In the intricate world of plant development, the transition from elongation to thickening—a process known as radial growth—remains a fundamental yet complex phenomenon that has long fascinated plant biologists. Radial growth is instrumental in producing wood, a vital structural tissue that not only supports the plant but also facilitates water and nutrient transport. This thickening of stems and roots occurs subsequent to apical growth and hinges critically on the activation of vascular stem cells within the cambium. Until recently, while the plant hormone cytokinin was recognized as a key player in initiating this switch, the precise cellular mechanisms orchestrating this vital developmental shift have eluded researchers. A groundbreaking study now unveils a dynamic and finely tuned hormonal mechanism that triggers and sustains radial growth by generating de novo multipotent stem cells within the vasculature, thereby shedding new light on how plants continuously grow beyond their embryonic phase.
At the heart of this developmental cascade lies the bifacial cambium stem cells, which are uniquely multifaceted: they generate xylem (the woody tissue) inward and phloem (the nutrient-transporting tissue) outward, ensuring the expansion of the plant’s girth. These cambial stem cells originate from normally dormant procambial cells, which awaken at the onset of radial growth to assume this bifacial role. The research, led by Shimadzu, Yonekura, Furuya and colleagues, centers on dissecting the enigmatic cytokinin response within these procambial cells, illuminating how a cytokinin response maximum (CRM) transiently forms in the root zones beyond the typical meristematic activity. This transient cytokinin signaling spike emerges as a pivotal trigger that activates dormant vascular procambial cells, effectively converting them into fully functional, bifacial cambium stem cells.
Advancing beyond prior knowledge, the study employs state-of-the-art cellular imaging and hormone manipulation techniques to capture the spatiotemporal dynamics of the CRM with unprecedented precision. By transiently enhancing or suppressing the CRM, the researchers demonstrate that the cytokinin response functions not merely as a promoter of cell division but as a molecular switch that fundamentally alters the differentiation potential of the procambial cells. Before encountering the CRM, procambial cells predominantly exhibit competence to differentiate into phloem; however, exposure to the CRM endows these cells with an expanded lineage potential that includes xylem differentiation and crucially, self-renewal capacity. This dual acquisition redefines the cellular identity of procambial cells, effectively configuring them as cambial stem cells essential for radial growth.
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To uncover the molecular underpinnings of this switch, the researchers integrated transcriptomic profiling of vascular tissues during CRM formation with sophisticated mathematical modeling. The transcriptome analyses revealed a network of cytokinin-responsive genes whose expression patterns oscillate in concert with the CRM, supporting a model of tightly regulated positive and negative feedback loops. These feedback loops fine-tune cytokinin biosynthesis and signaling components, ensuring the transient yet robust nature of the CRM. The mathematical models recapitulate these dynamics, emphasizing that the interplay of these feedback mechanisms is critical for creating a hormone response peak with precise temporal and spatial characteristics. Such a peak is indispensable for instructing procambial cells to recalibrate their differentiation landscape and enter a stem cell state suitable for bifacial cambium activity.
The discovery carries profound implications for our understanding of plant post-embryonic growth transitions. Typically, growth phases such as embryogenesis and meristematic organogenesis have been extensively studied; however, the mechanisms by which the plant initiates and sustains thickening growth later in development have remained poorly defined. This study reveals that a tightly regulated cytokinin response acts as a developmental switch that resurrects stem cell multipotency in vascular tissues after embryogenesis, thereby enabling plants to sustain vigorous growth and continuously adapt their form and function to environmental stimuli. The transient nature of the CRM suggests an elegant temporal control, allowing periods of stem cell activation punctuated by phases of maintenance and differentiation — a dynamic balance crucial for plant vitality.
Beyond its fundamental contribution to developmental biology, these findings open doors to applied plant sciences, particularly in forestry and agriculture. Understanding the hormonal and molecular regulation of wood formation could pave the way for engineering plants with optimized stem structures for higher yield or stress resilience. The study also hints at evolutionary conservation of hormone-regulated stem cell activation mechanisms, providing a conceptual framework to explore analogous processes in diverse plant species and even in response to environmental pressure or injury. The precise control of cytokinin dynamics could thus emerge as a universal strategy for modulating plant architecture and biomass accumulation.
