Methylamine interaction with proteins of photosystem II: A comparison with biogenic polyamines

Polyamines: Α bioenergetic smart switch for plant protection and development

The present review highlights the bioenergetic role of polyamines in plant protection and development and proposes a universal model for describing polyamine-mediated stress responses. Any stress condition induces an excitation pressure on photosystem II by reforming the photosynthetic apparatus. To control this phenomenon, polyamines act directly on the molecular structure and function of the photosynthetic apparatus as well as on the components of the chemiosmotic proton-motive force (ΔpH/Δψ), thus regulating photochemical (qP) and non-photochemical quenching (NPQ) of energy. The review presents the mechanistic characteristics that underline the key role of polyamines in the structure, function, and bioenergetics of the photosynthetic apparatus upon light adaptation and/or under stress conditions. By following this mechanism, it is feasible to make stress-sensitive plants to be tolerant by simply altering their polyamine composition (especially the ratio of putrescine to spermine), either chemically or by light regulation.

Plastid-associated polyamines: their role in differentiation, structure, functioning, stress response and senescence

Polyamines are low-molecular weight biogenic amines. They are a specific group of cell growth and development regulators. In the past decade biochemical, molecular and genetic studies have contributed much to a better understanding of the biological role of polyamines in the plant cell. Substantial evidence has also been added to our understanding of the role of polyamines in plastid development. In developing chloroplasts, polyamines serve as a nitrogen source for protein and chlorophyll synthesis. In chloroplast structure, thylakoid proteins linked to polyamines belong mainly to antenna proteins of light-harvesting chlorophyll a/b-protein complexes. The fact that LHCII oligomeric forms are much more intensely labelled by polyamines, in comparison to monomeric forms, suggests that polyamines participate in oligomer stabilisation. In plastid metabolism, polyamines modulate effectiveness of photosynthesis. The role of polyamines in mature chloroplasts is also related to the photo-adaptation of the photosynthetic apparatus to low and high light intensity and its response to environmental stress. The occurrence of polyamines and enzymes participating in their metabolism at every stage of plastid development indicates that polyamines play a role in plastid differentiation, structure, functioning and senescence.

Positive charges of polyamines protect PSII in isolated thylakoid membranes during photoinhibitory conditions

The effects of the positive charges of amines such as spermine (SPM), putrescine (PUT) and methylamine (MET) on the protection of PSII against excessive illumination were investigated in isolated thylakoid membranes. Under photoinhibition conditions, water oxidation, the kinetics of the Chl fluorescence rise and charge recombination in PSII were affected. A low concentration of SPM (1 mM) added before photoinhibition produced a significant improvement of F(v)/F(0), the oxygen yield and the amplitude of the B-band of thermoluminescence compared with the other amines. Amongst the amines studied, only SPM could protect the photosynthetic apparatus under photoinhibition conditions. This protection was probably provided by the polycationic nature of SPM (four positive charges at physiological pH), which can stabilize surface-exposed proteins of PSII through electrostatic interaction.

Polyamines interaction with thylakoid proteins during stress

The involvement of polyamines in plant responses to abiotic stresses is well investigated, while there has been few reports on the specific mode of action of polyamines on the photosynthetic apparatus. The objective of this review is thus to examine the mode of interaction of polyamines with proteins of photosystem II core and LHCII, including methylamine (monoamine) as a simplified model to better understand the mode of action of polyamines. Spectroscopic methods used to determine the binding mode of amines with PSII proteins showed that amines such as spermine, putrescine and methylamine interact with protein (H-bonding) through polypeptide C=O, C-N and N-H groups with major perturbations of protein secondary structure as the concentration of amines was raised. High concentration of amines added to PSII-enriched submembrane fractions causes a significant loss of PSII activity. However, at lower concentration, polyamines, especially spermine, improve the photosynthetic functions under stress. We concluded from this review that besides the conjugation of polyamines with LHC polypeptides, polyamines are likely to interact with extrinsic proteins and the hydrophilic part of intrinsic proteins of PSII by electrostatic interaction. This could stabilize the conformation of proteins under various stresses. However, at high concentration of polyamines a strong inhibition of PSII activity is observed.