Biology Reference
In-Depth Information
ide (Carter & Thornburg, 2004a). In addition, there is preliminary evidence
that dehydroascorbate can serve as a terminal electron acceptor to regenerate
ascorbate.
The high levels of hydrogen peroxide that accumulate in the nectar of or-
namental tobacco are thought to serve as a defence that protects the
metabolite-rich nectar from invading micro-organisms carried to the flower
by wind or by non-sterile pollinators. This biochemical pathway contained
wholly within soluble nectar serves to maintain nectar in a microbe-free state.
Thus in ornamental tobacco, nectar functions not only to attract insect polli-
nators, but also to protect the gynoecium from microbial invasion of the
metabolite-rich fluid (Thornburg et al., 2003, Carter et al., 2007).
To determine how widespread the nectar redox cycle is throughout the
angiosperms, Carter and Thornburg (2000) have examined the nectars of 15
plant species for
Nec1
homologues and identified nine species that showed
immunoreactive material in their nectars. Based upon this, they concluded
that
Nec I
and perhaps the Nectar Redox Cycle are widespread throughout
the angiosperms. In addition, insects may be well equipped to handle oxida-
tive nectar, because many insect guts are antioxidative (Ahmad et al., 1991;
Barbehenn et al., 2001) and enzymes such as catalase and peroxidase are
known to be localized in the insect gut and Malpighian tubules (Ahmad
et al., 1988; Felton & Summers, 1995).
Figure 3.
Nectar Redox Cycle.
