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#cytokinin

10 public questions tagged with this topic.

Plant tissue culture 1

High auxin and low cytokinin ratio promotes:

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. Auxin also enhances H+ ATPase activity acidifying wall and induction of expansins facilitating emergence. Low cytokinin is critical because cytokinin signaling via AHK-ARR pathway induces SHY2/IAA3 which suppresses PIN expression reducing auxin accumulation and inhibits root meristem activity. In vitro typical rooting medium contains IBA or NAA 1-3 mg/L with negligible or zero BAP, yielding functional roots with quiescent center expressing WOX5 and SCROW, essential for absorptive function and successful acclimatization after transfer from heterotrophic sterile environment to soil.

Ref: Perianez-Rodriguez et al., Front Plant Sci 2014 auxin root specification; Taiz & Zeiger Chap. 19.

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Plant tissue culture 1

Low auxin and high cytokinin ratio promotes:

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 zone. Simultaneously cytokinin represses auxin transport by downregulating PIN1 expression in shoot apex and upregulates type-A ARR which negatively modulates cytokinin oversignaling creating balanced meristem size. Reduced auxin prevents lateral root program mediated by ARF7/19 and LBD16 from dominating. Morphologically resulting tissue organizes shoot apical meristem dome with leaf primordia and provascular strands. Routinely formulation containing BAP 2-5 mg per L and NAA 0.1-0.2 mg per L achieves caulogenesis across diverse species including banana, apple, rose, coffee enabling rapid multiplication.

Ref: Campbell Biology Chap. 39; Teale et al., Nature Rev Mol Cell Biol 2006 auxin-cytokinin crosstalk.

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Plant tissue culture 1

Intermediate auxin : cytokinin ratio induces:

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 promoting type-B ARRs or root promoting ARF-LBD module. Auxin supports cell expansion through acid growth and induction of expansins and cell wall biosynthesis enzymes, while cytokinin enhances cytokinesis by regulating phragmoplast formation and suppressing KRP inhibitors. Neither pathway overwhelms the other, so cells stay in dedifferentiated meristematic condition comprising thin-walled parenchyma with dense cytoplasm and prominent nuclei capable of later redifferentiation. This callus state provides reservoir of totipotent cells exploited for subsequent directed differentiation into shoots, roots or embryos upon changing hormonal balance in subculture sequence.

Ref: Skoog & Miller 1957; NCERT Class XI Biology, Chap. Plant Growth, tissue culture.

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Cytokinin

Low cytokinin:auxin ratio promotes:

The right choice is B: Root formation. In Cytokinin, that matches how the process or concept actually works — the other choices mix up related ideas or use the wrong mechanism. Skip these: A) Shoot formation; C) Callus growth; D) Flowering. A quick check: if an option needs energy, pumps, or the opposite direction of movement, ask whether that really applies.

Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.

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Cytokinin

High cytokinin:auxin ratio in tissue culture promotes:

Correct option is C, Shoot formation. In Cytokinin problems like this, the accurate statement is Shoot formation; the others are common mix-ups. Not these: A) Root formation; B) Callus formation; D) Somatic embryogenesis. Tissue transport questions usually turn on xylem vs phloem, living vs dead cells, or source vs sink.

Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.

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Striglactone

Cytokinin generally acts as a:

Pick B: Antagonist of SL. Thinking through Striglactone step by step rules out the lookalikes and leaves Antagonist of SL. Skip these: A) Synergist of SL; C) Precursor of SL; D) Receptor of SL. For hormones and genes, match the molecule or gene to its real role, not a neighboring pathway.

Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.

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