Abstract
The effects of cold stratification and gibberellic acid (GA3) on dormancy breaking for seeds of the annual halophyte species Juncus ranarius were tested. Germination percentage and recovery responses of salt stressed seeds were also tested. Freshly collected seeds germinated slowly under all incubation conditions. Thus, the seeds of J. ranarius have physiological dormancy, e.g. they are water permeable, have a fully developed embryo and require cold stratification to come out of dormancy. Furthermore, promotion of germination by GA3 after-ripening in dry storage also indicated that these seeds have non-deep physiological dormancy. In general, the higher the GA3 concentration, the more germination occurred within the studied range. Juncus ranarius demonstrated a germination preference for light. The highest germination percentage and rate of germination were recorded under constant light conditions at 22 °C after 24 weeks of cold stratification. In saline solutions, the highest percentage of germination was obtained at 25 mM L-1 NaCl, and further increase in salinity resulted in a gradual decrease in germination. However, ungerminated seeds were not damaged by salt, showing a high level of recovery. The greater the reduction in salinity, the better the germination rate became. It was concluded that dormancy could be completely broken by cold stratification, indicating spring germination. Juncus ranarius can grow well at lower NaCl concentrations under constant light conditions at 22 °C.
Highlights
Halophytes, plants capable of growing and reproducing under saline conditions, vary in their upper limits of salt tolerance, while an increase in salinity usually delays seed germination (Gul et al, 2013; Khan and Ungar, 1996; Khan and Ungar, 1998; Ungar and Riehl, 1980; Ungar, 1995); other effects include reduction of the percentage of germinating seeds, delay in the initiation of the germination process and seeds’ dormancy
The seeds of halophytes germinate only when soil salinity levels are reduced, condition which usually occurs in saline environments in spring or during a season with high precipitation
Boscaiu et al (2011) demonstrated that in two related species of Juncus, J. acutus and J. maritimus, germination was optimal under non-saline conditions, while it was reduced by about 50% in the presence of 1.2% (200 mM L-1) NaCl, and completely inhibited by NaCl concentrations above 1.7% (300 mM L-1)
Summary
Halophytes, plants capable of growing and reproducing under saline conditions, vary in their upper limits of salt tolerance, while an increase in salinity usually delays seed germination (Gul et al, 2013; Khan and Ungar, 1996; Khan and Ungar, 1998; Ungar and Riehl, 1980; Ungar, 1995); other effects include reduction of the percentage of germinating seeds, delay in the initiation of the germination process and seeds’ dormancy. The seeds of halophytes under natural conditions are subjected to saline stress, which is dominated usually by NaCl. The effect of salinity on seed germination can be attributed to hyperosmotic stress resulting from more negative soil water potential and/or a specific ion toxicity (sodium, chloride), depending on a plant species (Huang and Redmann, 1995; Petruzzelli et al, 1992; Poljakoff-Mayber et al, 1994; Ungar and Hogan, 1970; Poljakoff-Mayber et al, 1994; Verslues et al, 2006; Zekri, 1993). The highest salinity concentration at which a seed was reported to germinate was 1.7 M NaCl (Khan and Gul, 2006)
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