ABSTRACT
Objective: To break the seed dormancy and improve the germination rate of the Nirtaria sibirica seeds. Methods: N. sibirica seeds were treated with soaking in warm water, storing with moisture sand, and immersing seed in H2SO4 (98%) and gibberellic acid (GA), then the germination rate, germination vigor, and germination peak period of the seeds were determined. Results: The germination rate and germination vigor were 30% and 10% under soaking in warm water. The seeds began to germinate on the day 7 and reached the germination peak on the day 10.The germination rate and germination vigor were 55.5% and 26.5% under storing with moisture sand for 37 d. The seeds began to germinate on the day 2 and reached the germination peak on the day 10.The germination rate and germination vigor were 86.8% and 60.3% under storing with moisture sand for 95 d. The seeds began to germinate on the day 2 and reached the germination peak on the day 7.The germination rate and germination vigor were both 90.0% under being treated with 98% H2SO4 for 2 h. The seeds began to germinate on the day 1 and reached the germination peak on the day 4.Seeds after being treated with 98% H2SO4 for 2 h were sowed on the dark medium of MS + 0.5 g/mL BA + 0.5 g/mL GA, and the germination rate and germination vigor both reached to 98.1%. The seeds began to germinate on the day 1 and reached the germination peak on the day 4. Conclusion: The dormancy of N. sibirica seeds is caused by hard seed vessels. The best way of breaking the seed dormancy is first treated with 98% H2SO4 for 2 h and then cultured in the dark medium of MS + 0.5 g/mL BA + 0.5 g/mL GA, which could effectively break the dormancy of hard seeds and reach a high germination rate.
ABSTRACT
The United Nations Environment Program estimates that approximately 20% of agricultural land and 50% of cropland in the world is salt-stressed. The gene NHX (Na+/H+ exchanger) encodes functional protein that catalyzes the countertransport of Na+ and H+ across membranes and may play an important role in plant salt tolerance. To clone the NHX from the wild plant Populus euphratica collected in Tarim basin and Xinjiang Wujiaqu district into a T-vector, designed primer was used to amplify 1kb NHX cDNA fragment with RT-PCR. Total RNA was extracted from Populus euphratica tissue (plant tissue was collected from Tarim basin and Xinjiang Wujiaqu district and stored in liquid nitrogen) according to the Plant RNA Mini Kits of Omega. First cDNAs were synthesized from 1 microg total RNA of Populus euphratica seedling. A pair of primers were used to perform RT-PCR. The amplified DNA fragment was purified and cloned into pMD18-T vector. However, 1kb and 2.3kb fragment were obtained from Tarim basin and Xinjiang Wujiaqu district and named as PtNHX and PwNHX, respectively. Sequence analysis reveals that the cloned PtNHX fragment of Populus euphratica contains partial NHX coding region with 98%, 86%, 84% and 80% identity comparing with Atriplex gemelini, Suaeda maritima, Arabidopsis thaliana and Oryza sativa, respectively. This analysis suggests that NHX gene would be highly conserved in terms of evolution in plant; and it also suggests that the NHX gene of Populus euphratica also would have the similarity with that of Arabidopsis. It may be of great importance in improvement of the plant salt tolerance and breed of crop. At the same time, sequence analysis shows that PwNHX gene includes a coding region about 1350bp with 99% identity comparing with transposon Tn10 IS10-left transposase of Shigella flexneri. On the one hand, the NHX gene may lose its function because it was inserted a fragment in coding region. On the other hand, its product may play a important role in salt tolerance. Populus grow in saline soil. It speculates that it may have other salt tolerance mechanism in Populus. The transposon can be used as transposon tagging to clone other genes and it will help us to understand farther the salt tolerance mechanism.