Developmental Changes in Effect of Cytokinin and Gibberellin on Shoot K+ and Na+ Accumulation in Salt-Treated Sorghum Plants

Abstract: The effect of cytokinin (CK) and/or gibberellin (GA) treatments on shoot accumulation of Na⁺ and K⁺ was investigated in Sorghum bicolor exposed to 150 mM NaCl. These hormonal treatments modified the shoot content of Na⁺ and K⁺, but the effect varied throughout development. Comparison of ion concentration versus ion content in shoots indicates that regulation of shoot concentration of K⁺ is modified during a transition period of development. This change is concomitant with reorganization of the regulation network for meristem activity, an event also involving changes in sensitivity to CK and GA. This evidence suggests a strong interdependency between dynamic changes in a between-organ network of relations and control of accumulation of monovalent ions in the shoot. Moreover, a new pattern of regulation of shoot Na⁺ concentration emerges during the transition period. During this process GA appears progressively involved in regulation of Na retranslocation, while CK is rather controlling the root uptake of Na⁺. Accordingly, the spontaneous emergence of Na-includer and Na-excluder individuals observed from an initially homogeneous population is interpreted as related to variations in sensitivity to GA and CK during differentiation of this newly emerging pathway of regulation.     

Maturation of integrated functions during development. I. Modifications of the regulatory network during transition periods in Sorghum bicolor

Gibberellin (GA) and cytokinin (CK) were exogenously supplied at different periods of the vegetative development in Sorghum bicolor. Growth response to these hormonal treatments differed according to the developmental stage. This reveals the existence of discrete phenophases, each one characterized by a specific sensitivity to plant growth regulations (PGRs). Developmental changes in sensitivity were less accentuated in plants grown in optimal conditions than in plants exposed to 150 mM NaCl. Variations in organ connectance (the level of coordination in growth of the shoot, adventitious roots and seminal root) were analysed during vegetative growth of salt‐treated plants. This analysis shows a temporary decrease in connectance during the transition period between phenophases. From the effect of hormonal treatments on connectance, it was concluded that (i) the transition period coincides with a partial dismantling of the initial regulatory network followed by the emergence of a new network coordinating growth of the different organs; (ii) GA is involved in the process of emergence of a transition period; and (iii) duration of the transition period is considerably enlarged for plants exposed to NaCl stress. This dynamics of alternance of phenophase and transition periods enables the integration of the two modes of action of the PGRs (dose–response and change in sensitivity) within a unified framework.     

Critical periods as fundamental events in life

Development is not a continuous phenomenon. Rather, phenophases are interspaced with short critical periods. This phenomenon reflects an alternance between stabilization (during a phenophase) and dismantling (during a critical period) of a network of between-organ relationships generating the organism. Networks of relationships may be compared to dissipative systems in physics. In this context, a critical period represents a transient phase of isolation of the systems enabling its evolution towards equilibrium. As suggested here, this transition from dissipative to isolated system represents the source of newly emerging dissipative structures in which environmental or developmental perturbations are adaptively integrated. In contrast to non-living systems, an endogenous control of the transition towards critical period seems to exist during development. By extension to other scales of biological organization, it is suggested that the capacity to self-define its status (dissipative or close-to-equilibrium) represents the key property of living systems. This asks for a reconsideration of some basic notions about life, such as the role of genes in normal development, in physiological adaptation, and even in the emergence of evolutionary novelty.     

心肌锚定重复序列蛋白CARP的研究进展

CARP是新发现的具有锚定重复序列,并在哺乳类动物中呈心肌特异性表达的蛋白,它在肌肉发育过程中对转录调控、肌纤维组装和拉伸信号传递等方面发挥重要的作用。本文综述了CARP基因与蛋白质结构、CARP的表达模式及其表达调控、参与调节CARP的细胞内信号转导通路、CARP在肌肉发育中的作用,以及MARP家族其他成员。     

Barrel cortex critical period plasticity is independent of changes in NMDA receptor subunit composition.

The regulation of NMDA receptor (NMDAR) subunit composition and expression during development is thought to control the process of thalamocortical afferent innervation, segregation, and plasticity. Thalamocortical synaptic plasticity in the mouse is dependent on NMDARs containing the NR2B subunit, which are the dominant form during the "critical period" window for plasticity. Near the end of the critical period there is a gradual increase in the contribution of NR2A subunits that happens in parallel to changes in NMDAR-mediated current kinetics. However, no extension of the critical period occurs in NR2A knockout mice, despite the fact that NMDA subunit composition and current kinetics remain immature past the end of the critical period. These data suggest that regulation of NMDAR subunit composition is not essential for closing the critical period plasticity window in mouse somatosensory barrel cortex.     

