The developing pollen grains are nourished by

Visualization(Photo Credit: Kylie Bucalo) The image to the right is of a young Lily anther. Within the image you will see two large chambers or “pollen sacs” on the left and a large chamber that is fusing to become one during step 2. At this point, however, there are a total of four “pollen sacs.” Within each of the chambers you will see white dots. These dots represent cells or “pollen-grains-in-training.” At this stage, the cells are known as microsporocytes. Visualization(Photo Credit: Kylie Bucalo) As the anther matures, the “pollen sac” walls between adjacent pairs breakdown, creating two chambers instead of four. You can see this process happening on the right side of the picture above to the left. The microspores within the chambers(white dots) within the chambers are almost ready to become pollen grains but first they must undergo 3 more changes which occur almost simultaneously! The 3 final steps are as follows: 1. Members of the quartet(groups of 4 microsporocytes/cells) separate from one another. 2. Each microspore then undergoes nucleus division. The two nucleus that are developed are the generative nucleus and the vegetative nucleus which are involved in how the pollen grain achieves fertilization. 3. A two layered wall develops around each microspore When these events are completed, the microspores have become pollen grains! See the picture to the right for a close up of the final product! TERM DEFINITION Anther The circular part of the stamen found atop the ...

The plant kingdom has not always had the diversity we know today. It has taken hundreds of millions of years of evolution to bring about the diverse, complex group of flowering plants known as angiosperms. And for many millions of years prior to the emergence of angiosperms, the plant kingdom consisted of primarily of gymnosperms. Today, these two branches of the plant family tree represent the primary dividing factor among land plants, with angiosperms much more abundant than their earlier kin, the gymnosperms. So, what are the major differences between angiosperms and gymnosperms and what factors lead to the incredible success of the angiosperms? To step back even further in time, prior to emergence of the gymnosperms, plant life on earth began in the oceans. Recent research suggests that the first plant life to inhabit land dates back to almost 500 million years ago. These early terrestrial plants were nonvascular, meaning they did not have a vascular system of conductive tissue (think of the circulatory system in humans) to circulate water and nutrients among cells. Mosses, hornworts, liverworts and some kinds of algae are modern day nonvascular plants and representatives of early plant life on land The development of a vascular system was a major step forward for the plant kingdom, occurring around 430 million years ago. Next came reproduction from seeds, which was yet another huge step forward at around 350 million years ago that ultimately lead to the emergence of t...

\( \newcommand\) • • • • • • Gnetophytes (approximately 70 extant species) Gnetophytes represent an anatomically and genetically difficult group to classify. They have several traits in common with angiosperms, such as vessel elements in the xylem, double fertilization, and a covering over their seeds (more on this in labs 21 and 22). Even their leaves are angiosperm-like, with netted venation. However, these traits are convergently evolved, meaning that angiosperms and gnetophytes each evolved these traits separately. Genetically, recent studies have placed the gnetophytes as a sister group to the Pinaceae (pine family) within the conifers. This would mean that pines, firs, and spruces are more closely related to strange gnetophytes like Ephedra than they are to other conifers like redwoods, cedars, and Pacific yew. However, the true nature of this evolutionary relationship remains murky and contentious. • Angiosperm-like features: vessel elements, double fertilization, fruit-like ovule coverings • Dioecious. Female plants have covered ovules, while male plants have pollen cones. • Leaves xerophytic with opposite arrangement • Primarily insect pollinated; brightly colored seeds are dispersed by birds Observe the gnetophyte specimens available in lab. Make notes and drawings of features that would help you recognize this group in the space below: Conifers (approximately 600 extant species) Conifers are the most species-rich lineage of gymnosperms. From the fossil record, ...

Learning Objectives • Compare and contrast the life cycles of angiosperms (flowering plants), gymnosperms (conifers), non-seed vascular plants (ferns), and nonvascular plants (mosses) • Describe the structures and functions of the flower, seed, and fruit in the angiosperm life cycle • Explain the process, locations, and significance of angiosperm gametogenesis and fertilization, including double fertilization • Explain the process and significance of seed maturation, dormancy, and germination • Predict mechanisms of pollination based on flower characteristics and dispersal based on fruit characteristics Sexual reproduction in plants: Alternation of Generations The text below is adapted from Plants have two distinct multicellular stages in their life cycles, a phenomenon called alternation of generations (in contrast to the gametophyte and the multicellular diploid sporophyte. This is very different from most types of animal reproduction where there is only one multicellular stage: a diploid organism which produces single-celled haploid gametes. Before we revisit this life cycle, a reminder of some terms: • Gamete: a mature haploid male or female germ cell that is able to unite with another of the opposite sex in sexual reproduction to form a zygote • Spore: a minute, typically one-celled, reproductive unit capable of giving rise to a new individual without sexual fusion Gametes are always haploid, and spores are usually haploid (spores are always haploid in the plant alter...

Donam Tushabe * and Sergey Rosbakh † • Ecology and Conservation Biology, Institute of Plant Sciences, University of Regensburg, Regensburg, Germany The correct choice of in vitro pollen germination media (PGM) is crucial in basic and applied pollen research. However, the methodological gaps (e.g., strong focus of current research on model species and cultivated plants along with the lack of general rules for developing a PGM) makes experimenting with pollen difficult. We closed these gaps by compiling a compendium of optimized in vitro PGM recipes from more than 1800 articles published in English, German, and Russian from 1926 to 2019. The compendium includes 1572 PGM recipes successfully used to germinate pollen grains or produce pollen tubes in 816 species representing 412 genera and 114 families (both monocots and dicots). Among the 110 components recorded from the different PGM recipes, sucrose (89% of species), H 3BO 3 (77%), Ca 2+ (59%), Mg 2+ (44%), and K + (39%) were the most commonly used PGM components. PGM pH was reported in 35% of all studies reviewed. Also, we identified some general rules for creating PGM for various groups of species differing in area of research (wild and cultivated species), phylogenetic relatedness (angiosperms vs. gymnosperms, dicots vs. monocots), pollen physiology (bi- and tri-cellular), biochemistry (starchy vs. starchless pollen grains), and stigma properties (dry vs. wet), and compared the component requirements. Sucrose, calcium, a...