Physiological Stress caused by Salinity in Cordyline fruticosa and Its Indicators

Abstract

Crop plants are usually nonhalophytes that tolerate only moderate saline concentrations; under salinity, they accumulate salt in their aboveground organs and, to a smaller extent, in roots. Enhanced synthesis of determined secondary metabolites (such as proline, phenolics, or malondyaldehide) under stressful conditions is believed to protect the cellular structures from oxidative damage, in addition to the osmotic advantage for the plants. The aim of this work is to study the influence of the fertigation water salinity on osmoprotectant content in Cordyline fruticosa var. ‘Red Edge.’ Four nutrient solutions with different electrical conductivity levels were applied: EC1.5 (1.5 dS m−1), EC2.5 (2.5 dS m−1), EC3.5 (3.5 dS m−1), and EC4.5 (4.5 dS m−1), obtained by the addition of different quantities of sodium chloride (NaCl) to a basic nutrient solution (EC 1.5 dS m−1), followed by stirring to dissolve the salt and make the solution homogeneous. The results show that malondialdehyde (MDA) content is not a good indicator of plant stress, as levels in EC1.5 and EC4.5 are similar, but flavonoids, phenols and sugars contents are more useful indicators, because the highest values in leaves are found with the more saline treatment. Proline plays an osmoregulatory role, increasing in roots when NaCl concentration in the nutrient solution is too high but also when it is too low.