Lecture 7 - Introduction to Plant Development Reading for Lectures 7 and 8: "Growth and Development of Flowering Plants" In Plants, Genes and Agriculture, p and p on Reserve in the library Review Lecture 7: Consequences of Immobility on Plant Development 1. How do genes instruct the building of large structures which make up a cell and whole organism? Demo of blocks -Genes encode enzymes. -Enzymes organize chemistry. -Enzymes build simple molecules (nucleotides, amino acids, sugars, etc.). -Other enzymes use these small molecules as subunits to build largermolecules. Once evolution could invent simple chemistry, it could then build large structures by simply making long chains of simple molecules, much like Lego blocks. What are the subunits of: DNA/RNA: Proteins: Cell walls (cellulose): Hydrophobic Membranes: Slide 7.1

Subunits Make Large Cellular Structures Fig. 3Glucose, Fructose, Sucrose, Starch cellulose Fig. 4. Fatty acids- 2C Acetyl CoA for compartment membranes: Slide 7.2 Figures 3 and 4 from : Plants, Genes and Agriculture,pp.86 and 89 M. Chrispeels and D.Sadava Jones and Bartlett Publishers, Boston, 1994 Fig 1 and 2 from: An Introduction to Genetic Analysis (6th ed) A.J. Griffiths et al., page346 W.H. Freeman and Co., New York, 1996 Fig. 1 - nucleotides = DNA Fig. 2 - amino acids - proteins:

Other Enzymes Assemble Large Macromolecules into Organized Subcellular Structures From Biochemistry and Mol. Biology of Plants p.3 Slide 7.03 Different cell types arise as different genes switch on/off to encode different subsets of enzymes to build and organize different subcellular structures or different biochemistry.

2. Plant vs Animal Cell Growth Plants do not move. Why do they not need to? Unlike animals, plants make their own food via photosynthesis. Plants-rigid due to cell walls. Why is this compared to animals? Animals have bones. Plants use cell walls for rigidity instead. walls consist of chains of sugars (5C and 6C) including cellulose, a polymer of linked glucose (6C) molecules (15-30% of walls). Cellulose is the most abundant compound in the world and full of potential calories. Why can cows, but not humans access energy from cellulose?? Slide 7.04 images from Biochemistry and Molecular Biology of Plants W.Gruissem, B. Buchanan and R.Jones p.67 + p.81 ASPP, Rockville MD, 2000

Unlike some animal cells, plant cells cannot move during development. Plant growth occurs through a combination of cell expansion and cell division. Plants growth like a building of "Lego building blocks", each locked together after it is formed. demo Lego blocks Understanding what controls plant cell growth and the orientation of the planes of cell division is crucial to understanding the shape of a plant organ (eg. leaf) Periclinal division - division plane is parallel to tissue surface Anticlinal division -- division plane is perpendicular to tissue surface With which divisions would you increase: -length of a stem? ______________ -width (girth) of a stem? ___________ 3. Immobile - Consequences for organ and cell types and overall architecture. Much of plant development (architecture, organ and cell types) can be explained by the fact that a plant is: (i) immobile; (ii) needs to compete for nutrients (carbon, Nitrogen, H20, etc.) to build complex molecules (DNA, RNA, proteins, lipids) in order to.... (iii) spread its DNA to the next generation (reproduction Slide 7.05 From Anatomy of Seed Plants (2 nd Ed) p. 278 K. Esau John Wiley and Sons, New York, 1977

Why? Let's design a land plant organism from scratch as evolution did noting that plants, unlike animals, produce their own energy via photosynthesis, and cannot move to obtain water and nutrients (N, S..): Need? Features of Organ/Cell type? Why this structure? The Result: Architecture of a Plant: How does the relative arrangement of leaves on the stem (="phyllotaxy") affect a plant's survival and utility to field agriculture? -whorled -- several leaves at the same node, but in a spiral –spiral - one leaf at each node, but in a spiral -decussate - two leaves at the same node, 180º apart -distichous - one leaf at each node, but alternating 180º (eg. corn) Hence, a plant is nothing but an efficient nutrient gathering machine designed to obtain nutrients in order to increase its survival and spread its DNA. What about animals (including plant pests/herbivores and you)?? All organisms have these same needs (nutrient acquisition and reproduction). Animals, however, are mobile. Because they are mobile, animals must have brains to integrate the environment with their needs -- this results in behaviour in order to choose where to go and not to go. Plants do not have brains (see....you learned something in this course after all). How do animals fulfill the above needs? Slide 7,06

4. Immobile - Consequences for body plan flexibility ("plasticity") A. A plant must remain flexible to changing environmental conditions: i) The need for sun in response to changing canopy competition or season/cloud cover. ii) The need for soil nutrients, hence continuous root growth. Demo - 2 twins vs 2 plants Oat root system A plant achieves this by elaborating its body plan post-embryonically via persistent meristems:. demo on board of plant vs animal body plan meristem - a region of a plant containing a population of embryonic, dividing cells that replenishes itself and gives rise to daughters that will assume specialized cell fates. Dicot Shoot Apical Meristem Root meristem Slide 7.07 From Biology of Plants p.470 P. Raven, R. Evert and S.Eichhorn Worth Publishers, New York, 1992 From Anatomy of Seed Plants (2 nd Ed) p.10 K. Esau John Wiley and Sons, New York, 1977

