220.127.116.11. Pollen viability
One approach is to evaluate viability prior to
germination. The most common test is the fluorochromatic reaction (FCR test)
based in fluorescein diacetate (FDA) (Heslop-Harrison and Heslop-Harrison, 1970;
Pinillos and Cuevas, 2008). This test evaluates the integrity of the
plasmalemma of the pollen vegetative cell and activity of nonspeciﬁc esterases
of the cytoplasm, and only viable pollen grains will fluoresce under the
microscope (Fig. 6). Another commonly used viability test is Alexander staining
(Alexander, 1969); viable pollen stains crimson red while aborted pollen stains
green. Additional tests such as the use of tetrazolium dyes, X-Gal, isatin or
Baker’s reagent can also be used (see Dafni and Firmage, 2000 for a review).
However, in most viability tests not all the viable pollen grains are able to
germinate, and consequently the percentage of pollen germination is usually
lower than the percentage of viable pollen.
Fig. 6. Pistachio pollen stained with FDA: viable pollen grains show bright fluorescence compared to non-viable pollen grains.