Changes in needle nitrogen partitioning and photosynthesis during 80 years of tree ontogeny in Picea abies

Needle nitrogen partitioning and photosynthesis of Norway spruce were studied in a forest chronosequence in Järvselja Experimental Forest, Estonia. Current- and previous-year shoots were sampled from upper and lower canopy positions in four stands, ranging in age from 13 to 82 years. A/c _i curves were determined to obtain maximum carboxylation rate (V _cmax) and maximum rate of electron transport (J _max), whereas needle nitrogen partitioning into carboxylation (P _R), bioenergetics associated with electron transport (P _B) and thylakoid light harvesting components (P _L) was calculated from the values of V _cmax, J _max and leaf chlorophyll concentration. The greatest changes in studied needle characteristics took place between tree ages of 13 and 26 years, and this pattern was independent of needle age and canopy position. Needle mass per projected area (LMA) was lowest in the 13-year-old stand and mass-based nitrogen concentration (N^M) was generally highest in that stand. The values of LMA were significantly higher and those of N^M lower in the 26-year-old stand. Mass-based V _cmax and J _max were highest in the 13-year-old stand. Area-based photosynthetic capacity was independent of tree age. The proportion of photosynthetic nitrogen (P _R, P _B and P _L) was highest and that of non-photosynthetic nitrogen lowest in the 13-year-old stand. Current-year needles had lower LMA and P _L, but higher photosynthetic capacity compared to 1-year-old foliage. Needles from lower canopy positions exhibited lower LMA, area-based nitrogen concentration and photosynthetic capacity than needles from upper canopy. The period of substantial reductions in needle photosynthetic capacity and changes in nitrogen partitioning coincides with the onset of reproductive phase during tree ontogeny.     

Ribosomal RNA secondary structure: compensatory mutations and implications for phylogenetic analysis

Using sequence data from the 28S ribosomal RNA (rRNA) genes of selected vertebrates, we investigated the effects that constraints imposed by secondary structure have on the phylogenetic analysis of rRNA sequence data. Our analysis indicates that characters from both base-pairing regions (stems) and non-base-pairing regions (loops) contain phylogenetic information, as judged by the level of support of the phylogenetic results compared with a well-established tree based on both morphological and molecular data. The best results (the greatest level of support of well-accepted nodes) were obtained when the complete data set was used. However, some previously supported nodes were resolved using either the stem or loop bases alone. Stem bases sustain a greater number of compensatory mutations than would be expected at random, but the number is < 40% of that expected under a hypothesis of perfect compensation to maintain secondary structure. Therefore, we suggest that in phylogenetic analyses, the weighting of stem characters be reduced by no more than 20%, relative to that of loop characters. In contrast to previous suggestions, we do not recommend weighting of stem positions by one-half, compared with that of loop positions, because this overcompensates for the constraints that selection imposes on the secondary structure of rRNA.      

Integrative analysis of multiple gene expression profiles with quality-adjusted effect size models

Background  

With the explosion of microarray studies, an enormous amount of data is being produced. Systematic integration of gene expression data from different sources increases statistical power of detecting differentially expressed genes and allows assessment of heterogeneity. The challenge, however, is in designing and implementing efficient analytic methodologies for combination of data generated by different research groups.     

Focus Issue on Calcium Signaling: Calcium-Dependent and -Independent Stomatal Signaling Network and Compensatory Feedback Control of Stomatal Opening via Ca2+ Sensitivity Priming

