In reduction in oil yield due to water

In principle, there are two quite different explanations
for why the concentrations of natural products are generally enhanced in plants
suffering drought stress. This effect could either be due to a stress related
change in the benchmark, i.e., the dry or fresh weight used as reference value,
or to a real increase in biosynthesis. In the first case, the drought stress
related decline in biomass production is associated with a more or less
unchanged rate of biosynthesis of natural products. Accordingly, when
calculated on a dry or fresh weight base, in the case of the stressed plants,
the corresponding concentration is increased. In the second case, stress does
result in an authentic increase in the total content of secondary plant
products caused by an enhanced biosynthesis. This increase is putatively due to
the stress related over-reduction, boosting the biosynthesis of highly reduced
compounds. Unfortunately, these simplified causal coherences become much more
intransparent, since both issues are frequently overlaid and interfere with
numerous factors and side effects (Al-Gabbiesh et al., 2015). Due to the
tremendous progress in molecular biology, a lot of information is available on
how the synthesis of the secondary metabolites is induced, modulated and
regulated by various biotic and abiotic factors, respectively. Drought stress
might also change the source-sink properties of the entire plant. This – in
addition to the inducing factors already mentioned – also impacts on the
overall performance of the biosynthesis, translocation and accumulation of
secondary plant products (Al-Gabbiesh et al., 2015).

Drought stress
reduces cell division, photosynthesis, leaf area index, stem extension and
vegetative growth (Dastborhan and Ghassemi-Golezani 2015), leading to grain yield
loss.

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Since oil
percentage of grains under different irrigation treatments was similar,
reduction in oil yield due to water deficit strongly related with grain yield
per unit area under different water supply (Fig. 1a). Oil content is a
quantitative trait and is controlled by several genes (Jensen et al. 1996);
therefore, the chance of damage to all genes under water stress is very low.
Similarly, oil percentage of grains was not significantly affected by
water-deficit in sesame (Ozkan and Kulak 2013) and sunflower (Peji? et
al. 2009). Seed oil
yield in comparison with the oil percentage was more affected by the shortage
of soil moisture (Wright et al. 1995; Ahmadi and Bahrani
2009; Ghassemi-Golezani and Lotfi 2013).

No
significant differences have also been observed in the O/L ratios of sunflower
(Unger 1982), rapeseed (Ullah et al. 2012)
and groundnut (Chakraborty et al. 2013) oils under different moisture
availability. Fatty acid
type is effective in determining oil quality. Indeed, the
presence of polyunsaturated fatty acids increases the potential beneficial
properties of the oils. Linoleic
acid and

-linolenic
acid are the most important polyunsaturated fatty acids. Since borage oil have
high levels of unsaturated fatty acids, especially

-linolenic
acid, then it can be used in diet for securing human health.

The
percentage of saturated fatty acids such as palmitic acid could be increased as
a result of water limitation in oilseeds (Mekki et al. 1999; Laribi et al. 2009;
Zarei et al. 2010).

Increasing
oleic acid percentage under water stress is in agreement with the findings of
Bellaloui et al. (2013) in soybean and Chaiyadeea et al. (2013) in peanut. The
increment in oleic acid under water stress was due to the decreasing activity
of ?-12 desaturase, reducing the conversion of oleic to linoleic acid (Baldini
et al. 2000), thus there was no change in linoleic acid and

-linolenic acid contents under different
irrigation intervals (Fig. 10). This enzyme acts only for a very short period
during the early development of the embryo in water stressed plants (Ali et al.
2009). Water stress causing accelerated and earlier embryo development and
lipid accumulation, therefore, leading to a shorter duration of all enzymatic
activities, including those of ?-12 desaturase, which could reflect on the
final acid composition (Baldini et al. 2002). The properties of the oils are
dependent on the fatty acids composition which has gained much attention owing
to its beneficial implications for human health (Sakouhi et al., 2011). In
fact, water deficit did not change the quality of borage oil because of
similarity in the ratio of unsaturated to saturated acids.

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