Abstract
Bacterial mannitol-1-phosphate dehydrogenase (mtlD) is known for its tolerance to salinity.
Previous work on a number of transgenics having mtlD established the role of mannitol
accumulation in alleviating salt stress. Populus species are extensively planted for landscaping, biomass production, and maintenance of the global environment due to their rapid growth and
ease of reforestation. However, salt stress tremendously limits these trees’ survivability,
particularly within saline areas. The objective of this study was to use Agrobacterium tumefaciens harboring the mtlD gene to infect Populus nigra x P. tomentosa hybrids and produce salt-resistant transgenic plants using a callus organogenesis system. Our results show that all transformants presented an expected fragment of the mtlD transgene of 1149 bp. Significantly higher rates of
callus induction, shooting, and rooting in poplar explants were observed in an MS-cultured
medium containing 1 mgL-1 thidiazuron and 0.1 mgL-1 naphthaleneacetic acid compared to
other of combinations plant growth regulators. The optimal infection time for A. tumefaciens to
infect explants was 8 min, and 300 ppm of cefotaxime was the best concentration for eliminating
A. tumefaciens. Survival and rooting rates in transgenic plants under 50, 85, and 120 mM NaCl
were both significantly higher than in nontransgenic (NT) plants. In addition, transgenic poplar
plants grew faster than NT plants subjected to 120 mM NaCl, as revealed by better growth,
longer shoots, and greater plant heights.