Introduction to Plant Biotechnology

1. Introduction to Plant Biotechnology Chapter 10

2. Learning Outcomes • Describe mechanisms of plant pollination and differentiate between haploid and diploid cells and their role in sexual reproduction • Identify various natural and artificial ways to propagate plants to increase genetic variety or maintain the genetic composition • Discuss the function and composition of different plant structures, tissues, and organelles and give examples of foods that are derived from various plant organs • Describe the processes of germination and plant growth • Perform the calculations to predict expected plant phenotypes for specific genetic genotypes, using Punnett Square analysis • Perform statistical calculations and analysis of data for a plant breeding experiment

3. 10.1 Introduction to Plant Propagation There are several methods of modifying or improving plants or plant parts. One of the first advances occurred when farmers discovered they could control pollination and the resulting seed crop. Plant breeding involves sexual reproduction. Plant breeding involves asexual reproduction (cloning).

4. Flower Structure. Most flowers are “complete” with both male (stamen) and female (pistil) sex organs. A seed develops when pollen reaches and fertilizes an ovule.

5. New Gene Combinations. Crossing-over and gene shuffling during meiosis (sex cell division) created new combinations of genetic information on chromosomes. The new combination of genes is carried in sex cells to the zygote of the next generation. What genetic information would a sex cell be carrying if it got one or another of the final chromosomes?

6. Vocabulary • Pollination – the transfer of pollen (male gametes) to the pistil (the female part of the flower) • Breeding – the process of propagating plants or animals through sexual reproduction of specific parents • Sexual reproduction – a process by which two parent cells give rise to offspring of the next generation by each contributing a set of chromosomes carried in gametes • Zygote – a cell that results from the fusion of a sperm nucleus and an egg nucleus • Embryo – a plant or animal in its initial stage of development • Gametes – sex cells (ie, sperm or eggs) • Meiosis – a special kind of cell division that results in four gametes (N) from a single diploid (2N) cell • Selective breeding – parent selection and controlled breeding for a particular characteristic • Cuttings – pieces of stems, leaves, or roots for use in asexual plant propagation • Tissue culture – the process of growing plant or animal cells in or on a sterile medium containing all the nutrients necessary for growth • Callus – a mass of undifferentiated plant cells developed during plant tissue culture

7. 10.1 Review Questions • How many parents are necessary for an offspring to be produced by sexual reproduction? How many parents are necessary for an offspring to be produced by asexual reproduction? • Which two cells fuse to make a zygote? From where do the chromosomes of a zygote come? • How does a cutting become a functioning, independent organism? • What is the smallest number of cells required to clone a plant through tissue culture?

8. 10.2 Basic Plant Anatomy Plants are multicellular organisms composed of organs and tissues. Plants have a wide variety of organ structures. Plant organs are grown as food or commercial crops. Plant Tissue Plant tissues are groups of similar cells with a specific function. Plant Cells Plant cells have all the organelles found in other cells, plus special organelles.

9. Vocabulary • Meristematic tissue – tissue found in shoot buds, leaf buds, and root tips that is actively dividing and responsible for growth

10. 10.2 Review Questions • List some foods that are examples of the following plant organs: stems, roots, leaves, flowers (ovaries), and seeds (fertilized ovules). • Which plant tissue type is the source of cells for tissue culture? • Give an example of a plant that has been modified by genetic engineering.

11. 10.3 Plant Growth, Structure, and Function Plants have specific regions where cell division can occur. Meristems are found at each growing tip.

12. During mitosis, cells make exact copies of themselves. The tightly wound mitotic chromosomes are visible using a microscope.

13. Monocot Seed Germination. Four germinated corn seedlings. The coleoptile protects the emerging leaves. Corn plants are monocots since they have only one section to the seed. Dicot See Germination. The diagram shows a germinating bean seed with an enlarged radicle growing down. The epicotyl will grow up into the leaves and stem. The two cotyledons emerge from the seed as a food source, but they wither after a short while.

14. Vocabulary • Meristems – regions of a plant where cell division occurs, generally found in the growing tips of plants • Radicle – an embryonic root-tip • Differentiation – the development of a cell toward a more defined or specialized function • Plant hormones – signaling molecules that, in certain concentrations, regulate growth and development, often by altering the expression of genes that trigger certain cell specialization and organ function • Herbaceous plants – plants that do not add woody tissues; most herbaceous plants have a short generation time of less than one year from seed to flower • Woody plants – plants that add woody tissue; most woody plants have a long generation time of more than one year from seed to flower; most woody plants grow to be tall, thick, and hard

15. 10.3 Review Questions • Name the parts of the plants that contain actively dividing cells. • After mitotic division, how many chromosomes do daughter cells have, compared with the parent? • When a seed germinates, what is the first plant part to emerge from the sprouting seed? • There is a vast diversity among plant cells and plant tissues. What are the chemicals called that trigger much of the cell and tissue specializations in plants?

