with some of the contributors above because not all plants have "wet" stigmas - some may be receptive and still look "dry" - see for example:
http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.1992.tb02941.x/pdf
In addition, in my experience the H2O2 test can be a bit hit and miss, and can give a false positive if the stigma is damaged.
A better way to test timing of receptivity is to add (very) fresh out-cross pollen to stigmas of different ages, leave for a few hours, then fix and look for pollen tube growth.
Dear Jeff!
Many thanks for article!! I study the features of pollination and self-incompatibility in heterostyled species of Linum. This genus has self-pollinated species - homostyled species and cross-pollinated species - heterostyled. It is known that in homostyled species stygma ready to pollination in the bud (the day before opened flowers). In heterostyled species this unknow, but heterostyled species have two types of flowers, jne of this have "wet" stygma and anjther - "dry"...Becides I tried pollinated buds and flowers, fixed and looked pollen tube growth...In buds pollen tubes not grow....
regards,
Hanna
Most available books on pollination techniques give you a range of techniques for determining when a stigma is receptive. The peroxidase technique has been discussed above. Check the literature and consider the use of the esterase test. It works equally well on wet and dry-type stigmas, Dr. Ollerton because, technically, ALL stigmas are wet stigmas since pollen grains can't hydrate on a stigma surface until the pistil gives them just a little drinkie of water and sugar... right? What we call dry stigmas do produce some fluids but they can not produce free-flowing fluid. Even the thin, proteinaceous pellicle of a stigma produces a little water while the so-called "wet" stigma of a petunia is really composed primarily of lipids (grease) instead of water. Virtually all stigmas release some sort of an esterase combination when they are ready to receive pollen (wet or dry) and that actually includes flowers that bloom underwater (they release esters into the water as a "stigmosphere." If this old technique was good enough for the Heslop-Harrisons, Bruce Knox, Cameron Mconchie (spelling?), Jo' Kendrick and their colleagues/students it's good enough for YOU!
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