Low-level lasers are used at low power densities and doses according to clinical protocols supplied with laser devices or based on professional practice. Although use of these lasers is increasing in many countries, the molecular mechanisms involved in effects of low-level lasers, mainly on DNA, are controversial. In this study, we evaluated the effects of low-level red lasers on survival, filamentation, and morphology of Escherichia colicells that were exposed to ultraviolet C (UVC) radiation. Exponential and stationary wild-type and uvrA-deficient E. coli cells were exposed to a low-level red laser and in sequence to UVC radiation. Bacterial survival was evaluated to determine the laser protection factor (ratio between the number of viable cells after exposure to the red laser and UVC and the number of viable cells after exposure to UVC). Bacterial filaments were counted to obtain the percentage of filamentation. Area-perimeter ratios were calculated for evaluation of cellular morphology. Experiments were carried out in duplicate and the results are reported as the means of three independent assays. Pre-exposure to a red laser protected wild-type and uvrA-deficient E. coli cells against the lethal effect of UVC radiation, and increased the percentage of filamentation and the area-perimeter ratio, depending on UVC fluence and physiological conditions in the cells. Therapeutic, low-level red laser radiation can induce DNA lesions at a sub-lethal level. Consequences to cells and tissues should be considered when clinical protocols based on this laser are carried out.

O tomate (Lycopersicon esculentum) é a segunda hortaliça em importância no Brasil. O controle de plantas daninhas na cultura representa um dos principais componentes do custo de produção, sendo imprescindível para a obtenção de produtividades elevadas e de frutos de qualidade. Neste texto são apresentados de forma detalhada os efeitos adversos da interferência das plantas daninhas sobre a cultura, tanto daquele cultivado a partir de mudas transplantadas como de semeadura direta. Também são discutidos, para diferentes situações de cultivo, aspectos sobre o período crítico de competição das plantas daninhas durante o ciclo da cultura. Por fim, são apresentadas as principais estratégias utilizadas para o controle de plantas daninhas na cultura do tomateiro, por meio de medidas preventivas, culturais, mecânicas e químicas, com base nas informações atualmente disponíveis sobre esse tema.

Tomato (Lycopersicon esculentum) is the second most important vegetable grown in Brazil. Weed control in tomato culture is one of the main components in crop production costs. However, weed management is indispensable to achieve both high yields and fruit quality. A detailed discussion is presented in this work concerning the adverse effects of weed interference in the crop, both grown from transplanted seedlings and field-sown tomato. Aspects related to the critical period of weed competition during the crop cycle for both growing conditions are also discussed. Finally, the major strategies used for weed management in tomato crops are also presented, such as preventive, cultural, mechanic, and chemical control measures, based on the literature currently available.