Effect of flower structure and flower colour on intrafloral warming and pollen germination and pollen-tube growth in winter flowering Crocus L. (Iridaceae)

Abstract

The internal temperature of the flowers of three colour variants of winter flowering Crocus chysanthus and of C. tommasinianus were compared with ambient in the dark, and when subject to artificial horizontal illumination with daylight spectra. Illuminated flowers warmed up to 3OC above ambient. In the dark, flowers also showed slight warming. In all varieties, pollen germinated more freely at 15°C compared to 6OC, and pollen tube growth also tended to be faster at the higher temperature, although pollen growth was inhibited at 20°C. Closed flowers began to open at between 10°C and 12"C, and tended to open more rapidly at higher temperatures. We conclude that flower warming at low ambient temperatures may mediate flower opening in Crocus and allow pollination, and may stimulate pollen germination and the fertilization process. Crom has the typical attributes of 'microgreenhouse' flowers, absorbing some spectra externally, transmitting other spectra internally, trapping heat energy by reflecting inner tepal surfaces, and storing energy in large gynoecia. Of the varieties tested, white and purple flowers showed the greatest flower warming, and yellow flowers the least. Yellow flowers transmit no light of less than 500 nm, suggesting that the transmission of short wavelength light may be important in flower warming.

Pollen tube competition as a mechanism of prezygotic reproductive isolation between Mimulus nasutus and its presumed progenitor M. guttatus

“…Although it is known that environmental factors can influence the rate of pollen tube growth (Cox, 1988 ;Aizen & Raffaele, 1998 ;McKee & Richards, 1998), there is substantial evidence supporting a longpredicted genetic basis for this variation (Marshall & Ellstrand, 1986 ;Elgersma et al, 1989 ;Snow & Spira, 1991 ;Johannsson et al, 1998). In our investigations we found that the difference in pollen tube growth rates between M. nasutus and M. guttatus remained consistently large, even when growth occured in excised pistils in a common environment.…”

Leaf and floral heating in cold climates: do sub-Antarctic megaherbs resemble tropical alpine giants?

“…1d). The greenish-yellow colour of the inflorescences of B. rossii is unlikely to contribute much towards heating the inflorescence (McKee & Richards 1998). However, the flower buds, and newly opened flowers, were more densely arrayed than older flowers, which may explain higher heat retention in the younger part of the inflorescence.…”

Petal Color, Flower Temperature, and Behavior in an Alpine Annual Herb, Gentiana leucomelaena (Gentianaceae)

“…In contrast, in arctic or cold alpine regions, flower color may have evolved to help keep interior temperatures warm and stable against fluctuating ambient temperatures (Seymour and SchultzeMotel, 1998;Ivancic et al, 2008;Li and Huang, 2009), which is critical to the development of pollen, ovules, and fertilization (McKee and Richards, 1998a;Li and Huang, 2009). For example, the white petals of Crocus chrysanthus, an arctic herb species, redirect light spectra into flower interiors, trapping heat energy to warm the gynoecia (McKee and Richards, 1998b). At the same ambient temperature, white flowers are usually warmer than yellow flowers in interior structures but not in corolla (McKee and Richards, 1998b;Mølgaard, 1989), because light-colored petals Arctic, Antarctic, and Alpine Research, Vol.…”

“…For example, the white petals of Crocus chrysanthus, an arctic herb species, redirect light spectra into flower interiors, trapping heat energy to warm the gynoecia (McKee and Richards, 1998b). At the same ambient temperature, white flowers are usually warmer than yellow flowers in interior structures but not in corolla (McKee and Richards, 1998b;Mølgaard, 1989), because light-colored petals Arctic, Antarctic, and Alpine Research, Vol. 42, No.…”

“…/ 219 1523-0430/10 $7.00 absorb short wavelengths more efficiently than dark ones (Bü del, 1959;Tikhomirov et al, 1960). Studies examining the relationships among petal colors, flower interior temperature, and pollinator visitation rates mostly employ a comparative methodology, i.e., interspecifically or among varieties of a single species (McKee and Richards, 1998b;Kevan, 1975Kevan, , 1989Tikhomirov et al, 1960;Kjellberg et al, 1982;Knutson, 1981). However, there might be a confounding factor involved in these studies.…”