Plant Signaling and Plant Hormones
Example of Plant Cell Signaling Response to a stem breaking through the ground for the first time Light activates Phytochromes (light receptor connected to a kinase) cGMP activated
Opens gated channels for Ca++ in cell membrane
Enzymes are phosphorylated
Calcium binds to Calmodulin
Turn on transcription factors
Activated kinases and turns on transcription factors
Make Photosynthesis enzymes Make enzymes to make chlorophyll
Make enzymes to decrease auxin production so don’t keep elongating the stems
Apakah itu hormon?
Batasan hormon • Respon tidak harus bersifat memacu • Ion K+ dan Ca2+ dapat menimbulkan respon penting bagi tumbuhan, apakah dikatakan hormon? • Sukrosa, apakah termasuk hormon? • Konsentrasi sukrosa utk menimbulkan efek sekitar 1-5mM, sedangkan hormon hanya ≤1µM
• Hormon adalah senyawa organik yang disintesis salah satu bagian tumbuhan dan dapat dipindahkan ke bagian lain, pada konsentrasi sangat rendah mampu menimbulkan respon fisiologis
Hormone Action The same hormone can have different effects depending on location, concentration, developmental stage or plant, etc.
• • • • • • •
Effect Gene Expression Effect Enzyme Activity Change Membrane Properties Open Gated Channels Change Metabolism Stimulate Cell Division Affect the differentiation and development of cells
General Action of Hormones 1. Bind to receptors 2. Receptors change shape in response to binding 3. 2nd messengers are activated which activate enzymes
OR 1. Directly activate or cause transcription of enzymes (particulary kinases which phosphorylate other enzymes) 2. Enzymes ultimately: 1. 2. 3. 4.
Activate gene transcription Activate transcription factors Deactivate transcriptional repressors Cause chemical reactions
Plant Hormones/Phytohormones • • • • •
Auxin Gibberellin Cytokinins Absicis Acid Ethylene
• Auksin berasal dari bahasa Yunani, yaitu Auxein yang berarti ‘meningkatkan’ • Pertama kali digunakan oleh Frits Went (1926) seorang mahasiswa pascasarjana di Belanda • Hormon auksin dapat berupa asam indolasetat (IAA), asam-4-kloroindolasetat (4kloroIAA), atau asam fenilasetat (PAA)
AUKSIN
Plant Hormones (internal signaling) Auxin • Produced by apical meristems, young leaves, developing seeds and fruit • Moves through the parenchyma cells themselves – not vascular tissue - Transported by chemiosmosis • In low conc. – causes cells to elongate faster – Stimulates pumps to pump H+ into cell wall, ↓pH activates enzymes that break down cell wall – allows water flowing in to expand wall – Phototropism – growing toward light – elongates cells on dark side faster
• In high concentrations - induces ethylene gas which slows cell growth • Control apical dominance • Controls stem elongation in developing shoots • Kills dicots/not monocots = pesticide for corn or grass fields • Causes fruit to grow – if spray on plants, fruit will develop without seeds = seedless fruit
Discovery of Gibberellins
Activity of gibberellins acid GA3 > GA1 > GA4 > GA2
Gibberellins • Produced in roots and young leaves • Elongation and cell division in stems and leaves (activates enzymes that allow cellulose digesting enzymes to penetrate the cell wall) • Cause germination of seeds – water stimulates release of gibberellins – stimulates production of amylase to break down carbohydrates • Important for pollen development, pollen tube growth • Works with auxin for fruit growth (spray to make seedless grapes)
Discover of Cytokinins • In 1955 Carlos Miller et al isolated a “cell-divisionstimulating factor” from yeast DNA. • It was named as kinetin because of its amazing power to stimulate cell division (cytokinesis) in the presence of an auxin. • In subsequent years, many other compounds promoting cell division have been synthesized. Miller and his associates (1956) have grouped all such compounds including kinetin under a generic name kinin. • D.S. Leetham (1963) of New Zealand proposed the term cytokinins for such substances. This term is the most acceptable one.
