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Plants respond to various stresses during their lifecycle among which abiotic stress is the most severe one comprising heat, cold, drought, salinity, flooding, etc. which take a heavy toll on crop yield worldwide in every corresponding year. ROS has a dual role in abiotic stress mechanisms where, at high levels, they are toxic to cells while at the same time, the same molecule can function as a signal transducer that activates a local as well as a systemic plant defense response against stress. The most common ROS species are Hydrogen peroxide (H2O2), Superoxide anions (O2-), Hydroxyl radicals (OH-), and Singlet oxygen (1O2) which are results of physiological metabolism often controlled by enzymatic and non-enzymatic antioxidant defense systems. ROS generally accumulate in plants during abiotic and biotic stress conditions resulting in oxidative damage which ultimately leads to programmed cell death. Many ROS scavenging pathways have been well studied against stress responses. Through careful manipulation of ROS levels in plants, we can enhance stress tolerance in plants under unfavorable environmental conditions. This chapter presents an overview of ROS regulation in plants and the essential enzymes involved in the abiotic stress tolerance mechanisms which are thoroughly discussed below.

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Variety identification has great significance from seed production, breeding as well as intellectual property rights point of view to ensure quality seed. The decrease in the morphological variation among the major rice varieties due to narrow genetic base makes it necessary for the development of quick and reliable tests for varietal identification particularly for those working in seed certification and quality maintenance. The study was conducted during 2019-20 at the laboratories of the Crop Improvement Division, ICAR-VPKAS, Almora. Two hundred Indica rice varieties/genotypes were identified on the basis of seed color (phenol, modified phenol, NaOH and KOH) to chemical tests. Phenol test grouped variety into three distinct groups viz., dark brown (15 varieties), brown (59 varieties) and light brown (95 varieties). With the help of modified phenol test these varieties were further sub grouped. NaOH test grouped varieties into two distinct groups i.e., light yellow (177 varieties) and wine red (23 varieties). These tests clearly differentiated the varieties of one group to that of another groups on the basis of seed coat color. However, KOH test was not reliable for the differentiation of these varieties because all these varieties showed light yellow color after treating with KOH solution. Though no individual chemical test was able to distinguish all the varieties, different chemical tests in conjunction were useful in identification of varieties. Thus these simple, reliable and quick tests can be used for varietal identification in rice crop.