BIOCHEMISTRY

WT Arabidopsis pollen stained with DAPI

DAPI (4',6-diamidino-2-phenylindole) binds to DNA and labels the nucleus.
 DAPI staining is a common way to monitor pollen development

During the tetrad and microspore stages, the single nucleus is very bright and located in the center of the pollen grain.  At the early bicellular stage, just after pollen mitosis I, the larger vegetative nucleus stains very diffusely, whereas the generative nucleus is very bright and compact.  This brighter staining is due to the more condensed state of the chromatin in the generative nucleus, probably indicating that it is less transcriptionally active than the vegetative nucleus.  As the bicellular stage progresses the vegetative nucleus gradually becomes more distinct, staining as a ring (also seen in the tricellular stage).  The generative cell divides during pollen mitosis II to create to two sperm cells, which are very small and bright.  The sperm cells have an elongated shape, and associate closely with the (now more distinct) vegetative nucleus to form the "male gametophytic unit" (MGU) of the tricellular grain.

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