Strategies to enhance the germination, growth and development of plant species have been studied for many years. Priming or hardening is one of the most famous strategies of pre-sowing to influence seedling development by modulating the metabolic activities of germination before the breakthrough of the radicle (reversible stages of germination). The hardening consists of incorporating an osmotic seed treatment (osmopriming) or hormonal (hormopriming) and/or a redehydration (hydropriming) that allows homogenization (synchronization) of germination, better growth, earlier flowering and a stronger tolerance to abiotic stresses such as drought and salinity. Our work is in line with this perspective and aims to study the consequences of hydropriming and osmopriming (by the PEG6000 at 10 and 30 %) on cowpea seeds (Vigna unguiculata).The results show that the priming allows a faster and more uniform germination and better growth of both radicle and aerial parts. We also demonstrated that a double redehydration (hydropriming) was more effective in improving these parameters. Thus, the application of this pretreatment to legume seeds, will improve germination and crop yield, as well as the tolerance to water deficit.

1. Double hydropriming applied to Vigna unguiculata seeds is better
than a simple hydropriming
Presented by:
Laboratory of Physiology and Organismal Biology, Faculty of Biological Sciences, University of Science and Technology Houari Boumediene
(USTHB), BP 39, El Alia, Bab Ezzouar, Algiers, Algeria corresponding author: reda_djebbar@yahoo.fr
INTRODUCTION
The second Adam Kondorosi Symposium 11 - 12 december 2014 Gif-sur-Yvette (France)
MATERIAL AND METHODS
Seed material:
Vigna unguiculata
(Cowpea or bean of
black eye)
Origin: Argentina
Parts used: Seeds
Kinetics of germination of Vigna unguiculata (cowpea) seeds
RESULTS AND DISCUSSION
Pretreatment of seeds
Germination
In D.Water
Shoot and
radicle
growth in non
stressed and
stressed
conditions
Germination
In condition
of osmotic
stress
(PEG 20%)
Methods of seed priming can be divided into two groups according to the
absorption of water is uncontrolled (hydro and hormopriming) or controlled
(osmopriming) (Taylor et al, 1998). It was clearly shown that the positive effects of this
hardness were associated with various physiological, genetic, biochemical and molecular
changes such as the mobilization of reserves, the degradation of the endosperm, the
activation of anti oxidative systems, the stimulation of the osmolytes synthesis, the
activation of cell cycle and some genes involved in tolerance to abiotic stresses (Bray
and al., 1989; Dell'Aquila and Bewley, 1989; Davison and Bray, 1991; Bray, 1995; Castro and al., 2000;
Vary and al., 2010).
CONCLUSION AND PERSPICTIVES
Seeds priming seem to be an effective and cheaper mean to improve germination,
growth and even stress tolerance of Vigna unguiculata. Seed priming causes
physiological, biochemical and molecular changes highly regulated and controlled by
the expression of many genes.
Some consequences of this hardening are due to DNA methylation or the spatial
conformation of chromatin. Thus, epigenetic phenomena are of great importance
for the understanding of many phenomena in plant biology. They play a key role in
the adaptation of plants to their environment. Accordingly, the use of new
molecular and genetic approaches are essential to better identifying the
expression of genes activated during priming.
Control
Any traitement
before germination
6h imbibition
Soaking for 6 hours
in distilled water
before germination
Simple Hydropriming
Soaking for 3 hours or
6 hours in distilled water
+ Dehydration
Osmopriming
PEG 30 %
Soaking for 6 hours
in the PEG at 30%
Double
Hydropriming
Double cycle of soaking
3 hours in distilled water
followed by Dehydration
0
20
40
60
80
100
0 1 2 3 4 5
Control 6h imbibition
3h hydro 6h hydro
3h Double hydro PEG 10%
PEG 30%
%
of
germination
Days 50
60
70
80
90
100
Capacité
of
germination
(%)
Effects of different priming methods on the germination of Vigna unguiculata seeds under normal conditions
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0
20
40
60
80
100
0 1 2 3 4 5 6 7
Control 6h imbibition
3h hydro 6h hydro
3h Double hydro PEG 10%
PEG 30%
%
of
germination
Days
40
50
60
70
80
90
100
Capacité
of
germination
(%)
Effects of different priming methods on the germination of Vigna unguiculata seeds under osmotic conditions (PEG 20 %)
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Effects of different priming methods on the radicle length (cm) for five days seedlings grown from seeds of Vigna unguiculata
controls and hardened seed germinated in distilled water and the PEG 20 %.
Seedlings (7 days old) from different seed treatments germinated
in PEG 20 %
Effects of different priming methods on shoot growth (cm) of seedlings grown from Vigna unguiculata controls and hardened
seeds germinated in distilled water, fifteen days old (before application of stress) and one month (fifteen days after stopping
the watering).
0
10
20
30
40
Before Stress After Stress
Shoot
Length
(cm)
Control 6h imbib PEG 10% PEG 30%
3h hydro 6h hydro 3h double hydro
0
2
4
6
8
10
12
In D. Water In PEG at 20 %
Lengths
of
roots
(cm)
Control 6h imbibition PEG 10%
PEG 30% 3h hydro 6h hydro
3h Double hydro
Effects of water stress
(watering stopped for two
weeks) on two months old
Vigna unguiculata plants, 15
days after watering.
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+106 % +294 %
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+83 % +103 %
+575 %
+25 %
Crop production and the establishment of good crops depend heavily on seed germination, which is a
crucial step in the life cycle of higher plants (Cheng and Bradford, 1999). Yet germination may be
heterogeneous because the seeds do not germinate all the same way or at the same time. To solve these
problems, called seeds undergo physiological conditioning appointed pre-germination or priming, which can
bring the seeds at the same physiological stage to synchronize germination and improve performance and
stress tolerance (Heydecker and al., 1973; Heydecker, 1978; Taylor and al., 1998).
Priming is partially hydrated seeds at sufficient moisture level to allow pre-germination metabolic
processes, but insufficient for the breakthrough of the radicle (during the reversible stage of germination)
(McDonald, 2000; Ghassemi -Golezani and al., 2010).