Primary meristem -- what is their purpose?? Secondary meristems: - What is their purpose?? R.A. Kerstetter and S. Hake (1997) Shoot meristem formation in vegetative development. Plant Cell 9, p ASPP Press, Rockville, MD, 2000 B. Meristems may help plants to survive herbivory eg. grasses - where is the shoot apical meristem located and why? Demo of corn C. In addition to meristems, plants produce"buds". The have the potential to produce branches. axillary bud - at leaf axil - gives rise to branch & may be dormant. adventitious bud - from undifferentiated cells in root or stem Slide 7.08 Plants, Genes and Agriculture,p.124 M. Chrispeels and D.Sadava Jones and Bartlett Publishers, Boston, 1994 From Anatomy of Seed Plants (2 nd Ed) p.10 K. Esau John Wiley and Sons, New York, 1977

D. The plant body plan can be very diverse and flexible by mixing and matching numbers of developmental units, through reiteration of organs. eg. the phytomer. E. The body plan of some plants is fixed ("determinate growth") whereas others are more flexible depending on the environmental condition ("indeterminate growth"). In large-scale agriculture, do farmers want plants with determinate or indeterminate growth and why?? 5. Immobile - Consequences from the transition from water to land What adaptations did plants have to make to grow on land?? Slide 7.09 From Patterns in Plant Development (2 nd ed), p.221 T.A. Steeves and I.M. Sussex Cambridge University Press, Cambridge, UK, 1990

6. Immobile - Consequences of an unpredictable environment on land for reproduction A. Unlike animals, the germline (gamete-producing cells) are NOT set- apart from the somatic cells early in development. Why is this strategy useful for the plant?? B. Plants can regenerate new shoot apical meristems from somatic cells (somatic regeneration). Why is this advantageous? demo C. Some plants use vegetative propagation (new shoots without meiosis or sex) as a means to produce seeds. Vegetative propagation allows the progeny to have the same genetic make-up as the parent and this is useful in propagating berries, nuts, and the grafting of fruit trees (apples, etc.). Why/when is this useful?? Examples of vegetative propagation: strawberries send out horizontal stems (runners) potatoes - underground thickened stems (tubers) that sprout stems tuberous roots of sweet potatoes, cassava Strawberry Potato Slide 7.10 Plants, Genes and Agriculture,p.153 M. Chrispeels and D.Sadava Jones and Bartlett Publishers, Boston, 1994

7. Immobile - Consequences of having parents that cannot look after a plant in its childhood Whereas many land animals protect, feed, and shelter their offspring after birth, plants do not. Instead, higher plants allow young embryos with the first leaves and primary root to develop inside a protected ovary and then, for after germination, provide their offspring with nutrient storage reserves made accessible to each embryo, and these are encapsulated and protected within the hard wall of a seed. What are the molecules that make up these seed reserves? For parents to do this, they must remobilize their nutrient reserves from leaves and roots to sinks (seeds and fruits). This is the basis of agriculture How can this "grain-fill" be enhanced? Slide 7.11 From Biology of Plants p.450 P. Raven, R. Evert and S.Eichhorn Worth Publishers, New York, 1992 Plants, Genes and Agriculture, p.135 M. Chrispeels and D.Sadava Jones and Bartlett Publishers, Boston, 1994

The plant invests differently in the storage reserves of the male pollen versus the female egg. Why?? Citrus egg inside ovary inside flower Seeds have a low water content (~15%) and a very low metabolic rate and may survive drought or wintering The storage reserves are used during germination to allow fast early growth of the seedling until it can photosynthesize and acquire nutrients at high rates. The weed lifestyle is to germinate and grow quickly. Why?? In general, fast seedling growth of annual crops in agriculture saves water -- in a study, when the number of corn plants/hectare was increased from 20,000 to 40,000, corn yield increased by 65%, but total water use by only 20%. The increase in total transpiration was compensated by a decrease in evaporation from the soil due to leaf cover Slide 7.12 From Anatomy of Seed Plants (2 nd Ed) p. 440 K. Esau John Wiley and Sons, New York, 1977

8. Immobile - Consequences on the need to spread DNA to the next generation What are the 3 main strategies have the flowering plants (Angiosperms) use to spread their DNA to new environments and/or to mate with a new population? eg. cucumber fruit Fruits may also develop without embryo fertilization (eg. banana, fig, melon, tomato, pumpkin) or have aborted (seedless) embryos (eg. cherry, grape, peach). 9. Summary of key concepts Slide 7.13 From Anatomy of Seed Plants (2 nd Ed) p. 441 K. Esau John Wiley and Sons, New York, 1977