AP2/ERF转录因子调控植物非生物胁迫响应研究进展

低温、干旱、高盐和缺氧等多种不良环境影响植物的生长发育, 植物通过长期进化形成复杂的调节机制来适应这些不利条件。AP2/ERF是植物特有的转录因子, 在各种胁迫响应过程中发挥关键调控作用。近年来, 越来越多的研究表明, 植物激素介导的信号级联通路与逆境胁迫响应关系密切, AP2/ERF转录因子可与激素信号转导协同形成交叉调控网络。许多AP2/ERF转录因子通过响应植物激素脱落酸和乙烯, 激活依赖或不依赖于脱落酸和乙烯的胁迫响应基因的表达。此外, AP2/ERF转录因子参与赤霉素、细胞分裂素和油菜素内酯介导的生长发育和胁迫应答。该文简要综述了AP2/ERF转录因子的结构特征、转录调控、翻译后修饰、结合位点、协同互作蛋白及其参与调控依赖或不依赖激素信号转导途径的非生物胁迫响应研究进展, 为解析不同AP2/ERF转录因子在调控激素和胁迫响应网络中的作用提供理论依据。     

Developmental pathways of somatic embryogenesis

Somatic embryogenesis is defined as a process in which a bipolar structure, resembling a zygotic embryo, develops from a non-zygotic cell without vascular connection with the original tissue. Somatic embryos are used for studying regulation of embryo development, but also as a tool for large scale vegetative propagation. Somatic embryogenesis is a multi-step regeneration process starting with formation of proembryogenic masses, followed by somatic embryo formation, maturation, desiccation and plant regeneration. Although great progress has been made in improving the protocols used, it has been revealed that some treatments, coinciding with increased yield of somatic embryos, can cause adverse effects on the embryo quality, thereby impairing germination and ex vitro growth of somatic embryo plants. Accordingly, ex vitro growth of somatic embryo plants is under a cumulative influence of the treatments provided during the in vitro phase. In order to efficiently regulate the formation of plants via somatic embryogenesis it is important to understand how somatic embryos develop and how the development is influenced by different physical and chemical treatments. Such knowledge can be gained through the construction of fate maps representing an adequate number of morphological and molecular markers, specifying critical developmental stages. Based on this fate map, it is possible to make a model of the process. The mechanisms that control cell differentiation during somatic embryogenesis are far from clear. However, secreted, soluble signal molecules play an important role. It has long been observed that conditioned medium from embryogenic cultures can promote embryogenesis. Active components in the conditioned medium include endochitinases, arabinogalactan proteins and lipochitooligosaccharides.     

Synaptic activity-dependent developmental regulation of NMDA receptor subunit expression in cultured neocortical neurons

The biophysical properties of NMDA receptors are thought to be critical determinants involved in the regulation of long-term synaptic plasticity during neocortical development. NMDA receptor channel properties are strongly dependent on the subunit composition of heteromeric NMDA receptors. During neocortical development in vivo, the expression of the NMDA receptor 2A (NR2A) subunit is up-regulated at the mRNA and protein level correlating with changes in the kinetic and pharmacological properties of functional NMDA receptors. To investigate the developmental regulation of NMDA receptor subunit expression, we studied NR2 mRNA expression in cultured neocortical neurons. With increasing time in culture, they showed a similar up-regulation of NR2A mRNA expression as described in vivo. As demonstrated by chronic blockade of postsynaptic glutamate receptors in vitro, the regulation of NR2A mRNA was strongly dependent on synaptic activity. In contrast, NR2B mRNA expression was not influenced by activity blockade. Moreover, as shown pharmacologically, the regulation of NR2A mRNA expression was mediated by postsynaptic Ca(2+) influx through both NMDA receptors and L-type Ca(2+) channels. It is interesting that even relatively weak expression of NR2A mRNA was correlated with clearly reduced sensitivity of NMDA receptor-mediated whole-cell currents against the NR2B subunit-specific antagonist ifenprodil. Developmental changes in the expression of NR1 mRNA splice variants were also strongly dependent on synaptic activity and thus might, in addition to regulation of NR2 subunit expression, contribute to developmental changes in the properties of functional NMDA receptors. In summary, our results demonstrate that synaptic activity is a key factor in the regulation of NMDA receptor subunit expression during neocortical development.     

