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• Apical dominance occurs when the growing shoot tip inhibits the outgrowth of axillary buds. Apically-derived auxin in the nodal stem indirectly inhibits bud outgrowth via cytokinins and strigolactones. Recently, sugar deprivation was found to contribute to this phenomenon. • Using rose and pea, we investigated whether sugar availability interacts with auxin in bud outgrowth control, and the role of cytokinins and strigolactones, in vitro and in planta. • We show that sucrose antagonises auxin’s effect on bud outgrowth, in a dose-dependent and coupled manner. Sucrose also suppresses strigolactone inhibition of outgrowth and the rms3 strigolactone-perception mutant is less affected by reducing sucrose supply. However, sucrose does not interfere with the regulation of cytokinin levels by auxin and stimulates outgrowth even with optimal cytokinin supply. These observations were assembled into a computational model in which sucrose represses bud response to strigolactones, largely independently of cytokinin levels. It quantitatively captures our observed dose-dependent sucrose-hormones effects on bud outgrowth and allows us to express outgrowth response to various combinations of auxin and sucrose levels as a simple quantitative law. • This study places sugars in the bud outgrowth regulatory network and paves the way for a better understanding of branching plasticity in response to environmental and genotypic factors.

Sugar has only recently been identified as a key player in triggering bud outgrowth, while hormonal control of bud outgrowth is already well established. To get a better understanding of sugar control, the present study investigated how sugar availability modulates the hormonal network during bud outgrowth in Rosa hybrida. Other plant models, for which mutants are available, were used when necessary. Buds were grown in vitro to manipulate available sugars. The temporal patterns of the hormonal regulatory network were assessed in parallel with bud outgrowth dynamics. Sucrose determined bud entrance into sustained growth in a concentration-dependent manner. Sustained growth was accompanied by sustained auxin production in buds, and sustained auxin export in a DR5::GUS-expressing pea line. Several events occurred ahead of sucrose-stimulated bud outgrowth. Sucrose upregulated early auxin synthesis genes (RhTAR1, RhYUC1) and the auxin efflux carrier gene RhPIN1, and promoted PIN1 abundance at the plasma membrane in a pPIN1::PIN1-GFP-expressing tomato line. Sucrose downregulated both RwMAX2, involved in the strigolactone-transduction pathway, and RhBRC1, a repressor of branching, at an early stage. The presence of sucrose also increased stem cytokinin content, but sucrose-promoted bud outgrowth was not related to that pathway. In these processes, several non-metabolizable sucrose analogues induced sustained bud outgrowth in R. hybrida, Pisum sativum, and Arabidopsis thaliana, suggesting that sucrose was involved in a signalling pathway. In conclusion, we identified potential hormonal candidates for bud outgrowth control by sugar. They are central to future investigations aimed at disentangling the processes that underlie regulation of bud outgrowth by sugar.

Bud outgrowth is controlled by environmental and endogenous factors. Through the use of the photosynthesis inhibitor norflurazon and of masking experiments, evidence is given here that light acts mainly as a morphogenic signal in the triggering of bud outgrowth and that initial steps in the light signaling pathway involve cytokinins (CKs). Indeed, in rose (Rosa hybrida), inhibition of bud outgrowth by darkness is suppressed solely by the application of CKs. In contrast, application of sugars has a limited effect. Exposure of plants to white light (WL) induces a rapid (after 3–6 h of WL exposure) up-regulation of CK synthesis (RhIPT3 and RhIPT5), of CK activation (RhLOG8), and of CK putative transporter RhPUP5 genes and to the repression of the CK degradation RhCKX1 gene in the node. This leads to the accumulation of CKs in the node within 6 h and in the bud at 24 h and to the triggering of bud outgrowth. Molecular analysis of genes involved in major mechanisms of bud outgrowth (strigolactone signaling [RwMAX2], metabolism and transport of auxin [RhPIN1, RhYUC1, and RhTAR1], regulation of sugar sink strength [RhVI, RhSUSY, RhSUC2, and RhSWEET10], and cell division and expansion [RhEXP and RhPCNA]) reveal that, when supplied in darkness, CKs up-regulate their expression as rapidly and as intensely as WL. Additionally, up-regulation of CKs by WL promotes xylem flux toward the bud, as evidenced by Methylene Blue accumulation in the bud after CK treatment in the dark. Altogether, these results suggest that CKs are initial components of the light signaling pathway that controls the initiation of bud outgrowth.

