Effects of Combined Abiotic Stresses on Growth, Trace Element Accumulation, and Phytohormone Regulation in Two Halophytic Species

Salicylic acid (SA) plays a key role in plant disease resistance and hypersensitive cell death but is also implicated in hardening responses to abiotic stressors. Cadmium (Cd) exposure increased the free SA contents of barley (Hordeum vulgare) roots by a factor of about 2. Cultivation of dry barley caryopses presoaked in SA-containing solution for only 6 h or single transient addition of SA at a 0.5 mM concentration to the hydroponics solution partially protected the seedlings from Cd toxicity during the following growth period. Both SA treatments had little effect on growth in the absence of Cd, but increased root and shoot length and fresh and dry weight and inhibited lipid peroxidation in roots, as indicated by malondialdehyde contents, in the presence of Cd. To test whether this protection was due to up-regulation of antioxidant enzymes, activities and transcript levels of the H(2)O(2)-metabolizing enzymes such as catalase and ascorbate peroxidase were measured in control and SA-treated seedlings in the presence or absence of 25 microM Cd. Cd stress increased the activity of these enzymes by variable extent. SA treatments strongly or completely suppressed the Cd-induced up-regulation of the antioxidant enzyme activities. Slices from leaves treated with SA for 24 h also showed an increased level of tolerance toward high Cd concentrations as indicated by chlorophyll a fluorescence parameters. The results support the conclusion that SA alleviates Cd toxicity not at the level of antioxidant defense but by affecting other mechanisms of Cd detoxification.

A rapid multiresidue method to quantify three different classes of plant hormones has been developed. The reduced concentrations of these metabolites in real samples with complex matrixes require sensitive techniques for their quantification in small amounts of plant tissue. The method described combines high-performance liquid chromatography with electrospray ionization tandem mass spectrometry. Deuterium-labeled standards were added prior to sample extraction to achieve an accurate quantification of abscisic acid, indole-3-acetic acid, and jasmonic acid in a single run. A simple method of extraction and purification involving only centrifugation, a partition against diethyl ether, and filtration was developed and the analytical method validated in four different plant tissues, citrus leaves, papaya roots, barley seedlings, and barley immature embryos. This method represents a clear advantage because it extensively reduces sample preparation and total time for routine analysis of phytohormones in real plant samples.