TWU Department of Biology Denton, Texas MAT Program

1. www.pnas.org/content/100/20/F1.medium.gif TWU Department of Biology Denton, Texas MAT Program COMPARISONS OF MORPHOLOGY AND EXINE CHARACTERISTICS OF POLLEN GRAINS FROM THREE DIFFERENT FAMILIES OF FLOWERS. A. VIETH, S. WESTMORELAND ABSTRACT METHODS RESULTS The flowers used to obtain pollen from for this study were purchased from a local community florist, Denton Florist in Denton, Texas. The flowers used were Tulipa gesneriana, common name Tulip, Lilium orientalis, common name Stargazer Lily, Gerberajamesonii, common name Gerber Daisy, Chrysanthemum maximum, common name Shasta Daisy Alstroemeria aurea, common name Alstroemeria. To view the exine patterns and structures of the pollen grains from each flower, a sample of pollen was taken from each source separately and placed on a corresponding SEM “stub” for viewing. Each SEM stub was labeled to ensure accurate exchange of pollen from flower to stub. A Hitachi 1000 Tabletop scanning electron microscope was used to view the pollen grains at high resolution magnifications. Due to the variations in size and surface structures between the different species, observations were recorded on micrographs at various magnifications from X400 up to X3000. Published literature was referenced to complete the study. The intent of this research was to investigate morphological and exine characteristics of pollen grains from three different families of flowers. The families of flowers from which the pollen was retrieved included the following: Asteraceae, Liliaceae, and Alstroemeriaceae. All samples were obtained from a local community florist. The various types of pollen grains were examined using the Hitachi 1000 Tabletop scanning electron microscope (SEM). Digital micrographs of pollen from the various flowers were compared to demonstrate the variety of different exine patterns that exist and investigate the morphology of those patterns. A. B. C. Figure 2. These pictures represent: A) original Tulipa gesneriana that pollen was obtained from, B) scanning micrograph of pollen (x400), C) scanning micrograph of pollen (x2000) PURPOSE B. C. A. The purpose of this study was to acquire basic microscopy skills using a scanning electron microscope and to investigate the morphological and exine characteristics of pollen grains from three different families of flowers. It was hypothesized that pollen grains from the same family of flowers, but of a different genus, will each have the same shape and same exine pattern. Figure 3. These pictures represent: A) original Lilium orientalis that pollen was obtained from, B) scanning micrograph of pollen (x400), C) scanning micrograph of pollen grain (x2,000) CONCLUSIONS Based on the evidence found within this study it is accurate to state that pollen grains are highly varied in their shape and exine sculpturing amongst the different genus’ of flowers within the same family. The exine surface has various patterns associated with it that differ from species to species and is of great taxonomic significance (Bowes and Mauseth 2008). For taxonomic purposes, most emphasis has been placed so far on the comparative features of the pollen grains themselves, especially those of apertures and wall structure (Stuessy 2009). Data from pollen grains are known to be useful at all levels of taxonomic hierarchy, especially in angiosperms and a general correlation can be noted with the use of SEM for external features that have value mostly at the lower levels of the taxonomic hierarchy and of transmission electron microscope for internal features useful at higher levels (Stuessy). The variety of morphology gives rise to the various ways of dispersal, water stress, pollination, germination, and stigmatic interactions. A. B. C. Biology Figure 4. These pictures represent: A) original Gerbera jamesonii that pollen was obtained from, B) scanning micrograph of pollen (x400), C) scanning micrograph of pollen (x2,000) INTRODUCTION Pollen is of fundamental importance in plant reproduction. The pollen wall is composed of two major layers: the intine and exine. The exine is the hard, outermost, desiccation resistant wall layer that provides the major structural support for the cytoplasm (Simpson 2006). Structurally, the exine is the most complex plant cell wall and contains a substance called sporopollenin that protects the pollen grain from mechanical damage and decay (Blackmore et al. 2007). Pollen sculpturing is a term used to describe the various patterns associated with the exine surface. With