Stimuli and a Stationary Life Plants receive signals

צמחים הם נייחים ועליהם להתמודד עם סביבתם המשתנה במקומם Stimuli and a Stationary Life • Plants receive signals from the environment and respond by altering growth and development

תגובת תפוח האדמה לאור הינה דוגמה אטיולציה - לתהליך בו מעבר אותות בו האור משרה דה 1 - A potato left growing in darkness produces shoots that look unhealthy, and it lacks elongated roots These are morphological adaptations for growing in darkness, collectively called etiolation 2 - After exposure to light, a potato undergoes changes called de-etiolation, in which shoots and roots grow normally • A potato’s response to light is an example of cell signal processing • How do plants respond to a signal?

תהליך מעבר אותות < תגובה - < מעבר - קבלה Figure 39. 3 CELL WALL 1 Reception Receptor CYTOPLASM 2 Transduction 3 Response Relay proteins and Activation of cellular responses second messengers Hormone or environmental stimulus Plasma membrane

1 Reception CYTOPLASM Plasma membrane Figure 39. 4 -1 Phytochrome activated by light Cell wall Light Internal and external signals are detected by receptors, proteins that change in response to specific stimuli

1 Reception Transduction 2 CYTOPLASM Plasma membrane Figure 39. 4 -2 c. GMP Second messenger produced Phytochrome activated by light Cell wall Protein kinase 1 Protein kinase 2 Light Ca 2+ channel opened Ca 2+ Second messengers transfer and amplify signals from receptors to proteins that cause responses

1 Reception 3 Transduction 2 Transcription factor 1 NUCLEUS CYTOPLASM Figure 39. 4 -3 Plasma membrane c. GMP Second messenger produced Phytochrome activated by light Response Protein kinase 1 P Transcription factor 2 P Cell wall Protein kinase 2 Transcription Light Translation Ca 2+ channel opened Ca 2+ De-etiolation (greening) response proteins

פקטורי שעתוק יכולים להשרות הפעלה או עיקוב של ביטוי גנטי Transcriptional Regulation בקרת שעתוק • Specific transcription factors bind directly to specific regions of DNA and control transcription of genes • Some transcription factors are activators that increase the transcription of specific genes • Other transcription factors are repressors that decrease the transcription of specific genes

במקרים מסוימים חלק מהבקרה נעשה על ידי שינויים ברמת החלבון Post-Translational Modification of Preexisting Proteins • Post-translational modification involves modification of existing proteins in the signal response • Modification often involves the phosphorylation of specific amino acids • Protein phosphatases “switch off” the signal transduction pathways by dephosphorylating proteins

הורמונים צמחיים מתווכים אותת מהסביבה Plant hormones mediate environmental signals

התפתחות ותגובה לסביבה , מבקרים גדילה - הורמונים צמחיים Concept 39. 2: Plant hormones help coordinate: growth, development, and responses to stimuli • Plant hormones are chemical signals that modify or control one or more specific physiological processes within a plant • Plant hormones are produced in very low concentrations, but can have profound effects on growth and development

זמן ומקום פעולתם - פעולתם של הורמונים מוכתבת על ידי כמות • Each hormone has multiple effects, but multiple hormones can influence a single process • Plant responses depend on amount and concentration of specific hormones and often on the combination of hormones present B הורמון A הורמון 2 תהליך 1 תהליך

A Survey of Plant Hormones The major plant hormones include העיקרים הצמחים • ההורמונים • Auxin • Cytokinins • Gibberellins (GA) • Abscisic acid • Ethylene • Brassinosteroids • Jasmonates • Strigolactones

תגובה של אורגניזם לגירוי חיצוני , נהיה , Tropism- טרופיזם Shaded side Control Light Figure 39. 5 a Illuminated side In the late 1800 s, Charles Darwin and his son Francis conducted experiments on phototropism, a plant’s response to light Any response resulting in curvature of organs toward or away from a stimulus is called a tropism

Video: Phototropism

קצה נבט החיטה מתכופף אל האור רק אם הקצה נוכח Darwin and Darwin They observed that a grass seedling could bend toward light only if the tip of the coleoptile was present Light Figure 39. 5 b Tip removed Opaque cap Transparent cap Opaque shield over curvature They postulated that a signal was transmitted from the tip to the elongating region

