Ecologia Mediterranea

caused by salt present in growth medium. Al
Kkatee (2006) found this specie adapted to
the dry climate of desert zones, temperature
and salinity which are the major factors that
influence its seed germination.
The germination percentage of P. dichotomum
showed a net decrease under osmotic
potential stress conditions, germination was
very low at –7.0 bar and no germination
occurred at –10.0 and –16.0 bar.
The reduction of germination rate under salinity
stress condition has been described by
numerous authors (Azhdari et al. 2010). The
inhibitory effects of NaCl on seed germination
could be due to its direct affect on the
growth of the embryo (Al Khatee 2006).
Alternatively, NaCl may also increase the
osmotic potential of the media causing
inhibitory effects on seed imbibition (Almansouri
et al. 2001).
Water deficit, induced by NaCl, reduced significantly
shoot and root length, especially at
9.0 g/l. When seeds were moistened with 12.0
and 15.0 g/l NaCl for 8 days, the seeds of
P. dichotomum completely we found no germination.
NaCl may be an inhibitory of the
activities of some enzymes that may play critical
roles in seed germination (Saha et al.
2010; Wang et al. 2011). Water uptake
declined rapidly when NaCl solution was
added at high concentrations. The first phase
of water uptake by the seeds involves movement
of water into the free space and does not
depend on the osmotic potential of the surrounding
solution (Mekhbordoran et al.
2009). The second slower linear phase of
water uptake involves the movement of water
across cell membranes into the cells of the
seeds and is determined by the difference
between the osmotic potential of the seed and
that of the medium (Bewly 1994).
The germination percentage and rate of germination
in the P. dichotomum -treated seeds
decreased with the increase of the osmotic
potential, NaCl concentration and also varied
significantly with temperature treatments.
This result corroborates other studies showing
that osmotic stress primarily reduces rate
of germination rather than germination percentage.
It is assumed that germination rate
and the final seed germination decrease with
the decrease of the water movement into the
seeds during imbibitions. Salinity stress can
affect seed germination through osmotic
effects percentage (Murillo-Amandor et al.
2002).
ecologia mediterranea – Vol. 38 (2) – 2012
Effects of abiotic stress on the germination of Pennisetum dichotomum
Salt induced inhibition of seed germination
could be attributed to osmotic stress or to specific
ion toxicity (Kaya et al. 2005). Germination
percentage also significantly decreased
as the level of salinity of the medium
increased. Jamil et al. (2006, 2007) found that
the mean time to germination of almost all
vegetables species increased with the addition
of NaCl and this increase in was greater in
higher concentration as compared to low concentration.
The reduction in root and shoot
development may be due to toxic effects of
the NaCl used as well as unbalanced nutrient
uptake by the seedlings. High salinity may
inhibit root and shoot elongation due to slowing
down the water uptake by the plant may
be another reason for this decrease (Jamil et
al. 2007). The results of this study showed a
greater reduction of HL and RL in comparison
to germination phase with the increase of
the osmotic potential with NaCl. In addition,
this work suggested that cell division, which
is a post-germination phenomenon responsible
for seedling elongation and development,
is more sensitive to the NaCl compared to cell
expansion, which drives germination.
Conclusion
The germination and early seedling growth
stages of P. dichotomum, showed different
responses to water stress induced by NaCl.
However, early seedling growth was more
sensitive than germination to water stress
induced by salinity. Results also indicated that
seed germination of P. dichotomum is more
resistant than seedling growth to osmotic
potential indicating that the seeds of the
specie are efficient in osmotic adjustment face
to soluble salts.
References
Ajmal Khan A. & Gulzar S., 2003. Light, salinity, and
temperature effects on the seed germination of perennial
grasses. American. J. Bot. 90: 131-134.
Akhter R. & Arshad M., 2006. Pakistan. Arid rangelands
in the Cholistan Desert (Pakistan). Science et changements
planétaires 17(1): 210-217.
Alatar A.A., 2011. Effect of temperature and salinity on
germination of Achellea fragrantissima and Moringa
peregrina from Saudi Arabia. African. J. Biot. 10:
3393-3398.
Al-Khatee S.A., 2006. Effect of salinity and temperature
on germination, growth and ion relations of
21