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

Abstract

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.

Study of interaction effect between triacontanol and nitric oxide on alleviating of oxidative stress arsenic toxicity in coriander seedlings

“…This leads to the disruption of energy flows in cells and finally represses the growth and development of plants. The growth-promoting effects of TRIA on various attributes especially those on fresh and dry weights, leaf-area and nodulation have been explored by Sharma and Dietz (2006) and Khan et al (2007) in various medicinal crops. A significant enhancement in TRIA values from treated plants could presumably be ascribed to the well-known effect of exogenously applied TRIA on elongation of internodes through cell division and cell extensibility .…”

“…Therefore, the measured decline in the contents of ASC and GSH in C. sativum could be partially due to its consumption while acting as antioxidant to limit lipid peroxidation. Moreover, GSH as a sulfur-containing tripeptide thiol is involved in plant protection against HMs as a precursor in the synthesis of phytochelatins (PCs) and in the scavenging of ROS by the ascorbate-glutathione cycle (Sharma & Dietz 2006;Xiong et al 2010). GSH levels in plant tissues are known to increase under metal stress (Koricheva et al 1997).…”

“…Recently, Gupta et al (2009) demonstrated that PC synthesis is stimulated by As supply in Brassica juncea due to the over-expression of the PC gene. The PC-metal complex is often sequestered in the vacuoles (Sharma & Dietz 2006). The chemical structure of PCs contains repetitions of the dipeptide Glu-Cys.…”

Glutathione in plants: biosynthesis and physiological role in environmental stress tolerance

“…It acts as a co-factor in different biochemical reactions, it interacts with hormones, signaling molecules, and its redox state triggers signal transduction (Foyer and Noctor 2005a, b). Another major function of GSH is the formation of phytochelatins (PCs) that bind heavy metals for safe transport and sequestration in the vacuole (Sharma and Dietz 2006). Thus it plays vital role in detoxifying toxic metals/metalloids and xenobiotics (Srivalli and Khanna-Chopra 2008).…”

Structure and Hydration of l-Proline in Aqueous Solutions

“…In general this class of molecules, known as osmolytes, has the ability to counter environmental water stress and to protect cellular proteins against denaturation under these extreme conditions. [2][3][4][5][6] These molecules are synthesized and accumulate in cells as a response to osmotically induced dehydration in the presence of high salt environments, 7 where proline in particular has been shown to stimulate growth and respiration in bacteria in the presence of low water activities. Proline, in essence, acts as a "chaperone" to protein formation in these conditions.…”