Stomatal Closure Stimulated By Inoculated Symbiotic Bacteria Increases Water Use Efficiency of Rice Plants.

Our previous work showed that di-nitrogen fixing bacteria produced abscisic acids (ABA) in an in vitro assay. Also, we found that decrease in stomatal conductance (g_s) of the bacteria inoculated poplar trees under drought condition in a greenhouse experiment. Based on our findings, we hypothesized that these symbionts were able to trigger stomatal closure and also affected stomatal development of rice leaves even under well-watered condition as rice is known to display isohydric behaviors. We inoculated M-206 rice with three strains of the bacteria a week after germination and examined stomatal reactions at panicle initiation stage. The rice plants were grown in a greenhouse and fertigated weekly with a quarter strength nitrogen level of Hoagland solution. Diurnal patterns of g_s of the rice leaves were measured on fully expanded leaves by using a steady state leaf porometer. On the following day, stomatal imprints were collected and then processed to calculate stomatal density. All the inoculated plants showed significantly lower g_s during the day time – from 3 pm to 6 pm, while no significance was found at the other time points. Stomatal density of the inoculated plants was declined as well. Accumulated water consumption of the inoculated plants was statistically lower than the control plants; yet, biomass of the inoculated plants was not affected, leading to slight increase in water use efficiency of productivity. Thus, the induction of closing stomata and the reduced number of stomata were likely to have aided the hosts in efficiently managing water loss during the day time. Probably in response to ABA produced by the bacteria, the inoculated plants became more sensitive to diurnal loss of water. These results suggested that the inoculation of the ABA-producing bacteria can possibly be used to improve water use efficiency of isohydric crops.