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Pollen and anther ontogeny in Cabomba caroliniana (Cabombaceae, Nymphaeales)
Mackenzie L. Taylor, Benjamin L. Gutman, Natalie A. Melrose, Angela M. Ingraham, Julie A. Schwartz and Jeffrey M. Osborn
American Journal of Botany
Vol. 95, No. 4 (April 2008), pp. 399-413
Published by: Botanical Society of America, Inc.
Stable URL: http://www.jstor.org/stable/20700385
Page Count: 15
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Cabomba is a small water lily genus that is native to the New World. Studies of pollen development and associated changes in the anther yield valuable characters for considering the evolution of reproductive biology in seed plants. Here we characterized the complete ontogenetic sequence for pollen in Cabomba caroliniana. Anthers at the microspore mother cell, tetrad, free microspore, and mature pollen grain stages were studied using scanning electron, transmission electron, and light microscopy. Tetragonal and decussate tetrads both occur in C. caroliniana, indicating successive microsporogenesis. The exine is tectate-columellate, and the infratectal columellae are the first exine elements to form, followed by a continuous tectum and a thin foot layer. A lamellate endexine initiates in the early free microspore stage, but becomes compressed in mature grains. Tectal microchannels and sculptural rods also initiate during the early free microspore stage, and significant pollenkitt deposition follows, supporting the hypothesis that these elements function in entomophily. The tapetum is morphologically amoeboid, with migratory tapetal cells directly contacting developing free microspores within the anther locule. Results from this study illustrate the importance of including ontogenetic data in analyzing pollen characters and in developing evolutionary and ecological hypotheses. The new palynological data also emphasize the character plasticity that occurs in basal angiosperms.
American Journal of Botany © 2008 Botanical Society of America, Inc.