High lithium tolerance of Apocynum venetum seeds during germination.

Identification and use of lithium (Li) accumulator plants is a promising strategy to remediate Li-contaminated soil. Apocynum venetum is reported as a Li accumulator. However, its tolerance to Li salt during germination is still unknown. The primary aim of this study was to investigate the effects of two Li salts on seed germination of A. venetum. At the same concentrations, germination percentages in LiCl solution were higher than that in Li2CO3 solution. At 25 °C, seeds germinated to 4-90% at 0-400 mmol L-1 LiCl and 3-91% at 0-150 mmol L-1 Li2CO3. Low concentration (0-50 mmol L-1) of LiCl did not significantly affect germination percentage. The simulated critical value (when germination percentage is 50%) in LiCl solution is 196 mmol L-1, and 36 mmol L-1 for Li2CO3. Activity of α-amylase, contents of MDA, soluble sugar, and proline were dramatically affected by Li salts, especially at medium and late germination stages. When compared with control, α-amylase activity of seeds under 25 mmol L-1 LiCl and 10 mmol L-1 Li2CO3 did not show significant difference. Germination percentage and index, radicle length, and physiological parameters indicate A. venetum seeds are highly tolerant to Li salts during germination, especially LiCl.

Molecular cloning and characterization of a salinity stress-induced gene encoding DEAD-box helicase from the halophyte Apocynum venetum.

The genes encoding DEAD-box helicases play a key role in various abiotic stresses, including temperature, light, oxygen, and salt stress. A salt-responsive gene, designated AvDH1, was isolated from the halophyte dogbane (Apocynum venetum) by using suppression subtractive hybridization and RACE (rapid amplification of cDNA ends) PCR. The deduced amino acid sequence has nine conserved helicase motifs of the DEAD-box protein family. The AvDH1 gene is present as a single copy in the dogbane genome. This gene is expressed in response to NaCl and not polyethlene glycol (PEG) nor abscisic acid, and its expression increases with time. The transcription of AvDH1 is also induced by low temperature (4 degrees C), but its accumulation first increases then decreases with time. The purified recombinant protein contains ATP-dependent DNA helicase activity, ATP-independent RNA helicase activity, and DNA- or RNA-dependent ATPase activity. The ATPase activity of AvDH1 is stimulated more by single-stranded DNA than by double-stranded DNA or RNA. These results suggested that AvDH1 belonging to the DEAD-box helicase family is induced by salinity, functions as a typical helicase to unwind DNA and RNA, and may play an important role in salinity tolerance.