34 public questions tagged with this topic.
Auxin promotes apical dominance; it does not inhibit it. Cytokinins help overcome apical dominance. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Morphology and Anatomy of Flowering Plants, Topic: Plant structure and tissue systems.
MP/ARF5 and NPH4/ARF7 auxin response factors become transcriptionally active when auxin triggers TIR1/AFB-mediated ubiquitination and proteasomal degradation of BODENLOS and other AUX/IAA repressors containing EAR motifs. Activated ARFs bind canonical auxin response elements TGTCTC in promoters of PLETHORA genes particularly PLT1, PLT2, PLT4/BABYBOOM, PLT5/AIL5 rapidly inducing their expression in basal and root pole during embryogenesis. MP-PLT module directly converts auxin accumulation into root stem cell specification program, stabilizing PIN expression creating self-reinforcing auxin-PLT-
Ref: Berleth & Jürgens, Development 1993: MP and NPH4/ARF7 promote PLT expression establishing root fate downstream of auxin.
PLETHORA family AP2-domain transcription factors PLT1, PLT2, PLT3, PLT5, PLT7 are directly transcriptionally induced by auxin maxima at root pole through ARF5, ARF7, ARF10, ARF16 after auxin-triggered degradation of AUX/IAA repressors via TIR1/AFB pathway. PLT proteins accumulate in graded manner highest near quiescent center promoting stemness, intermediate sustaining mitotic activity, low permitting differentiation and elongation. PLTs activate WOX5, PIN genes, and cell cycle regulators while repressing shoot determinants. Auxin-PLT-PIN positive feedback stabilizes auxin maximum defining ste
Ref: Aida et al., Cell 2004; Galinha et al., Development 2007: PLT genes are auxin-induced root identity transcription factors.
Somatic embryogenesis induction most frequently relies on auxin 2,4 dichlorophenoxyacetic acid 2,4-D applied at 0.5 to 10 mg per L because this synthetic phenoxy auxin resists degradation by IAA oxidases maintains prolonged auxinic signaling. High 2,4-D imposes stress and auxin response causing differentiated somatic cells to re-enter cell division and acquire totipotency through global epigenetic reprogramming involving DNA demethylation histone acetylation and activation of chromatin remodeling factors. It stimulates expression of embryogenic competence markers SERK1 glutathione S transferas
Ref: Dudits et al., J Exp Bot 2011 2,4-D embryogenesis; NCBI Book somatic embryogenesis.
High auxin coupled with low cytokinin specifies root regeneration from callus or shoots, principle underlying rooting stage of micropropagation and natural adventitious rooting of cuttings. Elevated auxin synthesized via TAA1/YUCCA and transported acropetally creates maximum at basal region where founder cells are specified. Auxin binds nuclear receptors TIR1/AFB forming SCF complex that ubiquitinates Aux/IAA repressors for 26S proteasome degradation, freeing ARF7 and ARF19 to transcribe LBD16, LBD18, LBD29 and PLETHORA family genes converting pericycle-like parenchyma into root primordia. Aux
Ref: Perianez-Rodriguez et al., Front Plant Sci 2014 auxin root specification; Taiz & Zeiger Chap. 19.
Low auxin combined with high cytokinin directs differentiation toward shoot regeneration, fundamental to shoot multiplication media. Cytokinin dominance activates signaling cascade: cytokinin binding to sensory histidine kinases AHK2, AHK3, AHK4 in endoplasmic reticulum triggers histidine-to-aspartate phosphorelay via AHPs to nucleus where type-B ARR transcription factors ARR1, ARR10, ARR12 switch on genes for shoot meristem identity. Key targets include WUSCHEL maintaining stem cell pool, SHOOT MERISTEMLESS KNOX gene preventing differentiation and CYCD3;1 promoting cell cycle in peripheral zo
Ref: Campbell Biology Chap. 39; Teale et al., Nature Rev Mol Cell Biol 2006 auxin-cytokinin crosstalk.
The concept of auxin cytokinin interaction governing morphogenesis was established by Skoog and Miller using tobacco pith cultures, showing distinct concentration ratios produce different developmental outcomes. Intermediate ratio where both hormones are present in approximately equal proportions sustains cell division without organ determination, leading to formation of unorganized callus mass. Mechanistically balanced signaling maintains expression of D-type cyclins particularly CYCD3;1 and cyclin dependent kinases driving G1 to S transition while preventing dominant activation of shoot prom
Ref: Skoog & Miller 1957; NCERT Class XI Biology, Chap. Plant Growth, tissue culture.
Cytokinin promotes cell division and is an essential component of tissue culture media.
Ref: NCERT Class 12 Biology Chapter 10: Biotechnology and its Applications Transgenic Animals - Models and Biological Products
Charles Darwin and his son Francis demonstrated that the tip of the coleoptile produces auxin, which causes phototropic bending.
Ref: NCERT Class 11 Biology Chapter 13: Plant Growth and Development Photoperiodism Vernalisation and Development
Charles Darwin and his son Francis observed that coleoptiles of canary grass bend towards light, demonstrating phototropism.
Ref: NCERT Class 11 Biology Chapter 13: Plant Growth and Development Plant Growth Regulators - Cytokinins Ethylene and Abscisic Acid
Auxin promotes apical dominance; it does not inhibit it. Cytokinins help overcome apical dominance.
Ref: NCERT Class 11 Biology Chapter 13: Plant Growth and Development Plant Growth Regulators - Auxins and Gibberellins
Auxin produced at the apical bud suppresses the growth of lateral buds, resulting in apical dominance.
Ref: NCERT Class 11 Biology Chapter 13: Plant Growth and Development Plant Growth Regulators - Auxins and Gibberellins
