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Soil salinity constitutes a major factor limiting crop production because it affects plant growth and survival.Quite a lot of attention has been paid to the salt tolerance of model plants (such as Arabidopsis thaliana,Oryza sativa, Medicago truncatula gaertn), most of which are salt sensitive.To comprehensively understand the salt tolerance mechanism in higher plants, and then improve salt tolerance in plants, it is necessary to enhance study with the halophytes, which can survive in saline environments, and may evolve multiple strategies in salt tolerance. Chenopodium album (Chenopodiaceae) is a plant species widely distributed in extremely harsh environments, such as the semi-arid and light-saline environments of Xinjiang province, China. Chenopodium album produces two distinct lots of seeds (black and brown), which exhibit different adaptabilities to heterogeous environments. Besides, C. album is also a salt-resistant species. So it is thought to be a promising plant species with capacity for commercial production in salinized soils.Based on above points, the present study firstly was designed to investigate some aspects of the heteromorphic seeds in C. album, including germination, dormancy mechanism, variation of seed heteromorphism among populations, and the possible factors responsible for such variation. The mechanism how seed heteromorphism was employed by C.album to adapt to the highly heterogeneous environments in semi-arid environments was elucidated. Secondly, effects of three salts (NaCl, KCl, and CaCl2) on germination and seedling survival of dimorphic seeds of C. album was investigated. Thirdly, having probed the relationship between antioxidant system and salt tolerance in C.album after long-term NaCl and KCl stress. Fourthly, performing investigation on whether the.plants derived form different seed types exhibit differential salt tolerance. The key results are as follows:(1) Heteromorphic seeds of C. album exhibited difference in seed morphology, germination, dormancy behaviour, and salt tolerance. Compared with black seeds, brown seeds with a thinner seed coat, larger seed size, are non-dormant, and germinated to higher percentage in higher concentrations of salt solutions. Furthermore, seed heteromorphism was confirmed to vary among populations, and such variation could be attributed to, at least partially, the salinity in environments.(2) NaCl and KCl stress exerted a similar influence on the seed germination and seedling survival in C. album.Addition of low concentration of calcium could alleviate the germination inhibition by high salinity, and such alleviatory effect was greater in brown seeds than in black seeds.(3) Plants of C. album could tolerate 300 mmol L-1 NaCl stress, but not 300 mmol L-1 KCl stress. The salt tolerance of C. album was due to, at least in part, its high antioxidant capacity, in which both of enzymatic and non-enzymatic antioxidants played a role.(4) Plants from different seed types showed different growth characters under salt stress, and such difference seemed not to be attributed to the variation of antioxidant system.
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