CHAPTER 38 PLANT REPRODUCTION Angiosperm Reproduction & Biotechnology

Floral Organs

Sepals and petals are nonreproductive organs. Sepals: enclose and protect the floral bud before it opens; usually green and more leaf-like in appearance. In many angiosperms, the petals are brightly colored to attract pollinators.

Stamens: male reproductive organs Stalk: the filament Anther: pollen sacs. The pollen sacs produce pollen.

Carpels: female reproductive organs Ovary- base of the carpel Ovules Egg cell Embryo Sac (female gametophyte), i.e., seed Stigma- platform for pollen grain Style- slender neck, connects ovary and stigma

The stamens and carpels of flowers contain sporangia, within which the spores and then gametophytes develop. The male gametophytes are sperm- producing structures called pollen grains, which form within the pollen sacs of anthers. The female gametophytes are egg- producing structures called embryo sacs, which form within the ovules in ovaries.

Pollination begins the process by which the male and female gametophytes are brought together so that their gametes can unite. Pollination- when pollen released from anthers lands on a stigma. Each pollen grain produces a pollen tube, which grows down into the ovary via the style and discharges sperm into the embryo sac, fertilizing the egg. The zygote gives rise to an embryo. The ovule develops into a seed and the entire ovary develops into a fruit containing one or more seeds. Fruits disperse seeds away from the source plant where the seed germinates.

Function of Flowers

Classification of Flowers Complete Versus Incomplete Flowers Complete: possess sepals, petals, stamens, and carpels Incomplete: lack one or more of these components Perfect Versus Imperfect Flowers Perfect: possess both stamens and carpels Imperfect: possess either stamens (staminate) or carpels (carpelate), but not both

Complete Flower

Monoecious Versus Dioecious Monoecious: both staminate and carpellate flowers are found together on the same plant (e.g., corn). Dioecious: staminate flowers occur on separate plants from those that carry carpellate flowers (e.g., date palms).

Monoecious

Dioecious

Angiosperm Life Cycle

The development of angiosperm gametophytes involves meiosis and mitosis.

The male gametophyte begins its development within the sporangia (pollen sacs) of the anther. Within the sporangia are microsporocytes, each of which will from four haploid microspores through meiosis. Each microspore can eventually give rise to a haploid male gametophyte.

A microspore divides once by mitosis and produces a generative cell and a tube cell. The generative cell forms sperm. The tube cell, enclosing the generative cell, produces the pollen tube, which delivers sperm to the egg.

Pollen Tubes

Pollen Grains This is a pollen grain, an immature male gametophyte.

Barriers to Self-Fertilization Stamens and carpels may mature at different times. Self-incompatibility- plant rejects its own pollen Plant design prevents an animal pollinator from transferring pollen from the anthers to the stigma of the same flower.

The Genetic Basis for the Inhibition of Self-Fertilization S-genes: self-incompatibility gene If a pollen grain and the carpel’s stigma have matching alleles at the S-locus, then the pollen grain fails to initiate or complete the formation of a pollen tube.

Pollen Tube Formation and Double Fertilization

Seed Development

Release of sugars from the endosperm during germination

embryo endosperm

Fate of the Endosperm Typical Monocot (e.g., corn) endosperm present in substantial quantities in mature seed. cotyledon absorbs nutrients from endosperm during seed germination. Typical Dicot (e.g, garden bean) endosperm completely absorbed into cotyledons before seed maturation. Other Dicots (e.g., castor bean) endosperm only partially absorbed by cotyledons during seed maturation. remainder of endosperm absorbed by cotyledons during germination.

Seed Structure

Relationship of the Flower to the Fruit

The ovary develops into a fruit adapted for seed dispersal As the seeds are developing from ovules, the ovary of the flower is developing into a fruit, which protects the enclosed seeds and aids in their dispersal by wind or animals. Pollination triggers hormonal changes that cause the ovary to begin its transformation into a fruit. If a flower has not been pollinated, fruit usually does not develop, and the entire flower withers and falls away.

The ovary wall becomes the pericarp, the thickened wall of the fruit Fruit Formation The ovary wall becomes the pericarp, the thickened wall of the fruit Other flower parts wither and are shed. However, in some angiosperms, other floral parts contribute to what we call a fruit. Development of a pea fruit (pod)

Functions of the Fruit Protection of the enclosed seed (e.g., pea pods). Facilitating dispersal. wings for wind dispersal (e.g., maple). hocks and barbs for attachment to animal fur or avian feathers (e.g., cocklebur). sweet, fleshy fruit encouraging ingestion and dispersal of seeds by animals (e.g., cherry).

