Soybean and Bees

sible that the nectar production dynamics of a species can be determined. The strategy of
the plant of offering nectar, the activity patterns, frequency and diversity of pollinators of a
plant species, the rates of nectar consumption by animals, among others, could not be understood
without deep knowledge of nectar characteristics and dynamics.
Nectar production and the role of enzymes
Several studies targeted the action of the apoplastic invertase on tissues surrounding the
phloem, which create the flowing of sugars to non-photosynthetic tissues, as is the case of
flowers. The apoplast is the free diffusional space outside the plasma membrane, interrupted
by air spaces between plant cells and by the plant cuticle. This way, the apoplast is formed
by the continuum of cell walls of adjacent cells as well as the extracellular spaces, forming
a tissue level compartment. The apoplastic route facilitates the transport of water and solutes
across a tissue or organ. This process is known as apoplastic transport. The apoplast is
important for all the plant’s interaction with its environment. The main carbon source (carbon
dioxide) needs to be solubilized in the apoplast before it diffuses through the plasma
membrane into the cytoplasm and is used by the chloroplasts during photosynthesis. The
apoplast is also a site for cell-to-cell communication.
Ruhlman et al. (2010) observed that the production of nectar is closely linked to the presence
of the enzyme apoplastic invertase, therefore, larger nectar production was dependent on
an increase in enzyme activity in addition to the photosynthetic capacity of the plant itself.
Then we can infer that increasing the volume of nectar promoted by its withdrawal is largely
linked to an increased activity of the invertase enzyme. These same authors observed that
in modified Arabdopsis, silencing the gene encoding one of the isoforms of the predominant
enzyme in the reproductive organs prevented the production of nectar.
The rationale of this process was proposed by Cheng and Chourey (1999). Invertase promotes
the hydrolysis of sucrose to the hexoses glucose and fructose and can be located in the cell
wall (apoplastic), vacuole (vacuolar) or cytoplasm (cytoplasmic). The cell wall invertase is
important when unloading the phloem apoplastic follows a path facilitating the passage of
sucrose to the drains tissues. The authors’ studies concluded that the importance of apoplastic
invertase is not restricted to the breakdown of the sucrose molecule, since the injection
of glucose and fructose has the same effect on the passage of photosynthates to the phloem
tissue drains. In this case, the authors attribute to the enzyme a possible broader role as signaling
or regulatory factor.
Further evidence of the importance of apoplastic invertase in phloem unloading process
that follows this path is the abundance of transcripts in these tissues, according to Jin et al.
64 SoybeAn and bees