Methyl jasmonate enhances salt tolerance of almond rootstocks by regulating endogenous phytohormones, antioxidant activity and gas-exchange.

The effects of methyl jasmonate (MeJA) foliar application (0, 0.025, 0.050 and 0.075 mM) on the growth and physiological responses of two almond rootstocks (GF677 and bitter almond) exposed to various concentrations of NaCl in irrigation water (0, 50, 100 and 150 mM) were evaluated. 60 days after salt stress exposure, the mitotic index of root apical meristem cells as well as shoot and root growth, activity of main antioxidant enzymes, gas exchange parameters and contents of cytokinins and ABA were determined. Salt stress decreased the plants' growth, particularly at higher levels. Application of MeJA in optimal concentrations of 0.025 to 0.05 mM alleviated the adverse effect of salt stress by increasing the photosynthetic rate, activity of antioxidant enzymes (APX, SOD and POX), root and shoot dry mass, as well as cell membrane integrity. Furthermore, MeJA application brought about a two-fold increase in the concentration of leaf cytokinins. This reposition of cytokinins was due to restriction of both the activity of cytokinin oxidase and gene expression of this enzyme. The MeJA mitigating effect on the growth of salt-stressed plants could be a result of the inhibition of cytokinin decline under salt stress. The results revealed the effective impact of endogenous cytokinins in protective and growth improvement effects of MeJA on almond rootstocks under salt stress.

Quantifying Residues from Postharvest Propylene Oxide Fumigation of Almonds and Walnuts.

A novel analytical approach involving solvent extraction with methyl tert-butyl ether (MTBE) followed by GC was developed to quantify residues that result from the postharvest fumigation of almonds and walnuts with propylene oxide (PPO). Verification and quantification of PPO, propylene chlorohydrin (PCH) [1-chloropropan-2-ol (PCH-1) and 2-chloropropan-1-ol (PCH-2)], and propylene bromohydrin (PBH) [1-bromopropan-2-ol (PBH-1) and 2-bromopropan-1-ol (PBH-2)] was accomplished with a combination of electron impact ionization MS (EIMS), negative ion chemical ionization MS (NCIMS), and electron capture detection (ECD). Respective GC/EIMS LOQs for PPO, PCH-1, PCH-2, PBH-1, and PBH-2 in MTBE extracts were [ppm (µg/g nut)] 0.9, 2.1, 2.5, 30.3, and 50.0 for almonds and 0.8, 2.2, 2.02, 41.6, and 45.7 for walnuts. Relative to GC/EIMS, GC-ECD analyses resulted in no detection of PPO, similar detector responses for PCH isomers, and >100-fold more sensitive detection of PBH isomers. NCIMS did not enhance detection of PBH isomers relative to EIMS and was, respectively, approximately 20-, 5-, and 10-fold less sensitive to PPO, PCH-1, and PCH-2. MTBE extraction efficiencies were >90% for all analytes. The 10-fold concentration of MTBE extracts yielded recoveries of 85-105% for the PBH isomers and a concomitant decrease in LODs and LOQs across detector types. The recoveries of PCH isomers and PPO in the MTBE concentrate were relatively low (approximately 50 to 75%), which confound improvements in LODs and LOQs regardless of detector type.