《植物细胞解剖学》课程教学资源（PPT）08

Figure 8-0 charles Darwin. This portrait was made shortly after Darwin returned to England from his voyage around the world.(The Granger Collection, New York)

Figure 8-0

4-dayold Darwin (1880) Lich From c tents or Darwin concloded op 3: that a growth stimulus is produced in the coleoptile ansmitted to the Intact seedling ip of coleoptile Opaque cap growth 2on t cm (curvature) no-p ROOTS Boysen-Jensen (1913) discover ed toys eeasonth T stimnulus passes through gelatin but not thr water-impermeable barriers Mica sheet Mica sheor phototropic and coleoptile curvature no curvature)(curvature) stump Paal(1919) In 1919.A. Paal provided produced in the tip was rip replaced rowth develops coleoptile stump a unilateral light stimulus wont(1926) n 1926. F w Went showed that the acti romoting substance can diffuse into a gelatin block Coleoptile tips Tips discarded: gelatin Each coleoptile bends in on gelatin t up into smaller aced on total darkness: angle ocks n of curvature car coleoptile stump be measured 20 0.050.100.150.200.250.30 Number of coleoptile IAA in gelatin block (mg/L) Figure 8-1 FIGURE 19.1 ummary of early

Figure 8-1

CHE COOH 2-0H Indole- 3-acetic acid 4-Chloroindole-3-acetic acid Indole-3-butyric acid 4+A FIGURE 19.3 Strucure of three natural auxins. Indole-3-acetic acid(IAA)occurs in butyric acid (IBA) Figue 8-2

Figue 8-2

IAA Plasma 1. IAA enters the cell. either membrane passively in the undissociated form(IAAH)or by secondary Permease H active cotransport in the IAA H anionic form(AA") Apex IAAH Cell wall IAAH pH5 cytosol ATP ATP 2. The cell wall is maintained at an acidic pH by the activity H← IAA PH 3. In the cytosol, which has a of the plasma membrane H neutral pH, the anionic form ATPase ATP pH 7 (IAA ) predominates H acue ATP H 4. The anions exit the cell via auxin anion efflux carriers that are concentrated at the basal ends of each cell in the Base IAA longitudinal pathway IAAH FIGURE 19.13 The chemiosmotic model for olar auxin transport. Shown here is one cell Pc Figure 8-5 in a column of auxin-transporting cells AT (From Jacobs and Gilbert 1983

Figure 8-5

(A) (C Indole-3-pyruvic acid pathway Tryptophan(Trp) Trp monooxygenase Trp decarboxylase IAN COOH TAM Indole-3-pyruvic acid (IPA) Indole-3-acetaldoxime IPA Tryptamine (TAM) Bacterial pathway decarboxylase Amine oxidase NHz Indole-3-acetaldehyde(IAld) Indole-3-acetamide(IAM) Indole-3-acetonitrile(IAN) IAld Nitrilase dehydrogenase .IAM hydrolase Indole-3-acetic acid (IAA) FIGURE 19.6 Tryptophan-dependent pathways of IAA biosynthesis in plants and bacteria. The enzymes that are present only in bacteria are marked with an asterisk. (After Bartel 1997. Figure 8-6

Figure 8-6

Decarboxylation: a minor pathway CH2 Peroxidase nd。le-3- acetic acie 3-Methyleneoxindole (B) Nondecarboxylation pathways conjugation Indole-3-acetylaspartate Di。xind。le-3 acetylaspartate cOOH Figure 8-7 Dxi ole-3-acetic acid (OXIAA) Figure 19.11 Biodegradation of IAA (A) The peroxidase route (decarboxylation pathway) plays a relatively minor role. (B) The two nondecarboxylation routes of IAA oxida tive degradation, A and B, are the most common metabolic pathways. (After Tuominen et al. 1994.)

Figure 8-7

1. In the absence 3. In the presence of 5. IAA-induced of lAA. the auxin AUX/AA degradation of the transcription proteins are targeted AUXAA proteins factor, ARF, forms for destruction by an allows active ARF inactive activated ubiquitin homodimers to heterodimers wit case AUX/AA proteins. Signal transduction Active ARF inactive ARF homodimer heterodimer pathway Activation of ARF AUXIAA ubiquitin ligase TGTCTC CTCTGTDNA Palindromic AUxRE AUXHAA and uBiquitin ⊥ATP 6. The active ARF other early genes homodimers bind to 4. The AUX/IAA palindromic AuxREs in 2. Inactive hetero- the promoters of the dimers block the Ubi proteins are tagged with ubiquitin and early genes, activating transcription of the (AUX/IAA degraded by the transcription early auxin genes 265 proteasome There is no auxin AUXHAA and response. other early genes 8. The stimulati Of AUX∥ AA genes introduces a Auxin-mediated negative feedback growth/development Figure 8-9 7. Transcription of the early genes initiates the auxin FIGURE 19.41 A model for auxin regulation of transcriptional activation of early response genes by auxin (After Gray et aL. 2001.)

Figure 8-9

Figure 8-10-1 Auxin and root development on stem cuttings. (Left) Many adventitious roots developed on a honeysuckle(Lonicera fragrantissima) cutting placed in a solution with a high concentration of synthetic auxin. (Middle) Fewer roots developed in a lower auxin concentration .(Right)The cutting placed in water(no auxin) served as a control and did not form roots in the same time period. (oe Eakes, Color Advantage/Visuals Unlimited)

Figure 8-10-1

Turgor pressure stretches weakened ce‖wal H2O Auxin binds to plasma Activated proton pumps membrane receptors transport H' out of cell cell wall plasma membrane ATP ATP cytoplasm ATP ATP H auxn-◎ Auxin mode of action After auxin binds to a receptor, the combination stimulates the proton pump so that hydrogen ions(H) are transported out of the cell. The resulting acidity causes the cell wall to weaken, and the electrochemical gradient causes solutes to enter the cell. Water follows by osmosis and the cell elongates Figure 8-10-2

Figure 8-10-2

stage 1 PLASTID enr-kcnurene ent-Copalyl diphosphate stage 2 CHO cOol onrkaurene GAvmldehyde ENDOPLASMIC RETICULUM OL stage 3 FIGURE 20.6 The three es of gibberellin biosynthesis 己pg(ps is hydroxylated carbon depending on plants the 1-hydroxylation pathway predominates. the GA oxidase the main path wty g atasthi eyo b roes:dis w sarles of oxidations at carbon 20. In the I3-hvdroxvlation HOCHa lon reaction (the non-130 converts GAo and GA, to the inactive forms GiA and GAg respectively COOH GAT-OL (R Active GA CA 20-exirlase CA-oxitdas cA dAxie COOH COOH ∈A;(= GAn (R H) COoH OH) GAyo(R- OH) GA4 (R-H GA 2oxidase GAa-D× idesp GAn(R-OH) Inactivation Figure 8-13 COOH Aa(R-H) GAN:(R- H) GAs(R=OH》 GAzo(R= OH)

Figure 8-13