Location: Fruit and Tree Nut ResearchTitle: Flavonoids, alkali earth and rare earth elements affect germination of pecan pollen
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2016
Publication Date: N/A
Interpretive Summary: A key factor affecting alternate bearing of pecan in commercial orchards is successful fertilization of female flowers by germinated pollen. Recent research at ARS Byron, Georgia, found germination of pollen grains in potentially influenced by flavonol, alkaline earth and rare earth metals within the liquid layer of receptive stigmatic surfaces of female flowers or as components of germination media for testing pollen viability. These finding identify a variety of factors that potentially affect successful fertilization of female flowers in orchards as well as that of determining pollen viability. It also targets flavonol composition of stigmatic exudates as a potential regulator of pollen compatibility and incompatibility.
Technical Abstract: The factors regulating pecan [Carya illinoinensis (Wangenh.) K. Koch] pollen grain germination on receptive stigmatic flower surfaces in vivo or in vitro in pollen viability assays are poorly understood. While there are many potential regulating factors, there is evidence for involvement of flavonols, non-Calcium alkali earth elements (AEEs) or rare earth elements (REEs). When various concentrations of certain naturally occurring simple flavonols (e.g., quercetin, kaempferol, myricetin, naringenin, and hesperetin) were tested in vitro by adding to standard pecan pollen germination medium, the flavonol, hesperetin, functioned as a strong ‘agonist’ at concentrations from 0.12-2.0 µM, increasing pollen germination from 12 to 25-38% over flavonol free media. The other flavonols functioned as ‘antagonist’ at concentrations from 0.062 µM to 16 µM. The addition of certain REEs, at the same molar concentration as Ca2+, but with absence of Ca2+ in the in vitro pollen germination media, results in certain REEs (e.g., Y, Gd, and Tm) partially substituting for Ca2+ as an essential alkali earth element metal (AEE) ion for pollen germination; thus, functioning in an agonist. All non-Ca AEEs (Be, Mg, Sr), expect for Ba, also partially substituted for Ca2+ at equivalent molar concentrations, but none were as efficacious as Ca2+. Pollen germination is therefore potentially influenced by any one of several flavonols, REEs, and AEEs. This is suggestive that pollen germination on stigmatic surfaces of flowers in orchards is potentially influenced or regulated by flavonol composition and Ca-like metals in the liquid matrix of the wet (receptive) stigmatic surface.