Page 38 - CSHS 2022 Book of Abstracts - 2022-08-22 web version

CSHS 2022 Conference

(VO.6) Catabolism of kaempferol rhamnosides in radish is associated with ⍺-rhamnosidase
activity during postharvest storage
Nicole Unterlander , Lili Mats , Laura C. McGary , Harley O.W. Gordon , Gale G. Bozzo
1*
2
1
1
1
1. Department of Plant Agriculture, University of Guelph, Guelph, ON; 2. Agriculture and Agri-Food Canada, Guelph, ON
________________
Flavonols are a class of phytochemicals that are ubiquitous in plants. Often occurring as glycoside conjugates such as
kaempferol 7-O-⍺-rhamnoside (K7R) and kaempferol 3-O-β-glucoside-7-O-⍺-rhamnoside (i.e., kaempferitrin),
flavonols have numerous biological roles in plants including modulation of auxin transport and developmental
processes associated with this hormone, as well as mitigation of oxidative stress. Flavonol rhamnosides undergo
turnover in response to fluctuations in abiotic factors during development, and senescence. The biochemical
mechanisms governing flavonol rhamnoside catabolism in plants have not been well explored. Here, we provide
biochemical evidence that kaempferol rhamnoside degradation occurs in radish leaves during postharvest storage
at low temperature, which is coincident with the induction of flavonol 7-O-α-rhamnoside α-rhamnosidase activity.
Leaf kaempferitrin concentrations decreased during 8 days of postharvest storage at 5 C, while the concentrations
of its hypothetical catabolites kaempferol 3-O-⍺-rhamnoside, K7R, and kaempferol tended to accumulate during
postharvest senescence. HPLC analysis of in vitro enzyme assays demonstrate these alterations in flavonol profiles
coincided with a marked increase in kaempferitrin and K7R 7-O-α-rhamnosidase activities with postharvest storage.
A flavonol rhamnoside 7-O-α-rhamnosidase activity from postharvest radish leaves was purified to homogeneity
and shown to hydrolyze various flavonol glycosides. Taken together, catabolism of 7-O-⍺-rhamnosides in
postharvest radish tissue is correlated with the induction of 7-O-α-rhamnosidase activity. Current efforts are
focused on establishing the kinetic properties of the radish flavonol rhamnoside 7-O- -rhamnosidase. This research
will facilitate production-related and/or biotechnological strategies for boosting flavonol levels in radish to limit
oxidative-stress related deterioration during postharvest storage of this vegetable.

(VO.7) Role of Bacteria-derived Flavins in Vegetable Growth Promotion
Nivethika Ajeethan 1,2* , Lord Abbey , Svetlana Yurgel
3
1
1. Department of Plant, Food, and Environmental Sciences, Faculty of Agriculture, Dalhousie University, Bible Hill, NS; 2.
Faculty of Technology, University of Jaffna, Sri Lanka; 3. United States Department of Agriculture, Pullman, WA, USA
________________
Riboflavin, commonly known as vitamin B2, is an essential element of living organisms and is the precursor of flavin
(FLs) cofactors, flavin mononucleotide and flavin adenine dinucleotide. Sinorhizobium meliloti 1021 establishes a
nitrogen-fixing symbiosis with Medicago plants and secretes considerable amount of FLs (FL+ strain). This strain
was also implicated in plant growth promotion in its association with non-legume plants. However, the mechanism
of this plant growth promotion is not well understood. In this study, we tested our hypothesis that bacteria derived
flavins are involved in the ability of S. meliloti 1021 to promote host-plant growth. We evaluated the growth and
development of lettuce (Lactuca sativa) and kale (Brassica oleracea L. var. acephala) plants inoculated with S.
meliloti 1021 and its mutant (FL- strain) with limited ability to secrete FLs. Our results indicated that inoculation
with FL+ strain significantly (P<0.05) increased the length and surface areas of root and hypocotyl of the seedlings
compared to seedlings that were inoculated with FL- strain. The total root lengths of 9-day old kale seedlings
inoculated with FL+ and FL- strain were 30.2 and 25.4 cm respectively, while the total root lengths of lettuce
seedlings were 20.1 and 17.7 cm respectively. This plant growth promoting effect might be the result of the
secretion of bacterial derived FLs. Proteomic approaches combined with the analysis of plant physiological
responses such as growth, photosynthetic rate, stomatal conductance, transpiration rate and chlorophyll content
will be used to evaluate the host-plant response to bacteria-derived FLs.

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