Biology Reference
In-Depth Information
amyloplasts at the end of secretion or after nectar reabsorption seems to be a
general feature.
In
Aloe
and
Gasteria
, which have septal nectaries, dedifferentiation of
amyloplasts to chloroplasts has been recorded after nectar secretion (Schnepf
& Pross, 1976; Nepi et al., 2005). This dedifferentiation allows secreting
cells to transform into fruit parenchyma cells.
Other patterns of nectary plastid development have also been observed.
In
Chamelaucium uncinatum
(Myrtaceae), the nectary parenchyma cells
have chloroplasts and secrete nectar for 11 days. At the end of the secretion
period the nectary becomes red, probably because of transformation of
chloroplasts into chromoplasts (O'Brien et al., 1996). The pattern of nectary
plastid development is more complicated in
Nicotiana tabacum
, where the
nectary parenchyma cells differentiate into chloroplasts in the early stages.
Later they accumulate starch, becoming amyloplasts, and when starch is hy-
drolysed they accumulate β-carotene becoming amylochromoplasts (Fig. 9)
(Thornburg, 2007).
Figure 10.
Floral nectaries of
Arabidopsis thaliana
(
left
) and
Cucurbita pepo
(
right
). Inserts
show the details of plastid structure in the nectary parenchyma cells. In
A. thaliana
there are
chloroamyloplasts with few thylakoids and very few starch grains. In
C. pepo
there are very
large amyloplasts with many large starch grains. Bars = 5 µm.
