Botanical Studies (2008) 49: 9-18.
*
Corresponding author: E-mail: hflo@faculty.pccu.edu.tw;
Tel: +886-2-28610511 ext. 31101.
INTRODUCTION
Environmental stress severely affects plants because
it can throw the production and scavenging of reactive
oxygen species (ROS) in plants out of balance (Gratao
et al., 2005). One of the major biological consequences
of soil flooding is oxygen deficiency. Roots suffer from
periodic or prolonged deprivation of oxygen, which
interferes with respiration at the level of electron transport.
The lack of a suitable electron acceptor leads to saturated
redox chains, accumulation of the reduced form of nicotine
adenine dinucleotide phosphate (NADPH), and a decline
in the generation of adenosine triphosphate (ATP). In plant
cells, oxidative stress reactions are associated with toxic
free radicals from the reduction of molecular oxygen to
superoxide radicals (O
2
-
), singlet oxygen (¡PO
2
), hydroxyl
radicals (¡POH) and hydrogen peroxide (H
2
O
2
). These
free radicals can inactivate various Calvin-Benson cycle
enzymes and are involved in oxidative systems, marking
proteins for degradation (Kennedy et al., 1992; Chaudiere
and Ilious, 1999). The toxic radicals can be removed
both enzymatically and chemically to protect plant cells
against oxygen toxicity and counter the hazardous effects
of ROS under stress (Gratao et al., 2005). The complex
antioxidative defense system that has evolved in plants
is composed of antioxidative enzymes (i.e., ascorbate
peroxidase (APX), catalase (CAT), superoxide dismutase
(SOD), glutathione reductase (GR)) and metabolites
(i.e., ascorbic acid (ASA), as well as reduced glutathione
(GSH), oxidized glutathione (GSSG), and vitamin E)
(Gratao et al., 2005). High levels of some antioxidative
enzymes and antioxidants are found to be important in
tobacco (Hurng and Kao, 1994a; Hurng and Kao, 1994b),
corn (Yan and Dai, 1996), wheat (Biemelt et al., 1998),
soybean (VanToai and Bolles, 1991), rice (Ushimaro et al.,
1992), tomato, eggplant (Lin et al., 2004), and sweetpotato
(Lin et al., 2006) survival of oxidative stress after being
subjected to different levels of flooding. Some oxidative
enzymes or oxidants have been useful in screening for
flooding-tolerant plants (Lin et al., 2004).
PBZ (paclobutrazol; (2RS, 3RS)-1-4 (-chlorophenyl)-4,
4-dimethyl-2-1, 2, 4-triazol-1-yl-penten-3-ol) is a member
of the triazole family. Triazoles have both fungitoxic and
plant-growth regulatory effects. In addition, they can
protect plants against various stresses, including drought,
Paclobutrazol leads to enhanced antioxidative protection
of sweetpotato under flooding stress
Kuan-Hung LIN
2
, Chao-Chia TSOU
2
, Shih-Ying HWANG
4
, Long-Fang O. CHEN
3
, and Hsiao-Feng
LO
1,
*
1
Department of Horticulture and Biotechnology, Chinese Culture University, Taipei 110, Taiwan
2
Graduate Institute of Biotechnology, Chinese Culture University, Taipei 110, Taiwan
3
Institute of Plant and Microbial Biology, Academia Sinica, Taipei 115, Taiwan
4
Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan
(Received May 16, 2007; Accepted September 28, 2007)
ABSTRACT.
The aim of this research was to study the effect of paclobutrazol pretreatment on the changes
of antioxidative enzymes and antioxidants in the flooding-stressed sweetpotato Ipomoea batatas (L.) Lam.
¡¥Tainung 57¡¦ was grown in plastic boxes in a screenhouse and maintained in optimal water conditions for
45 days followed by PBZ treatments (0 and 0.5 mg/plant) for 1 day. Then flooding was induced by raising
the water level to 5 cm above the soil medium surface for a 5-day period followed by drainage for 2 days.
A factorial experiment in randomized complete blocks with three replications was conducted. Young fully
expanded leaves from each plant were clipped to measure enzyme activities and antioxidant contents.
Increased ascorbate peroxidase activity, total glutathione, oxidized ascorbic acid, and total ascorbic acid
amounts on different days of flooding provided the sweetpotato with increased flooding tolerance. The levels
of glutathione reductase, ascorbate peroxidase, total glutathione, oxidized ascorbic acid, and malondialdehyde
were regulated and elevated by paclobutrazol pretreatment under non-flooded conditions. Paclobutrazol
pretreatment increased the levels of all antioxidative enzymes and antioxidants following different flooding
durations and drainage, and boosted the flooding tolerance of the sweetpotato.
Keywords: Antioxidant; Antioxidative enzyme; Flooding; Ipomoea batatas (L.) Lam.; Paclobutrazol.
BIOChemISTRy