Polyamines are common players in different facets of plant programmed cell death

Abstract

Programmed cell death (PCD) is a process that occurs throughout the life span of every plant life, from initial germination of the seed to the senescence of the plant. It is a normal physiological milestone during the plant's developmental process, but it can also be induced by external factors, including a variety of environmental stresses and as a response to pathogen infections. Changes in the morphology of the nucleus is one of the most noticeable during PCD but all the components of the plant cell (cytoplasm, cytoskeleton and organelles) are involved in this fascinating process. To date, relatively little is known about PCD in plants, but several factors, among which polyamines (PAs) and plant growth regulators, have been shown to play an important role in the initiation and regulation of the process. The role of PAs in plant PCD appears to be multifaceted acting in some instances as pro-survival molecules, whereas in others seem to be implicated in accelerating PCD. The molecular mechanism is still under study. Here we present some PCD plant models, focusing on the role of the enzyme responsible for PA conjugation to proteins: transglutaminase (TGase), an enzyme linked with the process of PCD also in some animal models. The role of PAs and plant TGase in the senescence and PCD in flowers, leaf and the self-incompatibility of pollen will be discussed and examined in depth.

Lead-stress induced changes in the content of free, thylakoid- and chromatin-bound polyamines, photosynthetic parameters and ultrastructure in greening barley leaves

“…As is well known, PAs are directly associated with the proteins of PSII by electrostatic interaction due to PAs' polycationic properties, or by covalent binding through transglutaminases (SobieszczukNowicka and Legocka, 2014, Cai et al, 2015, Sobieszczuk-Nowicka et al, 2015. Moreover, Put and Spm are bound to the photosynthetic complexes, mainly to the LHCII monomeric and oligomeric forms (Kotzabasis et al, 1993), and this could provide some stability to the conformation of thylakoid proteins and consequently help to maintain the photosynthetic activity.…”

Natural polyamines and synthetic analogs modify the growth and the morphology of Pyrus communis pollen tubes affecting ROS levels and causing cell death

“…If a cross linkage is formed by bis-PA, proteins remain bound to each other forming a strong net that is no more degraded by proteases; if only mono-PA are formed, the net cannot be built or it is less strong, thus allowing swelling [3,6,48].…”

The Role of Polyamines in Plant Disease Resistance

“…PAs are also conjugated to proteins by transglutaminase (TGase), which catalyzes their covalent binding to the -carboxamide groups of protein endoglutamine residues (Folk, 1980;Del Duca et al, 2014;Cai et al, 2015). The two terminal amino groups of PAs are conjugated to one or two glutamine residues, thereby giving rise to either mono-( -glutamyl)-PAs (mono-PAs) or bis-( -glutamyl)-PAs (bis-PAs).…”