Agriculture Reference
In-Depth Information
therefore, dependent on cell division at the shoot apex. More recent studies have
shown the same sharp decline in cell division at the shoot apex at bulb maturity
in northern European cultivars, as indicated by the low proportion of cells in
mitosis (see Fig. 7.2a) (Pak
et al.
, 1995). Cell division resumed within 2-4 weeks
of harvest. The messenger RNA needed to produce histone 2A, a protein
incorporated in chromosomes at mitosis and therefore associated with this cell
division, has also been shown to decline sharply in shoot apices at bulb maturity
and to begin to increase after harvest (see Fig. 7.2b; Carter
et al.
, 1999).
Fig. 7.2.
(a) Cell division in the shoot apex meristem of bulbs of onion cvs 'Hysam'
(
) shown as the percentage of dividing cells (the
mitotic index) starting 3 weeks before harvest (harvest was time 0) and during
subsequent storage at 16°C. Values are means of five apices (from Pak
et al
., 1995.
Courtesy of
Physiologia Plantarum
). (b) The relative expression of the messenger
RNA specifying the protein histone 2A that is necessary for cell division in the inner
bulb, which includes the shoot apex (
●
), 'Hystar' (
) and 'Centurion' (
) in the middle bulb (
) and the outer bulb
(
) of onion cv. 'Robusta' during bulb formation and subsequent storage. The bars
around the values for the inner bulb are standard errors of the mean based on three
determinations from three replicate bulbs. Percentage visible sprouting is shown as
●
(from Carter
et al
., 1999. Courtesy of
New Phytologist
©
, 1999).
