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14-1 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Part 3: Plant form and function.

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Presentation on theme: "14-1 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Part 3: Plant form and function."— Presentation transcript:

1 14-1 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Part 3: Plant form and function Chapter 14: Reproduction, growth and development of flowering plants

2 14-2 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Introduction Plant life cycles are characterised by an alternation of generations

3 14-3 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 14.1a: The life cycle of a homosporous plant Copyright © Professor Pauline Ladiges, University of Melbourne

4 14-4 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 14.1b: The life cycle of a heterosporous plant Copyright © Professor Pauline Ladiges, University of Melbourne

5 14-5 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Alternation of generations Many mosses and ferns are homosporous, in that their sporophytes produce only one type of haploid spore Flowering plants are heterosporous as they produce, by meiosis, separate male and female spores, each of which undergoes mitosis to produce male and female gametophytes

6 14-6 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint The angiosperm flower In angiosperms, the sporophyte is the dominant generation The sporophyte produces flowers, which are the sites of sexual reproduction A flower is a specialised shoot composed of four whorls of leaves, grouped around the tip of the flower stalk or receptacle These whorls, beginning with the outermost, are the sepals, petals, stamens and carpel

7 14-7 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint (cont.) Fig. 14.2a: Longitudinal section of a flower of oilseed rape, Brassica napus Copyright © E Evans

8 14-8 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 14.2b: Top view and longitudinal section of a typical flower

9 14-9 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint The angiosperm flower (cont.) Stamens are the male reproductive organs A stamen consists of a filament upon which is borne an anther A carpel is the female reproductive organ A single carpel consists of a stigma, style and ovary In some species of flowering plants, a number of carpels are fused together to form a gynoecium

10 14-10 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Anthers and carpels Development of angiosperm gametophytes involves meiosis and mitosis

11 14-11 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 14.3: Development of pollen and embryo sac (top)

12 14-12 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 14.3: Development of pollen and embryo sac (middle)

13 14-13 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 14.3: Development of pollen and embryo sac (botttom)

14 14-14 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint The anther An anther consists of two pollen sacs, each containing a large number of multicellular pollen grains Pollen grains are the sperm-producing male gametophytes Pollen forms when a unicellular microspore undergoes mitosis to produce a small generative cell and a larger vegetative cell When pollen lands on a stigma, it germinates to produce a pollen tube

15 14-15 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint The carpel The stigma may be wet or dry and either smooth or covered in elongated cells known as papillae, which trap pollen The pollen tube of a germinating grain grows down through the style into the ovary An ovary contains ovules, within each of which is an embryo sac A pollen tube enters the ovule via the micropyle, and releases sperm into the embryo sac, fertilising the egg

16 14-16 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Double fertilisation Each pollen tube contains a tube nucleus and two sperm nuclei The egg sac of an ovule contains an egg cell, situated near the micropyle, and two polar nuclei contained within a large central cell At fertilisation, one sperm fuses with the egg cell to form a diploid zygote The other sperm fuses with the polar nuclei to form triploid endosperm, which will support the growth of the embryo and in some cases the growth of a germinating seedling

17 14-17 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Apomixis Some plants have the capacity to reproduce without fertilisation e.g. apomictic species Apomicts produce a diploid megaspore that does not undergo meiosis, but instead divides by mitosis to produce an embryo, which then develops in the same way as sexually-produced embryos The absence of meiosis means that apomictic plants are identical to one another  lack of genetic variation Apomixis is common among successful species and provides a means of rapid reproduction

18 14-18 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Pollination in flowering plants Pollination, the first step in the chain of events leading to fertilisation, unites male and female gametophytes Most flowering plants have close interactions with insects, birds or other animals that convey pollen directly between flowers Plants (e.g. grasses, she-oaks) that lack such mutualisms may be wind-pollinated, compensating for the randomness of this form of dispersal by releasing large quantities of pollen (cont.)

19 14-19 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Pollination in flowering plants (cont.) Plants, which are essentially fixed in place, have evolved mechanisms that prevent cross-species pollination The stigma recognises pollen belonging to the same species and either prevents the pollen from other species from germinating, or blocks pollen tube growth down the style The flowers of most species contain both male and female reproductive organs—they are bisexual— and some of these may self-fertilise (cont.)

20 14-20 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Pollination in flowering plants (cont.) Many plants have evolved mechanisms that encourage fertilisation between separate individuals of the same species (cross-fertilisation) Cross-fertilisation maintains genetic variation in offspring, which is advantageous in unpredictable or changing environments –monoecious species: male and female organs occur on separate flowers of the same plant –dioecious species: male and female flowers occur on separate plants

21 14-21 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Enhancing cross-pollination In plants with bisexual flowers, a variety of mechanisms may prevent self-fertilisation –some species produce flowers that go through separate male and female phases –others have flower structures that inhibit self-pollination e.g. ‘pin’ and ‘thrum’ flowers on separate primrose plants

22 14-22 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Preventing self-fertilisation Self-incompatibility is the most common means by which plants prevent self-fertilisation This genetically-controlled recognition system stops eggs from being fertilised by pollen from the same plant If pollen is deposited on the stigma of a flower on the same plant, a biochemical block prevents the pollen from forming a pollen tube and fertilising an egg Recognition of ‘self’ pollen is based on genes for self-incompatibility, called S-genes

23 14-23 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Self-incompatibility As a pollen grain is haploid, it will be recognised as ‘self’ if its S allele is the same as either of the two S alleles of the diploid stigma

24 14-24 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig : Genetics of self-incompatibility

25 14-25 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Seed development After fertilisation, a zygote undergoes a series of rapid cell divisions to form an embryo In dicotyledons (e.g. beans) the embryo continues to develop and generates two seed leaves (cotyledons) between which is situated the shoot apical meristem (cont.)

