Seed development is
generally divided into two phases: embryogenesis and maturation. At maturity,
seeds are tolerant to desiccation, i.e. they survive a low water content of
about 5 to 10 % relative to the fresh seed mass and can even undergo further
drying. This allows the seed to be stored for long periods of time and remain
viable (A. J. Manfre et al., 2008 Hoekstra et al. 2001). During the late
maturation, several molecular processes are acquired that are important for
seeds to survive in the dry state. They include the accumulation of food
reserves such as lipid and storage proteins and the synthesis of protective
molecules such as soluble sugars (Blackman et al., 1992), glutathione as an
antioxidant marker (Kranner et al. 2006), small heat shock proteins
(HSPs) and the late embryogenesis abundant (LEA) proteins.

LEA proteins were
first described in cotton seeds (Dure et al. 1981; Galau et al. 1986). The name
is based on the initial discovery at high levels in the later stages of embryo
development in plant seeds (Close, 1997), where they may represent as much as
4% of cellular proteins (Hanin, 2011). These proteins are strongly associated
with the acquisition of desiccation tolerance in plant seeds (Espelund et al.
1992). The highlighting of an in vivo role of these proteins in seed
desiccation tolerance comes first from tow LEA proteins AtEm1 and AtEm6 from Arabidopsis thaliana that believed to
protect the Arabidopsis embryo during the phase of desiccation by replacing
water (Bies et al., 1998; Carles et al., 2002). Subsequently, Manfre et al.,
2009 showed that Arabidopsis thaliana Em6 deficient mutants defects in
maturation drying.  Additional evidences
for the association of LEA proteins with desiccation tolerance is provided by
proteomic studies (Boudet et al., 2006; Chatelain et al., 2012; Delahaie et al., ?2013)
which provide the presence of these proteins at high levels in mature seeds.

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There are several
different classes of LEA proteins of which dehydrins (LEA II) constitute the
most studied group. These proteins are generally hydrophilic, thermostable and
highly unstructured (Hanin et al., 2011). Experimentally, dehydrins have been
shown to have multitude functions such as chaperone activity, radical scavenger,
membrane protection and protein stabilization (Banerjee
and Roychoudhury, 2016). Previously, we showed
that the wheat dehydrin (DHN-5) exhibit an in vitro and in vivo
potent chaperone function under various stress conditions by protection enzymes
and proteins from denaturation and aggregation (Drira et al., 2013; 2015).
Furthermore, overexpression of DHN-5 in Arabidopsis thaliana enhance the
tolerance of plants to osmotic and salt stresses through ROS scavenger and
reducing oxidative damage (Drira et al., 2016). 

Opuntica ficus indica is a xerphytic plant which withstands water
shortage, high temperature and poor soil fertility (Barbera, 1995), and thus
adapted to the arid and semi-arid zones of the world. This plant has developed
physiological and structural adaptations favorable to their development in arid
and semiarid environments and their tolerance to drought and high salinity (Ben
Salem et al., 1996). The literature offers much information about the
nutritional value of the juice, cladode and the seed oil of cactus pear
(Feugang, et al., 2006; El-Mostafa et al., 2014) but little is known about Opuntica
seed protein (Samah et al., 2015). Our current study focus to develop an
extraction protocol from Opuntica ficus indica seeds to obtain a heat
stable fraction enriched with dehydrins and to explore this fraction to improve
our understanding the molecular mechanism by which LEA proteins exerts their
protective role in desiccation tolerance of seeds.