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