Signaling molecules and cell death in Melissa officinalis plants exposed to ozone

Abstract

The study focuses on the interaction between reactive oxygen species and hormones that regulate the programmed cell death in plants of Melissa officinalis exposed to ozone. Interaction between hormone and redox signaling pathways has been investigated in ozone-stressed (200 ppb, 5 h) lemon balm to verify if the response resembles the biotic defense reactions. In comparison to controls, plants exhibited foliar injury and the cell death was induced by (1) biphasic production of hydrogen peroxide and superoxide radical; (2) hormonal regulation of ozone-induced lesion formation with a significant production of ethylene, salicylic, jasmonic and abscisic acid; (3) ozone degradation to reactive oxygen species and their detoxification by some enzymatic (such as superoxide dismutase) and non-enzymatic antioxidant systems (such as ascorbic acid, glutathione and carotenoids), that worked in cooperation without providing a defense against free radicals (such as confirmed by the modification of the antioxidant properties of leaf tissue). This integrated view showed that reactive oxygen species interact with hormonal signaling pathway regulating cell death and the sensitivity of lemon balm to ozone.

Involvement of Phytohormones in Plant Responses to Ozone

“…riken.jp) on ABA content despite its recent role in controlling ET evolution in response to O 3 . ABA content was enhanced in O 3 -fumigated Melissa officinalis plants (200 ppb, 5 h) preceding the secondary ROS production peak (Pellegrini et al 2013). However, in some species, O 3 has no effect on its endogenous content (Döring et al 2014).…”

“…At a functional level, some experiments provide evidence that the SA perception amplifies downstream signals that lead to the cell death in a process similar to what occurs during plant-pathogen interactions (Tamaoki 2008). Pellegrini et al (2013) reported that O 3 triggers marked increases in SA (conjugated and free forms) in asymptomatic leaves of M. officinalis after 8 h from the beginning of exposure. In this case, SA may have a role in the upregulation of antioxidative systems during the lesion spread (as confirmed by the increase of ascorbate and glutathione content).…”

“…The induction of ET biosynthesis is one of the fastest O 3 -dependent biochemical responses observed in plants, occurring within few hours (Nakajima et al 2001;Moeder et al 2002;Pellegrini et al 2013). In O 3 -fumigated tomato plants, LE-ACS1A, LE-ACS2, and LE-ACS6 are induced, and the expression of ST-ACS4 and ST-ACS5 is increased in potato (Schlagnhaufer et al 1997;Tuomainen et al 1997).…”

“…A common element seen with O 3 and other abiotic and biotic stresses is the active production of ROS in the apoplast. Therefore, O 3 may also be used as a non-invasive tool to mimic and to study signaling pathways triggered by active apoplastic ROS formation (Pellegrini et al 2013;Vainonen and Kangasjärvi 2015).…”

“…HR, which often precedes systemic acquired resistance (SAR), is characterized by the induction of (1) various cellular protectant genes, (2) the host cell death, and (3) the restriction of pathogen growth and spread. PCD is a physiological process that selectively targets and eliminates unwanted cells, and it plays a role in influencing plant responses to a variety of biotic and abiotic stimuli (Rao et al 2000;Pellegrini et al 2013;Vainonen and Kangasjärvi 2015). Kangasjärvi et al (2005) proposed this mechanism of plant O 3 sensitivity as defined in the lesion formation: (1) regulation of O 3 flux to leaves, (2) O 3 degradation to reactive oxygen species (ROS, normally produced by the plant cellular metabolism) and detoxification [mainly by ascorbate (AsA)] in the apoplast, (3) O 3 sensing/perception, (4) O 3 -induced active production of ROS, (5) early activation by O 3 of mitogen-activated protein kinases (MAPK), and (6) hormonal regulation of the O 3 -induced lesion formation.…”