Heavy metals can represent a threat to the health of aquatic ecosystems. Unlike organic chemicals, heavy metals cannot be eliminated by natural processes such as their degradation into less toxic compounds, and this creates unique challenges for their remediation from soil, water, and air. Phytoremediation, defined as the use of plants for the removal of environmental contaminants, has many benefits compared to other pollution-reducing methods. Phytoremediation is simple, efficient, cost-effective, and environmentally friendly because it can be carried out at the polluted site, which simplifies logistics and minimizes exposure to humans and wildlife. Macrophytes represent a unique tool to remediate diverse environmental media since they can accumulate heavy metals from contaminated sediment via roots, from water via submerged leaves, and from air via emergent shoots. In this review, a synopsis is presented about how plants, especially macrophytes, respond to heavy metal stress and we propose potential roles that phytohormones can play in the alleviation of metal toxicity in the aquatic environment. We focus on the uptake, translocation, and accumulation mechanisms of heavy metals in organs of macrophytes and give examples of how phytohormones interact with plant defense systems under heavy metal exposure. We advocate for a more in-depth understanding of these processes to inform more effective metal remediation techniques from metal-polluted waterbodies.

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HighlightThis article comments on:Holalu SV Finlayson SA. 2017. The red light:far red light alters Arabidopsis axillary bud growth and abscisic acid signaling before stem auxin changes. Journal of Experimental Botany 67, 943–952.

Interactions between algal derived dissolved organic matter (DOM) and mercury (Hg) are crucial for understanding the fate, transport, and bioavailability of Hg to methylating microorganisms. For the first time, high resolution mass spectrometry (Q-Exactive Orbitrap) was used to examine Hg binding ligands released by Chlorella vulgaris, Chlamydomonas reinhardtii, and Scenedesmus obliquus grown at three light:dark photoperiods (i.e., 12:12, 16:8, and 20:4 h). Van Krevelen diagrams showed a significant increase in carbohydrate and protein DOM and a decrease in released lipid-like molecules as light exposure increased. Hg binding DOM were initially in the form of CHO molecular formulas whereas a shift to higher light durations prompted more Hg to be complexed to CHON and CHONS DOM structures. Despite an overall change in bulk DOM composition, molecular similarities existed in Hg binding DOM as light exposure increased. Hg binding ligands were more similar based on the exposed light duration than based algal species, suggesting growth photoperiods influence Hg binding more than algal taxa. Hg binding DOM at 16:8 and 20:4 h growth cycles were more aromatic and homologous in nature when compared to darker growth conditions that resulted in smaller, more aliphatic Hg-DOM complexes rich in sulfur and thiols. Together, these results highlight the importance of photoperiod on the composition of released DOM and its complexation with Hg.

Vegetable oil utilization is determined by its fatty acid composition. In soybean and other grain crops, during the seed development oil accumulation is important trait for value in food or industrial applications. Seed development is relatively short and sensitive to unfavorable abiotic conditions. These stresses can lead to a numerous undesirable qualitative as well as quantitative changes in fatty acid production. Fatty acid manipulation which targets a higher content of a specific single fatty acid for food or industrial application has gained more attention. Despite several successes in modifying the ratio of endogenous fatty acids in most domesticated oilseed crops, numerous obstacles in FA manipulation of seed maturation are yet to be overcome. Remarkably, connections with plant hormones have not been well studied despite their critical roles in the regulation and promotion of a plethora of processes in plant growth and development. While activities of phytohormones during the reproductive phase have been partially clarified in seed physiology, the biological role of plant hormones in oil accumulation during seed development has not been investigated. In this review seed development and numerous effects of abiotic stresses are discussed. After describing fatty acid and phytohormone metabolism and their interactions, we postulate that the endogenous plant hormones play important roles in fatty acid production in soybean seeds.