Lecture 4 Plant Development and Physiology 2106 Neal

Lecture 4 Plant Development and Physiology 2106 Neal Stewart

Overview • Know key plant anatomy and developmental stages of plant growth • Understand the importance of plant hormones in plant biology • Know the major plant hormones

Plant development • Growth: irreversible increase in the size of plant cells and organs cells grow by division and expansion • Differentiation: specialization of cells into tissues and organs • Development: life cycle progression of plants – Seed – Organogenesis – Reproduction

http: //www. slideshare. net/bcbgarcia/bio-130 microsporogenesis-gametogenesis-2013

Figure 4. 2 Gametogenesis. Schematics of (a) an Arabidopsis flower with the floral organs identified; (b) a cross section through the male organs (anther, filament) showing the site of male gamete formation; (c) the female ovule contained within the carpels of the flower showing the site of female gamete development. [Reprinted from Wilson and Yang C (2004), with permission from the Society for Reproduction and Fertility. ]

Figure 4. 4 Embryo development. (a) Schematic of embryo stages. [Reprinted from Lenhard and Laux (1999), with permission by Elsevier Science Ltd. ] (b) Scanning electron micrograph of Arabidopsis embryos in the globular and heart stages. The white lines indicate the cell division planes. [Reprinted from Costa and Dolan (2000), with permission from Elsevier Science Ltd. ]

Germination

Figure 4. 1 Plant anatomy and morphology. The seedling shoot and root systems are indicated, as are the shoot and root apical meristems, tissues that direct the major growth and differentiation of plants. Active cell division within the meristem is shown in the last panel; note the presence of two nuclei in some cells. Modified with permission from Dr. Dale Bentham’s Website (http: //biology. nebrwesleyan. edu/benham/plants/index. html).

Leaf cross section and physiology

Plant cell Celldiagram. net

Figure 4. 7 Leaf development. (a, b) Scanning electron micrographs of leaf primordia. Note the presence of trichomes in (b). (c) Schematic of leaf cross section showing the different leaf cell types. (d) Cross section through leaf vascular tissue. [Reprinted from Byrne (2006), with permission from the Public Library of Science. ]

Figure 4. 8 Flower development. Arabidopsis (a) wild-type, (b) ap 2, (c) pi, (d) ag, and (e) sep flowers. Below each photo is a rendering of the ABC model as it functions in that flower. [Reprinted from Krizek and Fletcher (2005), with permission from Nature Publishing. ] See color insert.

Figure 4. 10 A paradigm plant hormone signal transduction pathway. Hormone on the outside of a plant cell may be perceived by proteins present at or near the plasma membrane. Alternatively, the hormone may be transported across the plasma membrane. Signal cascade proteins are then activated. Once activated, these proteins can transmit signaling information (arrows) to the interior of the cell. Many signal transduction pathways converge on the stimulation of gene expression within the nucleus that results in the production of new proteins in the cytoplasm that can affect specific biological responses.

What is a hormone? • Biochemical which regulates growth based on biological and environmental influences • Synonyms: Plant hormones, plant growth regulators (PGRs), phytohormones • Regulate growth and development • Mobile throughout plant • Environment and stress responsive

Major plant hormones • • Auxin – Greek: auxein; to grow or increase Cytokinin – cytokinesis (cell division) Abscisic acid – abscission Jasmonic acid – found in jasmine oil Gibberellic acid – pathogen Gibberella Ethylene – chemical brother to ethanol Brassinosteroids – derived from Brassica spp.

Figure 4. 9 Plant hormones. Similarit between some plant and animal hormones. [Reprinted from Chow and Mc. Court (2006), with permission from Cold Spring Harbor Laboratory Press. ]

Finding plant hormones Observational: Darwin stumbles on auxin – Noticed grass tips grow toward light – With tip growth responded to light – Without tip growth had no response Mutation screening: (aka forward genetics) – Dwarf plants are can be hormone deficient

ABRC teaching tools website

General hormone biochemistry • Present in all cells at various levels • Classes of hormones work in signal cascades – Hormone-receptor interactions – Respond to a host of factors and biological needs • Abiotic – Water stress – Light – Nutrient deficiency • Biotic – Growth – Development – Herbivore stress

Hormone biosynthesis Made from four biosynthetic pathways: – Terpenoids • • AMP + IPP (cytokinins) Carotenoid breakdown (abscisic acid) Diterpene (gibberellic acid) Triterpene (brassinosteroids) – Fatty acids (jasmonic acid) – Tryptophan (auxins) – Methionine (ethylene)

EGG database: tp: //www. genome. jp/kegg/

Auxins • • Greek: auxein; to grow or increase Apical dominance growth Cell elongation Hormone level very important 2, 4 -dichlorophenoxyacetic Acid http: //pubchem. ncbi. nlm. nih. gov/

http: //www. nsf. gov/news_images. jsp? cntn_id=104205

Taiz and Zeiger. 2002. Plant Physiology, 3 rd Ed.

