Asian Research Thesis Index

Abstract

Climate change is one of the serious threats to food security throughout the world especially in arid and semi-arid regions, affecting agricultural productivity. Rapid changes in global climate such as alteration in rain fall pattern and increase in temperature lead to severe drought stress that limits the crop production by reducing photosynthetic rate and suppressing plant growth. Endophytic bacteria containing carbonic anhydrase may improve plant growth and elicit tolerance under water deficit stress by enhancing the photosynthesis in plants. Carbonic anhydrase (CA) catalyzes the reversible conversion of atmospheric carbon dioxide into bicarbonate, first substrate of photosynthesis in C3 and C4 plants. Therefore, present study was conducted to assess the potential of drought tolerant CA containing endophytic bacteria for improving photosynthesis and plant biomass of cereals under different moisture regimes. One hundred and fifty bacterial isolates were isolated form two cereals (wheat and maize) and tested for their ability to tolerate PEG-induced water deficit conditions. Fifty isolates exhibiting higher drought tolerance from each crop were further analyzed for CA activity. Ten drought tolerant isolates with higher CA activity were further assessed for growth promotion in wheat (C3) and maize (C4) plants. Isolates WR2, WS11 and WL19 showed higher photosynthetic rate and plant growth in both wheat cultivars; however, increase was more for Uqab-2000 than Fsd-2008 under PEG- induced water deficit conditions. Moreover, isolates MR17, MS1 and MG9 gave significant increase in photosynthesis and plant growth in both maize hybrids, especially for H2 hybrid under PEG-mediated water stress. Selected isolates from both crops were labeled with Gus and tested for plant growth promotion as well as colonization efficiency in wheat and maize under water deficit stress. Inoculation of selected isolates showed significant results for photosynthesis, growth and colonization efficiency of wheat and maize under well watered (100% FC) and stressed (70 and 40%) conditions especially for Uqab-2000 and H2. In the same ways, isolates WR2, WS11 and WL19 gave significant results for growth, physiology and yield of wheat under field condition where water deficit stress was induced by skipping irrigation at tillering, flowering and grain filling stage. On the other hand, inoculation with isolates MR17, MS1 and MG9 improved growth under normal and stressed conditions which were induced by withholding irrigation at vegetative and reproductive stage of maize. Selected isolates also proved to be efficient auxin producer and p-solubilizer under normal and stressed conditions. These isolates were identified as Bacillus sp. In separate study, it was observed that endophytic bacterial isolates carrying CA activity AR4 and AR14 (belonged to Microbacterium sp. and Psychrobacter sp., respectively) also stimulated the expression of various genes and transcription factors in Arabidopsis thaliana under normal as well as PEG-induced water deficit conditions. Therefore, it can be suggested that inoculation of endophytic bacterial isolates (WR2, WL19 for wheat and MR17, MG9 for maize) is good for enhancing photosynthesis and plant biomass under water deficit conditions. Moreover, multi-site field experiments for these isolates are suggested for evaluating the successful performance in field. However, molecular studies are required to confirm role of bacterially synthesized CA in photosynthesis.

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