Molecular Plant Breeding 2016, Vol.7, No.17, 1-7
2
Radi´c et al. (2006) analyzing the peroxidase activity in leaves and roots under salt stress, highlighted that POD
activity of salt-stressed plants changed with respect to different saline treatments and plant organs and this activity
was mainly due to the
de novo
synthesis of the enzyme in shoot and root.
Lee and Lee (2000) analyzing the changes of antioxidant enzyme isoforms against chilling stress in the leaves of
cucumber (
Cucumis sativus
L.) found five APX isoforms were presented in the leaves of cucumber. Furthermore,
these authors showed that intensities of APX-4 and APX-5 were enhanced by chilling stress, whereas that of
APX-3 was significantly increased in the post stress periods after chilling stress. Wang et al., (2009) suggested that
peroxidase (POD) activity in normal conditions in two alfalfa cultivars was higher in root than in shoots. However,
POD activities in shoot and root tissues of both cultivars showed similar level under chilling stress.
Keshavkant and Naithani (2001) reported that aerial parts of the chilling sensitive young sal (
Shorea robusta
)
seedlings showed overproduction of reactive oxygen species. To gain in a clear understanding of the reactions
exhibited by annuals
Medicago
plants under different duration of cold stress; we conducted a study with enzyme
activity (peroxidase) and peroxidase isoenzymatique pattern as biochemical markers in response to cold stress in the
aerial and roots tissues. These results may help in the development of a new variety of stress tolerant
Medicago
plants.
1 Results and Discussion
The biochemical changes observed in our study during cold stress in both vegetative tissues has been
demonstrated in many species and under many stresses. Sánchez-Calderón et al., (2013) showed that in root
vegetative system has to growth in media where the biotic and abiotic components are distributed heterogeneous.
As soon as the root makes contact with the soil must sense and integrate biotic and abiotic cues in order to adjust
their genetic program of post-embryonic root development. Ghosh
and Xu (2014) reported that proteomic analyses
of plant roots under various abiotic stress conditions revealed important information on proteins involved in the
abiotic stress response. This leads to the identification of molecular and cellular mechanisms that are specific to
certain abiotic stress or shared between two or more abiotic stress conditions. On the other hand, these authors
highlighted that higher abundance of ROS scavengers was detected in roots under drought, high salinity and cold
stress and can be looked upon as a preventive measure against oxidative damage caused due to high ROS levels.
To gain a better knowledge of the chilling response, Lee et al., (2009) suggested that it is imperative to analyze the
tissue-specific proteome patterns under chilling stress. Prasad (1996) investigated the mechanisms involved in
chilling injury or tolerance in developing maize seedlings subjected to low temperature, noted that peroxidase
activities in acclimated plants increased gradually with 14 to 120 % with age and remained slightly higher during
recovery in 2- to 4- days- old seedlings. Cavalcanti et al., (2007) comparing some antioxidative response during
short-term salt stress, spotlighted that roots and leaves display distinct mechanisms of response during salt stress
and recovery. However, these responses and/or the oxidative damage caused by oxygen species were not related
with the growth reduction.
1.1 Changes in the activity of POD
Chilling tolerance or sensitivity in plants is well correlated with inherent antioxidant responses. Tolerant plant
species generally have a better capacity to protect themselves from chilling-induced oxidative stress, via the
enhancement of antioxidant enzyme activity. In plants, elevated ROS without an efficient scavenging system may
lead to high injury index and finally death of the whole plant (Azzeme et al., 2016). These authors noted that in
response to different levels of drought in the root and leaf tissues in oil palm plants the guaiacol POD activity in
leaves was found to increase sharply under mild stress but dropped under moderate and further reduced under
severe drought conditions even though the levels were still higher than that for the control. In the roots, the
guaiacol POD activity significantly increased under mild and further increased moderate and severe stress
conditions. Liu et al., (2013) have observed an enhancement in activities peroxidase synthesis pathway during cold
acclimation. Yadegari et al., (2007) showed in soybean a significant changes in guaiacol peroxidase activity
