A Preliminary Study On The Salinity Of Halophytes

Soil salinization is increasely serious in China, and it has negatively affected a large number of cultuvated land. The ustalization of biological methods can fundamentally improves salt-affectted soil, so the study of salt resistance mechanism of halophytes and breeding of new varieties of salt-resistant crops is particularly important. Limonium bicolor is a recrehalophyte with a strong salt tolerance and has a very important economy in the improvement and utalization of saline soil.Therefore,Limonium bicolor is used as a model recrehalophyte in salt resistance mechanism of halophytes. Suaeda salsa belongs to one of euhalophytes and has strong salt resistance.In view of the current research on the salt resistance mechanism of halophytes,most of the research on the aboveground part (shoot) . However, the response of the plant roots to salt stress is little known. In this paper,the mechanism of the root growth and movement of Limonium bicolor and Suaeda salsa under salt stress was investigated compared to Arabidopsis thaliana. The main results are as follows:1. NaCl, KCl and Na2SO4 were used to study halotropism of the roots of L.bicolor and the A. thaliana seedlings on the vertical MS medium.The results showed that the elongation of the root of L. bicolor was significantly promoted by different salt treatments, but the elongation of the root of A. thaliana was markedly inhibited.These results suggest that the recretohalophytes have positive halotropism in high salt environments and non-halophytes have negative halotropism in high salt environments.2. Comapred with control (0 mM NaCl) , root diameter, root fresh and dry weight, root activity and salt-related root elongation rate were increased firstly and then decreased with the increase of salt concentration under the treatment of 100,200 and 300 mM NaCl. Compared with the control, the root hair of L. bicolor was sparse,short and straight, and root hair length, quantity and density were significantly reduced. Under the treatment of 100, 200 and 300 mM NaCl, the root of L. bicolor showed different degrees of halotropism to the salt environment,the maximal value of RSA appeared at 200 mM NaCl. Compared to NaCl, the same concentration of KCl and Na2SO4 treatment led to a significant decrease of the above physiological indicators. These results indicate that Na+ is the main effective factor for the halotropism of L. bicolor, and Cl- is more conducive to the halotropism of Limonium bicolor than SO42-.3. Compared with isosmotic mannitol, 200 mM NaCl promoted the elongation and halotropism of L. bicolor roots, which indicated that ion effect such as Na+ was beneficial to halotropism of L. bicolor rather than osmosis.4. Comapred with control (0 mM NaCl) , the contents of K+ and Ca2+ in the elongated parts of L. bicolor roots were significantly decreased and the K+ and Ca2+contents significantly decrased under the treatment of 100, 200 and 300 mM NaCl,but the root elongation was markedly promoted. The results suggested that it is Na+and Cl- accumulation were beneficial to the growth of roots instead of the decrease of K+ and Ca2+. Compared with NaCl,KCl and Na2SO4 treatment significantly inhibited the growth of L. bicolor, indicating that Na+ was more beneficial than K+ to contribution of salt-induced root growth, and Cl- was more effect than SO42. In conclusion, Na+ is the pivotal factor to the root halotropism of L. bicolor.5. The content of auxin in L. bicolor was significantly increased by the treatment of NaCl,KCl and Na2SO4, and exogenous auxin synthesis inhibitor (Kyn)and auxin transport inhibitor (NPA) inhibited the halotropism of L. bicolor roots. It indicated that auxin plays an important role in the halotropism of halophytes.6. NaCl was used to study the general root responses of euhalophyte S. salsa and the A.thaliana seedlings in halotropism on the vertical MS medium.The results showed that the elongation of the root of Suaeda salsa was significantly promoted,and the elongation of the root of A. thaliana was inhibited. These results also indicate that the euhalophytes have positive halotropism in high salt environments,and non-halophytes have negative halotropism in high salt environments. Na+ is the pivotal factor to the root halotropism of L. bicolor. IAA participates the plant halotropism.