1-Aminocyclopropane-1-carboxylic acid (ACC) deaminase-containing rhizobacteria protect Ocimum sanctum plants during waterlogging stress via reduced ethylene generation

Ocimum sanctum grown as rain-fed crop, is known to be poorly adapted to waterlogged conditions. Many a times the crop suffers extreme damages because of anoxia and excessive ethylene generation due to waterlogging conditions present under heavy rain. The usefulness of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-containing plant growth promoting rhizobacteria was investigated under waterlogging stress. The comparison of herb yield and stress induced biochemical changes of waterlogged and non-waterlogged plants with and without ACC deaminase-containing microbiological treatments were monitored in this study. Ten plant growth promoting rhizobacteria strains containing ACC-deaminase were isolated and characterized. Four selected isolates Fd2 (Achromobacter xylosoxidans), Bac5 (Serratia ureilytica), Oci9 (Herbaspirillum seropedicae) and Oci13 (Ochrobactrum rhizosphaerae) had the potential to protect Ocimum plants from flood induced damage under waterlogged glass house conditions. Pot experiments were conducted to evaluate the potential of these ACC deaminase-containing selected strains for reducing the yield losses caused by waterlogging conditions. Bacterial treatments protected plants from waterlogging induced detrimental changes like stress ethylene production, reduced chlorophyll concentration, higher lipid peroxidation, proline concentration and reduced foliar nutrient uptake. Fd2 (A. xylosoxidans) induced maximum waterlogging tolerance as treated waterlogged plants recorded maximum growth and herb yield (46.5% higher than uninoculated waterlogged plants) with minimum stress ethylene levels (53% lower ACC concentration as compared to waterlogged plants without bacterial inoculation) whereas under normal non-waterlogged conditions O. rhizosphaerae was most effective in plant growth promotion.

Phytoremediatory effect and growth of two species of Ocimum in endosulfan polluted soil

Endosulfan is a hazardous organochlorine pesticide banned or restricted in several countries. However, it has been found in the environment and in animal samples. To study a potential way to bioremediate soils contaminated with this pesticide, two plant species of the genus Ocimum were studied: Ocimum basilicum L. and Ocimum minimum L., since they are economically feasible and well adapted to the climatic conditions of the Nayarit zone (Mexican pacific coast). Young plants were transplanted into soil experimentally polluted with endosulfan. Growth of both species was not affected by endosulfan, the plants grew, flourished, and produced seeds; 30 days later, endosulfan concentration was lower in the soil with O. basilicum than in the soil without plants. On day 90, no differences in endosulfan concentrations were found between soil with or without O. minimum. At day 1, plants in the polluted soil showed lipoperoxidation, as measured by thiobarbituric acid-reactive species (TBARS). Interestingly, a higher TBARS value was observed at day 3 in transplanted plants as compared to non-transplanted plants. In conclusion, both species can endure endosulfan pollution (as high as 1 g kg(-1)) in soils. O. basilicum seems to be an adequate candidate for bioremediation of soils polluted with endosulfan.

Rosmarinic acid content and RAPD analysis of in vitro regenerated basil (Ocimum americanum) plants

Various in vitro cultures were established from shoot tips of Ocimum americanum seedlings. Rosmarinic acid content of the in vitro produced plants as well as parent plant were determined by HPLC analysis and subjected to RAPD analysis. MS medium with BA at a concentration of 1 mg/l and 0.25 mg/l IAA supports maximum rosmarinic acid production in plants produced from cultures grown on that medium. RAPD analysis revealed 64 scorable bands from four primers, including six polymorphic bands. The band pattern revealed differences between the parent plant and the in vitro regenerated plants. Certain band changes were found in O. americanum plants regenerated in vitro, suggesting the existence of genetic variation that might affect the biochemical synthesis of plants derived from tissue culture.

Essential oil yield and quality of methyl eugenol rich Ocimum tenuiflorum L.f. (syn. O. sanctum L.) grown in south India as influenced by method of harvest

A field experiment carried out during 2001--2002 under semi-arid conditions of Hyderabad, India investigated the effect of three different methods of harvesting at full bloom stage, on essential oil yield and quality of methyl eugenol rich sacred/holy basil (Ocimum tenuiflorum L.f.; Lamiaceae). The harvest methods were: harvesting of primary branches, secondary branches and shoot biomass cut at 30 cm above ground level. Four harvests at 102, 192, 287 and 360 days after transplanting of the crop were taken in 1 year in each method of harvest. Harvesting of secondary branches led to maximum plant height and number of secondary branches per plant compared to harvesting of primary branches or shoot biomass cut at 30 cm above ground during second, third and fourth harvests. On the contrary, secondary branch harvest gave least biomass yield in all the four harvests. But due to higher essential oil content, secondary branch harvest gave 25.2 and 15.4% higher total (sum total of all four harvests) essential oil yield (kg/ha per year) over primary branches and shoot biomass cut at 30 cm above ground methods of harvesting, respectively. A similar treatment difference was observed in respect of oil composition studied in the first harvest. Harvesting shoot biomass at 30 cm above ground produced oil containing highest amount of methyl eugenol. The content of methyl eugenol decreased in the order of shoot biomass cut at 30 cm above ground > primary branch > secondary branch treatments. A reverse trend was observed, however, in respect of (E)-cinnamyl acetate, eugenol and beta-elemene constituents of the oil. Little variability was, however, observed among the treatments in respect of 24 other constituents of the oils.