Ethylene acts as a negative regulator of glucose induced lateral root emergence in Arabidopsis

Plants, being sessile organisms, are more exposed to the hazards of constantly changing environmental conditions globally. During the lifetime of a plant, the root system encounters various challenges such as obstacles, pathogens, high salinity, water logging, nutrient scarcity etc. The developmental plasticity of the root system provides brilliant adaptability to plants to counter the changes exerted by both external as well as internal cues and achieve an optimized growth status. Phytohormones are one of the major intrinsic factors regulating all aspects of plant growth and development both independently as well as through complex signal integrations at multiple levels. We have previously shown that glucose (Glc) and brassinosteroid (BR) signalings interact extensively to regulate lateral root (LR) development in Arabidopsis.¹ Auxin efflux as well as influx and downstream signaling components are also involved in Glc-BR regulation of LR emergence. Here, we provide evidence for involvement of ethylene signaling machinery downstream to Glc and BR in regulation of LR emergence.     

Arterial Baroreceptor Reflex Counteracts Long-Term Blood Pressure Increase in the Rat Model of Renovascular Hypertension

Introduction

The present study tested the hypothesis that long-term effects of baroreceptor activation might contribute to the prevention of persistent arterial blood pressure (BP) increase in the rat model of renovascular hypertension (HTN).

Methods

Repetitive arterial baroreflex (BR) testing was performed in normo- and hypertensive rats. The relationship between initial arterial BR sensitivity and severity of subsequently induced two-kidney one-clip (2K1C) renovascular HTN was studied in Wistar rats. Additionally, the time course of changes in systolic BP (SBP) and cardiac beat-to-beat (RR) interval was studied for 8 weeks after the induction of 2K1C renovascular HTN in the rats with and without sinoaortic denervation (SAD). In a separate experimental series, cervical sympathetic nerve activity (cSNA) was assessed in controls, 2K1C rats, WKY rats, and SHR.

Results

The inverse correlation between arterial BR sensitivity and BP was observed in the hypertensive rats during repetitive arterial BR testing. The animals with greater initial arterial BR sensitivity developed lower BP values after renal artery clipping than those with lower initial arterial BR sensitivity. BP elevation during the first 8 weeks of renal artery clipping in 2K1C rats was associated with decreased sensitivity of arterial BR. Although SAD itself resulted only in greater BP variability but not in persistent BP rise, the subsequent renal artery clipping invariably resulted in the development of sustained HTN. The time to onset of HTN was found to be shorter in the rats with SAD than in those with intact baroreceptors. cSNA was significantly greater in the 2K1C rats than in controls.

Conclusions

Arterial BR appears to be an important mechanism of long-term regulation of BP, and is believed to be involved in the prevention of BP rise in the rat model of renovascular HTN.     

Identifying the critical period for waterlogging on yield and its components in wheat and barley

Background and aims

Crop tolerance to waterlogging depends on factors such as species sensitivity and the stage of development that waterlogging occurs. The aim of this study was to identify the critical period for waterlogging on grain yield and its components, when applied during different stages of crop development in wheat and barley.

Methods

Two experiments were carried out (E1: early sowing date, under greenhouse; E2: late sowing date, under natural conditions). Waterlogging was imposed during 15–20 days in 5 consecutive periods during the crop cycle (from Leaf 1 emergence to maturity).

Results

The greatest yield penalties occurred when waterlogging was applied from Leaf 7 appearance on the main stem to anthesis (from 34 to 92 % of losses in wheat, and from 40 to 79 % in barley for E1 and E2 respectively). Waterlogging during grain filling reduced yield to a lesser degree. In wheat, reductions in grain number were mostly explained by reduced grain number per spike while in barley, by variations in the number of spikes per plant.

Conclusions

The time around anthesis was identified as the most susceptible period to waterlogging in wheat and barley. Exposing the crop to more stressful conditions, e.g. delaying sowing date, magnified the negative responses to waterlogging, although the most sensitive stage (around anthesis) remained unchanged.     

YCZ-18 Is a New Brassinosteroid Biosynthesis Inhibitor

Plant hormone brassinosteroids (BRs) are a group of polyhydroxylated steroids that play critical roles in regulating broad aspects of plant growth and development. The structural diversity of BRs is generated by the action of several groups of P450s. Brassinazole is a specific inhibitor of C-22 hydroxylase (CYP90B1) in BR biosynthesis, and the application use of brassinazole has emerged as an effective way of complementing BR-deficient mutants to elucidate the functions of BRs. In this article, we report a new triazole-type BR biosynthesis inhibitor, YCZ-18. Quantitative analysis the endogenous levels of BRs in Arabidopsis indicated that YCZ-18 significantly decreased the BR contents in plant tissues. Assessment of the binding affinity of YCZ-18to purified recombinant CYP90D1 indicated that YCZ-18 induced a typical type II binding spectrum with a K_d value of approximately 0.79 μM. Analysis of the mechanisms underlying the dwarf phenotype associated with YCZ-18 treatment of Arabidopsis indicated that the chemically induced dwarf phenotype was caused by a failure of cell elongation. Moreover, dissecting the effect of YCZ-18 on the induction or down regulation of genes responsive to BRs indicated that YCZ-18 regulated the expression of genes responsible for BRs deficiency in Arabidopsis. These findings indicate that YCZ-18 is a potent BR biosynthesis inhibitor and has a new target site, C23-hydroxylation in BR biosynthesis. Application of YCZ-18 will be a good starting point for further elucidation of the detailed mechanism of BR biosynthesis and its regulation.     

