The structural requirements of flavonols that induce pollen germination of conditionally male fertile Petunia (original) (raw)

Flavonols Stimulate Development, Germination, and Tube Growth of Tobacco Pollen

PLANT PHYSIOLOGY, 1992

The effect of anther-derived substances on pollen function was studied using pollen produced by in vitro culture of immature pollen of tobacco (Nicotiana tabacum L.) and petunia (Petunia hybrida). Addition of conditioned medium consisting of diffusates from in situ matured pollen strongly increased pollen germination frequency and pollen tube growth, as well as seed set after in situ

Pollen tubes of flavonol-deficient Petunia show striking alterations in wall structure leading to tube disruption

Planta, 1999

Despite the vital role that flavonols play in fertilization and pollen tube growth of a number of species such as petunia and maize, their function is still unclear. Pollen tubes of the flavonol-deficient transformant T17.02 of Petunia hybrida L. are able to germinate and start growing in vitro, but eventually disrupt at the tip approximately 2 h after germination. In order to establish the possible role of flavonols in this process, wild-type and flavonol-deficient pollen tubes were subjected to cytological and ultrastructural analyses and screened for differences. The results showed that before disruption of the flavonol-deficient pollen tubes, the structure of the primary wall at the tip dramatically changed from layered to granular. Secretory vesicles at the tip still fused with the wall but lost their capacity to melt into the wall and to form layers. Instead they remained as dark, electron-dense granular structures surrounded by an electron-translucent matrix. Apparently the matrix is not able to sustain the wall's coherence and as a consequence the tube disrupts. No other remarkable cytological or ultrastructural differences between the transformant and the wild-type pollen tubes could be found before tip disruption. Even a morphometric analysis of abundance and distribution of endoplasmic reticulum, dictyosomes and mitochondria did not reveal any significant difference. However, for the first time, obvious morphological differences were observed in the wall of the flavonol-deficient pollen tubes. We conclude that flavonols act on precursors of the pollen tube wall of petunia and interfere with a cross-linking system in the wall, possibly via extensins.

Isolation and Characterization of cDNAs Expressed in the Early Stages of Flavonol-Induced Pollen Germination in Petunia

PLANT PHYSIOLOGY, 2000

Petunia (Petunia hybrida) pollen requires flavonols (Fl) to germinate. Adding kaempferol to Fl-deficient pollen causes rapid and synchronous germination and tube outgrowth. We exploited this system to identify genes responsive to Fls and to examine the changes in gene expression that occur during the first 0.5 h of pollen germination. We used a subtracted library and differential screening to identify 22 petunia germinating pollen clones. All but two were expressed exclusively in pollen and half of the clones were rare or low abundance cDNAs. RNA gel-blot analysis showed that the steady-state transcript levels of all the clones were increased in response to kaempferol. The sequences showing the greatest response to kaempferol encode proteins that have regulatory or signaling functions and include S/D4, a leucine-rich repeat protein, S/D1, a LIM-domain protein, and D14, a putative Zn finger protein with a heme-binding site. Eight of the clones were novel including S/D10, a cDNA only expressed very late in pollen development and highly up-regulated during the first 0.5 h of germination. The translation product of the S/D3 cDNA shares some features with a neuropeptide that regulates guidance and growth in the tips of extending axons. This study confirmed that the bulk of pollen mRNA accumulates well before germination, but that specific sequences are transcribed during the earliest moments of Fl-induced pollen germination.

Altering expression of the flavonoid 3′-hydroxylase gene modified flavonol ratios and pollen germination in transgenic Mitchell petunia plants

Functional Plant Biology, 2006

Antisense technology was successfully used to reduce flavonoid 3′-hydroxylase (F3′H) gene expression and enzyme activity and to promote the accumulation of monohydroxylated flavonols in petunia flower tissue. The hydroxylation pattern of specific flavonoid groups is a target for modification because of the possible associated changes in a range of factors including colour, stress tolerance and reproductive viability. Petunia (cv. Mitchell) plants were transformed to express in the antisense orientation the sequences encoding the F3′H (asF3′H). Transformants showed a range of responses, in terms of the level of endogenous F3′H gene expression and the relative proportion of the monohydroxylated flavonol (kaempferol) glycosides that accumulated. Kaempferol glycosides increased from 7% of the total flavonols in flower limb tissue of the wild type plants, to 45% in the flower limb tissue of line 114, the transgenic line that also showed the greatest decrease in F3′H expression in flower ...

Chalcone Synthase and Flavonol Accumulation in Stigmas and Anthers of Petunia hybrida

1993

Flavonol aglycones are required for pollen germination in pe- tunia (Petunia hybrida 1.). Mutant plants lacking chalcone synthase (CHS), which catalyzes the first committed step in flavonoid syn- thesis, do not accumulate flavonols and are self-sterile. lhe mutant pollen can be induced to germinate by supplementing it with kaempferol, a flavonol aglycone, either at the time of pollination or by

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

THE PLANT CELL ONLINE, 1994

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.

Patterns of Phenolic Compounds in Betula and Pinus Pollen

Plants

In this study, phenolic compounds and their antioxidant activity in the pollen of anemophilous Betula and Pinus were determined. Spectrophotometric, high-performance thin-layer and liquid chromatography methods were applied. Free phenolic compounds (free PC) and phenolic compounds bound to the cell wall (bound PC) were analysed in the pollen extracts. Regardless of the pollen species, their content was 20% higher than that in bound PC extracts. Pinus pollen extracts contained 2.5 times less phenolic compounds compared to Betula. Free PC extraction from the deeper layers of Pinus pollen was minimal; the same content of phenolic compounds was obtained in both types of extracts. The bioactivity of pollen (p < 0.05) is related to the content of phenolic compounds and flavonoids in Betula free PC and in bound PC, and only in free PC extracts of Pinus. Rutin, chlorogenic and trans-ferulic acids were characterised by antioxidant activity. Phenolic acids accounted for 70–94%, while rutin...

Purification, cloning, and heterologous expression of a catalytically efficient flavonol 3-O-galactosyltransferase expressed in the male gametophyte of Petunia hybrida

The Journal of biological chemistry, 1999

Flavonols are plant-specific molecules that are required for pollen germination in maize and petunia. They exist in planta as both the aglycone and glycosyl conjugates. We identified a flavonol 3-O-galactosyltransferase (F3GalTase) that is expressed exclusively in the male gametophyte and controls the formation of a pollen-specific class of glycosylated flavonols. Thus an essential step to understanding flavonol-induced germination is the characterization of F3GalTase. Amino acid sequences of three peptide fragments of F3GalTase purified from petunia pollen were used to isolate a full-length cDNA clone. RNA gel blot analysis and enzyme assays confirmed that F3GalTase expression is restricted to pollen. Heterologous expression of the F3GalTase cDNA in Escherichia coli yielded active recombinant enzyme (rF3GalTase) which had the identical substrate specificity as the native enzyme. Unlike the relatively nonspecific substrate usage of flavonoid glycosyltransferases from sporophytic tis...