Biology Reference
In-Depth Information
mannose, and stachyose (2 species each); and arabinose, lactose, and treha-
lose (1 species each) (Petanidou, 2005).
Considering only the three main sugars, this phryganic community can be
divided into species with “high sucrose” floral nectars (sucrose-dominant to
sucrose-rich, according to the terminology of Baker and Baker (1983), which
uses the sucrose/hexose ratio as a discriminating value) and “low sucrose”
(hexose-dominant to hexose-rich) nectars (Petanidou, 2005). This does not
imply that sugar composition of nectar is constant throughout the flower life-
span. Petanidou et al. (1996) showed that in
Capparis spinosa,
flower aging
had an irreversible effect on nectar quality, which was expressed as a con-
tinuous decrease of the nectar sucrose/hexose ratio (as a result of sucrose
breakdown) while the glucose/fructose ratio remained practically constant
(approximately 1). The authors also concluded that the rate of sucrose break-
down was regulated (slowed down) by high sugar concentration, which
implies a high invertase activity in dilute nectars versus low activity in con-
centrated nectars (see also Pate et al., 1985). This is very important from the
nectar conservation point of view in regions with high temperatures such as
the Mediterranean.
Just over half the species in Mediterranean communities have high-
sucrose nectars (53.5% of the species according to Petanidou, 2005).
Furthermore, species with high-sucrose nectars have the propensity to flower
in spring and summer (60.8% of the species flowering then have high-
sucrose nectars), whereas high-hexose nectars occur in winter flowers (63.6%)
(Petanidou, 2005). The selection of high-sucrose against high-hexose nectars
can be partly explained as a result of the drought constraint in the Mediterra-
nean area, because high-hexose nectars consume more water than nectars
with high concentrations of sucrose for the same amount (weight) of sugars
contained, i.e., for the same sugar content (see discussion under “Water stress”
on page 355; cf. Nicolson, 1998, 2002). It is unknown whether this is a spe-
cific characteristic of the Mediterranean region as no comparable data are
available for other world communities.
2.1.2
Amino acids
Several amino acids have been found in floral nectars, all in much lower
quantities than sugars (Baker & Baker, 1978, 1982, 1986; Gottsberger et al.,
1984; Gardener & Gillman, 2001b; Chapter 5 in this volume). In the phryganic
nectars, 22 amino acid compounds or groups of compounds have been detected
(Petanidou et al., 1996, 2006). Cysteine and proline (including hydroxypro-
line) were not detected in phryganic nectars, owing to the analytical methods
