Increased salt and drought tolerance by D-ononitol production in transgenic Nicotiana tabacum L.

Abstract

A cDNA encoding myo-inositol O-methyltransferase (IMT1) has been transferred into Nicotiana tabacum cultivar SR1. During drought and salt stress, transformants (15A) accumulated the methylated inositol D-ononitol in amounts exceeding 35 μmol g-1 fresh weight in 15A, photosynthetic CO2 fixation was inhibited less during salt stress and drought, and the plants recovered faster than wild type. One day after rewatering drought-stressed plants, 15A photosynthesis had recovered 75% versus 57% recovery with cultivar SR1 plants. After 2.5 weeks of 250 mM NaCl in hydroponic solution, 15A fixed 4.9 ± 1.4 μmol CO2 m-2 s-1, whereas SR1 fixed 2.5 ± 0.6 μmol CO2 m-2 s-1· myo-Inositol, the substrate for IMT1, increases in tobacco under stress. Preconditioning of 15A plants in 50 mM NaCl increased D-ononitol amounts and resulted in increased protection when the plants were stressed subsequently with 150 mM NaCl. Pro, Suc, Fru, and Glc showed substantial diurnal fluctuations in amounts, but D-ononitol did not. Plant transformation resulting in stress-inducible, stable solute accumulation appears to provide better protection under drought and salt-stress conditions than strategies using osmotic adjustment by metabolites that are constitutively present.