Physiological and biochemical responses of gerbera (Gerbera jamesonii Hook.) to physical and chemical mutagenesis By MINERVA GHANI 1 * , SURINDER KUMAR 2 and MANISHA THAKUR Department of Biotechnology, University of Horticulture and Forestry, Nauni Street, Solan-173230, Himachal Pradesh, India (e-mail: minervaghani@yahoo.in) (Accepted 10 December 2013) SUMMARY The physiological effects of physical and chemical mutagenesis on in vitro-raised plants of Gerbera jamesonii Hook. were investigated. In vitro cultures of gerbera were established through capitulum explants cultured on 1.0 Murashige and Skoog (MS) medium supplemented with 5 mg l –1 benzyladenine (BA) and 0.5 mg l –1 indole-3-acetic acid (IAA). In vitro-regenerated shoots were treated separately with ethyl methyl sulphonate (EMS) at 0.1, 0.2, 0.5, 0.8, or 1.0% (v/v) or -irradiation (at doses of 1.5, 2.0, 2.5, 5.0, or 10.0 Gy). The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), catalase (CAT), and polyphenol oxidase (PPO) increased significantly compared to untreated control shoots and reached a maximum at the highest dose of either mutagen. Overall, 18.3% and 20.5% reductions in chlorophyll concentration were observed in 2 month-old hardened plants following -irradiation or EMS treatment, respectively.The mutated shoots showed significant increases in total phenolic compound concentrations (36% and 21.7%) and total protein concentrations (17.6% and 17.1%) at the highest dose of -rays or EMS, respectively. Increases in the activities of the five enzymes, and in the concentrations of phenolic compounds and proteins, indicated the importance of these biomolecules in protecting gerbera plants grown under abiotic stress conditions. G erbera jamesonii Hook. belongs to the family Asteraceae (or the Compositeae), which is the largest family of flowering plants. The natural distribution of this genus extends to Africa, Madagascar, tropical Asia, and South America (Altaf et al., 2009). Gerbera (Gerbera hybrida) is one of the most important cut and pot flowers cultivated worldwide and ranks fifth in the global cut-flower trade after rose, carnation, chrysanthemum, and tulip (Teeri et al., 2006; Bhatia et al., 2009). The induction of mutations in crop plants generates variability that may not be present in the natural gene pool, or may not exist in the particular genotype, which can then be combined with the desired variety by conventional cross-breeding. X-rays and -rays have been used by many workers to induce mutations in plants (Arunyanart and Soontronyatara, 2002; Sheela et al., 2006). Among the many chemical mutagens available, only alkylating agents such as ethyl methyl sulphonate (EMS), diethyl sulphate, ethylene imine, or sodium azide have given promising results so far. Gamma-rays and EMS are often used to develop plant varieties that are agriculturally and economically important and have high potential productivity. Gamma-rays are also important for mutation breeding and in vitro mutagenesis to develop the required features in plants and to increase genetic variability. In many vegetatively-propagated crops, the induction of mutations in combination with in vitro culture techniques may be the only effective method for plant improvement (Kozgar et al., 2012). Gerbera spp. are clonally propagated plants. Once a new mutation has been induced and identified, there is the added advantage that the newly created trait can be fixed and preserved. Physiological and biochemical processes in plants are significantly affected by the stress of mutagenesis. Irradiation of plant material with high doses of -rays inhibits or perturbs the biosynthesis of proteins, the endogenous hormone balance, gas-exchange in leaves, water exchange, and enzyme activities (Peykarestan and Seify, 2012). Hormesis, defined as the dose-response phenomenon, is characterised by a counter-intuitive switchover from low-dose stimulation to high-dose inhibition, an action occasionally encountered in the course of toxicity assays (Calabrese, 2002). The hormetic effects of low-doses of ionising radiation, or low concentrations of chemical mutagens on plants and on photosynthetic micro-organisms frequently become apparent as accelerated cell proliferation (Chakravarty and Sen, 2001), stimulated germination and growth (Kim et al., 2001; Tugay et al., 2006), improved stress-resistance (Zaka et al., 2002; Lee et al., 2002; 2003), and/or increased yields (Moussa, 2011). In many cases, such effects have been characterised as being due to the modulation of photosynthetic and anti-oxidant mechanisms. Plants have developed anti-oxidant mechanisms involving enzymes such as superoxide dismutase (SOD), glutathione reductase (GR), catalase (CAT), ascorbate peroxidase (APX), and glutathione-S-transferase (GST), to protect themselves against the harmful effects of reactive oxygen species (ROS). Evidence has shown that *Author for correspondence. 1 Present address: Chowgan 3, Chamba-176310, Himachal Pradesh, India. 2 Present address: HIG29 Housing Board Colony, Saproon, Solan-173230, Himachal Pradesh, India. Journal of Horticultural Science & Biotechnology (2014) 89 (3) 301–306