Hormone profiling and heat-induced tolerance to cold stress in citrus fruit

Abstract

The involvement of jasmonic acid (JA), different JA-related metabolites, salicylic acid (SA), indole-3-acetic acid (IAA) and abscisic acid (ABA) in the heat-induced cross-adaptation to chilling has been investigated in citrus fruit. The effects of heating ‘Fortune’ mandarins at 37 ºC, and storing them at a chilling temperature (2 ºC) after being exposed, or not, to a heat-conditioning treatment (3 d at 37 ºC) on the levels of these signalling molecules were examined. Jasmonate metabolism activation at 37 ºC was followed by that of SA, and then by a rise in IAA and a drop in ABA. Storage at 2 ºC transiently increased the contents of IAA, of the JA precursor, cis-(+)− 12-oxo-phytodienoic acid (OPDA), and of the JA-derivatives jasmonoyl-isoleucine (JAIle) and methyl jasmonate (MeJA), and decreased ABA in the non-conditioned fruit. The results also indicated that fruit were protected from developing chilling symptoms by virtue of the heat-conditioning treatment having higher JAIle levels than the non-conditioned fruit for very long cold storage periods, while the heat-induced rises in SA, OPDA and MeJA noted in the cold-stored fruit were transient.