Cytokinins • Produced by the roots, Moves through the xylem. • Stimulates cell division in roots, embryos, fruits, retards protein breakdown and prevents aging in leaves and fruits (florists spray on cut flowers to keep them fresh), stimulates seed germination. • Works with auxin, relative concentrations control growth and differentiation of plant parts • Works opposite auxin to control height vs. bushiness (more auxin – grow tall, more cytokinins – more axillary buds – bushier)
Penemuan Asam Absisat • Tahun 1963, Frederick T Addicott menemukan senyawa yang menyebabkan gugurnya buah kapas, senyawa tsb adl absisin I dan II • Philip F Wareing menemukan senyawa yang menyebabkan dormansi pada tumbuhan berkayu, Acer pseudoplatanus, senyawa tsb dinamakan dormin • RFM Van Steveninck meneliti senyawa yg mempercepat gugurnya bunga dan buah pada Lupinus luteus • Tahun 1967, nama asam abisisat disepakati
Abscisic Acid • Readies the plant for winter – slow growth of buds, inhibits growth • Causes stomates to close in a wilting plant, opens the K+ channels so K+ leaves guard cells, water follows • Keep seeds dormant when conditions not suitable (light, rain, etc. inactivates abscisic acid to cause seeds to germinate)
Penemuan Etilen • Sudah sejak lama diketahui bahwa buah menghasilkan suatu gas yang berperan pada proses pematangannya • Pada tahun 1934, R Gane membuktikan bahwa gas etilen yg disintesis oleh tumbuhan menyebabkan pemasakan buah tersebut
Ethylene • Gas – causes fruit ripening (breakdown of starch to sugar, breakdown of cell walls to soften, chlorophyll breaks down) • Inhibits axillary growth in response to high auxin • Causes leaf death in winter (can’t get water from frozen ground – don’t want to lose water from leaves) • Produced also in response to stress (drought, flood, infection) • Destroys inside of xylem to make hollow tubes • Plant growth in sprouting plant – when hits something solid – secretes ethylene – plant grows horizontally to escape object then turns upward again
Brassinosteriods • Cells elongation and division in stem (like auxin) • Prevents leaves from falling off
• Promotes root growth at low conc. and stops root growth at high concentrations
Circadian Rhythms • Fluctuations based on a 24 hour cycle – not due to environmental stimuli – based on some internal time clock • Devoid of environmental clues – it deviates slightly from the 24 hour cycle (vary from 2127 hours)
External Signaling in Plants Light, Gravity, Mechanical Stimuli • Phototropism – growing toward sun (Auxin) • Gravitropism – roots grow down, stems grow up (Auxin) • Thigmotropism – change in growth due to mechanical stress (vines grow straight until contact – wrap around due to differential growth on opposite sides) • Rapid Leaf Movements – loss of K+ causes water loss and leaves to fold up • Sleep movements – transport K+ from 1 side of leaf to another – changing water flow • Rubbing or touching a plant changes gene expression – can make plants shorter by rubbing the stem a couple of times a day
Plant response to light • Two types of light receptors – Blue light receivers – Phytochromes – receive red light – photoreceptor linked to a kinase
• Photoperiodism – control of flowering and leaf growth by length of days – Short Day/Long Night – flower when light is shorter than a critical length (flower late summer) – Long Day/Short Night – flower when light is longer than a critical length (flower in spring) – Controlled by phytochromes – bound to a light absorbing molecule – light changes shape of phytochrome which change cellular responses)
Plant Response to Stress • Lack of Water – activate abscisic acid = K+ leaves and so does water – guard cells close – Leaf growth inhibited due to lack of turgor pressure, so less water lost
• Lack of Oxygen (from overwatering – reduces air in soil) – Some form air tubes in roots (ethylene causes cell death in ground cells in roots forming tubes, or roots are out of soil)
• Too much salt (causes water deficit) – Make internal solutes to deep water potential lower in plant
• Heat (enzymes denature, water evaporates) – Transpiration for evaporative cooling – Make heat shock proteins – may help prevent denaturation of proteins
Plant Response to Stress Continued • Cold – Plants increase amt. of unsat. Fatty acids in membrane to make them more fluid – Change solute concentration in cells to prevent cooling with out ice crystals forming in cells
• Herbivores – Physical defenses – thorns, stickers – Chemical toxins (ex. Make a weird aa that when incorporated into insect proteins – proteins are misshapen and the insects die) (ex. 2 – plant sends chemical signal in response to damage – signal causes wasps to come and inject eggs into catepillars eating the plant, wasp babies eat their way out)
• Infections – Tough epidermis – Phytoalexins and PR proteins – kill bacteria by dissolving their cell walls – Express defense genes – apoptosis of infected cells, produce antibiotics – Produce Salicylic Acid – makes cells resistant to attack
