Two-particle correlations in azimuthal angle and pseudorapidity in inelastic p + p interactions at the CERN Super Proton Synchrotron

Results on two-particle ΔηΔϕ correlations in inelastic p + p interactions at 20, 31, 40, 80, and 158 GeV/c are presented. The measurements were performed using the large acceptance NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. The data show structures which can be attributed mainly to effects of resonance decays, momentum conservation, and quantum statistics. The results are compared with the Epos and UrQMD models.ISSN:1434-6044ISSN:1434-605

Centrality evolution of the charged-particle pseudorapidity density over a broad pseudorapidity range in Pb-Pb collisions at root s(NN)=2.76TeV

Peer reviewe

The role of phytohormones in the shade avoidance syndrome

Bibliography: p. 138-15

Developmental and Embryo Axis Regulation of Gibberellin Biosynthesis during Germination and Young Seedling Growth of Pea

The expression patterns of five genes (PsGA20ox1, PsGA20ox2, PsGA3ox1, PsGA2ox1, and PsGA2ox2) encoding five regulatory gibberellin (GA) biosynthesis enzymes (two GA 20-oxidases, a GA 3β-hydroxylase, and two GA 2β-hydroxylases) were examined to gain insight into how these genes coordinate GA biosynthesis during germination and early postgermination stages of the large-seeded dicotyledonous plant pea (Pisum sativum). At the time the developing embryo fills the seed coat, high mRNA levels of PsGA20ox2 (primarily responsible for conversion of C20-GAs to GA(20)), PsGA2ox1 (primarily responsible for conversion of GA(20) to GA(29)), and PsGA2ox2 (primarily responsible for conversion of GA(1) to GA(8)) were detected in the seeds, along with high GA(20) and GA(29) levels, the enzymatic products of these genes. Embryo maturation was accompanied by a large reduction in PsGA20ox2 and PsGA2ox1 mRNA and lower GA(20) and GA(29) levels. However, PsGA2ox2 transcripts remained high. Following seed imbibition, GA(20) levels in the cotyledons decreased, while PsGA3ox1 mRNA and GA(1) levels increased, implying that GA(20) was being used for de novo synthesis of GA(1). The presence of the embryo axis was required for stimulation of cotyledonary GA(1) synthesis at the mRNA and enzyme activity levels. As the embryo axis doubled in size, PsGA20ox1 and PsGA3ox1 transcripts increased, both GA(1) and GA(8) were detectable, PsGA2ox2 transcripts decreased, and PsGA2ox1 transcripts remained low. Cotyledonary-, root-, and shoot-specific expression of these GA biosynthesis genes and the resultant endogenous GA profiles support a key role for de novo GA biosynthesis in each organ during germination and early seedling growth of pea

Flowering in snow tussock (Chionochloa spp.) is influenced by temperature and hormonal cues

Snow tussocks (Chionochloa spp.) in New Zealand exhibit extreme mast (episodic) seeding which has important implications for plant ecology and plantinsect interactions. Heavy flowering appears to be triggered by very warm/dry summers in the preceding year. In order to investigate the physiological basis for mast flowering, mature snow tussock plants in the field and younger plants in a glasshouse and shadehouse were subjected to a range of manipulative treatments. Field treatments included combinations of warming, root pruning and applications of two native gibberellins (GAs) GA3, which is known to be highly floral inductive and GA4, which is associated with continued floral apex development in another long-day grass. Warming, GA3 alone and especially warming+GA3, significantly promoted flowering, as did applications of GA4 alone and GA4+CCC (2-chloroethyltrimethylammonium chloride, which is a known synergist of GA3-induced flowering in the annual grass, Lolium temulentum L.). Our results provide support for the concept that mast flowering events in tussock species are causally related to high temperature-induced increases in endogenous gibberellin levels. It is likely that GAs (endogenous or applied) promote the continued development of a previously long-day induced floral apex. In addition to the promotion of flowering, applied GA3 also disturbed the plant's innate resource threshold requirements, as shown by the death, over winter, of many non-flowering tillers. Applied GA4 did not show this effect, likely due to its rapid catabolic metabolism to an inactive form. High temperature-induced flowering mediated by elevated levels of endogenous floral-promotive GAs could have important implications for regulating the evolutionary interaction between these masting plants and their seed predators

Interactions between plant hormones and light quality signaling in regulating the shoot growth of Arabidopsis thaliana seedlings

The effects of a decrease in red to far-red (R/FR) ratio on shoot growth of two-week-old Arabidopsis thaliana (L.) Heynh. seedlings were examined in the context of possible causal involvement of key plant growth hormones. Decreasing the R/FR ratio significantly increased petiole elongation and leaf area expansion of the Columbia (Col) line seedlings. In contrast, seedlings of the Landsberg erecta (Ler) line showed no significant change in leaf area and only a marginal increase in petiole growth. This low R/FR ratio-induced growth was accompanied by significant increases in concentrations of the growth "effector" gibberellin (GA4) and an auxin (indole-3-acetic acid (IAA)) in shoot tissues of Col. However, cytokinins (CKs) in Col shoot tissues were decreased and ethylene evolution was reduced when the R/FR ratio was decreased from that of normal sunlight to a low R/FR ratio. Several A. thaliana genotypes with plant hormone-related mutations were also assessed, including auxin resistant, axr2-1; GA insensitive, gai-1; and ethylene over-producing, eto2. None of these increased their petiole length or leaf area growth in response to lowering the R/FR ratio. We thus conclude that both GA4 and IAA are causally involved in the increased shoot growth of A. thaliana Col seedlings that occurs in response to a lower than normal R/FR ratio

Tissue-Specific Regulation of Gibberellin Biosynthesis in Developing Pea Seeds1[W][OA]

Previous work suggests that gibberellins (GAs) play an important role in early seed development. To more fully understand the roles of GAs throughout seed development, tissue-specific transcription profiles of GA metabolism genes and quantitative profiles of key GAs were determined in pea (Pisum sativum) seeds during the seed-filling development period (8–20 d after anthesis [DAA]). These profiles were correlated with seed photoassimilate acquisition and storage as well as morphological development. Seed coat growth (8–12 DAA) and the subsequent dramatic expansion of branched parenchyma cells were correlated with both transcript abundance of GA biosynthesis genes and the concentration of the growth effector GA, GA1. These results suggest GA1 involvement in determining the rate of seed coat growth and sink strength. The endosperm’s PsGA20ox transcript abundance and the concentration of GA20 increased markedly as the endosperm reached its maximum volume (12 DAA), thus providing ample GA20 substrate for the GA 3-oxidases present in both the embryo and seed coat. Furthermore, PsGA3ox transcript profiles and trends in GA1 levels in embryos at 10 to 16 DAA and also in embryo axes at 18 DAA suggest localized GA1-induced growth in these tissues. A shift from synthesis of GA1 to that of GA8 occurred after 18 DAA in the embryo axis, suggesting that deactivation of GA1 to GA8 is a likely mechanism to limit embryo axis growth and allow embryo maturation to proceed. We hypothesize that GA biosynthesis and catabolism are tightly regulated to bring about the unique developmental events that occur during seed growth, development, and maturation