Copper is an essential metal for normal plant growth and development, although it is also potentially toxic. Copper participates in numerous physiological processes and is an essential cofactor for many metalloproteins, however, problems arise when excess copper is present in cells. Excess copper inhibits plant growth and impairs important cellular processes (i.e., photosynthetic electron transport). Since copper is both an essential cofactor and a toxic element, involving a complex network of metal trafficking pathways, different strategies have evolved in plants to appropriately regulate its homeostasis as a function of the environmental copper level. Such strategies must prevent accumulation of the metal in the freely reactive form (metal detoxification pathways) and ensure proper delivery of this element to target metalloproteins. The mechanisms involved in the acquisition of this essential micronutrient have not been clearly defined although a number of genes have recently been identified which encode potential copper transporters. This review gives a briefly overview of the current understanding of the more important features concerning copper toxicity and tolerance in plants, and brings information of recent findings on copper trafficking including copper detoxification factors, copper transporters and copper chaperones.

Copper is an essential metal for plants. It plays key roles in photosynthetic and respiratory electron transport chains, in ethylene sensing, cell wall metabolism, oxidative stress protection and biogenesis of molybdenum cofactor. Thus, a deficiency in the copper supply can alter essential functions in plant metabolism. However, copper has traditionally been used in agriculture as an antifungal agent, and it is also extensively released into the environment by human activities that often cause environmental pollution. Accordingly, excess copper is present in certain regions and environments, and exposure to such can be potentially toxic to plants, causing phytotoxicity by the formation of reactive oxygen radicals that damage cells, or by the interaction with proteins impairing key cellular processes, inactivating enzymes and disturbing protein structure. Plants have a complex network of metal trafficking pathways in order to appropriately regulate copper homeostasis in response to environmental copper level variations. Such strategies must prevent accumulation of the metal in the freely reactive form (metal detoxification pathways) and ensure proper delivery of this element to target metalloproteins. The mechanisms involved in the acquisition and the distribution of copper have not been clearly defined, although emerging data in last decade, mainly obtained on copper uptake, and both intra- and intercellular distribution, as well as on long-distance transport, are contributing to the understanding of copper homeostasis in plants and the response to copper stress. This review gives an overview of the current understanding of main features concerning copper function, acquisition and trafficking network as well as interactions between copper and other elements.

Transition metals are involved in essential biological processes in plants since they are cofactors of metalloproteins and also act as regulator eleme

Hydrogen sulfide negatively regulates the progress of autophagy through persulfide modification of the Arabidopsis AtATG4a protease.

Hydrogen sulfide (H₂S) is an endogenously generated gaseous signaling molecule, which recently has been implicated in autophagy regulation in both plants and mammals through persulfidation of specific targets. Persulfidation has been suggested as the molecular mechanism through which sulfide regulates autophagy in plant cells. ATG18a is a core autophagy component that is required for bulk autophagy and also for reticulophagy during endoplasmic reticulum (ER) stress. In this research, we revealed the role of sulfide in plant ER stress responses as a negative regulator of autophagy. We demonstrate that sulfide regulates ATG18a phospholipid-binding activity by reversible persulfidation at Cys103, and that this modification activates ATG18a binding capacity to specific phospholipids in a reversible manner. Our findings strongly suggest that persulfidation of ATG18a at C103 regulates autophagy under ER stress, and that the impairment of persulfidation affects both the number and size of autophagosomes. Significance Endoplasmic reticulum (ER) stress is a condition triggered by adverse environmental conditions, which in plants include extreme heat, pathogen infection, and drought. These stresses can have a devastating effect on agricultural productivity, and the appropriate responses of plants to stress are therefore critical. Autophagy is a macromolecular degradation pathway that is activated in response to stress, including ER stress, but the mechanism by which it is regulated is still unclear. Here, we describe a modification, persulfidation, of the key autophagy protein ATG18a that affects its binding to membranes and controls its activity. This tight regulation of autophagy therefore allows plants to control the tradeoff between growth and stress tolerance.

It is shown that restoration of photoinduced electron flow and O ₂ evolution with Mn ²⁺ in Mn-depleted photosystem II (PSII) membrane fragments isolated from spinach chloroplasts is considerably increased with bicarbonate in the region pH 5.0–8.0 in bicarbonate-depleted medium. In buffered solutions equilibrated with the atmosphere (nondepleted of bicarbonate), the bicarbonate effect is observed only at pH lower than the pK of H ₂ CO ₃ dissociation (6.4), which indicates that HCO ₃ ⁻ is the essential species for the restoration effect. The addition of just 2 Mn ²⁺ atoms per one PSII reaction center is enough for the maximal reactivation when bicarbonate is present in the medium. Analysis of bicarbonate concentration dependence of the restoration effect reveals two binding sites for bicarbonate with apparent dissociation constant ( K _d ) of ≈2.5 μM and 20–34 μM when 2,6-dichloro- p -benzoquinone is used as electron acceptor, while in the presence of silicomolybdate only the latter one remains. Similar bicarbonate concentration dependence of O ₂ evolution was obtained in untreated Mn-containing PSII membrane fragments. It is suggested that the K _d of 20–34 μM is associated with the donor side of PSII while the location of the lower K _d binding site is not quite clear. The conclusion is made that bicarbonate is an essential constituent of the water-oxidizing complex of PSII, important for its assembly and maintenance in the functionally active state.