Plants exposed to heavy metals accumulate an array of metabolites, some to high millimolar concentrations. This review deals with N-containing metabolites frequently preferentially synthesized under heavy metal stress such as Cd, Cu, Ni, and Zn. Special focus is given to proline, but certain other amino acids and oligopeptides, as well as betaine, polyamines, and nicotianamine are also addressed. Particularly for proline a large body of data suggests significant beneficial functions under metal stress. In general, the molecules have three major functions, namely metal binding, antioxidant defence, and signalling. Strong correlative and mechanistic experimental evidence, including work with transgenic plants and algae, has been provided that indicates the involvement of metal-induced proline in metal stress defence. Histidine, other amino acids and particularly phytochelatins and glutathione play a role in metal binding, while polyamines function as signalling molecules and antioxidants. Their accumulation needs to be considered as active response and not as consequence of metabolic dys-regulation.

The significance of amino acids and amino acid-derived molecules in plant responses and adaptation to heavy metal stress

Role of Polyamines in the Control of Cell Proliferation and Differentiation

https://mmbr.asm.org/content/mmbr/49/1/81.full.pdf

Polyamines in microorganisms.

The degradation of eukaryotic mRNAs plays important roles in the modulation of gene expression, quality control of mRNA biogenesis and antiviral defenses. In the past five years, many of the enzymes involved in this process have been identified and mechanisms that modulate their activities have begun to be identified. In this review, we describe the enzymes of mRNA degradation and their properties. We highlight that there are a variety of enzymes with different specificities, suggesting that individual nucleases act on distinct subpopulations of transcripts within the cell. In several cases, translation factors that bind mRNA inhibit these nucleases. In addition, recent work has begun to identify distinct mRNP complexes that recruit the nucleases to transcripts through different mRNA-interacting proteins. These properties and complexes suggest multiple mechanisms by which mRNA degradation could be regulated.

The enzymes and control of eukaryotic mRNA turnover.

Polyamines: Mysterious Modulators of Cellular Functions

The amounts of normal and compensatory polyamines of polyamine-requiring Escherichia coli mutants grown in the absence of polyamines were determined. Although aminopropylcadaverine, a compensatory polyamine, was synthesized by MA135 (speB) and DR112 (speA speB), no aminopropylcadaverine or only small amounts of aminopropylcadaverine were synthesized by EWH319 (speA speB speC speD) and MA261 (speB speC), respectively. The average mass doubling times of MA135, DR112, MA261, and EWH319 grown in the absence of polyamines were 113, 105, 260, and 318 min, respectively. The correlation of these values with the sum of spermidine plus aminopropylcadaverine suggested that aminopropylcadaverine is important for cell growth in the presence of limiting amounts of normal polyamines. This hypothesis is supported by the results of aminopropylcadaverine stimulation of the in vitro synthesis of polyphenylalanine and MS2 RNA replicase and of its stimulation of the growth of MA261. For the following reasons, it was concluded that aminopropylcadaverine was synthesized preferentially from cadaverine made by ornithine decarboxylase: aminopropylcadaverine was synthesized in relatively large amounts in cells (MA135 and DR112) which possess ornithine decarboxylase; ornithine decarboxylase catalyzed the decarboxylation of lysine in vitro, and the in vivo formation of aminopropylcadaverine was inhibited by an inhibitor of ornithine decarboxylase.

Formation of a compensatory polyamine by Escherichia coli polyamine-requiring mutants during growth in the absence of polyamines.

Inhibition by polyamines of lipid peroxide formation in rat liver microsomes

The addition of polyamines to an Escherichia coli cell-free polypeptide synthetic reaction mixture containing dialyzed ribosomes, Sephadex-treated supernatant from 100000 × g centrifugation, and suitable amounts of Mg2+ increased the polyphenylalanine synthesis from either [14C]phenyl-alanine or [14C]phenylalanyl-tRNA up to twice that synthesized in the same system without polyamines but at optimal Mg2+ concentration. No similar effect was observed with cadaverine, agmatine, histamine, Ca2+ or Mn2+. These results, together with the presence of polyamines in unwashed ribosomes and the rapid incorporation of polyamines into ribosomes incubated with polyamines, suggest that polyamines are essential components of E. coli ribosomes for maximum polypeptide synthesis.



The increase of polyphenylalanine synthesis by polyamines in an E. coli cell-free system occurred at the level of aminoacyl-tRNA binding to ribosomes, but not at the levels of peptide bond formation and translocation.



In the rat-liver cell-free system, an approximately 1.6-fold increase of polyphenylalanine synthesis was observed by the addition of spermidine. However, the addition of putrescine to the reaction mixture caused only a sparing effect on the Mg2+ requirement for polyphenylalanine synthesis.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1974.tb03790.x

Effect of Polyamines on Polyphenylalanine Synthesis by Escherichia coli and Rat‐Liver Ribosomes

Interaction between polyamines and nucleic acids or phospholipids

Polyphenylalanine synthesis was carried out with Escherichia coli Q13 50-S ribosomal subunits and reconstituted 30-S particles containing different combinations of 23-S core particles and 30-S subunit split proteins obtained from a polyamine-requiring mutant of E. coli during its growth in the presence or absence of putrescine. It was concluded that the defect in the amount of some kinds of 30-S subunit split proteins was responsible for the decrease of polypeptide synthesis in a polyamine-requiring mutant of E. coli grown in the absence of polyamines.



The methylation of 16-S RNA during growth in the absence of putrescine was decreased, while the degree of methylation of 23-S RNA did not change significantly. The decrease in methylation of 16-S RNA in the absence of putrescine was due mainly to a decrease of methylation of adenine.



The relationship between the decrease of polypeptide synthetic activity of 30-S ribosomal subunits obtained from a polyamine-requiring mutant of E. coli grown in the absence of polyamines and the decrease of methylation of 16-S RNA is discussed.

Defect in the Split Proteins of 30‐S Ribosomal Subunits and Under‐Methylation of 16‐S Ribosomal RNA in a Polymamine‐Requiring Mutant of Escherichia coli Grown in the Absence of Polymines

Seiyu Hirose

Papers

Formation of a compensatory polyamine by Escherichia coli polyamine-requiring mutants during growth in the absence of polyamines.

Inhibition by polyamines of lipid peroxide formation in rat liver microsomes

Effect of Polyamines on Polyphenylalanine Synthesis by Escherichia coli and Rat‐Liver Ribosomes

Interaction between polyamines and nucleic acids or phospholipids

Defect in the Split Proteins of 30‐S Ribosomal Subunits and Under‐Methylation of 16‐S Ribosomal RNA in a Polymamine‐Requiring Mutant of Escherichia coli Grown in the Absence of Polymines