Polymorphic forms of nucleic acids provide platforms for new nanomaterials, and transition metal cations give access to alternative arrangements of nucleobases by coordinating with electron-rich functional groups. Interaction of Ag+ with 5’-guanosine monophosphate (5’-GMP) is considered in this work. Ag+ promotes nucleotide stacking and aggregation, as indicated by the increased viscosity of 5’-GMP solutions with Ag+, magnification of the circular dichroism response of guanine by Ag+, and exothermic reactions between Ag+ and guanine derivatives. Isothermal titration calorimetry studies show that the reaction is favored starting at 10 μM 5’-GMP. Utilizing the exothermic heat change associated with reaction of Ag+ with 5’-GMP, local structure within the aggregate was assessed. Based on salt dependence and comparison with the corresponding nucleoside, the dianionic phosphate of 5’-GMP is one binding site for Ag+, although this electrostatic interaction is not a dominant contribution to the overall heat change. Another binding site is the N7 on the nucleobase, as determined via studies with 7-deazaguanosine. Besides this binding site, Ag+ also associates with the O6, as earlier studies deduced from the shift in the carbonyl stretching frequency associated with adduct formation. With these two binding sites on the nucleobase, the empirical stoichiometry of ~1 Ag+:nucleobase derived from the calorimetry studies indicates that Ag+ coordinates two nucleobases. The proposed structural model is a Ag+-mediated guanine dimer within a base stacked aggregate.

The importance of biostimulants, defined as plant growth-promoting agents that differ notably from fertilizers, is increasing steadily because of their potential contribution to a worldwide strategy for securing food production without burdening the environment. Based on folkloric evidence and ethnographic studies, seaweeds have been useful for diverse human activities through time, including medicine and agriculture. Currently, seaweed extracts, especially those derived from the common brown alga Ascophyllum nodosum, represent an interesting category of biostimulants. Although A. nodosum extracts (abbreviated ANEs) are readily used because of their capacity to improve plant growth and to mitigate abiotic and biotic stresses, fundamental insights into how these positive responses are accomplished are still fragmentary. Generally, the effects of ANEs on plants have been attributed to their hormonal content, their micronutrient value, and/or the presence of alga-specific polysaccharides, betaines, polyamines, and phenolic compounds that would, alone or in concert, bring about the observed phenotypic effects. However, only a few of these hypotheses have been validated at the molecular level. Transcriptomics and metabolomics are now emerging as tools to dissect the action mechanisms exerted by ANEs. Here, we provide an overview of the available in planta molecular data that shed light on the pathways modulated by ANEs that promote plant growth and render plants more resilient to diverse stresses, paving the way toward the elucidation of the modus operandi of these extracts.

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