Cotyledon Numbers of Two Peganum Species (Peganaceae) in Mongolia
Institute of Botany, Mongolian Academy of Sciences, Ulaanbaatar 210351, Mongolia
Most seedlings of Peganum harmala and P. nigellastrum have two cotyledons, but up to 10% of all seedlings of P. harmala have to three cotyledons, and up to 1.7% has four cotyledons. Up to 5.4% on P. nigellastrum have only three cotyledons. Frequency of three cotyledonous seedlings among these two species was signifi cantly different. The present results report three cotyledonous seedlings, as well as four cotyledonous seedlings in the family Peganaceae, in addition to two cotyledonous seedlings. On both species, the frequency of three cotyledonous seedlings was increased with increased annual precipitation and decreased air temperature, and in localities, which isolated from main distribution range. The frequency of three cotyledonous seedlings of P. harmala increased with increasing soil alkalization, but that of P. nigellastrum increased with decreasing alkalization.
Keyword: Peganum harmala,Peganum nigellastrum,cotyledon,seedlings
Most angiosperms are mono- or dicotyledonous, but three cotyledons have also been reported for plants of over 15 families (Conner & Agrawal, 2005). The number of cotyledons was unclear for species of Peganaceae van Tieghem. Previous studies supposed that cotyledon number range is related with hormonal asymmetric distribution (Liu et al., 1993; Mayer et al., 1993; Hadfi et al., 1998; Al-Hammadi et al., 2003; Orlova et al., 2006; Swarup et al., 2004), some kind of selection (Taylor & Mundell, 1999), lack of genetic variation (Conner & Agrawal, 2005), and maternal effects (Al-Hammadi et al., 2003). The purpose of this study is to seek whether three cotyledons occur in the family Peganaceae and to determine whether cotyledon number range is related with loss of habitat.
Material and Methods
Climatic data is given according to the report of Namkhaijantsan (2009). Mean air temperature in July was fl uctuated between 20 and 25oC in the Dzungaria, Valley of Lakes, Gobi Altai and north of East Gobi regions; between 10 and 15oC in the Mongol-Dahuria region, and more than 25oC in the Trans-Altai Gobi and East Gobi regions. Annual precipitation was 100 -150 mm in Dzungaria, East Gobi and Valley of Lakes; 150-200 mm in Gobi Altai; 50-100 mm in west of East Gobi region; less than 50 mm in Trans-Altai Gobi, and 300-400 mm in Mongol-Dahuria. Soil pH is one of main factors for plant metabolism (Fink, 1976), and it was 7.4-8.0 (slight alkalic) in Valley of Lakes, Gobi Altai and east of East Gobi; 8.1-9.0 (strong alkalic) in Dzungaria, Trans-Altai Gobi, west of East Gobi and Mongol- Dahuria (Batkhishig, 2009). The seed collection at the Institute of Botany, Mongolian Academy of Sciences was used for seed germination and seedling morphology. In total, 13 seed samples were examined (Table 1), collected between 1983-2007, from above-mentioned regions.
Mongol-Dahuria and Dzungaria belong to the province Western Siberia and Dzungaria of Mts. Tien Shan, respectively, and Valley of Lakes, East Gobi, Gobi Altai, Trans-Altai Gobi belong to the province Mongolia, according to botanygeographic divisions (Grubov, 1963; Takhtajan, 1978). When plants shed seeds, we harvested capsules then dried them in paper bags. The seeds were sampled randomly in the population. Weight of thousand seeds was measured with 10 repetitions using an analytic scale - Shimadzu AY220 (d-0.1 mg). Seed germination was determined at 25±1oC for 10 days in the seed germinator, without dormancy breaking treatments using Petri dishes and moist blotter with distilled water. Frequency of three and four cotyledons has counted on 1000 seedlings in each seed sample. Main distribution range of P. harmala is in the Dzungaria, Mts. Tien Shan (Central Asia). This species is very rarely distributed in Mongolia. The main distribution range of P.nigellastrim is in Mongolia, but this is rarely distributed in Siberia. Frequency of cotyledon number between species were compared by Mann-Whitney U-test (Avery, 2004), and between cotyledon number range and precipitation, air temperature, soil pH by effect test, using statistic software JMP 4.0.
Most seedlings of P. harmala and P. nigellastrum being with two cotyledons, but 10% of all seedlings of P. harmala bear up to three cotyledons, and 1.7% has four cotyledons (Fig. 1A). Up to 5.4% on P. nigellastrum have only three cotyledons (Fig. 1B).