The plant-parasitic plant interaction is a interesting model to study sink-source relationship and phloem unloading. The parasitic plants, such as the achlorophyllous plant , connect to the host phloem through the haustorium and act as supernumerary sinks for the host-derived photoassimilates, primarily sucrose. The application of the fluorescent symplastic tracer, carboxyfluorescein (CF) derived from carboxyfluorescein diacetate (CFDA), to the leaves of the host plant ( ) showed direct phloem connections at the host-parasite interface. These experiments also evidenced the dominant apoplastic pathway for phloem unloading in major vegetative sinks of the parasite, including tubercles and shoots, except the adventitious root apices. The CF experiments showed also the symplastic isolation of the phloem tissues from the sink tissues in tubercle and shoot of the parasite, then suggesting the pivotal role of sucrose transporters in sucrose unloading in . sinks. Three cDNAs encoding sucrose transporters ( ) were isolated from the parasitic plant. transcripts accumulated at the same level in the tubercle throughout the parasite growth while a significant increase in transcript accumulation occurred after emergence in the flowering shoot, notably in the growing apical part. The hybridization experiments revealed the transcript accumulation in the mature phloem cells of both subterranean and flowering shoots, as well as in shoot terminal sinks corresponding to apical meristem, scale leaf primordia and immature vasculature. The transient expression experiments in protoplasts showed that PrSUT1 was localized at the plasma membrane, suggesting its role in phloem functioning and sucrose uptake by the sink cells in . . Conversely, the transcript accumulation was constantly low in tubercles and shoots but transcripts accumulated markedly in the subterranean and flowering shoots, in concordance with the mRNA accumulation in multiple sink areas including apical meristem, scale-leaf primordia, immature vasculature and even storage parenchyma. However, the transcripts did not accumulate in the mature phloem cells. The transient expression experiments in protoplasts suggested a tonoplast localization of PrSUT3, for which nevertheless the involvement in intracellular sucrose transport needs clarification.

After a conditioning period, seed dormancy in obligate root parasitic plants is released by a chemical stimulus secreted by the roots of host plants. Using Phelipanche ramosa as the model, experiments conducted in this study showed that seeds require a conditioning period of at least 4 d to be receptive to the synthetic germination stimulant GR24. A cDNA-AFLP procedure on seeds revealed 58 transcript-derived fragments (TDFs) whose expression pattern changed upon GR24 treatment. Among the isolated TDFs, two up-regulated sequences corresponded to an abscisic acid (ABA) catabolic gene, PrCYP707A1, encoding an ABA 8'-hydroxylase. Using the rapid amplification of cDNA ends method, two full-length cDNAs, PrCYP707A1 and PrCYP707A2, were isolated from seeds. Both genes were always expressed at low levels during conditioning during which an initial decline in ABA levels was recorded. GR24 application after conditioning triggered a strong up-regulation of PrCYP707A1 during the first 18 h, followed by an 8-fold decrease in ABA levels detectable 3 d after treatment. In situ hybridization experiments on GR24-treated seeds revealed a specific PrCYP707A1 mRNA accumulation in the cells located between the embryo and the micropyle. Abz-E2B, a specific inhibitor of CYP707A enzymes, significantly impeded seed germination, proving to be a non-competitive antagonist of GR24 with reversible inhibitory activity. These results demonstrate that P. ramosa seed dormancy release relies on ABA catabolism mediated by the GR24-dependent activation of PrCYP707A1. In addition, in situ hybridization corroborates the putative location of cells receptive to the germination stimulants in seeds.

