Pak. J. Bot., 43(1): 539-548, 2011. EFFECT OF SALINITY ON BIOMASS PRODUCTION AND ACTIVITIES OF SOME KEY ENZYMATIC ANTIOXIDANTS IN KOCHIA (KOCHIA SCOPARIA) JAFAR NABATI 1 , MOHAMMAD KAFI 2 , AHMAD NEZAMI 2 , PARVIZ REZVANI MOGHADDAM 2 , ALI MASOUMI 1 AND MOHAMMAD ZARE MEHRJERDI 1 1 Faculty of Agriculture, Ferdowsi University of Mashhad, Iran 2 Faculty of Agriculture, Ferdowsi University of Mashhad, Iran. Abstract Soil salinity is a major constraint to food production due to its negative impact on crop yield. Kochia (Kochia scoparia) is a salinity-resistant plant that can widely be used as emergency forage for livestock by using saline waters and soils in desert ecosystems. In order to investigate physiological mechanism, antioxidants activity and potential production of Kochia in response to different levels of salinity, an experiment was performed in a split plot based on randomized complete block design with three replications. Saline waters (5.2, 10.5 and 23.1 dS m -1 ) and three Kochia ecotypes (Birjand, Borujerd and Sabzevar) were allocated as main and sub plots, respectively. The results showed that salinity did not impose any significant effect on dry matter production but relative water content (RWC) and seed yield decreased by salinity stress. In general, no positive correlation coefficient was observed between dry matter production and physiological and biochemical parameters except superoxide dismutase (SOD) at 23.1 dS m -1 . There was no significant difference among ecotypes in dry matter production and seed yield. Sabzevar ecotype showed the highest proline, total phenol content and peroxidase (POX) activity. Ascorbate peroxidase (APX), catalase (CTA), and superoxide dismutase (SOD) activity was higher in Borujerd ecotype, while highest soluble sugar, glutathione reductase (GR) activity and DPPH - radical scavenging activity was observed in Birjand ecotype. According to these results, Kochia has a reliable tolerance to elevated levels of salinities up to 23 dS m -1 and it seems that it can control oxidative stress by continuing growth. Introduction Salinity is one of the most important environmental factors limiting crop production of marginal agricultural soils in many parts of the world. It is estimated that about a third of the world’s cultivated land affected by salinity. Kochia scoparia (L., Schrad) is a highly, drought and salinity resistant plant widely used as emergency forage for livestock (Gul et al., 2010). Kochia can establish on saline soils, not only to produce protective short-lived vegetation coverage, but also is being used as an alternative forage crop, especially in regions faced with forage shortage (Jami Al-Ahmadi & Kafi 2006). Kochia also has high forage yield potential; Kafi et al., (2010) reported an annual forage yield up to 11 ton ha -1 . Salinity can affect growth and yield of most crops, high salinity is known to cause both hyper ionic and hyper osmotic effects in plants, leading to membrane disorganization, increase in activated oxygen species production and metabolic toxicity (Joseph & Jini, 2011). Reactive oxygen species (ROS) are highly reactive and, in the absence of any protective mechanism, can seriously disturb normal metabolism through oxidative damage toward pigments, lipids, proteins and nucleic acids (Molassiotis et al.,