172 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.
Abscisic acid induces seed dormancy, helping seeds survive unfavorable conditions. Cytokinins promote, not inhibit, ll division, and ethylene promotes, not delays, fruit ripening.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Biology - Botany portion covering relevant concept, Topic: Plant structure, physiology and applications.
Cytokinins are produced in root tips and promote ll division and shoot growth. They delay, not promote, leaf senescence. This follows from NCERT principle where relation explains outcome clearly for students.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Biology - Botany portion covering relevant concept, Topic: Plant structure, physiology and applications.
Ethylene synthesis pathway involves ACC as obligate intermediate bridging methionine metabolism and hormonal action. Methionine sulfur is conserved via Yang cycle, while ethylene formation proceeds via S-adenosylmethionine intermediate SAM, then ACC. ACC, chemically 1-aminocyclopropane-1-carboxylic acid, is a strained cyclic nonprotein amino acid accumulating transiently in cytosol and vacuole. It is synthesized in cytosol, can be conjugated to N-malonyl-ACC by ACC N-malonyltransferase for vacuolar storage or to γ-glutamyl-ACC, or transported long distance from flooded roots to shoots via xyle
Ref: Buchanan Biochemistry Molecular Biology Plants Ch 17 ACC pathway; PMID 11536542 Ethylene biosynthesis.
Gibberellins are tetracyclic diterpenoid hormones with GA1 GA3 GA4 most bioactive functions centered on stem elongation, seed germination and floral transition. Biosynthesis proceeds from geranylgeranyl diphosphate via ent kaurene ent kaurenoic acid to GA12 catalyzed by terpene synthases and cytochrome P450 monooxygenases GA20 oxidase and GA3 oxidase. Signaling involves soluble receptor GID1 binding GA causing conformational change enabling interaction with DELLA repressors which are then ubiquitinated by SCF SLY1 GID2 complex and degraded via proteasome allowing transcription of growth genes.
Ref: Sun, Annu Rev Plant Biol 2008 GA-DELLA signaling; NCBI NBK10975 gibberellin pathway.
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
Abscisic acid (ABA) is a stress hormone that induces stomatal closure to reduce water loss during drought. It promotes dormancy, not germination.
Ref: NCERT Class 11 Biology Chapter 13: Plant Growth and Development Photoperiodism Vernalisation and Development
ABA (abscisic acid) induces seed dormancy and promotes stomatal closure during water stress.
Ref: NCERT Class 11 Biology Chapter 13: Plant Growth and Development Photoperiodism Vernalisation and Development
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