26 14-26 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig a: The zygote divides into a two- celled proembryo

27 14-27 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Seed development (cont.) Mitotic divisions of the triploid endosperm nucleus ultimately generate liquid endosperm, which as it forms cell walls, solidifies and expands In this state, endosperm is the major nutritive tissue of the seed, rich in lipids or carbohydrates As a seed matures, it enters dormancy, a state of extremely low metabolic rate with deferral of growth and development Dormancy increases the likelihood that when the seed germinates, it will be under conditions (light, temp. etc.) that most advantage the seedling

28 14-28 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fruit development As seeds develop from ovules, other changes occur in the flower, including swelling of the ovary to form a fruit, which protects the seeds and assists in their dispersal Fruits normally ripen at about the same time as its seeds are completing their development In cereals and grasses, the fruit contains a single fertilised ovule and develops into a grain If a flower is not pollinated, fruit will not normally develop and the flower will shrivel and drop

29 14-29 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Seed germination Germination of seeds relies on imbibition, which is the uptake of water resulting from the low water potential of the dry seed As the seed expands, it ruptures the seed coat, providing oxygen to the embryo and triggering metabolic changes that enable growth to restart

30 14-30 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig b: Seed structure, germination and development in a dicot Copyright © Ed Reschke

31 14-31 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Organogenesis Plant growth describes the irreversible increase in mass that results from cell division and expansion Development, on the other hand, is the sum of all the changes that together define the plant body Most plants demonstrate indeterminate growth, growing for as long as they remain alive In contrast, most animals and certain plant organs, such as leaves and flowers, undergo determinate growth, ceasing to grow after they attain a certain size (cont.)

32 14-32 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Organogenesis (cont.) Growth involves the production of new cells by repeated mitotic division, together with enlargement of existing cells These cells will differentiate into a range of cell types, each of which will assemble into the three- dimensional structures characteristic of mature organs Growth and development of new organs begins in specialised regions of cells found at the tips of shoots and roots—the apical meristems

33 14-33 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint The shoot apex The shoot apical meristem produces stems and leaves, and also flowers when the plant enters its reproductive phase The apex of the shoot is a spherical dome of meristematic cells that divide to produce leaf primordia, structures that develop into leaves

34 14-34 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig : Shoot apical meristem

35 14-35 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint The root apex The root apical meristem of flowering plants contains a zone of rapidly dividing cells that gives rise to the mature tissues of the root Include root hairs, which arise by elongation of an epidermal cell, and lateral roots, which arise deep within the tissues of more mature parts of the root

36 14-36 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig : Barley root tip Copyright © Professor S Y Zee, University of Hong Kong

37 14-37 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Asexual reproduction in plants Many plants have the ability to clone themselves by asexual, or vegetative, reproduction Some plants, such as strawberries and Spinifex grass, have stolons, long stems that grow horizontally along the soil surface, forming roots and leaves that eventually form independent units (cont.)

38 14-38 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig : Spinifex grass (Spinifex hirsutus) Copyright © Susan Gehrig

39 14-39 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Asexual reproduction in plants (cont.) Some species have the ability to form shoots from underground storage organs such as corms and bulbs, or from root tubers Rhizome-producing species such as bracken, and those that have horizontal roots, such as wattle, also have the capacity to reproduce vegetatively These clones are genetically identical to the parent Plants have the ability, under suitable conditions, to generate an entire plant from a single cell—a property known as totipotency

40 14-40 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Biotechnology and plants Plant biotechnologists use a number of in vitro methods to generate new plant varieties Tissue culture is a propagation technique in which one or a few cells are grown on artificial media, containing nutrients and hormones, to generate large numbers of plants Via manipulation of the hormonal balance, the callus (a mass of dividing undifferentiated cells) that forms can be induced to develop shoots and roots with fully differentiated cells

41 14-41 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Genetic engineering of plants Tissue culture techniques are now used to produce genetically-modified (transgenic) plant species Desirable plant traits can be introduced into crop plants to increase disease resistance, improve nutritional value and increase crop survival in adverse environments The gene that codes for the plant trait is identified and isolated, and then incorporated into the nuclear DNA of a host cell (cont.)

42 14-42 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Genetic engineering of plants (cont.) Transformation is the process by which the genetic makeup of a single cell is altered This process uses vectors such as bacterial plasmids to transfer the gene

43 14-43 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig a: Transferring cloned genes


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