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Polyamines (PAs), especially spermidine and spermine (which are involved in various types of abiotic stress tolerance), have been reported in many plant species. In this study, we identified 14 put...

Polyamines play essential roles in plant development and various stress responses. In this study, one of the cotton S-adenosylmethionine decarboxylase (SAMDC) genes, GhSAMDC1, was constructed in the pGWB17 vector and overexpressed in tobacco. Leaf area and plant height increased 25.9–36.6% and 15.0–27.0%, respectively, compared to the wild type, and flowering time was advanced by 5 days in transgenic tobacco lines. Polyamine and gene expression analyses demonstrated that a decrease in spermidine and an increase in total polyamines and spermine might be regulated by NtSPDS4 and NtSPMS in transgenic plants. Furthermore, exogenous spermidine, spermine and spermidine synthesis inhibitor dicyclohexylamine were used for complementary tests, which resulted in small leaves and dwarf plants, big leaves and early flowering, and big leaves and dwarf plants, respectively. These results indicate that spermidine and spermine are mainly involved in the vegetative growth and early flowering stages, respectively. Expression analysis of flowering-related genes suggested that NtSOC1, NtAP1, NtNFL1 and NtFT4 were upregulated in transgenic plants. In conclusion, ectopic GhSAMDC1 is involved in the conversion of spermidine to spermine, resulting in rapid vegetative growth and early flowering in tobacco, which could be applied to genetically improve plants.

Two protocols of plant regeneration for cotton were adopted in this study, namely, 2, 4-D and kinetin hormone combination and IBA and kinetin hormone combination. Twenty-eight embryogenic cell lines via somatic embryogenesis and 67 regenerated plants from these embryogenic calli were selected and used for random amplified polymorphic DNA (RAPD), simple sequence repeat (SSR), chromosomal number counting, and flow cytometric analysis. The roles of RAPD and SSR markers in detecting somaclonal variation of cotton (Gossypium hirsutum L.) were evaluated. Two cluster analyses were performed to express, in the form of dendrograms, the relationships among the hormone combinations and the genetic variability. Both DNA-based techniques were able to amplify all of the cell clones and regenerated plantlets genomes and relative higher genetic variation could be detected in the culture type with 2, 4-D and kinetin hormone combination. The result suggested that 2, 4-D and kinetin hormone combination could induce relative high somaclonal variation and RAPD and SSR markers are useful in detecting somaclonal variation of regenerated cotton plants via somatic embryogenesis. Chromosome number counting and flow cytometry analysis revealed that the number of chromosomes and ploidy levels were nearly stable in all regenerated plants except two regenerated plantlets (lost 4 and 5 chromosomes, respectively) which meant that cytological changes were not correlated with the frequency of RAPD and SSR polymorphisms. This result also might mean that the cell lines with variation of chromosome numbers were difficult to regenerate plants.

Low efficiency of somatic embryogenesis and asynchronous embryo development results in a lot of difficulties to physiological, biochemical, and molecular biological studies of the embryogenesis processes in cotton ( Gossypium hirsutum L.). A simple and efficient method was developed to improve somatic embryogenesis frequency and synchronous development of mass somatic embryos from cultured cells of the cotton cultivar Coker 201. The embryonic calli obtained after several rounds of subculture were scattered in a liquid medium by shaking for 2 d and then resuspended in the same liquid medium after discarding the larger callus aggregates over a 30 mesh-size-sieve. The suspensions cultured for 14 d were filtered through a 50 mesh-size-sieve and the aggregates over the sieve were incubated for 21 d onto the surface of a Whatman filter paper that was placed on the solid medium containing 2.46 μmol L −1 indole-3-butyric acid (IBA) and 0.70 μmol L −1 kinetin. The amount of somatic embryos obtained by this system was 15.5-fold and 3-fold higher than that of suspension culture and solid culture without filter papers, respectively. About 70.2% for globular, 52.3% for torpedo-shaped, and 73.0% for cotyledonary embryos were obtained during the culture. The method combining suspension culture and solid culture (with filter paper) proved to be efficient for synchrony of somatic embryogenesis and mass embryo development.