Overexpression of the Arginine Decarboxylase Gene Improves Tolerance to Salt Stress in <italic>Lotus tenuis</italic> Plants.

To analyse the putative effects of putrescine on the plant response to salinity, micropropagated <italic>Lotus tenuis</italic> plants from wild-type and transgenic lines harbouring the <italic>pRD29A::oat arginine decarboxylase</italic> (ADC, EC 4.1.1.19) construct were subjected to a gradual increase in salinity that was applied gradually by means of sodium chloride irrigation (from 0 to 0.3 mol L⁻¹) every 5 days up to the maximum concentration. At the end of the experiment, the transgenic lines were healthier than the wild-type plants and displayed a smaller reduction in shoot biomass and a slight increase in root growth in response to stress. The overexpression of <italic>ADC</italic> increased osmotic adjustment (5.8-fold) via the release of proline. The salinity treatment doubled the potassium uptake by roots from transgenic ADC stressed plants with a concomitant decrease in the accumulation of sodium, balancing the Na⁺/K⁺ ratio. Analysis of gene expression, enzymatic activities and hormone metabolism suggests a crosstalk between polyamines and abscisic acid in response to salinity via modulation of the abscisic acid biosynthesis-related enzyme 9-<italic>cis</italic>-epoxycarotenoid dioxygenase (EC 1.13.11.51) at the transcriptional level. [ABSTRACT FROM AUTHOR]