The Photoprotective Behavior of a Motile Benthic Diatom as Elucidated from the Interplay Between Cell Motility and Physiological Responses to a Light Microgradient Using a Novel Experimental Setup.

It has long been hypothesized that benthic motile pennate diatoms use phototaxis to optimize photosynthesis and minimize photoinhibitory damage by adjusting their position within vertical light gradients in coastal benthic sediments. However, experimental evidence to test this hypothesis remains inconclusive, mainly due to methodological difficulties in studying cell behavior and photosynthesis over realistic spatial microscale gradients of irradiance and cell position. In this study, a novel experimental approach was developed and used to test the hypothesis of photosynthesis optimization through motility, based on the combination of single-cell in vivo chlorophyll fluorometry and microfluidic chips. The approach allows the concurrent study of behavior and photosynthetic activity of individual cells of the epipelic diatom species Craspedostauros britannicus exposed to a light microgradient of realistic dimensions, simulating the irradiance and distance scales of light microgradients in benthic sediments. Following exposure to light, (i) cells explored their light environment before initiating light-directed motility; (ii) cells used motility to lower their light dose, when exposed to the highest light intensities; and (iii) motility was combined with reversible non-photochemical quenching, to allow cells to avoid photoinhibition. The results of this proof-of-concept study not only strongly support the photoprotective nature of photobehavior in the studied species but also revealed considerable variability in how individual cells reacted to a light microgradient. The experimental setup can be readily applied to study motility and photosynthetic light responses of other diatom species or natural assemblages, as well as other photoautotrophic motile microorganisms, broadening the toolset for experimental microbial ecology research.

Hysteresis light curves: a protocol for characterizing the time dependence of the light response of photosynthesis.

Photosynthesis vs. light curves (LCs) have played a central role in photosynthesis research for decades. They are the commonest form of describing how photosynthesis responds to changes in light, being frequently used for characterizing photoacclimation. However, LCs are often interpreted exclusively regarding the response to light intensity, the effects of time of exposure not being explicitly considered. This study proposes the use of 'hysteresis light curves' (HLC), an experimental protocol focused on the cumulative effects of light exposure to obtain information on the time dependence of photosynthetic light responses. HLC are generated by exposing samples to a symmetrical sequence of increasing and decreasing light levels. The comparison of the light-increasing and the light-decreasing phases allows the quantification of the hysteresis caused by high-light exposure, the magnitude and direction of which inform on the activation, and subsequent relaxation of high-light-induced photosynthetic processes. HLCs of the chlorophyll fluorescence indices rETR (relative electron transport rate of photosystem II) and Y(NPQ) (index of non-photochemical quenching) were measured on cyanobacteria, algae, and plants, with the aim of identifying main patterns of hysteresis and their diversity. A non-parametric index is proposed to quantify the magnitude and direction of hysteresis in HLCs of rETR and Y(NPQ). The results of this study show that HLCs can provide additional relevant information on the time dependence of the light response of photosynthetic samples, not obtainable from conventional LCs, useful for phenotyping photosynthetic traits, including photoacclimation state and kinetics of light activation and relaxation of electron flow and energy dissipation processes.

Percepções atuais na orientação e re-orientação profissional / Current perceptions in the professional orientation and re-orientation

O presente artigo refere-se aos determinantes implícitos numa escolha profissional, ou seja, motivações, desejos e aspirações internas que levam a pessoa a construir uma identidade profissional. Esta escolha se dá desde o início de nossa vida no momento em que começamos a nos construir como sujeitos. Porém, esta construção fica dependente da forma como internalizamos o meio no qual nos encontramos, sendo isto marca decisiva para a construção do nosso psiquismo. A sociedade nos impõe que tenhamos consolidado uma identidade profissional no momento em que somos adolescentes, sendo esta uma grande fase de individuação. Contudo, percebe-se que esta consolidação pode se dar numa fase mais tardia do nosso desenvolvimento. Este é o objetivo central deste artigo, qual seja, o de analisar, através de uma experiência com orientação profissional, o motivo que leva uma pessoa a repensar suas atividades profissionais (AU)

Percepções atuais na orientação e re-orientação profissional / Current perceptions in the professional orientation and re-orientation

O presente artigo refere-se aos determinantes implícitos numa escolha profissional, ou seja, motivações, desejos e aspirações internas que levam a pessoa a construir uma identidade profissional. Esta escolha se dá desde o início de nossa vida no momento em que começamos a nos construir como sujeitos. Porém, esta construção fica dependente da forma como internalizamos o meio no qual nos encontramos, sendo isto marca decisiva para a construção do nosso psiquismo. A sociedade nos impõe que tenhamos consolidado uma identidade profissional no momento em que somos adolescentes, sendo esta uma grande fase de individuação. Contudo, percebe-se que esta consolidação pode se dar numa fase mais tardia do nosso desenvolvimento. Este é o objetivo central deste artigo, qual seja, o de analisar, através de uma experiência com orientação profissional, o motivo que leva uma pessoa a repensar suas atividades profissionais