The influence of pre-floral growth and development on the pathway of floral development, dry matter distribution and seed yield in oilseed rape (Brassica napus L.)

Patterns of floral development, dry matter distribution and seed yield were examined in winter oilseed rape plants subjected to different pre-floral growth environments. The duration of pre-floral growth and plant size at flower initiation, measured in terms of total mainstem leaf number, were manipulated by varying the temperature between seedling emergence and flower initiation. Exposure of seedlings to low temperatures from cotyledon expansion onwards markedly reduced the duration of pre-floral growth and the number of leaves on the mainstem. The subsequent development pattern of plants was largely dependent on the date of flower initiation and therefore vernalisation requirement. Indeed, the period of growth from flower initiation to maturity, considered on the basis of thermal time, was directly related to the duration of pre-floral growth and mainstem leaf number. The thermal durations of the bud development phase and flowering period in plants exposed to different pre-floral cold treatments but with a common date of flower initiation were similarly linked to these two parameters. Plants exposed to prolonged periods of low temperature treatment from cotyledon expansion onwards initiated fewer mainstem leaves during a relatively short pre-floral growth phase and their yield potential was limited by a reduction in branch and flower numbers. Plants maintained at higher temperatures produced more mainstem leaves during an extended period of pre-floral growth and supported a greater number of branches and flowers. However, this additional yield potential was not realised due to a reduction in seed numbers and mean seed weight. It appeared that seed yield of these plants was limited by increased competition between an excessive number of lower branches and flowers, a problem apparently created by excessive pre-floral growth. Minimal competition for available assimilates between the limited number of branches of plants with a shorter pre-floral growth phase and fewer mainstem leaves, resulted in lower levels of pod abortion, greater seed production and ultimately increased seed yields.     

Neural strategies for learning during sensitive periods of development

Precise patterns of neural connectivity and synaptic communication are modified by experience during restricted "sensitive" periods of development, and the circuitry and associated behaviors that emerge during such periods are frequently preserved throughout the lifespan. In many neural systems, the expression of various molecules that influence synaptic transmission and neuronal morphology are developmentally regulated and may serve to constrain the timing of enhanced sensitivity to experiential inputs. In this highly selective review I concentrate on recent findings from the visual system and the song system that provide novel insights into the mechanisms that regulate sensitive period plasticity, and that raise new questions concerning what makes sensitive periods so sensitive.     

非编码RNA在骨骼肌发育中的功能

近几年的研究表明,非编码RNA的功能几乎涉及生命活动的各个方面。非编码RNA在骨骼肌发育中的功能研究揭示了骨骼肌发育调控的复杂性。该文总结了骨骼肌发育中非编码RNA的系统发现与鉴定以及非编码RNA在骨骼肌发育和再生中的功能研究。     

Influence of hydrologic attributes on brown trout recruitment in low-latitude range margins

Factors controlling brown trout Salmo trutta recruitment in Mediterranean areas are largely unknown, despite the relevance this may have for fisheries management. The effect of hydrological variability on survival of young brown trout was studied during seven consecutive years in five resident populations from the southern range of the species distribution. Recruit density at the end of summer varied markedly among year-classes and rivers during the study period. Previous work showed that egg density the previous fall did not account for more than 50% of the observed variation in recruitment density. Thus, we expected that climatic patterns, as determinants of discharge and water temperature, would play a role in the control of young trout abundance. We tested this by analyzing the effects of flow variation and predictability on young trout survival during the spawning to emergence and the summer drought periods. Both hatching and emergence times and length of hatching and emergence periods were similar between years within each river but varied considerably among populations, due to differences in water temperature. Interannual variation in flow attributes during spawning to emergence and summer drought affected juvenile survival in all populations, once the effect of endogenous factors was removed. Survival rate was significantly related to the timing, magnitude and duration of extreme water conditions, and to the rate of change in discharge during hatching and emergence times in most rivers. The magnitude and duration of low flows during summer drought appeared to be a critical factor for survival of young trout. Our findings suggest that density-independent factors, i.e., hydrological variability, play a central role in the population dynamics of brown trout in populations from low-latitude range margins. Reported effects of hydrologic attributes on trout survival are likely to be increasingly important if, as predicted, climate change leads to greater extremes and variability of flow regimes.