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

Abstract

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 pollination. Thin-layer chromatography and depletion of phenolic substances by Dowex treatment indicated that flavonols are present in the diffusate and may be the active compounds. When added to the germination medium, flavonols (quercetin, kaempferol, myricetin) but not other flavonoids strongly promoted pollen germination frequency and pollen tube growth in vitro. The best results were obtained at very low concentrations of the flavonols (0.15-1.5 Mm), indicating a signaling function. The same compounds were also effective when added during pollen development in vitro.Male gametophyte and gamete formation in plants occurs by a close interaction with the surrounding sporophytic tissues, particularly the tapetum (1,14,28). A variety of factors have been suggested to play a role in this interaction. However, their function is still largely unknown.Flavonoids are secondary plant products that include pigments (chalcones, anthocyanins) and colorless compounds (flavanones, flavones, and flavonols) that are involved in pollination, seed dispersal, UV light protection, and plant/ pathogen interaction (9,11,23). Flavonoids are present in pollen of many species of angiosperms and gymnosperms, as well as in spores of ferns and mosses (29). Flavonoid biosynthesis is initiated by chalcone synthase, followed by the synthesis of flavanones by chalcone isomerase. Recently, it was shown that the chs and chi genes are coordinately In vitro culture of isolated microspores has shown that an important function of the anther for the development of the microspores and pollen grains is the stepwise provision of low mol wt nutrients and anabolic precursors (2, 4,18,20). Germination frequency and seed set of this pollen are, however, lower compared with mature pollen taken directly from the plant (2, 20). Obviously, in vitro pollen lacks factors that are provided in vivo by the sporophyte. The in vitro pollen can thus be considered as 'minimal pollen' that fulfills the minimal requirements for pollination and fertilization but lacks factors for optimal reproductive success (28). It should, therefore, react very sensitively to added compounds that in vivo are provided by the anther wall. Here, we show that flavonols but not other flavonoids produced by the anther are present in diffusates of mature tobacco (Nicotiana tabacum L.) pollen and have a strong stimulatory effect on in vitro pollen development, pollen germination, and pollen tube growth. MATERIALS AND METHODS

Pollen Flavonoid/Phenolic Acid Composition of Four Species of Cactaceae and its Taxonomic Significance

“…Flavonoids are present in pollen of many species of Angiosperm and Gymnosperm and in spores of moss and ferns [18] . Particularly kaempferol and quercetin are two required flavonols to pollen tube germination and growth in tobacco [18] , petunia and maize [19] .…”

“…Particularly kaempferol and quercetin are two required flavonols to pollen tube germination and growth in tobacco [18] , petunia and maize [19] . However, these two flavonols have not been shown to carry a similar function in Arabidopsis [20] .…”

Antisense and Sense CHS cDNA Expressed by a Tapetum-specific Promoter Causes Partial Male Sterility in Transgenic Tobacco

“…It has been reported that the accumulation of the flavonols is observed in stigma, ovaries, pollen grains and pollen tubes [20][21][22] . Moreover, it has also been reported that flavonols stimulate development, germination, and pollen tube growth of tobacco [1]. Reduction of flavonols has been demonstrated to assign to abnormal microspore, pollen development and pollen tube growth [23][24][25] .…”

“…as a side branch of the phenylpropanoid pathway are a principal component of pollen pigments. It has been suggested that one role of these flavonoids is to function during pollen germination and pollen tube growth in many plant species [1,2]. It has also been suggested that the transition of phenylpropanoids to flavonoids is essential for the development of viable pollen grains [3,4].…”

Pollen selection: a transgenic reconstruction approach.

“…Petite Havana SR1 plants were grown in a growth chamber at 25°C with a 16-h light/8-h dark regime. Transgenic tobacco plants containing dc3-hgB and 35S-uidA constructs were produced by leaf disk transformation using the disarmed Agrobacterium tumefaciens LBA4404 as described by Horsch et al (12 16]. In these modified conditions, high germination frequencies could be achieved.…”