The application of synthetic iron chelates to overcome iron deficiency in crops is leading to a high impact on the environment, making it necessary to find more friendly fertilizers. A promising alternative is the application of biodegradable iron chelates, such as those based on siderophores. In the present work, seven bacterial strains of the genus Pseudomonas were selected for their ability to secrete pyoverdine, a siderophore with a high affinity for iron, which could be used as a biofertilizer. The concentration of siderophores secreted by each bacterium expressed as desferrioxamine B equivalents, and the pyoverdine concentration was determined. Their potential as Fe biofertilizers was determined based on their capacity to complex Fe, determining the maximum iron complexation capacity at alkaline pH and selecting the RMC4 strain. The biostimulant capacity of the RMC4 strain was evaluated through the secretion of organic acids such as the hormone Indol-3-acetic acid or glutamic acid, among others, in a kinetic assay. Finally, the genome of RMC4 was determined, and the strain was identified as Pseudomonas monsensis. The annotated genome was screened for genes and gene clusters implicated in biofertilization and plant growth promotion. Besides iron mobilization, genes related to phosphorus solubilization, production of phytohormones and biological control, among others, were observed, indicating the suitability of RMC4 as an inoculant. In conclusion, RMC4 and its siderophores are promising sources for Fe biofertilization in agriculture.

Despite the increasing demand for non-formal science learning activities, few studies report on practitioners' perspectives and experiences with designing and implementing such activities worldwide. This paper focuses on their challenges by drawing upon twenty-two interviews with practitioners involved in diverse science learning activities in various non-formal settings in seven European countries. By including diverse activities and settings, this study contributes to the existing knowledge base, addresses the aforementioned gap in the literature, and informs future practices. Our findings suggest that despite the existing and celebrated diversity, practitioners face similar challenges related to (a) the activities' organisation and management, (b) the competencies required to run such activities, and (c) the attitudes held by the parties involved in them. Direct interview quotes exemplify each theme, further pinpointing the interconnection of multiple factors that inform the organisation and implementation of non-formal science learning activities. The findings allowed for a deeper understanding of challenges reported in the literature and shed light on the challenges voiced by the practitioners including the multiple competencies required and the workload. We conclude with a discussion foregrounding the need to build a knowledge base of shared practices in the field of non-formal science learning.

Zinc (Zn) is an essential micronutrient involved in a large variety of physiological processes, and its deficiency causes mainly growth and development disturbances, as well as oxidative stress, which results in the overproduction and accumulation of reactive oxygen species (ROS). A possible environmentally friendly solution is the application of silicon (Si), an element that has shown beneficial effects under abiotic and biotic stresses on many crops. Si could be applied through the roots or leaves. The aim of this work is to study the effect of Si applied to the root or shoot in cucumber plants under different Zn statuses (sufficiency, deficiency, and re-fertilization). Cucumber plants were grown in hydroponics, with 1.5 mM Si applied at the nutrient solution or sprayed on the leaves. During the different Zn statuses, SPAD index, fresh weight, ROS, and Si, Zn, P, Cu and B mineral concentration were determined. The results suggested that Si application had no effect during sufficiency and deficiency periods, however, during re-fertilization foliar application of Si, it showed faster improvement in SPAD index, better increment of fresh weight, and a decrease in ROS quantity, probably due to a memory effect promoted by Si previous application during the growing period. In summary, Si application to cucumber plants could be used to prepare plants to cope with a future stress situation, such as Zn deficiency, due to its prompt recovery after overcoming the stress period.