Agriculture Reference
In-Depth Information
Spm or thermospermine (tSpm) (Knott et al.
2007
). In plants, PAs distribution dif-
fers among tissues and developmental stages, being Put and Spd more abundant
than Spm and tSpm (Naka et al.
2010
). Also, tSpm seems to be present in all plants,
while Spm appears to be restricted to flowering plants (Fuell et al.
2010
).
Besides Put, Spd and Spm, less common PAs in plants have been described as
cadaverine (Cad), norspermidine, norspermine, homocaldopentamine, homocaldo-
hexamine, 1,3-diaminopropane and 4-aminobutylcadaverine, among others (Kuehn
et al.
1990
; Fujihara et al.
1995
; Kuznetsov et al.
2007
).
Although their concentrations in plants are much higher than those of phytohor-
mones, plant PAs are considered as growth regulators, as they play fundamental
roles in a wide range of growth, differentiation and morphogenetic processes during
the course of plant ontogeny. Roles in embryogenesis, seed germination, rhizogen-
esis, organogenesis, floral initiation and development, as well as in vascular devel-
opment, leaf senescence, fruit development and ripening have been described for
these molecules (Slocum
1991
; Kakkar et al.
2000
; Kakkar y Sawhney
2002
; Pang
et al.
2007
). Lately, a great deal of attention has been paid to the protective effect
of PAs during plant response to biotic and abiotic stresses (Liu et al.
2007
; Gill and
Tuteja
2010
; Vera-Sirera et al.
2010
).
2 Polyamine Biosynthesis
Concentration of intracellular PAs is tightly regulated through their biosynthesis and
catabolism, and modulated by cellular transport and conjugation with other organic
molecules such as hydroxycinnamic acids and proteins (Bagni and Tassoni
2001
;
Edreva et al.
2007
; Fincato et al.
2011
). Polyamines can be found as conjugated
forms, e.g., covalently attached to compounds of low molecular weight (typically
hydroxycinnamic, p-coumaric, caffeic and ferulic acids) and high molecular weight
molecules (proteins or cell wall polymers). Enzymes such as putrescine-cafeoil-
CoA transferase are responsible for the formation of hydroxycinnamic acid conju-
gates (Martin-Tanguy
1997
), phenolics compounds that are related to the flowering
process and the plant response to pathogen attack (Flores and Martin-Tanguy
1991
;
Martin-Tanguy
1997
). On the other hand, transglutaminases channel the conjugation
of polyamines to the γ-carboxamide group of endo-glutamic residues of proteins,
especially in the chloroplast, where this activity is stimulated by light (Del Duca
et al.
1995
; Dondini et al.
2003
). In addition, the compartmentalization of enzymes
involved in PA metabolism suggests a spatio-specific regulation of these important
amines (Borrell et al.
1995
; Kamada-Nobusada et al.
2008
; Fincato et al.
2011
).
The first step in PAs biosynthesis is the diamine Put formation. In plants and
some bacteria, this process occurs by decarboxylation of arginine via arginine de-
carboxylase (ADC; EC 4.1.1.19) in a pathway involving agmatine and N-carbam-
oylputrescine as intermediates, and the corresponding enzymes agmatine iminohy-
drolase (EC 3.5.3.12) and
N
-carbamoylputrescine amidohydrolase (EC 3.5.1.53)
(Fig.
5.1
). The ADC pathway for Put biosynthesis in plants appears to be derived