Frequency of three cotyledonous seedlings between two species was signifi cantly different (U=33, Z=2.31, P=0.02). Frequency of three cotyledonous seedlings in P. harmala was varied between 2.7-3.4% when annual precipitation was less than 100 mm, and mean of air temperature in July was more than 25oC, but that was 4.7-10.2% when annual precipitation is more than 100 mm and mean of air temperature is less than 25oC. This frequency in P. nigellastrum was 0.9-1.4% when annual precipitation is less than 200 mm and mean of air temperature in July is more than 20oC while, the above value was 5.4% when annual precipitation was more than 200 mm and mean of air temperature was less than 20oC. The frequency of three cotyledonous seedlings of P. harmala was more than 3.4% when soil pH is more than 8.1, whereas that was less than 3.4% when soil pH is less than 8.1. This frequency of P. nigellastrum has opposite relation (Fig. 2).
Three cotyledonous seedlings on P. harmala were occurred for 3.4-10.2% of all seedlings in East Gobi and Dzungaria, and 2.7% in Trans- Altai Gobi. The three cotyledonous seedlings in P. nigellastrum were 0.3-1.4% in East Gobi, Gobi Altai and Valley of Lakes, but 5.4% in Mongol- Dahurian region (Fig 3a, b).
The three cotyledonous seedlings have been found before this study in many families such as Aceraceae, Juglandaceae, Rubiaceae, Pedaliaceae, Protaceae, Ranunculaceae, Papaveraceae, Brassicaceae, Fabaceae, Geraniaceae, Chenopodiaceae, Onagraceae, Solanaceae, Scrophulariaceae, Salicaceae and Euphorbiaceae (Gates, 1910; Went, 1944; Harrison, 1964; Dessureaux, 1967; Magsar & Tsagaanmaam, 1984; Rajora & Zsuffa, 1986; Taylor & Mundell, 1999; Graz, 2001; Conner & Agrawal, 2005; Chandler, 2008). The present fi ndings report not only three cotyledonous, but also four cotyledonous seedlings in the family Peganaceae, in addition to two cotyledonous seedlings. The other authors reported that 5-69% and 19% of all seedlings might have three and four cotyledons, respectively based on selection experiments (Taylor & Mundell, 1999; Conner & Agrawal, 2005). Naturally, 0.5-5% of all seedlings bear more than two cotyledons (Magsar & Tsagaanmaam, 1984; Conner & Agrawal, 2005). Our results indicate that three and four cotyledonous seedlings can be found in more than 0.5% of all seedlings. Cotyledon number range of P. harmala that is very rare in Mongolia was higher than that of common P. nigellastrum (U=34, Z=2.45, P=0.01), and the cotyledon number range of P. harmala was larger than that of P. nigellastrum. This might indicate that P.nigellastrum better adapted in Mongolia than P. harmala. Both species can be considered as adapted well in dry condition because of frequency of three cotyledonous seedlings on both species increased with increasing annual precipitation (effect test, DF=1; SS=178; F=9.9; P<0.0344) and decreasing air temperature (effect test, DF=1; SS=198; F=11; P<0.0293). The frequency of three cotyledonous seedlings of P. harmala increased with raise of soil alkalization, but that of P. nigellastrum increased with decreased alkalization. This means that P. harmala adapted in slight alkalic soil, but the other species is in strong alkalic soil. On the other hand, embryogenesis of P. harmala altered by increasing soil alkalization, whereas that of other species altered by decreasing alkalization. Frequency of three cotyledonous seedlings of P. harmala was higher in the regions Dzungaria and Trans-Altai Gobi than in the East Gobi, while that of P. nigellastrum was higher in the Mongol- Dahurian region than other regions. Because of localities that are high frequency of three cotyledonous seedlings for both species isolated from main distribution range. Al-Hammadi et al. (2003) reported that the earliest defects were observed at the transition from the globular to the heart stage of embryogenesis with the formation of multiple cotyledons. In this case, cotyledon number of P. harmala and P. nigellastrum can be related with embryogenesis. Embryogenesis of P. harmala altered in the wet and strong alkali condition while that of P. nigellastrum in the wet and slight alkali condition. Occurrence of three and four cotyledons show that embryogenesis of P. harmala altered stronger than of P. nigellastrum. The embryogenesis of P. harmala in the region East Gobi altered stronger than in other regions, but that of P. nigellastrum in the Mongol-Dahurian region was stronger than in other regions. The results indicate that the cotyledon number range of P. harmala and P. nigellastrum is related with habitat loss, which is soil moisture gradient and soil alkalization.
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