Recipient Organization
UNIV OF MINNESOTA
(N/A)
ST PAUL,MN 55108
Performing Department
Plant Biology
Non Technical Summary
Over 100 crops in the US are dependent on animal-mediated pollination, with honey bees providing more than $15 billion in value annually. For the pollinator, nectar is the primary reward essential for growth and development. Aside from its sugar content, roughly 10% of nectar dry weight contains non-carbohydrates, such as proteins, amino acids, lipids, and specialized metabolites that greatly impact pollinator health. Glucosinolates (GLSs) are sulfur-rich specialized metabolites found in the Brassicaceae, a plant family that includes several vegetable and oilseed crops such as canola. GLSs are known for their defensive properties against herbivory, but their recent identification in nectar suggests they may impact plant-pollinator relationships. Species within the genus Brassica vary in their GLS leaf tissue profiles in terms of type, quantity and time of day abundances. It is unclear whether these dynamic changes occur in nectar and what effect GLSs in nectar have on pollinator visitation. The proposed work will quantify differences in GLS in nectar and leaf tissue across Brassica morphotypes and assess their pollinator visitation patterns. Sampling will occur at three times of day in order to detect diel variation in GLS accumulation that may uncover additional associations with pollinator preference. Results from this work will provide the first temporal analysis of GLSs in paired leaf and nectar of Brassica spp. along with associated pollinator visitation. This will inform future work into identifying breeding targets for crop improvement and the conservation of pollinator biodiversity.
Animal Health Component
0%
Research Effort Categories
Basic
100%
Applied
0%
Developmental
0%
Goals / Objectives
The goals of the proposed project are to quantify differences in glucosinolates in nectar and leaf tissue across Brassica morphotypes and assess their pollination visitation patterns. To achieve these goals we will pursue two main objectives:(1)Quantify differences in glucosinolate diversity and accumulation in nectar and leaves ofBrassicamorphotypes. The "byproduct hypothesis" suggests that nectar specialized metabolites are derived from synthesis in other tissues and delivered to nectar by the vasculature. We will quantify glucosinolates in leaves and nectar to determine how the vasculature might contribute to the glucosinolate nectar composition. Samples will be collected at three time points throughout the day to understand at what stage glucosinolates are produced and whether their chemical diversity changes in nectar throughout the day.(2)Assess pollinator abundance and diversity visitingBrassicamorphotypes. We predict thatBrassicamorphotypes will have variable GLS concentration and diversity, which may correlate to patterns of pollinator visitation. Previous research suggests that both the diversity and behavior of pollinators on Brassica rapa differs in high and low glucosinolate lines. While hybrid varieties of canola dominate the market, the response of these strains to pollinators remains unexplored yet we know that pollinator visitation can make a significant impact on crop yield. In this objective we will assess the diversity of pollinators on Brassica morphotypes as well as the patterns of visitation throughout the day.
Project Methods
The methods for Objective 1:B. rapa and B. napus morphotypes will be germinated in the greenhouse, lines requiring vernalization will be put in a 4°C cold room for 30 days prior to transplanting into test plots. Plant growth will be staggered and randomized to have enough samples for analysis and prevent positional effects. Once flowering, nectar from flowers (bagged plants in test plots) and leaf tissue will be collected at three time points, one in the morning (secretory), one in the afternoon (post-secretory #1) and one in theevening (post-secretory #2), with 3 replicates per time point. Samples will be ground into a fine powder in a bead mill homogenizer. To extract glucosinolates, nectar and leaf extracts will be loaded onto a packed DEAE Sephadex A-25 column for anion-exchange chromatography. After binding and washes, an on-column sulfatase treatment will be performed to release the GLSs from the column. Once eluted, desulfo-glucosinolates will be separated by HPLC and detected by UV absorption at 229 nm. Authentic GLS standard compounds and HPLC-high resolution mass spectrometry will be used to confirm the compound identities and the quantitative performance for this analysis. The nectar will also be evaluated for total volume, sugar type, and concentration, which will be normalized on a per flower and per plant basis. This will also provide an additional normalization for the GLS quantification. Morphotype and time point specific glucosinolate measurements will be analyzed using principle component analysis to evaluate the signatures of variation.Objective 2:Brassica morphotypes will be grown on test field plots at the University of Minnesota, Saint Paul campus, and St. Catherine's University in St. Paul. We will grow morphotypes of B. rapa and B. napus under greenhouse conditions. After vernalization, they will be moved into a field site and randomly arranged. Neighboring growth of other crops will be recorded to ensure that the effect of these crops on bee communities across the site is considered.At each of the plots bee species abundance will be measured by, on-the-wing identification and netting all individual bees observed visiting crop flowers at standard times of day. Netted specimens will be identified to species. For specimens identified on the wing, we will combine morphologically similar species groups when necessary. Data will be collected only on days that are favorable for bee activity (above 14°C by 10:00h and above 17°C by 12:00h, clear to partly cloudy skies). Sampling will involve walking along the plots at a standard pace for 20 minutes and recording insect identities. After this, a second walk will involve netting pollinators that are visiting the morphotypes. Data from the visual identification and netting will be combined for a total abundance of morphotype-visiting bees. Floral bloom density will also be recorded by counting the number of open flowers (secretory vs post-secretory #1) and buds (pre-secretory) on multiple plants from each morphotype randomly selected. In addition to tracking pollinator visitation, we will record the number of days after first flower opening, mean petal size, number of flowers and plant height to give us a proxy of the flowering stage of the plant. Nectar chemistry (GSLs, sugars, volatiles) from Aim 1 and pollinator visitation profiles in Aim 2 will be evaluated using analyses such as generalized linear models that account for rates of visitation, GLS levels, and other aspects of floral morphology.