Bacterial Endophytes Living in Intercellular Spaces of Leaves Lower Leaf Water Potential of Rice (Oryza sativa) Plants.

Diazotrophic bacterial endophytes are known to live in their host plants as helping them to gain more biomass by producing phytohormones and fixing the atmospheric nitrogen for the plants to use. Recent anatomical studies have shown that these bacteria mainly reside in the intercellular-air space and also they tend to aggregate within the space. Therefore, their presence possibly alters bio-physical pathways of various plant resources, for example, water vapor, carbon dioxide, organic or inorganic acids, inside the cells. However, this is never tried to be proved by apparently empirical results. This study aimed to find out the difference of bio-physical characteristics between inoculated and non-inoculated rice (Oryza sativa) plants caused by inoculation of the endophytes. We hypothesized that the presence of bacteria in the intercellular space occupy free space where should have been filled with water vapor, leading to increase the hydrostatic pressure inside leaves. In order to test this hypothesis, we used the Scholander pressure chamber to estimate the hydrostatic pressure in the leaves by measuring midday leaf water potential. At the same time, we recorded stomatal conductance (g_s) with a commercial gas exchange system to see if there were any changes of water relations attributed to the endophytes. Using a fluorescence microscopy, we found the red fluorescence protein labelled bacteria (PTD-1, Rhizobium tropici) living inside the leaves. The leaf water potential of the inoculated leaves significantly decreased around 20% of that of the non-inoculated leaves. However, the g_s didn’t change by the inoculation. Our results show that the inoculated plants had lower leaf water potential due to the higher hydrostatic pressure, which implies endophytes-inoculated plants might hold more water inside them, and also they can attract more solubilized nutrients from the soils.