Plant Biology ISSN 1435-8603
RESEARCH PAPER
Sub-lethal UV-C radiation induces callose, hydrogen peroxide and defence-related gene expression in Arabidopsis thaliana S. J. L. Mintoff, J. E. Rookes & D. M. Cahill Centre for Chemistry and Biotechnology, School of Life and Environmental Sciences, Deakin University, Geelong, Vic., Australia
Keywords Arabidopsis; callose; cross-tolerance; leaf curling; PDF1.2; PR1; ultraviolet light. Correspondence S. J. L. Mintoff, Centre for Chemistry and Biotechnology, School of Life and Environmental Sciences, Deakin University, Pigdons Road, Geelong campus at Waurn Ponds, Geelong, Vic. 3217, Australia. E-mail:
[email protected] Editor W. Adams Received: 9 September 2014; Accepted: 2 November 2014 doi:10.1111/plb.12286
ABSTRACT Exposure of plants to UV-C irradiation induces gene expression and cellular responses that are commonly associated with wounding and pathogen defence, and in some cases can lead to increased resistance against pathogen infection. We examined, at a physiological, molecular and biochemical level, the effects of and responses to, sublethal UV-C exposure on Arabidopsis plants when irradiated with increasing dosages of UV-C radiation. Following UV-C exposure plants had reduced leaf areas over time, with the severity of reduction increasing with dosage. Severe morphological changes that included leaf glazing, bronzing and curling were found to occur in plants treated with the 1000 Jm 2 dosage. Extensive damage to the mesophyll was observed, and cell death occurred in both a dosage- and time-dependent manner. Analysis of H2O2 activity and the pathogen defence marker genes PR1 and PDF1.2 demonstrated induction of these defence-related responses at each UV-C dosage tested. Interestingly, in response to UV-C irradiation the production of callose (b-1,3-glucan) was identified at all dosages examined. Together, these results show plant responses to UV-C irradiation at much lower doses than have previously been reported, and that there is potential for the use of UV-C as an inducer of plant defence.
INTRODUCTION In order to limit the damaging effects of ultraviolet (UV) radiation, plant cells possess protective mechanisms that aid their survival, which includes DNA repair via photo-reactivation and UV-induced production of secondary metabolites such as flavonoids, anthocyanins, tocopherols and polyamines that have UV-shielding or antioxidant properties (Li et al. 1993; Landry et al. 1995; Vonarx et al. 1998; Britt 1999; Bashandy et al. 2009; Hectors et al. 2014). A number of studies have examined the effects of increased levels of UV-B radiation on plants following the discovery of stratospheric ozone depletion, and subsequent meta-analysis has indicated that increased UV-B exposure generally results in a reduction in plant biomass (Newsham & Robinson 2009; Ballare et al. 2011). Conversely, it is becoming increasingly apparent that the exposure of plants to UV radiation can be of benefit in plant development and in responding to other stresses. For example, studies of plants grown under natural, ambient UV-B radiation in field conditions showed less insect herbivory when compared to plants grown under attenuated UV-B conditions (Ballare et al. 1996; Mazza et al. 2013). In reality,
