Flowers

1. Flowers

2. Remember … Three more differences between gymnosperms and angiosperms 4. Angiosperm ovules are protected within an enclosed structure rather sitting on a modified leaf 5. Double fertilization in the angiosperms produces a diploid zygote and triploid endosperm nucleus 6. In the angiosperms there are generally hermaphrodite flowers and cross pollinating (70%). Wind pollination is typical in the gymnosperms animal pollination widespread in angiosperms First some basic naming of parts

3. Basic structure of the angiosperm flower STAMEN (male reproductive part) CARPEL (female reproductive part) filament anther stigma style ovary OVULE (forms within ovary) petal (all petals combined are the flower’s corolla) sepal (all sepals combined are the flower’s calyx) receptacle This is a hermaphrodite flower with a single carpel Fig. 31.3, p. 532

4. Collective nouns that can cause confusion! Calyx The outer whorl of a flower made up of sepals that are usually green, and protect the flower in bud. Carpel Bears the stigma, and frequently an elongated style, and encloses the ovules (sometimes gynaecium). The megasporophyll of the flower Corolla The collective term for the petals of a flower

5. Collective nouns that can cause confusion! Ovary The total of the carpels in a flower is the ovary Perianth The floral envelope, it includes the calyx and corolla. Pistil Each separate carpel when there are lots of them in the ovary Stamen The anther and its supporting filament. The microsporophyll of the flower

6. Evolution of the pistil 4. Angiosperm ovules are protected within an enclosed structure rather sitting on a modified leaf Remember, angeion case – this is how we think it evolved

7. Life cycle of Angiosperms BUT mature sporophyte seed meiosis (within anther) meiosis (within ovary) DIPLOID HAPLOID fertilization gametes (sperm) microspores (mitosis) male gametophyte gametes (eggs) megaspores female gametophyte (mitosis) The basic life cycle appears similar to that of the Gymnosperms … there is a well developed receiving system for the pollen so that the male gametophyte can penetrate the angion, the female gametophyte has a more complex structure that results in an endosperm, nutritive material for the embryo

8. Overview of cherry life cycle Flower Ovule formation Seedling Seed Diploid Stage Meiosis Meiosis Double Fertilization Haploid Stage Pollen development Development of embryo sac Pollination

9. How pollen grains develop and germinate pollen sac Anther (cutaway view) filament one of the microspore mother cells inside a pollen sac Meiosis I and II each followed by cytoplasmic division results in four haploid (n) microspores Mitosis in a microspore gives a 2 celled, haploid, pollen grain. One cell will grow to be the pollen tube. The other will produce two sperm nuclei. pollen tube Pollen release sperm nuclei stigma style of carpel (see next slide) Diploid Stage Meiosis Haploid Stage (see next slide) mature male gametophyte Fig. 31.6a, p. 534

10. 5. Double fertilization in the angiosperms produces a diploid zygote and triploid endosperm Ways in which Angiosperms are different from Gymnosperms

11. Somatic cell division involves two successive steps: mitosis and cytokinesis. Now, remind me, what is cytokinesis again … ? In mitosis, the nuclear DNA duplicates and chromosomes segregates equally between the two daughter nuclei; cytokinesis divides these two nuclei and cytoplasm, including related cytoplasmic organelles, into two individual cells.

12. The fertilization process in Angiosperms an ovule ovary wall cell integument stalk seed coat seed embryo (2n) ovary (cutaway view) endosperm (3n) Meiosis I and II each followed by cytoplasmic division result in 4 haploid megaspores 3 megaspores disintigrate pollen tube embryo sac inside ovule Three rounds of mitosis with NO CYTOPLASMIC DIVISION produces a megaspore with 8 haploid nuclei endosperm mother cell (n + n) integuments egg (n) seedling (2n) How many ovules in a cherry? Diploid Stage Double Fertilization Meiosis Haploid Stage One sperm nucleus to the egg, one to the endosperm mother cell Cytoplasmic division then gives 7 cells – the endosperm mother cell with 2 nuclei Fig. 31.6b, p. 535

13. What goes on in the endosperm? The triploid nucleus divides and the endosperm cell becomes a supercell with many nuclei and a milky consistency. Cyotkinesis forms membranes and walls between the nuclei and makes the endosperm more solid. In most dicots the developing embryo moves the nutrients stored in the endosperm to the cotyledons and the endosperm is not present in a mature seed. In moncots the endosperm remains and is used by the seedling after germination.

14. Look what happens when you eat your endosperm!

15. 6. In the angiosperms there are generally hermaphrodite flowers and cross pollinating (70%). Wind pollination is typical in the gymnosperms animal pollination widespread in angiosperms Ways in which Angiosperms are different from Gymnosperms HERMAPHRODITOS was one of the EROTES, and a handsome son of Hermes and Aphrodite. He was loved by the Nymphe Salmakis who prayed that she could be with him forever. The gods, on hearing her prayer, merged their two forms into one, forming a being that was both male and female. Hermaphrodite: organism with the organs of both sexes.

16. That should make fertilization easier. Pollen can fertilize the egg and endosperm mother cell of the same flower. Hmm! I’m not so sure that is such a good idea. How can self-fertilization be prevented for hermaphrodite flowers? [1] Differences in timing of maturity of male and female parts [2] Incompatibility mechanisms

17. Pollen and stigma incompatibility There can be dozens of alleles of the S-gene. If a pollen grain has an allele that matches an allele of the stigma upon which it lands, then the pollen tube fails to grow. This system prevents self-fertilization AND fertilization from close relatives.

18. Rye grass incompatibility Pollen Grain Size and Surface Morphology in a Perennial Rye Grass Hybrid Attempts to hybridize between particular varieties resulted in production of a web-like substance and incompatibility Pollen grain on stigma Stacey Lacoste

19. The efficiency of animal pollination Nucleus of tube cell Generative cell Its not just the honey guys! Lilium pollen Pollen is up to 30% protein Animal pollination is targeted and so is more efficient than wind pollination. Animal pollinated flowers generally produce much less pollen than wind pollinated flowers. Pollen is important for animals – and many animal pollinated plants do produce some excess pollen. http://www.uri.edu/artsci/bio/plant_anatomy/images/153.gif

20. Reproduction and diversity of angiosperms Animal pollination is efficient and associated with the development of the hermaphrodite reproductive axis The diversity of flowers represent mechanisms promoting efficient pollination Prevention of self-fertilization maintains genetic variation by promoting cross pollination Sophistication of the reproductive process enables a large number of ways reproductive isolation can occur and so maintains genetic diversity