Agriculture Reference
In-Depth Information
oxidase: PAO, EC 1.4.3.4), present in the apoplastic and peroxisomal compart-
ments (Medda et al.
1995
; Sebela et al.
2001
). In the apoplast, Put, Spm, and Spd
are oxidized to 1,3-diaminopropane, H
2
O
2
, and the corresponding aldehyde, while
in the peroxisome, Spm is converted to Put,
via
the intermediate Spd (Rea et al.
2004
; Cona et al.
2006
; Moschou et al.
2008
). The Cu
+2
- amine oxidase oxidizes
the primary amine of diamines and polyamines, with the concomitant production of
H
2
O
2
, NH
4
+
and the corresponding aldehyde, while the flavin oxidase oxidizes the
secondary amino of Spd and Spm, producing H
2
O
2
, 1, 3-diaminopropane and the
corresponding amino aldehyde. Also, both mono- and dicotyledonous species may
catabolize Put to γ-aminobutyric acid (GABA), an important modulator of several
physiological processes (Bouchereau et al.
1999
).
Aside from their participation in the catabolism and their contribution to cellular
homeostasis, amine oxidases take part in important physiological events through their
reaction products, mainly H
2
O
2
. On one hand, they are related to lignin biosynthesis
and crosslinking reactions of the cell wall, occurring during xylem maturation and
plant cell elongation (Cona et al.
2003
; Federico and Angelini
1991
; Laurenzi et al.
1999
; Laurenzi et al.
2001
; Moller and McPherson
1998
) as well as to the cell wall
strengthening that takes place during the infection by plant pathogens (Cona et al.
2006
). On the other hand, they regulate cell PAs level in plants subjected to stress
conditions (Bagni and Tassoni
2001
; Cona et al.
2006
). For example, a steep decline
of Spd and Spm observed in rice (
Oryza sativa
) plants, six days after imposition of
drought stress was assigned to PAO amino oxidation (Capell et al.
2004
). It has also
been reported that ethylene promotes DAOs and PAOs activities, which could be
related to reductions in PAs contents observed in several crop species (Li et al.
2004
).
5 Involvement of PAs on Crop Plant Response to Drought,
Salt and Cold Stresses
5.1 Drought Stress
Polyamines are thought to play protective roles during drought stress. These mol-
ecules may act as osmolytes and bind non-covalently to the negatively-charged
groups of membrane phospholipids, thus contributing to stabilizing membrane con-
formation (Hanzawa et al.
2000
). They also regulate pH alterations due to osmotic
stress, by reversing H
+
-ATPase and H
+
-PPase inactivity. Table
5.1
shows main
results obtained in diverse studies on polyamine metabolism in several crop species
cultivated under water deficit-related conditions. In barley (
Hordeum vulgare)
, a
close relationship between PAs metabolism and leaf turgor was found: when leaf
turgor was at or near the control level, Put and Spm accumulated, whereas the lev-
els of both PAs sharply diminished when leaf turgor was lost (Turner and Stewart
1986
). Moreover, Flores and Galston (
1984
) postulated that turgor maintenance is a
requirement for PAs accumulation during drought stress.
