Sunflower (Helianthus annuus L.) and maize (Zea mays L.) were chosen as C₃and C₄ crop plants and assessed for the impact of enhanced CO₂ (700 ppm) and its interaction with drought stress in open top chambers (OTCs). The ameliorative effect of higher CO₂ concentration (eCO₂) under drought stress was quantified. It is interesting to note that the C₃ crop responded significantly and positively with eCO₂ under both well-watered and drought stress treatments for root: shoot ratio while C₄ crop showed a better response only with the drought stress environment. Root volume showed a positive significant response with CO₂ concentration enhanced over ambient level and the increment in root volume was 146% and 340% in sunflower and maize crops, respectively. The leaf water potential, stomatal conductance and transpiration showed a decreasing trend in both the crops with drought stress and eCO2 showed an ameliorative effect leading to higher P_n rates in sunflower crop under drought stress treatment. The findings reveal that improvement of root traits is worth attempting for the future crop behavioral responses under eCO₂ and drought stress environments. The study confirmed the beneficial effect of eCO₂ in maize and sunflower by ameliorating the adverse affects of drought stress.

The response of blackgram (Vigna mungo L. Hepper) to two levels of elevated carbon dioxide (550 and 700 ppm) in terms of growth and yield was investigated and compared with ambient CO 2 level (365 ppm) using open-top chambers. The growth parameters viz., length and weight of root and shoot, root:shoot ratio, leaf area and weight significantly increased at 700 ppm CO 2 when compared with 550 ppm. The percentage increase in total biomass at 700 and 550 ppm CO 2 was 65.4% and 39%, respectively compared to the ambient (chamber) control. The increase in total seed yield at 700 ppm (129%) was due to an increase in number of pods per plant and 100 seed weight, whereas at 550 ppm (88.7%) it was due to an increased number of pods/plant and seeds/pod. The results indicate variable responsive effects at different levels of CO 2 emphasizing the pertinence of research on elevated CO 2 in various agroecological inhabitations all over the world. The indication of higher responses for root and leaf at initial growth stages at the higher elevated level of CO 2 (700 ppm), which leads to better root establishment, achieving early photosynthetic efficiency and also better biomass production, and its improved partitioning can be reckoned as a positive aspect of increasing concentrations of CO 2 in atmosphere. The harvest index increased significantly to 35.7 and 38.4% at 550 and 700 ppm, respectively; it is a very important phenomenon in pulses for breaking the yield barrier.

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Growth and yield responses of castor bean (Ricinus communis L.) to two elevated CO 2 levels (550 and 700 ppm) were evaluated up to the maturity of first order spikes in open top chambers (OTCs). The growth characteristics -root and shoot lengths, root volume, root:shoot ratios, leaf area, dry weights of different plant parts, leaf area duration and crop growth rate increased with 550 and 700 ppm of CO 2 levels compared with ambient control. The spike length, pod and seed yield of first order spikes increased under enhanced CO 2 levels over ambient control. Elevated CO 2 levels significantly increased the total biomass and yield of castor bean, however enhanced CO 2 levels per se did not changed the content and quality of the castor oil. A positive response of castor bean to increased CO 2 concentrations is a good indication for its future existence in potentially changed climatic conditions.

An efficient and rapid regeneration protocol was developed using shoot apices from germinating seedlings of two cultivars of sorghum, SPV-462 and M35-1, as explants. A vertical slit given from the base of each dissected apex enhanced the efficiency of callusing response by two fold. MS medium containing 0.5 mg dm -3 each of 2,4-D and kinetin was most effective in producing friable and embryogenic calli. Scanning electron microscopy of these calli detected somatic embryogenesis. Calli thus induced gave rise to approximately 42 green shoots per callus in both the genotypes when transferred to regeneration medium containing 1.5 mg dm -3 kinetin.Additional key words: 2,4-dichlorophenoxyacetic acid, kinetin, plant growth regulators, Sorghum bicolor (L.) Moench. ⎯⎯⎯⎯Until recently, improvement of sorghum for agronomic and quality traits such as tolerance to biotic and abiotic stresses and grain protein quality was carried out largely by traditional plant breeding methods. The application of biotechnology for the genetic improvement of this crop has been lagging behind that of other cereal crops. Sorghum has been categorized as one of the more difficult plant species to manipulate for tissue culture and regeneration (Zhu et al. 1998, Maqbool et al. 2001). The major bottlenecks include 1) genotype dependent response, 2) very low regeneration, 3) production of phenolics and 4) problems in acclimatization. Nevertheless, there are reports of successful regeneration of sorghum from certain explants. In general, immature inflorescence (Brettell et al. 1980, Boyes and Vasil 1984, Murty et al. 1990, Cai and Butler 1990, Eapen and George 1990 and immature embryo (Ma et al. 1987, Oldach et al. 2001) are considered to be excellent explants. However, production of these explants is a space, time and labour consuming task. Explants such as mature embryos from seed (Botti and Vasil 1983, MacKinnon et al. 1987, Zapata et al. 2004) shoot tips or meristems (Bhaskaran et al. 1992, Zhong et al. 1998) are definitely more convenient. In this paper, we report a highly efficient, rapid and season independent protocol for plant regeneration from shoot apices of sorghum.Mature seeds of Sorghum bicolor (L.) Moench cv. SPV-462 and M35-1 were used for generating the shoot apex explants. SPV-462 is a popular sorghum cultivar grown predominantly during the rainy season (June -October) whereas, M35-1 is a land race grown quite extensively during the post rainy season (November -March). Seeds were washed with Tween-20, rinsed 2 -3 times with distilled water and then surface sterilized with 0.1 % HgCl 2 for 10 min. Subsequently, seeds were washed 5 -6 times with sterile distilled water and were aseptically germinated on wet cotton in culture bottle (50 seeds per bottle) in dark at 27 °C. After 48 h of germination, 3 mm sections of shoot apices were carefully dissected from the germinating seedlings. A vertical slit was given from the base of each dissected apex for enhancing the efficiency of callus induction. The sections were then cultured on Murashi...