Guard cells use compensatory feedback controls to adapt to conditions that produce excessively open stomata.In the past 15 years or more, many mutants that are impaired in stimulus-induced stomatal closing and opening have been identified and functionally characterized in Arabidopsis (Arabidopsis thaliana), leading to a mechanistic understanding of the guard cell signal transduction network. However, evidence has only recently emerged that mutations impairing stomatal closure, in particular those in slow anion channel SLOW ANION CHANNEL-ASSOCIATED1 (SLAC1), unexpectedly also exhibit slowed stomatal opening responses. Results suggest that this compensatory slowing of stomatal opening can be attributed to a calcium-dependent posttranslational down-regulation of stomatal opening mechanisms, including down-regulation of inward K⁺ channel activity. Here, we discuss this newly emerging stomatal compensatory feedback control model mediated via constitutive enhancement (priming) of intracellular Ca²⁺ sensitivity of ion channel activity. The CALCIUM-DEPENDENT PROTEIN KINASE6 (CPK6) is strongly activated by physiological Ca²⁺ elevations and a model is discussed and open questions are raised for cross talk among Ca²⁺-dependent and Ca²⁺-independent guard cell signal transduction pathways and Ca²⁺ sensitivity priming mechanisms.Stomatal pores formed by two guard cells enable CO₂ uptake from the atmosphere, but also ensure leaf cooling and provide a pulling force for nutrient uptake from the soil via transpiration. These vitally important processes are inevitably accompanied by water loss through stomata. Stomatal opening and closure is caused by the uptake and release of osmotically active substances and is tightly regulated by signaling pathways that lead to the activation or inactivation of guard cell ion channels and pumps. Potassium ions enter guard cells through the inward-rectifying K⁺ channels (K+_in) during stomatal opening and are released via outward-rectifying K⁺ channels during stomatal closure (Schroeder et al., 1987; Hosy et al., 2003; Roelfsema and Hedrich 2005). Cytosolic Ca²⁺, an important second messenger in plants, mediates ion channel regulation, particularly down-regulation of inward-conducting K+_in channels and activation of S-type anion channels, thus mediating stomatal closure and inhibiting stomatal opening (Schroeder and Hagiwara, 1989; Dodd et al., 2010; Kim et al., 2010). Stomatal closure is initiated by anion efflux via the slow S-type anion channel SLAC1 (Negi et al., 2008; Vahisalu et al., 2008; Kollist et al., 2011) and the voltage-dependent rapid R-type anion channel QUICK-ACTIVATING ANION CHANNEL1 (Meyer et al. 2010; Sasaki et al., 2010).In recent years, advances have been made toward understanding mechanisms mediating abscisic acid (ABA)-induced stomatal closure (Cutler et al., 2010; Kim et al., 2010; Raghavendra et al., 2010). The core ABA signaling module, consisting of PYR/RCAR (for pyrabactin resistance 1/regulatory components of ABA receptors) receptors, clade A protein phosphatases (PP2Cs), SNF-related protein kinase OPEN STOMATA1 (OST1), and downstream targets, is Ca²⁺-independent (Ma et al., 2009; Park et al., 2009; Hubbard et al., 2010). However, ABA-induced stomatal closure was reduced to only 30% of the normal stomatal closure response under conditions that inhibited intracellular cytosolic free calcium ([Ca2+]_cyt) elevations in Arabidopsis (Siegel et al., 2009), consistent with previous findings in other plants (De Silva et al., 1985; Schwartz, 1985; McAinsh et al., 1991; MacRobbie, 2000). Together these and other studies show the importance of [Ca2+]_cyt for a robust ABA-induced stomatal closure. Here, we discuss Ca²⁺-dependent and Ca²⁺-independent signaling pathways in guard cells and open questions on how these may work together.Plants carrying mutations in the SLAC1 anion channel have innately more open stomata, and exhibit clear impairments in ABA-, elevated CO₂-, Ca²⁺-, ozone-, air humidity-, darkness-, and hydrogen peroxide-induced stomatal closure (Negi et al., 2008; Vahisalu et al., 2008; Merilo et al., 2013). Recent research, however, unexpectedly revealed that mutations in SLAC1 also down-regulate stomatal opening mechanisms and slow down stomatal opening (Laanemets et al., 2013).     

Exenatide promotes cognitive enhancement and positive brain metabolic changes in PS1-KI mice but has no effects in 3xTg-AD animals

Recent studies have shown that type 2 diabetes mellitus (T2DM) is a risk factor for cognitive dysfunction or dementia. Insulin resistance is often associated with T2DM and can induce defective insulin signaling in the central nervous system as well as increase the risk of cognitive impairment in the elderly. Glucagone like peptide-1 (GLP-1) is an incretin hormone and, like GLP-1 analogs, stimulates insulin secretion and has been employed in the treatment of T2DM. GLP-1 and GLP-1 analogs also enhance synaptic plasticity and counteract cognitive deficits in mouse models of neuronal dysfunction and/or degeneration. In this study, we investigated the potential neuroprotective effects of long-term treatment with exenatide, a GLP-1 analog, in two animal models of neuronal dysfunction: the PS1-KI and 3xTg-AD mice. We found that exenatide promoted beneficial effects on short- and long-term memory performances in PS1-KI but not in 3xTg-AD animals. In PS1-KI mice, the drug increased brain lactate dehydrogenase activity leading to a net increase in lactate levels, while no effects were observed on mitochondrial respiration. On the contrary, exenatide had no effects on brain metabolism of 3xTg-AD mice. In summary, our data indicate that exenatide improves cognition in PS1-KI mice, an effect likely driven by increasing the brain anaerobic glycolysis rate.     

Comparative use patterns of plant resources in rural areas of South Africa and Zimbabwe

Documentation of use patterns of plants across national boundaries is of relevance in understanding the importance of plant resources to livelihood strategies of different ethnic groups. Plant resources have gained prominence as a natural asset through which families derive food, firewood, income, medicines and timber, enabling particularly poor communities to achieve self-sufficiency. The objective of this study was to investigate the trends in plant usage in South Africa and Zimbabwe. An ethnobotanical investigation was conducted between January 2012 and January 2013 in the Limpopo Province, South Africa and the Midlands Province, Zimbabwe. The study used questionnaire surveys and interviews with a total of 143 participants to explore plant use patterns in South Africa and Zimbabwe. A total of 98 plant species were identified, with Zimbabwe contributing 70 species and 47 species from South Africa. The uses were classified into 15 categories, major use categories were firewood, food plants, medicine and timber. Food plant was a major plant use category in Zimbabwe, contributing 55.1%, followed by medicinal plants (36.8%), firewood (35.7%) and timber (31.6%). In contrast, firewood was the major plant use category in South Africa, contributing 18.4%, followed by food plants (17.3%), medicinal (14.3%) and timber (1.0%). Comparison of the two countries demonstrated remarkable differences in plant use patterns. The results showed that rural households in Zimbabwe were more reliant on plant resources than their counterparts in South Africa. Such a trend could be attributed to a close relationship between the local people, and their natural and agricultural environment leading to a rich knowledge base on plants, plant use and related practices. This comparative analysis strengthens the firm belief that utilization of plant resources represents an important shared heritage, preserved over the centuries, which must be exploited in order to provide further new and useful body of ethnobotanical knowledge.