Responses of lipoxygenase, jasmonic acid, and salicylic acid to temperature and exogenous phytohormone treatments in Gracilariopsis lemaneiformis (Rhodophyta)

Jasmonates (jasmonic acid (JA) and methyl jasmonate (MJ)) and salicylic acid (SA) play roles in the growth and developmental processes of plants and the defense response against adverse stresses as phytohormone signals. To investigate their roles in algae, we analyzed the sequences of two genes encoding lipoxygenase (LOX) and their expression profiles in response to temperature and phytohormone treatments in the macroalga Gracilariopsis lemaneiformis (Rhodophyta). The two lox sequences from Gp. lemaneiformis (Gllox1 and Gllox2) shared only 23.90% identity. The following results were observed: (1) high temperature (33 degrees C) strongly stimulated Gllox2 mRNA level, LOX activity, and endogenous JA and SA contents; (2) exogenous MJ promoted Gllox2 expression (4.91-fold at 6 h), LOX activity (2.44-fold at 6 h), and JA level at normal temperature (23 degrees C); however, it only slightly increased Gllox2 expression and internal JA content and inhibited LOX activity at 33 degrees C; (3) similarly, SA induced Gllox2 expression (2.32-fold at 12 h), LOX activity (approximately 2.00-fold at 6 and 12 h) and SA level at 23 degrees C, but it mainly decreased these parameters at 33 degrees C; and (4) the addition of MJ had either no effect or an inhibitory effect on endogenous SA content, and analogous effects of exogenous SA on the endogenous JA content were observed at both temperatures. From these results we conclude that lipoxygenase positively participated in the responses to high temperature and exogenous MJ or SA stimuli, and meanwhile, exogenous MJ or SA exerted a promoting effect on its corresponding endogenous phytohormone accumulation.