Low-dimensional behavior of large systems of globally coupled oscillators has been intensively investigated since the introduction of the Ott-Antonsen ansatz. In this report, we generalize the Ott-Antonsen ansatz to second-order Kuramoto models in complex networks. With an additional inertia term, we find a low-dimensional behavior similar to the first-order Kuramoto model, derive a self-consistent equation and seek the time-dependent derivation of the order parameter. Numerical simulations are also conducted to verify our analytical results.

The emergence of cluster synchronization, as a universal phenomenon in complex systems, depends on the underlying networks and corresponding dynamics. Modifying network structures to achieve a desired cluster synchronization is a fundamental yet challenging task. Here, we address this problem by conducting a dimensional reduction in order to analyze the cluster stability of coupled phase oscillators. In particular, we exploit an optimization procedure to obtain a desired cluster synchronization pattern and analyze its stability and robustness based on Dirac delta perturbations. We find that altering the cluster synchronization pattern enhances the stability in comparison with the initial network configuration. Furthermore, we define the energy functions quantify the corresponding robustness, which rely on the phase differences between nodes in same clusters (intra-cluster) and nodes in different clusters (inter-cluster). The results show that, modifying cluster synchronization pattern has little impact on the intra-cluster energy variations, yet the inter-cluster energies monotonically increase with the number of clusters. Consequently, the global energy variations increase with the number of clusters, i.e., the higher the number of clusters, the more energy is spent to achieve the cluster synchronization pattern. Our approach to obtain a desired cluster synchronization pattern minimally modifies the network connections, while the corresponding system may not exhibit optimal stability. This work has implications for the development of optimal procedures to obtain a target cluster synchronization patterns with optimal stability.

After a conditioning period, seed dormancy in obligate root parasitic plants is released by a chemical stimulus secreted by the roots of host plants. UsingPhelipanche ramosaas the model, experiments conducted in this study showed that seeds require a conditioning period of at least 4 d to be receptive to the synthetic germination stimulant GR24. A cDNA-AFLP procedure on seeds revealed 58 transcript-derived fragments (TDFs) whose expression pattern changed upon GR24 treatment. Among the isolated TDFs, two up-regulated sequences corresponded to an abscisic acid (ABA) catabolic gene,PrCYP707A1, encoding an ABA 8′-hydroxylase. Using the rapid amplification of cDNA ends method, two full-length cDNAs,PrCYP707A1andPrCYP707A2, were isolated from seeds. Both genes were always expressed at low levels during conditioning during which an initial decline in ABA levels was recorded. GR24 application after conditioning triggered a strong up-regulation ofPrCYP707A1during the first 18 h, followed by an 8-fold decrease in ABA levels detectable 3 d after treatment.In situhybridization experiments on GR24-treated seeds revealed a specificPrCYP707A1mRNA accumulation in the cells located between the embryo and the micropyle. Abz-E2B, a specific inhibitor of CYP707A enzymes, significantly impeded seed germination, proving to be a non-competitive antagonist of GR24 with reversible inhibitory activity. These results demonstrate thatP. ramosaseed dormancy release relies on ABA catabolism mediated by the GR24-dependent activation ofPrCYP707A1. In addition,in situhybridization corroborates the putative location of cells receptive to the germination stimulants in seeds.

We study the collective dynamics of identical phase oscillators on globally coupled networks whose interactions are asymmetric and mediated by positive and negative couplings. We split the set of oscillators into two interconnected subpopulations. In this setup, oscillators belonging to the same group interact via symmetric couplings while the interaction between subpopulations occurs in an asymmetric fashion. By employing the dimensional reduction scheme of the Ott-Antonsen (OA) theory, we verify the existence of traveling-wave and \\(\\pi\\)-states, in addition to the classical fully synchronized and incoherent states. Bistability between all collective states is reported. Analytical results are generally in excellent agreement with simulations; for some parameters and initial conditions, however, we numerically detect chimera-like states which are not captured by the OA theory.