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#shoot apical meristem

6 public questions tagged with this topic.

plant Development -ll

SAM stem cells primarily divide in:

Histologically shoot apical meristem contains central zone harboring large vacuolated slowly dividing pluripotent stem cells, peripheral zone comprising smaller rapidly dividing cells recruited into leaf or flower primordia, and rib meristem generating pith and vasculature. Central zone divisions predominantly anticlinal at low frequency preserving reservoir while displacing daughters peripherally toward organogenic zones. Signals from organizing center WUS maintain CZ fate, auxin maxima via PIN1 polarity initiate organs in PZ, and CLV feedback restricts overall size, ensuring balanced self-renewal versus lateral organ production sustaining indeterminate growth characteristic of flowering plants.

Ref: Long & Barton, Development; Taiz Plant Physiology: SAM central zone contains slowly dividing pluripotent stem cells.

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plant Development -ll

Primary role of CLV genes:

CLAVATA family comprising CLV1, CLV2, CLV3, and CORYNE/CRN forms conserved receptor-ligand module regulating stem cell homeostasis in shoot and floral meristems across flowering plants. CLV3 peptide secreted from apical stem cells activates CLV1/CLV2-CRN receptor complexes in deeper layers to restrict WUS expression to small organizer domain. WUS in turn sustains stem cells and stimulates CLV3 expression completing circular feedback. Balanced negative regulation ensures appropriate meristem dimensions by controlling number of pluripotent cells versus cells recruited into leaf or floral organ primordia, integrating peptide signaling with cytokinin, auxin, and HAM factors.

Ref: Clark et al., Development; Taiz, Plant Phys: CLV genes primary role is regulation of shoot meristem size homeostasis.

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plant Development -ll

Loss of CLV3 results in:

Loss-of-function clv3 null mutants lack functional CLE peptide ligand, causing derepression, expansion, and ectopic accumulation of WUSCHEL expression domain well beyond organizing center into broader central zone and even peripheral zone. Consequently central zone stem cells overproliferate massively, apical meristem size increases dramatically, peripheral zone generates supernumerary primordia resulting in fasciated stems, enlarged floral meristems producing extra floral organs including stamens and carpels, and club-shaped siliques. Phenotype conclusively shows CLV3 functions as critical brake preventing runaway stem cell accumulation and ensuring proper size control.

Ref: Clark et al., Cell 1995; Lenhard & Laux, Development: clv3 mutants develop enlarged SAM with excess stem cells.

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plant Development -ll

CLAVATA3 (CLV3) in SAM:

CLAVATA3 encodes small secreted CLE peptide family ligand predominantly produced in central zone stem cells of shoot apical meristem, processed into twelve amino acid arabinosylated mature peptide with hydroxylated prolines. It diffuses apoplastically into organizing center where leucine-rich repeat receptor kinases CLV1 homodimer and CLV2-CORYNE heterodimer perceive it activating downstream POLTERGEIST phosphatase and MAPK signaling to repress WUS transcription. This short-range paracrine signal limits WUS domain and stem cell number preventing overproliferation while preserving reservoir required for organ initiation, exemplifying peptide-mediated homeostasis essential for meristem size control.

Ref: Fletcher et al., Science 1999; Laux & Jürgens, Plant Cell: CLV3 maintains stem cell pool via WUS repression.

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plant Development -ll

WUSCHEL (WUS) primarily maintains:

WUSCHEL encodes homeodomain transcription factor expressed specifically in organizing center cells located below central zone of shoot apical meristem. WUS protein moves via plasmodesmata upward into L1-L3 central zone stem cells where it represses differentiation-promoting regulators ASYMMETRIC LEAVES, KANADI, and YABBY while maintaining pluripotency. Additionally WUS directly activates CLV3 transcription in stem cells; secreted CLV3 peptide signals back through LRR receptors CLV1 homodimer and CLV2-CORYNE heterodimer to repress WUS, forming exquisite negative feedback loop that maintains constant stem cell number supporting lifelong indeterminate shoot organogenesis.

Ref: Mayer et al., Nature; Laux et al., Development: WUSCHEL maintains stem cell identity in shoot apical meristem via CLV feedback.

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PSS-Sec-E-Sensory biology

Which protein forms a complex with FT in the shoot apical meristem?

FD (C) is correct here. This is core PSS-Sec-E-Sensory biology: once you know the definition or pathway step, FD is the clear fit. The wrong ones are A) FLC; B) CO; D) FRI. If the topic is about gradients or potentials, water/solutes move from higher to lower of the relevant quantity.

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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