Abstract Detail

Development and Structure

McInnes, Holly [1], Tuma, Trevor T [2], Harding, Scott [3], Tsai, Chung-Jui [4].

Characterizing extrafloral nectary development and secretion in Populus.

Extrafloral nectaries (EFNs) are secretary organs associated with non-floral tissue. Although EFNs and floral nectaries both produce secretions rich with sugars and amino acids, they are thought to have distinct functions. Unlike floral nectaries which facilitate reproduction through the attraction of pollinators, EFNs are proposed to play a role in indirect defense by attracting predatory insects to deter herbivorous pests. EFN general morphology and the role they play in recruiting predatory insects has been well documented across several species. We wish to contribute to this field by characterizing EFNs in Populus tremula x alba (717-1B4) through documenting EFN emergence and secretion, profiling nectar metabolite abundance using Gas Chromatography-Mass Spectrometry (GC-MS), and visualizing EFN structure using histology. Observations indicated that emergence onset and secretion were impacted by plant health, maturity, temperature, insect feeding, and damage. In healthy plants, EFN emergence began once the trees had grown to at least ~three feet in height, and EFNs emerged on newly expanded leaves (i.e., leaf plastocron index (LPI)-3). Secretion initiated around LPI-6 to LPI-10 and EFNs actively secreted anywhere from a day to almost a month depending on ambient conditions and plant health. Nectary visualizations across a developmental gradient showed relatively large concave structures that progressively became larger, deeper, and broader as the organ developed from the presecretory, secretory, and post-secretory organ stages. Paraffin sections of EFN tissue were used for histological examination of cellular morphology. We found that EFNs emerged from the adaxial leaf side to form a raised, cuplike structure that consisted predominantly of mesophyll tissue loosely associated with the leaf’s vascular tissue. Furthermore, as secretion commenced, the spongy mesophyll cells compacted, the organ flattened, and the area of secretion interface became larger.  Post-secretory organs were distinct from secretory organs only in that the mesophyll cells were more tightly packed and the organ itself became thinner with a secretion interface spanning almost the entire organ breadth. GC-MS analysis of the nectar revealed that the majority of the metabolite content consisted of sucrose, glucose, and fructose, while mannose, inositol, malic acid, and succinic acid were also present, but detected in lower amounts. In general, sucrose levels were two to three times larger than fructose or glucose abundance and at times thirty times larger than the next most abundant sugar, mannose. However, metabolite content varied between collection dates and by plant health. Given that extrafloral nectar is so rich in sucrose, it is likely that the mobilization of sucrose for EFN secretion requires the action of sucrose transporters (SUTs). To investigate SUT involvement, in-situ hybridization is being used to examine the spatiotemporal localization of SUT transcripts during EFN development. Future work will utilize the CRISPR-Cas9 gene editing technology to create SUT knockouts to further illuminate SUT function in Populus EFNs through metabolite analysis of tissue samples and secretions.

1 - University of Georgia, Plant Biology , B310 Davison Life Sciences, 120 E Green St. , Athens, GA, 30602, USA
2 - University of Georgia, B310 Davison Life Sciences , 120 E Green St. , Athens, Ga, 30602, USA
3 - University of Georgia, Genetics, C310 Davison Life Sciences, 120 E Green St. , Athens, University of Georgia, 30602, USA
4 - University of Georgia, Plant Biology, Genetics, Warnell School of Forestry , B310 Davison Life Sciences, 120 E Green St., Athens, GA, 30602, United States

extrafloral nectary
secretion content
gas chromatography-mass spectrometry .

Presentation Type: Poster
Number: PDS012
Abstract ID:515
Candidate for Awards:None

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