? כיצד מועבר אות האור בצמח In 1913, Peter Boysen-Jensen demonstrated that the signal was a mobile chemical substance Light Figure 39. 5 c Boysen-Jensen Gelatin (permeable) Mica (impermeable)

AUXIN אוקסין • Indole Acetic Acid (IAA) is the common auxin in plants; in this lecture the term auxin refers specifically to IAA • Auxin is primarily produced in shoot tips and is transported down the stem • Auxin transporter proteins move the hormone from the basal end of one cell into the apical end of the neighboring cell

ממוקמים בחלקו התחתון של התא PIN – חלבוני ה Cell 1 100 µm Cell 2 Epidermis Cortex Phloem Xylem Pith Figure 39. 6 25 µm Basal end of cell

4 Cell wall-loosening enzymes cleave cross-linking polysaccharides. CELL WALL 3 Low p. H activates expansins. H+ 2 Acidity increases. H+ H+ H+ 1 Proton pump activity increases. H+ ATP Figure 39. 7 a H+ H+ H+ Plasma membrane H+ CYTOPLASM

התרככות הדופן מאפשרת התארכות H 2 O Figure 39. 7 b Plasma membrane Nucleus Cell wall Cytoplasm Vacuole 5 Sliding cellulose microfibrils allow cell to elongate.

לסיכום חלק זה מעבר פולרי של אוקסין לוקח חלק בתהליך התארכות התא • The Role of Auxin in Cell Elongation • According to the acid growth hypothesis, auxin stimulates proton pumps in the plasma membrane • The proton pumps lower the p. H in the cell wall, activating expansins, enzymes that loosen the wall’s fabric With the cellulose loosened, the cell can elongate

תהליכים המבוקרים על ידי אוקסין • Practical Uses for Auxins • Auxin stimulates adventitious roots and is used in vegetative propagation of plants by cuttings • An overdose of synthetic auxins can kill plants • For example 2, 4 -D is used as an herbicide on eudicots

Cytokinins- ציטוקינין • Cytokinins are so named because they stimulate cytokinesis (cell division)

ציטוקינין מבקר חלוקה ודיפרנציאציה • Control of Cell Division and Differentiation • Cytokinins are produced in actively growing tissues such as roots, embryos, and fruits • Cytokinins work together with auxin to control cell division and differentiation

Gibberellins( GA ) חומצה גיברילית = ג'יברלין • Gibberellins have a variety of effects, such as stem elongation, fruit growth, and seed germination

GA מתפקידיו של ההורמון ג'יברלין • Stem Elongation התארכות הגבעול • Gibberellins are produced in young roots and leaves • Gibberellins stimulate growth of leaves and stems • In stems, they stimulate cell elongation and cell division

מאפשר בצמחים מסוימים התפתחות פרי ללא זרעים GA מתן . תקין זרע התפתחות ללא , מלאכותי או טבעי באופן פרי של ייצור תהליך הוא – פרתנוקרפים פירות יצירת • In many plants, both auxin and gibberellins must be present for fruit to develop • Gibberellins are used in spraying of Thompson seedless grapes (b) Grapes from control vine (left) and gibberellintreated vine (right)

ג'יברלין מעורב בתהליך הנביטה -GA עמילאז מפרק את שרשרת העמילן -α- והפעלת אנזים Germination After water is imbibed, release of gibberellins from the embryo signals seeds to germinate Aleurone Endosperm 1 2 α-amylase GA GA Water Scutellum (cotyledon) Figure 39. 10 3 Radicle Sugar

GA תהליך מעבר האותות המושרה על ידי ג'יברלין CELL WALL 1 Reception Receptor CYTOPLASM 2 Transduction 3 Response Relay proteins and Activation of cellular responses second messengers Hormone or environmental stimulus Figure 39. 3 Plasma membrane

Abscisic Acid ( Ab. A ) - חומצה אבסיסית • ABA was originally believed to be involved in abscission הזדקנות וניתוק עלה • Abscisic acid (ABA) slows growth • Two of the many effects of ABA • Drought tolerance • Seed dormancy

בעמידות ליובש – בקרת סגירת פיוניות ABA תפקידו של • Drought Tolerance • ABA is the primary internal signal that enables plants to withstand drought • ABA accumulation causes stomata to close rapidly

ABA דוגמאות לתהליכים מרכזים בהם מעורב • Seed Dormancy- תרדמת זרעים • Seed dormancy ensures that the seed will germinate נביטה מעקב ABA only in optimal conditions ABA בחישת הפגוע מוטנט גבוהות ABA ברמות גם נובט • In some seeds, dormancy is broken when ABA is removed by heavy rain, light, or prolonged cold • Precocious (early) germination can be caused by inactive or low levels of ABA( Vivipary= )וויפריה

- בנק הזרעים יישום של מנגנוני השהיה 1. Different strategies of Germination 2. Seed Bank- Mechanisms allowing germination of seeds (originated from the same plant) to germinate at different seasons.

