Overexpression of the Arginine Decarboxylase Gene Improves Tolerance to Salt Stress in Lotus tenuis Plants

To analyse the putative effects of putrescine on the plant response to salinity, micropropagated Lotus tenuis plants from wild-type and transgenic lines harbouring the pRD29A::oat arginine decarboxylase (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 ADC 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- cis -epoxycarotenoid dioxygenase (EC 1.13.11.51) at the transcriptional level.