Floral nectary, nectar production dynamics and chemical composition in five nocturnal Oenothera species (Onagraceae) in relation to floral visitors
Floral nectary, nectar production dynamics and chemical composition in five nocturnal Oenothera species (Onagraceae) in relation to floral visitors
Sebastian Anton´ 0 1 2
Elwira Komon´ -Janczara 0 1 2
Boz_ ena Denisow 0 1 2
0 Department of Biotechnology, Human Nutrition and Science of Food Commodities, University of Life Sciences in Lublin , Skromna 8, 20-704 Lublin , Poland
1 Department of Botany, University of Life Sciences in Lublin , Akademicka 15, 20-950 Lublin , Poland
2 & Sebastian Anton ́
Main conclusion The floral nectars were sucrose-dominant; however, nectar protein and amino acid contents differed, indicating that composition of nitrogenous compounds may vary considerably even between closely related plant species, irrespectively of nectary structure.
Amino acids; Anatomy; Anthesis; Morphology; Pollination syndrome; Protein
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Numerous zoophilous plants attract their pollinators by
offering floral nectar; an aqueous solution produced by
specialized secretory tissues, known as floral nectaries.
Although many papers on nectaries and nectar already
exist, there has been a little research into the structure of
nectaries and/or nectar production and composition in
species belonging to the same genus. To redress this
imbalance, we sought, in the present paper, to describe the
floral nectary, nectar production, and nectar composition in
five nocturnal Oenothera species with respect to their floral
visitors. The structure of nectaries was similar for all the
species investigated, and comprised the epidermis (with
nectarostomata), numerous layers of nectary parenchyma,
and subsecretory parenchyma. Anthesis for a single flower
was short (ca. 10–12 h), and flowers lasted only one night.
The release of floral nectar commenced at the bud stage
(approx. 4 h before anthesis) and nectar was available to
pollinators until petal closure. Nectar concentration was
Abbreviation
GABA c-Aminobutyric acid
Introduction
The ecological importance of floral nectar as a food-reward,
offered by animal-pollinated plants to their pollen vectors,
has long been recognized
(Simpson and Neff 1981;
Nicolson 2007)
. Floral nectar is synthesized and produced by
floral nectaries, i.e., secretory structures that may be found
on different parts of the flower. These vary considerably
both in terms of anatomical structure and nectar-secretory
mechanisms
(Nepi 2007)
. Nectar is the main floral
foodreward for pollinators, and, as such, is subject to selection
pressures imposed by nectar consumers. As a consequence,
nectar characters can be similar between unrelated plants
sharing the same pollination syndrome, or completely
different, even between closely related plant species having
different pollinators
(Baker and Baker 1982)
.
In general, carbohydrates dominate the total solutes
present in floral nectar
(Nicolson and Thornburg 2007)
;
however, other compounds, such as amino acids, proteins,
and lipids, have also been detected in floral nectars
(Baker
and Baker 1983a; Heil 2011; Nepi 2014)
. Moreover,
secondary compounds (such as phenols, alkaloids, and
terpenoids) that are mostly associated with resistance to
herbivory have been documented in floral nectars, and
hence, many plants produce nectar that is toxic or repellent
to some visitors
(Adler 2000)
. Nectar composition may be
conservative due to phylogenetic constraints
(Galetto et al.
1998)
; however, some nectar traits may be subject to
ecological factors imposed by the habitat
(Stiles and
Freeman 1993; Petanidou 2005)
. For example, nectar
production and concentration may be subject to
considerable fluctuations resulting from subtle changes in the
environment (e.g., temperature, humidity, and wind), as
well as other extrinsic factors such as pollinator behaviour,
presence of nectar robbers, or nectar contamination by
yeasts
(Baker and Baker 1983a; Galetto and Bernardello
2004; Herrera et al. 2009)
. In many cases, nectar
components, and consequently, nectar sugar ratios, reflect the type
of pollinator, and flower and inflorescence morphology
may provide a valuable indicator of the pollination
syndrome employed
(Baker and Baker 1983b)
. For example,
sucrose-rich nectar has often been recorded for flowers
pollinated by hummingbirds or by insects with long
mouthparts (e.g., long-tongued bees and butterflies),
whereas hexose-rich nectars occur in flowers pollinated by
short-tongued bees, flies, and bats
(Percival 1961; Baker
and Baker 1983b; Stiles and Freeman 1993; Perret et al.
2001; Nicolson 2007)
. Other carbohydrates, e.g., mannose,
arabinose, maltose, stachyose, or xylose, have also been
detected in small quantities in floral nectars
(Nicolson and
Thornburg 2007)
.
Nitrogenous compounds, i.e., proteins and amino acids,
have also been detected in floral nectars
(Nicolson and
Thornburg 2007)
, but to date, their ecological significance
and evolutionary significance have received a little
attention, and it is only recently that these compounds and (...truncated)