the aid of a scanning electron microscope, greater exine pattern detail can be viewed. Specialized terms have been given to describe the patterns associated with pollen exine surfaces; they include: baculate, clavate, echinate, fossulate, foveolate, gemmate, psilate, reticulate, rugulate, spinulose, striate, and verrucate (see Figure 1). The surface of the pollen wall, or exine, may also function to facilitate pollination. Those surfaces that tend to be more smooth (psilate), as in many wind-pollinated species, function more efficiently aerodynamically for wind transport (Campbell et al. 2002). Those with more elaborate sculptured surfaces, such as those with spines, striations, reticulating ridges, knobs, and others features, facilitate attachment as in most animal pollinated species (Campbell). A. B. C. Figure 5. These pictures represent: A) original Chrysanthemum maximum that pollen was obtained from, B) scanning micrograph of pollen (x400), C) scanning micrograph of pollen (x3,000) B. C. A. Figure 6. These pictures represent: A) original Alstroemeria aurea that pollen was obtained from, B) scanning micrograph of pollen (x400), C) scanning micrograph of pollen (x2,000) ACKNOWLEDGEMENTS RESULTS I would like to thank Dr. Sandra Westmoreland for giving me the opportunity to engage myself in a full science inquiry based study. I would also like to thank the staff of Denton Florist for providing me with the flowers and pollen for my research purposes. A sincere thank you to Dr. Varsha Shah for sharing her resources and expertise in the field of palynology. The results of this investigation rejected my original hypothesis. It was discovered that pollen grains from the same family of flowers but of a different genus are not identical in morphological and exine structural characteristics. The shape and exine, as seen in figures 2 and 3, show there to be significant differences within the Liliaceae family. The Tulipa (Figures 2B, 2C) has a distinct three sided concaved looking shape and also has a surface that looks to be of a rugulate type of exine pattern. The Lilium orientalis pollen grain (Figures 3B, 3C) is noticeably folded over but the length of the grain itself is representative of a more prolate shape (elongated along the polar axis) and consists of a reticulum type of exine pattern. The Asteraceae family shows another significant difference between pollen grains of the same family of flowers. Gerbera jamesonii (Figure 4B, 4C) represents a type of tricolporate shape with convexed sides but has a rather smooth exine surface. The micrograph taken (Figure 4C) does not provide enough detail to give an accurate term for the type of exine surface pattern of the Gerbera jamesonii. Micrographs of the Chrysanthemum maximum (Figures 5B, 5C) display a definite spheroidal (round ball like) shape with an echinate surface. Echinate refers to having spinelike elements; these would be the spines seen covering the entire surface of the pollen grain. The Alstroemeriaceae family, represented by the flower Alstroemeria(Figures 6B, 6C), are inconclusive of the exact shape because they have folded over due to water loss. They do have a more elongated shape which could be representative of a prolate shape rather than spheroidal. The micrograph of the exine surface (Figure 6C) represents a highly striated exine pattern. These micrographs conclude that pollen grains are not morphologically and structurally the same within the same family of flowers. Pollen grains do differ amongst the various genus of a particular family in terms of shape, structure and exine pattern. REFERENCES Blackmore S, Rowley JR, Skvarla JJ, Wortley AH. 2007. Pollen wall development in flowering plants. New Phytologist [Internet]. [cited 2013 Mar 21]; 174: 483-198. Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1469- 8137.2007.02060.x/pdf doi:10.1111/j31469-8137.2007.02060.x Bowes BG, Mauseth JD. 2008. Plant structure: A color guide (2nd ed.). Sudbury (MA): Jones and Bartlett Publishers. Campbell CS, Donoghue MJ, Judd WS, Kellogg EA. 2002. Plant systematics: A phylogenetic approach (2nd ed.). Sunderland (MA): Sinauer Associates, Inc. Simpson MG. 2006. Plant systematics. Burlington (MA): Elsevier Academic Press. Stuessy TF, 2009. Plant taxonomy: The systematic evaluation of comparative data (2nd ed.) Chichester (NY): Columbia University Press. Figure 1 Pollen sculpturing. A. Echinate. B. Verrucate. C. Foveolate D. Rugulose. E. Striate. F,G. Reticulate(From Simpson, M., 2006) MAT Program- Masters of Arts in Teaching TWU Department of Biology