Silencing of NtMPK4 impairs CO-induced stomatal closure, activation of anion channels and cytosolic Casignals in Nicotiana tabacum guard cells

Light-induced stomatal opening in C3 and C4 plants is mediated by two signalling pathways. One pathway is specific for blue light and involves phototropins, while the second pathway depends on photosyntheticaly active radiation (PAR). Here, the role of Nt MPK4 in light-induced stomatal opening was studied, as silencing of this MAP kinase stimulates stomatal opening. Stomata of Nt MPK4-silenced plants do not close in elevated atmospheric CO₂, and show a reduced response to PAR. However, stomatal closure can still be induced by abscisic acid. Measurements using multi-barrelled intracellular micro-electrodes showed that CO₂ activates plasma membrane anion channels in wild-type Nicotiana tabacum guard cells, but not in Nt MPK4-silenced cells. Anion channels were also activated in wild-type guard cells after switching off PAR. In approximately half of these cells, activation of anion channels was accompanied by an increase in the cytosolic free Ca²⁺ concentration. The activity of anion channels was higher in cells showing a parallel increase in cytosolic Ca²⁺ than in those with steady Ca²⁺ levels. Both the darkness-induced anion channel activation and Ca²⁺ signals were repressed in Nt MPK4-silenced guard cells. These data show that CO₂ and darkness can activate anion channels in a Ca²⁺-independent manner, but the anion channel activity is enhanced by parallel increases in the cytosolic Ca²⁺ concentration. Nt MPK4 plays an essential role in CO₂- and darkness-induced activation of guard-cell anion channels, through Ca²⁺-independent as well as Ca²⁺-dependent signalling pathways.     

Ultrafast heme-residue bond formation in six-coordinate heme proteins: implications for functional ligand exchange

A survey is presented of picosecond kinetics of heme-residue bond formation after photolysis of histidine, methionine, or cysteine, in a broad range of ferrous six-coordinate heme proteins. These include human neuroglobin, a bacterial heme-binding superoxide dismutase (SOD), plant cytochrome b 559, the insect nuclear receptor E75, horse heart cytochrome c and the heme domain of the bacterial sensor protein Dos. We demonstrate that the fastest and dominant phase of binding of amino acid residues to domed heme invariably takes place with a time constant in the narrow range of 5-7 ps. Remarkably, this is also the case in the heme-binding SOD, where the heme is solvent-exposed. We reason that this fast phase corresponds to barrierless formation of the heme-residue bond from a configuration close to the bound state. Only in proteins where functional ligand exchange occurs, additional slower rebinding takes place on the time scale of tens of picoseconds after residue dissociation. We propose that the presence of these slower phases reflects flexibility in the heme environment that allows external ligands (O2, CO, NO, . . .) to functionally replace the internal residue after thermal dissociation of the heme-residue bond.     

Estimations of the importance of plant resources extracted by inhabitants of the Peruvian Amazon flood plains

Extractions/applications of plant-resources were investigated in Mestizo communities in the Jenaro Herrera district, Peruvian Amazon. Knowledge differences between genders on forest resource uses were also examined. Two methods were applied: (1) a forest survey based on structured interviews of ten informants on potential uses of 334 pre-selected trees and lianas in permanent sample plots, and interviews of 20 male and female informants concerning potential uses of 85 trees and lianas; and (2) a household survey recording extracted materials in or near the dwellings of 73 families. The conclusions are: (i) most forest products are extracted from a limited number of species, whereas a large number of species is mentioned as important/potentially useful for identical purposes; (ii) coherence exists between extracted species and their abundance in easily accessible forest formations; (iii) knowledge of forest resources is gender correlated; and (iv) a combination of methods for collection of information on use and extraction of plant resources provides more detailed and profound results than using each method separately.     

ADHD symptoms in healthy adults are associated with stressful life events and negative memory bias

Stressful life events, especially Childhood Trauma, predict ADHD symptoms. Childhood Trauma and negatively biased memory are risk factors for affective disorders. The association of life events and bias with ADHD symptoms may inform about the etiology of ADHD. Memory bias was tested using a computer task in N = 675 healthy adults. Life events and ADHD symptoms were assessed using questionnaires. The mediation of the association between life events and ADHD symptoms by memory bias was examined. We explored the roles of different types of life events and of ADHD symptom clusters. Life events and memory bias were associated with overall ADHD symptoms as well as inattention and hyperactivity/impulsivity symptom clusters. Memory bias mediated the association of Lifetime Life Events, specifically Childhood Trauma, with ADHD symptoms. Negatively biased memory may be a cognitive marker of the effects of Childhood Trauma on the development and/or persistence of ADHD symptoms.