Auxin: Apical dominance http: //users. rcn. com/jkimball. ma. ultranet/Biology. Pages/A/Auxin. html

Cytokinin • • • Cytokinesis (cell division) Organization and development of xylem tissue Response to light Lateral growth of shoots Kinetin Open stomata http: //pubchem. ncbi. nlm. nih. gov/

Application: cotton spraying • Adding cytokinins to young cotton increase droughtresistance • Arizona – 31% US cotton, highest yield acre-1

Auxin and cytokinin ratio importance • Auxin alone = Large cells (no division) • Cytokinin alone = Cells have no change • Auxin + Cytokinin = Normal cell growth and division • Auxin + >Cytokinin = Shoot growth • >Auxin = Cytokinin = Root growth

Auxin Cytokinin http: //users. ugent. be/~p debergh/pri 4 ez 04. jpg

Abscisic acid (ABA) • • • Originally implicated in leaf and fruit abscission Involved in leaf senescence Maintains seed dormancy (opposed to GA) Involved in stomata regulation (closes) Single hormone unit http: //pubchem. ncbi. nlm. nih. gov/

Jasmonic acid • First identified in jasmine oil • Response to biotic stress – Wounding induces JA biosynthesis – Microbial and fungal invasion • Plant growth effects similar to auxin – Specialty growth structures http: //pubchem. ncbi. nlm. nih. gov/

Jasmonic acid: Plant-insect co-evolution Tri-trophic interactions Degenhardt (2009) Plant Physiology 149: 96 -102

Jasmonic acid: Pathogen response http: //park. itc. u-tokyo. ac. jp/biotec-res-ctr/kampo/eng/research_plant. html

Gibberellic acid • Originally found in Gibberella (rice pathogen) – Responsible for ‘foolish seedling’ phenomenon – Uninhibited growth until breaking • Involved in cell elongation • Flowering and seed germination http: //pubchem. ncbi. nlm. nih. gov/

Modification of GA in rice Miyako Ueguchi-Tanaka 2005 Nature 437, 693 -698

Spraying GA for increased fruit yield GA induces fruiting in absence of seed http: //www. extension. org/pages/31607/using-plant-growth-regulators-toincrease-the-size-of-table-grape-berries#. Ut 9 EYb. ROm. M 8

Ethylene: the cell phone of PGRs • • A hydrocarbon gas Involved in fruit ripening, stress response Inhibition of growth in dark conditions Excess ethylene inhibits callus growth

Brassinosteroids • Stress responses – Switchgrass suspension cells have minor amounts of lignin (small amounts of H monolignols) – Addition of brassinolide induces normal lignin formation and composition • • Stem elongation Seed germination Pollen tube growth Cell differentiation control Brassinolide http: //pubchem. ncbi. nlm. nih. gov/

Overview of hormone mutants Cytokinin mutant Brassinosteroid mutant Cytokinin mutant closer look Ethylene mutant grown in dark Abscisic acid mutant Bishopp A et al. Development 2006; 133: 1857 -1869

Hormones (PGR) pathways • PGRs work in complex cascades to produce signals – Synergistic – Anatognistic • Variety of actions in cell – Gene transcription – Protein degradation http: //chriscarterart. wordpress. com/2010/05/09/m others-day-2/mikado-plant-watercolor-sketch-chriscarter-050910/

Arabidopsis histidine kinase sensing and signaling; 2) A histidine phosphotransferase protein nuclear translocation; 3) A response regulation transcription activation; and 4) a negative feedback loop through cytokinininducible ARR gene products. http: //molbio. mgh. harvard. edu/sheenweb/cytokinin_signaling. html

Introduction: the importance of manipulation of hormones for tissue culture • Auxins and cytokinins are very important – Higher auxin induces root growth – Equal ratio induces callus and cell enlargement – Lower auxin induces shoot growth • Gibberellic acid germinates difficult seeds • Add brassinosteroids for cell wall induction

Lecture summary • Plant growth and responses under hormonal control • Auxin and cytokinin are key for plant growth • Cell signaling is regulated by specific receptors on cell membranes