16. 10.4 Introduction to Plant Breeding Alternation of generations. Each sex cell gets one copy (1N) of each chromosome and, therefore, one copy of each gene. Most genes exist in one of two or more forms (alleles). When the zygote (2N) forms, it receives both sets of chromosomes (and genes) for the two sex cells. Depending on what was carried in the sex cells, the zygote could receive two matching alleles or two different alleles for a particular trait. The alleles of an organism are its genotype and, ultimately, determine the traits expressed (phenotype).

17. Genotypes and Phenotypes The alleles an organism possesses are called its genotype. They determine the plant’s characteristics. Breeding Plants for Desired Phenotypes Plant breeders try to study, predict, and manipulate crosses between flowers in an attempt to produce plants of desired phenotypes. Using Punnett Square Analysis Shows the possible gene combinations that could result when crossing specific genotypes.

18. Vocabulary • Diploid – having two sets (2N) of homologous (matching) chromosomes • Haploid – having only one set (1N) of chromosomes • Alleles – alternative forms of a gene • Dominant – referring to how an allele for a gene is more strongly expressed than an alternate form (allele) of the gene • Recessive – referring to how an allele for a gene is less strongly expressed than an alternate form (allele) of the gene; a gene must be homozygous recessive (ie, hh or rr) for an organism to demonstrate a recessive phenotype • Homozygous – having two identical forms or alleles of a particular gene (ie, hh or RR) • Homozygous dominant – having two of the same alleles for the dominant version of the gene (ie, HH or RR) • Heterozygous recessive – have two different forms or alleles of a particular gene (ie, Hh or Rr) • Polygenic – traits that result from the expression of several different genes • Punnett Square Analysis – a chart that shows the possible gene combinations that could result when crossing specific genotypes • Monohybrid cross – a breeding experiment in which the inheritance of only one trait is studied • Dihybrid cross – a breeding experiment in which the inheritance of two traits is studied at the same time

19. 10.4 Review Questions • Which of the following are diploid (2N) and which are haploid? egg, zygote, embryo, parent plant, sperm, and seed? • A plant has purple flowers and hairy stems. Is this description its genotype or phenotype? Propose some allelic symbols for purple flowers and hairy stems. • Consider a cross between two Brassica rapa parent plants known to be heterozygous tall. Using the same allelic symbols as in the text, show the entire cross (problem), including the chances of this breeding resulting in short plants.

20. 10.5 Statistical Analysis of Data Using Numerical Data to Ensure Accuracy Instead of using words to describe data, scientists try to make all observations of experiments in numerical form. Using Multiple Replications to Determine Averages Experiments must be repeated enough to ensure that results reflect what really happens.

21. Evaluating Validity of Data Standard Deviation. If the SD is twice as large (right graph) as another (left graph), then we know that the data for the right graph are very dissimilar, and we would have less confidence in the data collection. The 10% RuleStandard Deviation

22. Using Goodness of Fit (Chi Square Analysis) to Test the Hypothesis How To Calculate the Chi Square Value (c2) C2 = S[(O-E)2/E] The terms represent the following: O = observed number for a phenotype group E = expected number for a phenotype group S = the Greek letter Sigma, which represents “sum of”

23. Vocabulary • Average – a statistical measure of the central tendency, that is calculated by dividing the sum of the values collected by the number of values being considered • Mean – the average value for a set of numbers • Standard deviation – a statistical measure of how much a dataset varies • Chi Square – a statistical measure of how well a dataset supports the hypothesis or the expected results of an experiment • Degrees of freedom – a value used in Chi Square analysis that represents the number of independent observations (eg, phenotypic groups) minus one • Null hypothesis – a hypothesis that assumes there is no difference between the observed and expected results

24. 10.5 Review Questions • A set of plant DNA extractions is measured on the UV spec. There are 13 samples and the average concentration is 18.8 mg/mL. One sample has a value of 17.2 mg/mL. Using the 10% rule, is the sample’s value valid and acceptable? • An experiment is conducted to determine the number of kindergarten children with attention deficit disorder (ADD) in the United States. The result shows that 80 out of 1000 students, on average, with a standard deviation of 5, exhibit ADD. A town near a nuclear plant has an average of 84 students per 1000 with ADD. Should the citizens be concerned? Why or why not? • A family had 22 children; 14 boys and 8 girls. Calculate the Chi Square value for such a cross and determine whether the results are due to a random mating or an environmental or genetic disorder.

25. Questions and Comments?