Development and Chemical Changes in Nectar of Borage Flowers

Jim Crocker
27th May, 2024

Development and Chemical Changes in Nectar of Borage Flowers

Image Source: Natural Science News, 2024

Key Findings

  • Researchers at the University of Rome Tor Vergata studied nectar production in borage flowers, finding it peaks at 5.1µL per flower during full bloom and decreases over nine days
  • The study revealed that nectar is transported through the apoplastic route and possibly via exocytotic processes, supported by advanced microscopy techniques
  • High levels of phenolics in early-phase nectar suggest these compounds help defend against pathogens and attract pollinators, influencing plant-pollinator interactions
Borage, scientifically known as Borago officinalis L., has long been recognized as a valuable nectar source for many insects. Despite this, detailed knowledge about its nectar production and nectaries has been limited. A recent study conducted by researchers at the University of Rome Tor Vergata sheds new light on the nectar production dynamics, chemistry, and potential pollinator interactions of borage[1]. The study observed that nectar secretion in borage flowers peaks at around 5.1µL per flower during anthesis, which is the period when the flower is fully open and functional. This secretion then decreases linearly over the following nine days. The researchers employed transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to analyze the ultrastructure and physiological changes in the nectary before, during, and after the secretory phase. Their findings suggest that nectar is transported via the apoplastic route and possibly through exocytotic processes, known as granulocrine secretion. This was further supported by Thiéry staining and ESI/EELS techniques, which monitored the presence of complex polysaccharides and calcium. After the secretory phase, the nectary undergoes degeneration, likely through autophagic events or senescence induction. This aligns with previous findings on plant responses to environmental stresses, where cellular pathways are activated to manage stress and eventually lead to cell death[2]. The study also characterized the secondary metabolites in different flower structures, including nectar, sepals, gynoecia, and petals, at both early (E-) and late (L-) phases from anthesis. Using spectrophotometry and HPLC-DAD, the researchers quantified the phytochemical content, revealing significant biological roles for these compounds. Notably, a high accumulation of nine phenolics was observed in early-phase nectar (E-Nec) compared to late-phase nectar (L-Nec). This suggests that these phenolics might serve functional purposes, such as defending against pathogens or attracting pollinators. The presence of these secondary metabolites in nectar is known to influence its palatability, encouraging the approach of specialist pollinators while deterring nectar robbers and altering insect behavior. This is consistent with findings from other studies on plant-pollinator interactions, where plant metabolites play crucial roles in shaping these relationships[3]. Moreover, the study's findings on the role of calcium in nectar secretion and cellular responses resonate with previous research on Ca2+-calmodulin (Ca2+-CaM) signaling. This signaling pathway is critical for various cellular functions and has been shown to influence protein expression and cytological responses in plants[4]. The involvement of calcium in nectar secretion underscores its broader significance in plant physiology and stress responses. In the context of environmental stress, the findings also align with research on Sulla coronaria, a Mediterranean forage legume. This plant has demonstrated complex antiradical molecular responses to drought and salinity, highlighting the role of redox components in acclimation to stress[5]. Similarly, the study on borage suggests that secondary metabolites in nectar may play a role in stress defense mechanisms. Overall, the research from the University of Rome Tor Vergata provides valuable insights into the nectar production dynamics and chemistry of borage, highlighting the intricate relationships between plant physiology, secondary metabolites, and pollinator interactions. This study not only expands our understanding of borage but also contributes to the broader knowledge of plant-pollinator dynamics and plant stress responses.

HerbsBiochemPlant Science

References

Main Study

1) Ultrastructure and development of the floral nectary from Borago officinalis L. and phytochemical changes in its secretion.

Published 24th May, 2024

https://doi.org/10.1016/j.plantsci.2024.112135

Related Studies

2) The role of calcium and activated oxygens as signals for controlling cross-tolerance.

Journal: Trends in plant science, Issue: Vol 5, Issue 6, Jun 2000

3) Comparative studies on structure of the floral nectaries and the abundance of nectar production of Prunus laurocerasus L.

https://doi.org/10.1007/s00709-019-01412-z

4) Combined proteomic and cytological analysis of Ca2+-calmodulin regulation in Picea meyeri pollen tube growth.

https://doi.org/10.1104/pp.108.127514

5) Investigating the Drought and Salinity Effect on the Redox Components of Sulla Coronaria (L.) Medik.

https://doi.org/10.3390/antiox10071048


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