Biology of generative reproduction of Colobanthus quitensis (Kunth) Bartl. from King George Island, South Shetland Islands

Abstract

Our macroscopic observations and microscopic studies conducted by means of a light microscope (LM) and transmission electron microscope (TEM) concerning the re− production biology of Colobanthus quitensis (Caryophyllaceae) growing in natural condi− tions in the Antarctic and in a greenhouse in Olsztyn (northern Poland) showed that this plant develops two types of bisexual flowers: opening, chasmogamous flowers and closed, cleistogamous ones. Cleistogamy was caused by a low temperature, high air humidity and strong wind. A small number of microspores differentiated in the microsporangia of C. quitensis, which is typical of cleistogamous species. Microsporocytes, and later micro− spores, formed very thick callose walls. More than twenty spheroidal, polypantoporate pol− len grains differentiated in the microsporangium. They germinated on the surface of recep− tive cells on the dry stigma of the gynoecium or inside the microsporangium. A monosporic embryo sac of the Polygonum type differentiated in the crassinucellar ovule. During this differentiation the nucellus tissue formed and stored reserve materials. In the development of generative cells, a male germ unit (MGU) with differentiated sperm cells was observed. The smaller cell contained mainly mitochondria, and the bigger one plastids. In the process of fertilization in C. quitensis only one nucleus of the sperm cell, without cytoplasm frag− ments, entered the egg cell, and the proembryo developed according to the Caryophyllad type. Almost all C. quitensis ovules developed and formed perispermic seeds with a com− pletely differentiated embryo both under natural conditions in the Antarctic and in a green− house in Olsztyn.

Soluble carbohydrates in developing and mature diaspores of polar Caryophyllaceae and Poaceae

“…Flowers and fruit are more abundant when weather conditions are more favorable, which happens every few years or even every ten or more years (Piro_ znikow 1993). Plant species native to the Antarctic produce numerous flowers and inflorescences nearly every year, but mature seeds do not emerge regularly on an annual basis (Convey 1996;Giełwanowska et al 2011).…”

Development of generative structures of polar Caryophyllaceae plants: the Arctic Cerastium alpinum and Silene involucrata, and the Antarctic Colobanthus quitensis

“…Some grains do not leave the theca and germinate in microsporangia, whereas in most angiosperms, the theca opens when pollen grains reach the stage of a two-celled male gametophyte, and their generative cells divide into two sperm cells only during the growth of the pollen tube. The production of trinucleate gametophytes in closed microsporangia of Colobanthus quitensis was observed in our earlier study (Giełwanowska et al 2011). This strategy shortens the period between pollen release and successful fertilization, which minimizes the risk that pollen will be adversely influenced by external factors during its transport to the stigma.…”

“…-In this study, microscopic analyses revealed that Caryophyllaceae produced flower buds with (in most cases) normally developed microsporangia, microspores and male gametophytes. Selected attributes of microsporangia and male germ line cells in Antarctic phanerogams growing in their native habitats were discussed in our previous studies (Giełwanowska et al 2011).…”

Generative reproduction of Antarctic grasses, the native species Deschampsia antarctica Desv. and the alien species Poa annua L.

“…-The results of microscopic analyses performed in this study indicate that both D. antarctica and P. annua produce flower buds with normally developed micro− sporangia, microspores and male gametophytes. The development of microspo− rangia and male germ line cells in polar plants growing in Antarctica was dis− cussed in our previous studies (Giełwanowska et al 2005(Giełwanowska et al , 2011. We observed that pollen grains of D. antarctica and P. annua reached the three−celled stage be− fore pollen discharge and that many grains did not leave the thecae and germinated inside microsporangia.…”