The production of reactive oxygen species (ROS) is one of thebiochemical changes occurring in plants subjected to various abiotic stressesDat et al. 2000. Reactive oxygen species are highly reactive and they arepartially reduced forms of atmospheric oxygen.
ROS are typically resulted fromthe excitation of O2 to form singlet oxygen (O2), or fromtransferring one, two or three electrons to O2 for generation of asuperoxide (O2–), hydrogen peroxide (H2O2)or a hydroxyl radical (OH-), respectively Shigeoka et al.2002. ROS are necessary for intracellular signaling Smirnoff 1993, but theirproduction at high levels can seriously damage plants by increasing lipidperoxidation, protein degradation, DNA fragmentation and ultimately cell deathFarooq et al. 2009. Water stress causes an imbalance between light trappingand its utilization, which reduces photosynthetic activity in leaves.
Dissipation of excess light energy in photosynthetic apparatus results ingeneration of ROS Lisar et al. 2012. Plants with high antioxidant levels canbetter prevent oxidative damage Parida and Das 2005.
Antioxidant enzymes suchas superoxide dismutase (SOD), glutathione reductase (GR), catalase (CAT) andperoxidase (POX) play a key role in scavenging those activated species, thepreservation of membrane integrity, protection of DNA and proteins degradationScandalios 1997. Changes of antioxidants reflect the impact of environmentalstresses on plant metabolism.Seed priming isa simple technique, which is used to speed up and synchronize seedlingemergence of many horticultural and field crops 7. Early emergence ofseedlings could be resulted in production of vigorous plants. Moreover, enhancingseedling emergence percentage could help to establish optimum plant populationdensity under a wide range of environmental conditions 25. Seedling emergenceand establishment could be considerably improved by hydro-priming 22, 23 andsalt priming 21, 22. Despitethe popularity of herb cultivation in different parts of Iran, littleinformation is available about the accumulation of compatible solutes andantioxidant enzymes activity and their role in borage response to stresses.
Also,changesin photosynthetic pigments and fluorescence of borage plants in response toseed priming and water limitation were not documented so far. Thus, these objectives are conclusivelyinvestigated in this research.