Open Access Maydica 58-2013 Original Paper RECEIVED 03/08/2013 The effects of foliar application of ascorbic acid (vitamin C) on physiological and biochemical changes of corn (Zea mays L) under irrigation withholding in different growth stages Mahmoud Darvishan 1 , Hamid R Tohidi-Moghadam 1 *, Hossein Zahedi 2 1 Department of Agronomy, Varamin-Pishva Branch, Islamic Azad University,Varamin, Iran 2 Department of Agronomy and Plant Breeding, Eslamshahr Branch, Islamic Azad University,Tehran, Iran *Corresponding author: E-mail: hamid_tohidi2008@yahoo.com Keywords: antioxidant enzymes activity, relative water content, chlorophyll To study the effects of ascorbic acid foliar application and limited irrigation in different growth stages on physi- ological and biochemical changes of corn, an experiment was conducted in Varamin, Iran during the growing season of 2012. The experimental design was randomized complete blocks in split plots arrangement with three replications. Main plots included four different levels of irrigation (complete irrigation, irrigation withholding at 8-leaf stage, irrigation withholding at silks appearance stage and irrigation withholding at both 8-leaf stage and silks appearance stages) and different concentration of foliar application of ascorbic acid (vitamin C) (0, 75, and 150 ppm) were allocated to subplots. The results showed that irrigation withholding conditions in different growth stages significantly decreased seed yield, RWC and total chlorophyll but by contrast increased proline content, antioxidant enzymes activity. Ascorbic acid foliar application in irrigation with holding in different growth stages had positive effect on all attributes in this experiment. In general, the results of the present study indicate that us- age of AsA reduces the harmful effects of water deficit stress and increases resistance to drought stress in corn plant. Abstract Introduction Today, across the globe, corn is a direct staple food for millions of individuals and, through indirect consumption as a feed crop, is an essential compo- nent of global food security (Campos et al, 2004). In many regions of the world, including Iran, drought stress is one of the most important factors respon- sible for decreasing crop yield. Identification of the critical irrigation timing and scheduling of irrigation based on a timely and accurate basis to the crop is the key to conserving water and improving irrigation performance and sustainability of irrigated agriculture (Ngouajio et al, 2007). Water stress induces oxidative stress in plants (Hajiboland and Joudmand, 2009). Zahedi et al (2011) reported that antioxidant enzymes activity were increased when plants were exposed to water stress. Under conditions of water stress and other types of environmental stress, reactive oxygen species (ROS), such as superoxide anion radicals, hydrogen peroxide and hydroxyl radicals, are gen- erated (Zhu, 2000). Plant cells contain an array of protection mechanisms and repair systems that can minimize the occurrence of oxidative damage caused by reactive oxygen species (ROS) (Abdel Latef, 2010). The induction of ROS-scavenging enzymes, such as superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase is the most common mecha- nism for detoxifying ROS synthesized during stress response (Gressel and Galun, 1994). In the antioxi- dants system, which involves antioxidant substances such as tocopherols and AsA (Foyer et al, 1994). This last compound is a small, water-soluble antioxidant molecule, that acts as a primary substrate in the cy- clical pathway for detoxification and neutralization of superoxide radicals and singlet oxygen (Noctor and Foyer, 1998). It has also been reported that applica- tion of exogenous ascorbate can increase resistance to salt stress and reduce oxidative stresses (Shalata and Neumann, 2001). Ascorbate has been shown to play multiple roles in plant growth, such as in cell division, cell wall expansion, and other develop- mental processes (Pignocchi and Foyer, 2003). The work was aimed also whether a foliar supply of AsA to plant might be a strategy for increasing the water deficit tolerance. Abbreviations: RWC - relative water content, AsA - ascorbic acid, ROS - reactive oxygen species, CAT - catalase, SOD - Superoxide dismutase, GPX - Glutathione peroxidase, Pro - proline, Chl - Chlorophyll Materials and Methods The experiment was conducted in an experimen- tal field area of the Azad University, Varamin Branch in Iran during 2012 growing season. The site of study was situated at 31°519’E and 20°359’N and 1,050