Electron spin echo studies on chloroplasts. Spectral characteristics of electron transport components and light-induced transients

Electron-spin resonance echoes are used to study the complex overlapping ESR spectra of whole chloroplasts. By varying the repetition rate of the microwave pulse sequence, delay time, and pulse width, signals with different longitudinal and transverse relaxation times were extracted. We have identified the echo signals due to plastocyanin and ferredoxins. In addition, we have found a strong signal at g = 4.3, that possibly arises from distorted cytochrome, and weak signals in the region g = 6-9. The strong echo signal at g = 2.0047 (Signal II), is made up of at least three "dark" components that differ in their relaxation times. Upon illumination at 1.2 K several of the echo signals including Signal II show reversible light-induced components. The kinetics of these transients depend on the addition of 3(3,4-dichlorophenyl)-1,1-dimethyl urea. Part of the transients are believed to arise from cyclic electron flow around Photosystem I.     

Interactions that drive Sec-dependent bacterial protein transport

Understanding the transport of hydrophilic proteins across biological membranes continues to be an important undertaking. The general secretory (Sec) pathway in Escherichia coli transports the majority of E. coli proteins from their point of synthesis in the cytoplasm to their sites of final localization, associating sequentially with a number of protein components of the transport machinery. The targeting signals for these substrates must be discriminated from those of proteins transported via other pathways. While targeting signals for each route have common overall characteristics, individual signal peptides vary greatly in their amino acid sequences. How do these diverse signals interact specifically with the proteins that comprise the appropriate transport machinery and, at the same time, avoid targeting to an alternate route? The recent publication of the crystal structures of components of the Sec transport machinery now allows a more thorough consideration of the interactions of signal sequences with these components.     

Receiver psychology and the evolution of multicomponent signals

Many animals produce and respond to signals made up of multiple components. For example, many avian sexual displays are highly extravagant combinations of visual and acoustic elements, and are described as being 'multicomponent'. One possible reason for the evolution of such complex signals is that they provide more reliable information for receivers. However, receivers also influence signal evolution in another important way, by how they perceive and process signals: signallers will be selected to produce signals that are more easily received. The potential role of receiver psychology in the evolution of multicomponent signals has not previously been considered; in this review I present psychological results that support the notion that two components are better received than one alone. Detection can be improved by producing two components together, thus reducing the reaction time, increasing the probability of detection and lowering the intensity at which detection occurs. Discriminability of multicomponent stimuli is also made easier through better recognition, faster discrimination learning and multidimensional generalization. In addition, multicomponent stimuli also improve associative learning. I show that multicomponency does indeed improve signal reception in receivers, although the benefits of producing components in two sensory modalities (bimodal multicomponent signals) may be larger and more robust than producing them in just one (unimodal multicomponent signals). This highlights the need for consideration of receiver psychology in the evolution of multicomponent signals, and suggests that where signal components do not appear to be informative, they may instead be performing an important psychological function. Copyright 1999 The Association for the Study of Animal Behaviour.