Types of Fruits Stigma Carpels Style Stamen Flower Petal Ovary Stamen Fig. 38-10 Types of Fruits Stigma Carpels Style Stamen Flower Petal Ovary Stamen Stamen Sepal Stigma Ovary (in receptacle) Ovule Ovule Pea flower Raspberry flower Pineapple inflorescence Apple flower Each segment develops from the carpel of one flower Remains of stamens and styles Carpel (fruitlet) Stigma Sepals Seed Ovary Stamen Seed Receptacle Pea fruit Raspberry fruit Pineapple fruit Apple fruit (a) Simple fruit (b) Aggregate fruit (c) Multiple fruit (d) Accessory fruit

Seed Dormancy Function: allows seeds to germinate at the most optimal time. Length of dormancy Signals triggering the end of dormancy. occurrence of water period of cold temperature fire light scarification

Germination of Bean

Germination of a Pea

Germination of Corn

Asexual and Sexual Reproduction in the Life Histories of Plants

Asexual Propagation

Asexual Propagation of Plants in Agriculture Shoot or stem cuttings generate roots. Cloning from single leaves. Potato eyes used to generate whole potato plants. Plant tissue culture. Grafting.

Plant Tissue Culture: Plant biotechnologists have adopted in vitro methods to create and clone novel plants varieties.

Axel N. Erlandson (1884-1964) Figuring out how he did it. Axel seemed to enjoy working on a large-scale using timber trees like sycamore and box Elder. Later in life he trialled many others tree species. Old photographs show the elaborate framework Axel build to guide the growth, the photos reveal some of his secrets. By looking closely one can see a series of small wooden blocks to guide the growth around curves. In one of the photos, he is building new framing for a existing design to further guide the tree when it grows that far. He also used timber spacers to maintain the design until the trees could support themselves. Axel used a gradual shaping method. In his daughter's book (Wilma Erlandson) 'My Father "Talked to Trees"' she wrote "When the stems of the trees were very young and flexible he shaped them as desired." Wilma also talks about the role of the framework in the process of shaping the trees. Rather than forcing the trees into place as one author has suggested, Wilma talks about the framing supporting the trees. Quote from 'My Father "Talked to Trees"' "They were then held in place by framework for several years until they were strong enough to stand on their own." Modern Tree shapers who use a gradual method of shaping are GrownUp Furniture and Pooktre. On the web site GrownUp Furniture by Dr Chris Cattle there is a how to guide about shaping trees. http://www.grown-furniture.co.uk/how-to-grow.html Axel Erlandson Axel Erlandson with his four legged giant. Where are the trees now Though out the life of the Circus Trees there has been much media attention about them. They have appeared 12 times in Ripley's believe it or not. They continue to appear in media around the world. Axel never took on an apprentice, this meant that as he grew older and frailer he was unable to attend and care for his trees. After many years of trying to sell his trees he managed to sell them in 1963. It was only a year later that he died at the age of 79. After Axel's death the trees had a series of owners. Disney tried to buy them but loss interest when they found out how much the owner wanted for them. During this time the trees were slowly dying from neglect. Robert Hogan purchased the land the trees where living on in 1977, for development. Joseph Cahill, a landscape designer, paid Hogan $12,000 for the trees and was given two and a half years to move them. About this time a young architect Mark Primack went to great lengths to ensure the survival of the remaining Circus Trees. Mark received an arts grant to draw and record them as they were. He went onto the property without permission to tend and water the trees. He became an impassioned advocate for saving Axel's Trees. Efforts to have the trees declared historical or a cultural resource failed. Mark continues to have an interest in the Circus Trees and the potential they represent. He is considered the Leading authority on Axel Erlandson's Trees in the world today. On Mark's web site there are some photos of Axel's trees Finally, in 1984, Michael Bonfante come forward to buy the trees for a horticultural amusement park. He moved 24 trees to the new location called Bonfante Gardens Theme Park in Gilroy. Where they are happily growing and open to the public today. Bonfante Gardens later changed their name to Gilroy Gardens. Wilma Erlandson's book My Father "Talked to trees" is available at Gilroy Gardens. Axel N. Erlandson (1884-1964)

Genetic Engineering Applications of Plant Tissue Culture Injecting foreign DNA into host cells Protoplast fusion

A DNA Gun

Protoplasts

Monoculture Risks and Benefits 1 million dies Phytophthora infestans Irish Potato Famine (1845) Potato blight Phytophthora infestans

