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Percentages priming and seem to be related to

Percentages
of linoleic acid and gamma-linolenic acid and oleic/linoleic ratio in borage
grains were statistically similar under different irrigation intervals (Table 6).
In contrast, percentage of palmitic acid as saturated fatty acid of borage oil,
were significantly increased under limited irrigations (I3 and I4),
so that palmitic acid content of seed oil under mild (I2), moderate
(I3) and severe water limitation (I4) were 1.5%, 11.1%
and 9.9% higher than that under well irrigation (Fig. 6a).The
highest percentage of oleic acid was also obtained under I4. The
oleic acid content was 3.9% and 9.3% higher in the plants irrigated after 120
mm (I3) and 150 mm evaporation (I4), compared to well
watering, respectively (Fig. 6b).

 

4.
Discussion

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Drought
stress occurs when the available water in the soil is reduced to such critical
levels and atmospheric conditions add to continuous loss of water. Under
natural conditions, plants are exposed to unfavorable environments that lead to
stress. Therefore, plants yield at the end of the growth season is only part of
their genetic potential (Tayz and Zayger, 2002). Decrement in growth due to
water deficit is a main reason of reduced yield under drought stress (Grasiano
et al., 2005). Reduction of borage yield under moderate and severe water stress
(Fig. 1 and 2) can be attributed to reducing the photosynthetic surface and
leaf area (Dastborhan and Ghassemi-Golezani, 2015) in these conditions. On the
other hand, increasing yield of plants from treated seeds, especially under
favorable irrigation conditions, can be linked to the positive effects of seed
priming on increasing the rate of emergence) and the optimal use of available
resources, increment in the green cover and improvement of leaf area index
(Dastborhan and Ghassemi-Golezani, 2015).

Some
studies have reported that seeds hydrate slowly during osmotic priming,
allowing a longer time for the repair of macromolecules and for a more
favorable metabolic balance at the beginning of germination. Increases in enzymatic
and metabolic activities, DNA synthesis, ATP production, and membrane damage
repairs allow tissue formation in a more direct way, reducing the risks of
damage to the embryo axis. These characteristics are inherent to osmotic
priming and seem to be related to the increase in the seed vitality during the
subsequent germination step (Khan, 1992).

Since the measurement of secondary metabolites of
harvested plants in the first year was performed after harvesting the plants in
the second year, part of the differences between the metabolites content in two
years can be attributed to the effect of the storage period on these compounds.

Plant secondary metabolites are often referred to as compounds that
have no fundamental role in the maintenance of life processes in the plants,
but they are important for the plant to interact with its environment for
adaptation and defense ().Plant secondary metabolites are unique sources for
food additives, flavors, pharmaceuticals and industrially important
pharmaceuticals (Ravishankar and Rao, 2000). Abiotic stresses such as osmotic stress, water restriction and
salinity are among the factors that can lead to a variation in the content of
secondary metabolites (Taiz and Zeiger,
2010). The biosynthetic and metabolic pathways followed by each species
are very specific (Jahangir et al., 2009) and some of the generated products participate in the secondary
plant metabolismand play a role in protecting or minimizing stress that a plant
may undergo. Under ambient
environmental conditions, the surplus of energy is dissipated effectively by
various mechanisms, i.e., non-photochemical quenching, photorespiration, or
xanthophyll cycle. However, under drought stress the situation changes
markedly. Due to water shortage, stomata are closed, and thus the CO2-influx
is diminished. As a result, far less reduction equivalents are consumed
(re-oxidized) within the Calvin cycle. Thus, although the energy dissipating
mechanisms are enhanced, they are overstretched. Therefore, electrons are transferred
to molecular oxygen and superoxide radicals are generated, which are generally
detoxified by superoxide dismutase (SOD) and ascorbate peroxidase (APX).
Nonetheless, the chloroplastic reduction status increases and the ratio of
NADPH+H+ to NADP+ is enhanced. In consequence, all
reactions consuming NADPH+H+, such as the biosynthesis of highly
reduced secondary plant products, will be favoured without the need for any
change in enzyme activity. As a result of the stress related increase in the
biosynthesis rate of highly reduced natural products, large amounts of NADPH +
H+ are consumed and the over-reduced state is mitigated.
Accordingly, this process could be evaluated as a further and supplementary
mechanism for energy dissipation. The extent of this NADPH + H+ re-oxidation
is impressively demonstrated by the strong isoprene emission of various drought
stressed plants.