Pollen
outing takes a rain check
The release of pollen from the anther is
generally regarded as consisting of two main phases. The first is the opening
of the stomium, the aperture through which the pollen escapes. The second is
the bending back of the anther wall, thus exposing the aperture to the outside
world. This is a process that in many species involves desiccation of the
tissue and may be subject to external environmental influences. It is this
subject that has been investigated by Carrizo
García et al., Córdoba, Argentina and
Siena, Italy (pp. 521–527), working with Allium triquetum. Morphological examination of anthers at different
stages showed that anthers in the inner whorl opened first, in the morning, and
the outer whorl followed in the afternoon of the same day. In their baseline
studies at 40–45 % relative humidity (RH), the authors observed that complete
bending back of anther walls took between 0.5 and 1.5 h. However, the effects
of changing humidity were complex. Reducing the RH to 20 %, a desiccating
environment, did bring about some acceleration of opening in the inner whorl
but, somewhat unexpectedly, actually delayed opening in the outer whorl.
Indeed, most outer whorl anthers did not open until the next day, while some
did not open at all. Increasing the RH above that of the controls (expected to
inhibit desiccation) also delayed significantly the opening of outer whorl
anthers. At 55 % RH, the pattern for outer whorl anthers was similar to that at
20 %, while at 98 % RH over 45 % of outer anthers did not open at all. Inner
anthers were more tolerant of increasing humidity: even at 98 % RH, only
approx. 20 % showed a 24 h delay in opening and only 15 % failed to open. The
authors conclude that phase two of anther opening is subject both to environmental
and specific developmental controls, the relative importance of which varies
between the whorls.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
