Analysis of biochemical-physiological mechanisms involved in responses to drought in soybean

Resumo

Water deficit limits soybean crop productivity and reduces yield stability. Many parameters have been associated with tolerance to water deficit, where the control of leaf water loss is by far the most important. Since most of the water loss occurs through the stomata, the objective of this thesis was to deepen the understanding of the response to water deficit in soybeans through the control of stomatal closure and to determine how this can affect the water consumption of soybeans and its tolerance to water deficit. To achieve this, we delved into the study of stomatal closure control. We focused on the role of nitric oxide (•NO) as a key molecule in the control of stomatal opening/closing. •NO kinetic accumulation was analyzed from the establishment of the hydric deficit, and its association with stomatal closure was assessed. Our work showed an endogenous •NO accumulation at the guard cell level before stomatal closure, which allowed us to postulate that in the early perception of stress there is an accumulation of •NO that inhibits stomatal closure, potentially through blocking responses to ABA. This initial fine control of the stomatal closure by •NO would be decisive to define the final responses of water loss/consumption during the establishment of the water deficit. Furthermore, we developed an empirical mathematical model in soybean that describes the kinetics of water consumption under water deficit conditions of a controlled plant-pot-substrate growth system. The model defined two parameters that determine the water consumption curve, t0.5 (time at which the system lost half of the maximum amount of potentially evapotranspirable water) and Gw(t0.5) (stomatal conductance at t0.5). A correspondence analysis between t0.5 and Gw(t0.5), and the genetic structure of two soybean populations, indicated the existence of genetic associations with consumption phenotypes based on these parameters. On the other hand, using data from the drought susceptibility index (DSI) in the field, generated by previous work on one of the populations of this thesis, and through a correspondence analysis, a grouping between the model parameter t0.5 and DSI is observed. This would indicate that the developed phenotyping strategy could also be useful in the characterization of genotypes at the field level.