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To maximize reproductive success, flowering plants must correctly time entry and exit from the reproductive phase. While much is known about mechanisms that regulate initiation of flowering, end-of-flowering remains largely uncharacterized. End-of-flowering in Arabidopsis (Arabidopsis thaliana) consists of quasi-synchronous arrest of inflorescences, but it is unclear how arrest is correctly timed with respect to environmental stimuli and reproductive success. Here, we showed that Arabidopsis inflorescence arrest is a complex developmental phenomenon, which includes the arrest of the inflorescence meristem (IM), coupled with a separable "floral arrest" of all unopened floral primordia; these events occur well before visible inflorescence arrest. We showed that global inflorescence removal delays both IM and floral arrest, but that local fruit removal only delays floral arrest, emphasizing their separability. We tested whether cytokinin regulates inflorescence arrest, and found that cytokinin signaling dynamics mirror IM activity, while cytokinin treatment can delay both IM and floral arrest. We further showed that gain-of-function cytokinin receptor mutants can delay IM and floral arrest; conversely, loss-of-function mutants prevented the extension of flowering in response to inflorescence removal. Collectively, our data suggest that the dilution of cytokinin among an increasing number of sink organs leads to end-of-flowering in Arabidopsis by triggering IM and floral arrest. [ABSTRACT FROM AUTHOR]

Plant vasculature transports molecules that play a crucial role in plant signaling including systemic responses and acclimation to diverse environmental conditions. Targeted controlled delivery of molecules to the vascular tissue can be a biomimetic way to induce long distance responses, providing a new tool for the fundamental studies and engineering of stress‐tolerant plants. Here, a flexible organic electronic ion pump, an electrophoretic delivery device, for controlled delivery of phytohormones directly in plant vascular tissue is developed. The c‐OEIP is based on polyimide‐coated glass capillaries that significantly enhance the mechanical robustness of these microscale devices while being minimally disruptive for the plant. The polyelectrolyte channel is based on low‐cost and commercially available precursors that can be photocured with blue light, establishing much cheaper and safer system than the state‐of‐the‐art. To trigger OEIP‐induced plant response, the phytohormone abscisic acid (ABA) in the petiole of intact Arabidopsis plants is delivered. ABA is one of the main phytohormones involved in plant stress responses and induces stomata closure under drought conditions to reduce water loss and prevent wilting. The OEIP‐mediated ABA delivery triggered fast and long‐lasting stomata closure far away from the delivery point demonstrating systemic vascular transport of the delivered ABA, verified delivering deuterium‐labeled ABA. [ABSTRACT FROM AUTHOR]

• Frost stress leads to up-regulation of abscisic and jasmonic acid in all genotypes. • Tolerant genotype exhibits stimulation of cytokinin cis- zeatin after direct frost. • Cold acclimation diminishes stimulation of stress hormones. • Cold acclimation promotes elevation of trans- zeatin in crowns and roots. Complex phytohormonal analyses revealed hormone changes underlying the freezing response of perennial ryegrass (Lolium perenne L.). Comparisons among sensitive (code of accession 1/61), highly tolerant (5/101) and semi-tolerant (6/104; sensitive without acclimation, but tolerant after acclimation) genotypes allowed identification of changes associated with freezing tolerance. The main response to freezing stress (−7 °C for four days) was a significant elevation of abscisic acid (ABA) in all tissues of all genotypes, supported by elevation of jasmonic acid (JA) in leaves, and of salicylic acid (SA) in crowns and roots. Jasmonate-isoleucine increase was observed in roots of the tolerant genotype. The auxin (indole-3-acetic acid) levels showed relatively minor changes, while cytokinins exhibited up-regulation in crowns of sensitive genotypes. Tolerant genotypes exhibited decreased levels of highly active cytokinin trans- zeatin compensated by elevated low-active cis -zeatin, involved in stress responses. Cold acclimation (3 °C for seven days) applied prior frost treatment was associated with stimulation of plant defences, especially expression of ice recrystallisation inhibition protein LpIRI3. Acclimation diminished the impact of subsequent freezing treatment as indicated by lower up-regulation of stress hormones ABA, JA and SA in all tested tissues (with the exception of SA in crowns and roots of sensitive genotype) and up-regulation of active cytokinins in tolerant and semi-tolerant genotypes, especially in crowns and roots. [ABSTRACT FROM AUTHOR]