Genetically modified rice Fig. 38-18 Genetically modified rice Ordinary rice

The Papaya Ring Spot Virus (PRSV) was identified on Oahu in the 1940s and became a significant threat to the industry in the 1950s. The industry was moved to the then virus-free island of Hawaii where it thrived in the Puna region, producing 95% of Hawaiian papaya in the state. However, it was clear that the virus would eventually infest the island of Hawaii. Commercial production of papaya on the Big Island dropped 50% from 53 million pounds in 1992—when the ringspot virus hit—to 25 million pounds in 1999. Fortunately for Hawaii, research had already begun on developing a disease-resistant papaya—the Rainbow Papaya—by Cornell researcher and Kamehameha Schools graduate, Dr. Dennis Gonsalves. Once seeds were available to growers, adoption was rapid. Within the first year, 98% of Puna growers had registered to receive the Rainbow Papaya seed, and 73% were growing it. By the second year, 56% of the fruit-bearing acreage was transgenic. The availability of GE papaya brought struggling growers back into the papaya business and by 2003, production in the region had rebounded to 40 million pounds per year. Cross Pollination of Genetically Engineered Crops in Hawaii The papaya seed planted determines the type of fruit on the tree. If the tree is genetically engineered, so is the fruit from the tree. If the seed is not genetically engineered, the fruit won’t be either. If a person growing papaya wants to make sure they have seeds to produce a particular color, shape, or a variety of fruit, they would follow the usual and customary horticultural practice of covering or “bagging” flowers to produce the seed of the desired type. Biotech plants in Hawaii cannot cross-pollinate with indigenous species, so they do not threaten the purity of our native varieties. Pollen movement and gene exchange between compatible plants is a well-understood and natural occurrence, especially in commodity agriculture. Regulatory authorities carefully examine the potential for spread of genes from biotech crops to native plants before biotech crops are authorized for commercial use. The term papaya ringspot (PRS) was first coined by Jensen in 1949 to describe a papaya disease in Hawaii.  Previously described diseases such as papaya mosaic (caused by Papaya mosaic virus) and watermelon mosaic (caused by Watermelon mosaic virus-1) were shown recently to be caused by Papaya ringspot virus (PRSV).  The virus (PRSV) causes a major disease of papaya and cucurbits and is found in all areas of the world where papaya and cucurbits are cultivated.  The primary host range of PRSV is limited to papaya (Caricaceae) and cucurbits (Cucurbitaceae), with Chenopium amaranticolor and C. quinoa (Chenopodiaceae) serving as local lesion hosts.  The virus is grouped into the papaya infecting type (PRSV-P) which affects both papaya and cucurbits, and the cucurbit infecting type (PRSV-W) which affects cucurbits but not papaya.  PRSV belongs to the genus Potyvirus, a large and economically important group of plant infecting viruses in the family Potyviridae.  Virions of PRSV are filamentous and flexuous measuring 760-800 x 12 nm with a monopartite single-stranded positive sense RNA as its genome.  Like other potyviruses, PRSV is transmitted in a nonpersistent manner by several species of aphids.  Genetically engineered (GE) papaya has been used to successfully control the disease caused by PRSV in Hawaii. Symptoms and Signs Papaya ringspot virus infects papaya and cucurbits systemically.  Symptoms on papaya are somewhat similar to those on cucurbits.  In papaya, leaves develop prominent mosaic and chlorosis on the leaf lamina, and water soaked oily streaks on the petioles and upper part of the trunk.  Severe symptoms often include a distortion of young leaves which also result in the development of a shoestring appearance that resembles mite damage.  Trees that are infected at a young stage remain stunted and will not produce an economical crop.  Fruit from infected trees may have bumps similar to that observed on fruit of plants with boron deficiency and often have ‘ringspots’, which is the basis for the disease’s common name (Figure 1).  A severe PRSV isolate from Taiwan is also known to induce systemic necrosis and wilting along with mosaic and chlorosis. Ringspot virus Papya

Latest plant developments Bioengineering Latest plant developments Make plants disease resistant Use less pesticides and herbicides Create plants that are more nutritious Improve crop yields Drought resistance Medicine

Bioengineering Plants Risks Inadvertent consequences: allergies (nuts) Ethics: patents and ownership of genes Herbicide tolerance- fear of producing a herbicide resistant weed that could get out of control Loss of biodiversity Food safety Cutting choices for vegetarians Cross pollination with human food crops

Humans as Genetic Engineers