A study of free ubiquitin and ubiquitinated proteins has been carried out i
n olive (Olea europaea L.) during the late stages of pollen development and
during in-vitro pollen hydration. As described in relatively few plant spe
cies, immunoblot experiments carried out using crude protein extracts have
shown a reduction ill the free ubiquitin level taking place during the matu
re pollen stage. This reduction does not coincide with a pal allel reductio
n in the level of the corresponding transcripts, as detected by RT-PCR anal
ysis, suggesting the existence of a post-transcriptional regulatory mechani
sm. Relatively high levels of free ubiquitin are quickly restored upon in-v
itro pollen hydration. TEM immunocytochemical localisation of ubiquitin-con
jugated compounds in the mature pollen grain showed the antibodies bound to
the cytoplasm, the chromatin and the nucleolus of the vegetative and gener
ative cells. Within the cytoplasm, labelling was concentrated in the cytoso
l, the endoplasmic reticulum membranes and minuscule vesicles associated to
the Golgi apparatus. The fibrillar material adhering to the exine, and pro
bably derived from the tapetum, also showed Sold particles. Lipid bodies, a
perture regions, mitochondria, the intine and the cell wall were devoid of
labelling. The changes observed throughout pollen development, as well as t
he specific localisation, reflect the involvement of the ubiquitin-mediated
degradative pathway in regulation of pollen metabolism.