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

• Published in: Botanical journal of the Linnean Society Vol. 128; no. 4; pp. 369 - 384
• Main Authors: MCKEE, JUNO, RICHARDS, A.J.
• Format: Journal Article
• Language: English
• Published: Elsevier Science Ltd 01.12.1998
• Subjects: flower opening – microgreenhouse flowers – spectral absorption – spectral reflectance – spectral transmission – temperature; flower opening – microgreenhouse flowers – spectral absorption – spectral reflectance – spectral transmission – temperature
• ISSN: 0024-4074; 1095-8339
• DOI: 10.1006/bojl.1998.0205

The internal temperature of the flowers of three colour variants of winter floweringCrocus chrysanthusand ofC. tommasinianuswere compared with ambient in the dark, and when subject to artificial horizontal illumination with daylight spectra. Illuminated flowers warmed up to 3°C above ambient. In the dark, flowers also showed slight warming. In all varieties, pollen germinated more freely at 15°C compared to 6°C, 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 inCrocusand allow pollination, and may stimulate pollen germination and the fertilization process.Crocushas 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.