The transient cytokinin response maximum represents a novel paradigm in hormone signaling—one where not only hormone concentration but also spatially localized, temporally constrained signaling peaks orchestrate stem cell fate decisions. Unlike static hormone gradients, these peaks are dynamically generated and resolved through feedback circuits, thus enabling responsive and flexible developmental programming. Such a mechanism supports the concept of intercellular communication networks within plant tissues being capable of creating ‘information hotspots’ that activate cellular reprogramming programs critical for organogenesis and growth transitions. The application of mathematical modeling alongside empirical data application underscores the importance of interdisciplinary approaches in decoding complex biological systems.
The researchers’ approach also involved painstaking differentiation competence assays, which demonstrated that phloem differentiation potential remains largely intact before and after CRM exposure, confirming that the acquisition of xylem and self-renewal potential is an additive priming event. This suggests that procambial cells possess inherent plasticity that cytokinin signaling unlocks, a finding that could recalibrate our understanding of stem cell hierarchies within plant vascular development. The identification of molecular markers and regulatory gene networks specific to the CRM state will provide invaluable tools for future studies probing the molecular choreography of cambial stem cells.
Moreover, the temporal resolution of CRM dynamics reveals that cytokinin production is not merely upregulated but cyclically modulated during radial growth initiation, suggesting a rhythmic patterning mechanism. Such cyclic hormonal signaling may be integrated with mechanical or environmental cues, resulting in a robust development program that balances growth with stability. This insight enhances our comprehension of how endogenous hormonal signals integrate with exogenous factors to finely control plant form — a question central to developmental and ecological plant sciences.
The findings also underscore the central role of vascular tissues as not only conduits for resource transport but as dynamic hubs of developmental regulation. Prior models often placed cambial activity as a relatively passive consequence of meristematic emanations; however, this study emphasizes cambial tissue as an active stem cell niche whose activation is hormonally and transcriptionally choreographed. This perspective enriches the conceptual landscape of plant tissue organization and suggests new targets for modulating stem cell niches in vivo.
Intriguingly, this work challenges the traditional view that stem cell potency is invariably established during embryogenesis and subsequently restricted. Instead, the cytokinin-driven CRM demonstrates that plants possess the remarkable capacity to ‘reset’ cellular potential in post-embryonic stages, endowing cells with multipotency anew. This plasticity may underlie plants’ extraordinary regenerative capabilities and longevity, reinforcing the notion that hormone-mediated niche dynamics are central to their life history strategies.
In conclusion, the elucidation of a cytokinin response maximum as a switch for bifacial stem cell induction constitutes a milestone in plant developmental biology. It provides a molecular framework to understand how hormone signaling sculpts plant architecture through the generation and maintenance of multipotent stem cells in the cambium. The study’s integration of advanced imaging, hormone manipulation, transcriptomics, and computational modeling produces a holistic picture of radial growth initiation that will undoubtedly catalyze further research. These insights deepen our grasp of how plants control post-embryonic growth transitions, revealing the sophisticated interplay between hormonal cues and stem cell biology that underpins plant vitality and resilience.
As plant scientists delve deeper into hormonal regulation and stem cell dynamics, the findings presented here set a new precedent, emphasizing the importance of transient, spatially defined hormone response maxima in developmental switches. Such concepts are likely to resonate beyond botany, offering analogies applicable to stem cell biology and regenerative medicine in broader biological contexts. The discovery that cytokinin orchestrates a transient maximum to orchestrate growth transitions vividly demonstrates nature’s intricate regulatory logic and opens exciting avenues for harnessing plant growth at the cellular level for sustainable agriculture and forestry innovation.
Subject of Research: Plant developmental biology; cytokinin signaling; vascular stem cell activation; radial growth; cambium formation
Article Title: A cytokinin response maximum induces and activates bifacial stem cells for radial growth
Article References:
Shimadzu, S., Yonekura, T., Furuya, T. et al. A cytokinin response maximum induces and activates bifacial stem cells for radial growth. Nat. Plants (2025). https://doi.org/10.1038/s41477-025-02051-4
Image Credits: AI Generated
Tags: apical to radial growth transitionbifacial cambium stem cellscambial growth dynamicscytokinin hormonal mechanismsmultipotent stem cells in vasculaturenutrient transport in plantsplant biology researchplant development and growthradial growth in plantsthickening of stems and rootsvascular stem cell activationwood production in plants
