Full Text: 1 Introduction Proline accumulation is a common metabolic response of higher plants to water deficits, and salinity stress, and has been the subject of numerous reviews over the last 20 years (Stewart & Larher, 1980; Stewart,1981; Hanson & Hitz, 1982; Taylor,1996; Rhodes et al.,1999). Proline primarily accumulated in the cytosol under water stress conditions (Leigh et al., 1981; Pahlich et al., 1983). Similarly, Singh et al. (1972) reported that amount of proline found higher in drought resistance verities as compared to susceptible verities of barley. Mohammed & Sen (1987) have examined 65 Indian desert plant species for proline contents under stressed and non- stressed condition and have reported contradictory findings that some of the well adapted desert plants do not accumulate proline. Rathore & Sharma (1988) investigated proline contents during stress and non-stress conditions in 11 species of ferns of Rajasthan. These authors confirmed that drought resistant ferns possess more amount of proline than the aquatic or moisture loving plants. They further concluded that proline influences stress tolerance in ferns probably trough its effect on the degradation of chlorophylls and accumulation of carotenoids. Meena (2013) investigated free proline content in 12 species of family Acanthaceae in Southern Rajasthan India. Euphorbiaceae, the spurge family, is one of the most complexes, large and diverse family of Angiosperms (Wurdack et al., 2004) with 334 genera (Webster, 1994) and over 8,000 species (Radcliffe-Smith, 2001), which are distributed mainly in the tropics in the several types of vegetations and habitats. In India, 73 genera and 410 species have been reported by Divya et al. (2011). The present study, enumerates 7 species of family Euphorbiaceae which were collected from Sikar district of Rajasthan, India and investigated for their proline content. The studied plants include Croton bonplandianum Bail, Euphorbia heterophylla L., Euphorbia hirta L., Euphorbia thymifoliaL., Phyllanthus fraternus Webster, Phyllanthus maderaspatensis L.andPhyllanthus virgatus Forst. 2 Materials and Methods 2.1 Sampling area The sampling area is situated on the north eastern part of Rajasthan it lies between 27°21' to 28°12' N latitudes and 74°44' to 75°25' E longitudes. The major part of the region is an undulating sandy tract. The soil of the region varies from sandy to loam. 2.2 Sample collection and processing Root, stem and leaves of all seven plant species viz., C. bonplandianum, E. heterophylla, E. hirta, E. thymifolia, P. fraternus, P. maderaspatensis and P. virgatus were collected during rainy and summer seasons of 2015 and 2016. The collected samples were brought to laboratory in plastic bags, shaded-dried and ground to make powder. Free proline was estimated in different plant parts according to Bates et al. (1973). In the process, 200mg of plant material was homogenized in Sulphosalicylic acid, after centrifugation, supernatant was used for free proline estimation. Optical density was recorded 2206 double beam UV-VIS Spectrophotometer at 540 nm wavelength. Standard curve was prepared using pure proline. 3 Results Proline was estimated in rainy and summer seasons, the root, stem and leaves of C. bonplandianum, E. heterophylla, E. hirta, E. thymifolia, P. fraternus, P. maderaspatensis and P. virgatus of family Euphorbiaceae. The results of proline concentration have been presented in Table 1 and 2. Organ wise, among the tested various root tissues, E. heterophylla (9.83 mg/gdw) possesses highest quantity of proline while lowest  proline concentration was reported from the root tissue of  P. maderaspatensis (2.33 mg/gdw). In case of stem and leaves, maximum proline concentration was reported from the stem of E. hirta (26.02 mg/gdw and 24.57 mg/gdw respectively) while minimum from P. virgatus stem and P. maderaspatensis leaves (4.65 mg/gdw and 5.64 mg/gdw respectively).  It has been observed that the average proline content was higher in E. hirta (18.35 mg/gdw), E. thymifolia (13.82 mg/gdw) and P. fraternus (10.91 mg/gdw) as compared to the other members of family Euphorbiaceae. On the basis of proline content, C. bonplandianum, E. hirta, E. thymifolia and P. fraternus can be consider as the most drought tolerant species while, E. heterophylla, P. maderaspatensis and P. virgatus may be treated as the least drought tolerant species among the selected species of Euphorbiaceae. According to table 1 and 2 the proline content was analyzed minimum in rainy season and highest in summer season. 4 Discussion             Accumulation of Proline in higher plants is an indication of disturbed physiological condition, triggered by biotic or abiotic stress condition. Free proline content can increase by exposure of various drought conditions such as salinity, cold, heavy metals, or certain pathogens. Determination of free proline levels is a useful assay to monitor physiological status and to assess stress tolerance of higher plants.   Table 1 Total free proline content (mg/gdw) in different organs of the selected species of family Euphorbiaceae during rainy season S. No. Names of species Root Stem Leaves Total Average   Croton bonplandianum 6.31 11.80 13.10 10.40     Euphorbia heterophylla 9.10 6.45 13.98 9.84     Euphorbia hirta 3.12 25.13 24.12 17.45     Euphorbia thymifolia 8.72 14.18 17.13 13.34     Phyllanthus fraternus 5.21 6.72 19.70 10.54     Phyllanthus maderaspatensis 2.33 8.17 5.64 5.38     Phyllanthus virgatus 4.15 4.65 9.21 6.003                                                                                                  Table 2 Total free proline content (mg/gdw) in different organs of the selected species of family euphorbiaceae during summer season S. No. Names of species Root Stem Leaves Total Average   Croton bonplandianum 6.89 12.17 14.02 11.02   Euphorbia heterophylla 9.83 6.86 14.07 10.25   Euphorbia hirta 4.46 26.02 24.57 18.35   Euphorbia thymifolia 8.97 14.69 17.80 13.82