High temperature stress and exogenous applications of methyl jasmonate on peaches

High temperature shocks has been useful in some peach (Prunus persica) cultivars to prevent chilling injury, although undesirable side effects have been determined. Jasmonates play a role in signal transduction cascades, on the defense mechanism that plants have developed against biotic and abiotic stresses. Jasmonic acid (JA) and Methyl Jasmonate (MJ) show similar physiological responses. In this way, it would be expected that exogenous application of jasmonates may elicit a response similar to stress, to defend against stress, but without the undesirable effects or damage to fruits that stress may cause. The aim of this experiment was to compare thermal stress (40 degrees C by 46 h) against different exogenous applications of MJ. Fruits of 'Dixiland' were immersed into solutions of 0, 10, 100 and 1000 mu M by 30 s. Ethylene production was analyzed after the treatments every day up to ten days, and activities of Polygalacturonase (PG) an Pectinesterase (PE) were evaluated on days 0, 3 and 6 after treatments. Heat treated fruits and those treated with the highest concentration of MJ had a similar pattern in ethylene evolution, while on the other hand control fruits and those treated with 10 and 100 mu M showed lower production of ethylene. This results may be an indication that, at least, some effects produced by heat treatments may be similarly induced by the external application of MJ. PE activity of fruits treated with MJ was lower than control and heat treated fruits only after 6 days since the end of treatments. There were no significant difference in PE activity among treatments by the end of treatments and after 3 days at 20 degrees C. PG activity of MJ 1000 increased continuously from the end of treatment up to day 6 as compared to heat-treated and control fruit.