Ethylene- אתילן • Plants produce ethylene in response to stresses such as drought, flooding, mechanical pressure, injury, and infection • The effects of ethylene include response to: • mechanical stress • senescence הזדקנות מבוקרת • leaf abscission ניתוק עלה • fruit ripening הבשלת פרי

The Triple Response to Mechanical Stress אתילן משרה תגובה משולשת • Ethylene induces the triple response, which allows a growing shoot to avoid obstacles • The triple response consists of: • 1 - a slowing of stem elongation, • 2 - a thickening of the stem, and • 3 - horizontal growth High Ethylene concentration Low Ethylene concentration

מסלול העברת האותות בתגובה להורמון CELL WALL 1 Reception Receptor CYTOPLASM 2 Transduction 3 Response Relay proteins and Activation of cellular responses second messengers Hormone or environmental stimulus Figure 39. 3 Plasma membrane

מוטנט שאינו רגיש לאתילן - ברור מנגנון התגובה לאתילן בגישה גנטית ein 2 mutant Ethylene-insensitive( ein) mutants fail to undergo the triple response after exposure to ethylene Figure 39. 13 a (a) ein 2 mutant

מוטנט בו מופעלת התגובה לאתילן ללא אתילן ctr 1 mutant constitutive triple response (ctr) mutants undergo the triple response in air but do not respond to inhibitors of ethylene synthesis Figure 39. 13 b (b) ctr 1 mutant

Senescence - מעורבותו של אתילן בהזדקנות • Senescence is the programmed death of cells or organs • A burst of ethylene is associated with apoptosis, the programmed destruction of cells, organs, or whole plants

שלכת / מעורבותו של אתילן בניתוק עלה Leaf Abscission A change in the balance of auxin and ethylene controls leaf abscission, the process that occurs in autumn when a leaf falls 0. 5 mm Figure 39. 14 Protective layer Stem Abscission layer Petiole

השפעתו של אתילן על הבשלת פירות • Fruit Ripening • A burst of ethylene production in a fruit triggers the ripening process • Ethylene triggers ripening, and ripening triggers release of more ethylene • Fruit producers can control ripening by picking green fruit and controlling ethylene levels

ברסינוסטרואידים More Recently Discovered Plant Hormones • Brassinosteroids are chemically similar to the sex hormones of animals • They induce cell elongation and division in stem segments • They slow leaf abscission and promote xylem differentiation

Jasmonates ( גסמונט ) מתיל גסמונט מעורב בתהליכי הגנה והתפתחות • Jasmonates, including jasmonate (JA) and methyl jasmonate (Me. JA) play important roles in plant defense and development • They are produced in response to wounding and involved in controlling plant defenses

Jasmonates ( מתפקידיו של גסמונט ) מתיל גסמונט • Jasmonates also regulate many other physiological processes, including: • • • Nectar secretion Fruit ripening Pollen production Flowering time Seed germination Root growth Tuber formation Mycorrhizal symbiosis Tendril coiling

סטירגולקטונים • Strigolactones are xylem-mobile chemicals that • • Stimulate seed germination Suppress adventitious root formation Help establish mycorrhizal associations Help control apical dominance • Strigolactones are named for parasitic Striga עלקת plants • Striga seeds germinate when host plants exude strigolactones through their roots STRIGA עלקת

Figure 39. UN 03 Plant Hormone Major Responses Auxin Stimulates cell elongation; regulates branching and organ bending Cytokinins Stimulate plant cell division; promote later bud growth; slow organ death Gibberellins Promote stem elongation; help seeds break dormancy and use stored reserves Abscisic acid Promotes stomatal closure in response to drought; promotes seed dormancy Ethylene Mediates fruit ripening and the triple response Brassinosteroids Chemically similar to the sex hormones of animals; induce cell elongation and division Jasmonates Mediate plant defenses against insect herbivores; regulate a wide range of physiological processes Strigolactones Regulate apical dominance, seed germination, and mycorrhizal associations