Pollination- or Wound-Induced Kaempferol Accumulation in Petunia Stigmas Enhances Seed Production.

Abstract

Flavonols are essential for pollen germination and tube growth in petunia and can be supplled by either the pollen or stigma at pollinatlon. HPLC analysis and a sensitive bloassay demonstrated that both pollinatlon and wounding induce flavonol accumulation, especlally kaempferol, in the outer cell layers and exudate of the stigma. Pollination and wounding induced nearly identical flavonol kinetics and patterns of accumulation in the same target tissue, suggesting that they sham elements of a common signal transductlon pathway. The wound response was systemlc, because kaempferol accumulated in the stlgma when dista1 tissues, such as the corolla, stamens, or sepals, were wounded. We have exploited the germination requirement for flavonols and the high leve1 of kaempferol that accumulates after wounding to enhance plant fecundity. Seed set was slgnificantly increased by mechanically wounding the corolla and stamens prior to the application of pollen to the stigma. A reproductive role for a plant secondary metabolite and the specific function of stigmatic kaempferol are discussed from an evolutionary perspective. INTRODUCTIONIn angiosperms, the stigma is the pollen-receptive surface of the female gametophyte-bearing pistil. In many species, the stigmatic surface is covered with a chemically complex exudate that provides the hospitable conditions and factors required for pollen adhesion, hydration, germination, and pollen tube penetration (Konar and Linskens, 1966;Knox, 1984; HeslopHarrison, 1987). In addition, discriminatory events, such as the rejection of self-pollen in sporophytic incompatible reactions, occur at the stigmatic surface (Nasrallah et al., 1991).The stigma also appears to offer a hostile environment to bacteria and fungi because growth of these organisms on the stigma is rare (Jung, 1956).Transcripts homologous to genes induced by wounding and stress have been detected in flowers from nonwounded plants (Gasser, 1991), and in some cases, defenserelated compounds have been found to accumulate specifically in the stigma. For example, high levels of proteinase inhibitor (PI) proteins (Atkinson et al., 1993) and chitinase (Leung, 1992) have been measured in stigmas of solanaceous plants, and the promoters of an hydroxyproline-rich glycoprotein gene and a phenylpropanoid biosynthetic gene, phenylalanine ammonia-lyase, direct transcription of a reporter gene in transgenic tobacco stigmas (Liang et al., 1989; Wycoff et al., 1990). Although thedefensive Current address: lnstitut für Pflanzenbiochemie, Halle, Germany. To whom correspondence should be addressed.role of these compounds in wounded tissue is well known, a reproductive function has not been established.Phenolic compounds function as stress indicators because they accumulate to high levels in many plant tissues in response to a wide range of biotic and abiotic signals, including wounding (Lawton and Lamb, 1987). Biosynthesis and accumulation of phenolics also occur as part of normal developmental programs in most higher plants (Wiermann, 1981). Ch...

Genome-Wide Gene Expression Profiling Reveals Conserved and Novel Molecular Functions of the Stigma in Rice

“…Defense-related compounds have been found to accumulate specifically in the stigma; the proteinase inhibitor proteins and chitinase are highly enriched in stigmas of Solanaceous plants (Leung, 1992;Atkinson et al, 1993). It has been shown that the pollination and wounding induced nearly identical flavonol kinetics in petunia and patterns of the accumulation in the outer cell layers and exudates of the stigma, suggesting that they share elements of a common signal transduction pathway (Vogt et al, 1994). In petunia flowers, both pollination and stigma wounding induced a transient increase in ethylene production and hastened corolla senescence (Woltering et al, 1997).…”

The Jasmonate-ZIM-Domain Proteins Interact with the WD-Repeat/bHLH/MYB Complexes to Regulate Jasmonate-Mediated Anthocyanin Accumulation and Trichome Initiation inArabidopsis thaliana

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