Physiological and metabolic responses of rice to reduced soil moisture: Relationship of water stress tolerance and grain production

Authors: Barnaby, Jinyoung; Rohila, Jai; HENRY, CHRIS - University Of Arkansas; Sicher Jr, Richard; Reddy, Vangimalla; McClung, Anna

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2019
Publication Date: 4/15/2019
Citation: Barnaby, J.Y., Rohila, J.S., Henry, C.G., Sicher Jr, R.C., Reddy, V., McClung, A.M. 2019. Physiological and metabolic responses of rice to reduced soil moisture: Relationship of water stress tolerance and grain production. International Journal of Molecular Sciences. https://doi.org/10.3390/ijms20081846.
DOI: https://doi.org/10.3390/ijms20081846

Interpretive Summary: Alternate wetting and drying (AWD) is a new rice production practice that will significantly save water resources; however, this has to be done without significant loss in grain production. In this study, we selected seven rice varieties displaying a wide range of yield response to reduced irrigation to understand and evaluate differences in stress response under soil water deficit conditions. Each variety integrates their distinctive physiological characteristics in response to water stress in combination with changes at biochemical or metabolic level to produce the final crop yield. Compared to many previous studies that explain correlations between single traits, our study used a holistic approach to evaluate physiological, biochemical, and agronomic traits under field conditions to understand varietal yield potential to water deficits. We identified two varieties, Saber and Francis, that lost no yield under soil water stress indicating they have the capability of tolerating or escaping physiological stress. This was in contrast to the varaieties PI312777 and Teqing which were less able to adjust at a metabolic level and had greater grain yield loss. Varietal yield performance is determined as a result of a suite of physiological and biochemical responses to water stress. It is less likely to be the case that contribution of single metabolite or single physiological trait can enhance yield potential as each genotype performs distinctively by integrating their physiological and biochemical traits in a concerted response.

Technical Abstract: Climatic uncertainty, particularly in regard to water resources, may affect irrigation management of rice, an essential cereal grain acknowledged as the primary food source for more than half the world’s population. To reduce water use, an alternate wetting and drying (AWD) system has been developed for use at the farm level, but understanding crop mechanisms to withstand water stress is necessary to optimize this water-saving technology. The most critical stage for yield reduction is during grain fill, and farmers generally do not apply AWD beyond the heading stage. Water deficits at the transition from vegetative to reproductive stage can also result in yield reduction by altering photosynthetic capacity and metabolic adjustments. Therefore, understanding varietal responses to water stress can provide insight into critical traits for cultivar selection and breeding. Although previous efforts to identify drought tolerance in rice utilized phenotypic traits, a more effective assessment may be to link foliar metabolite profiles to seed yield. Here, seven rice (Oryza sativa) varieties with varying yield in response to water stress were grown under four different irrigation regimes to understand physiological and metabolic responses to water stress at the reproductive transition stage. Our objectives were twofold: (1) to utilize soil water content and single leaf photosynthetic rates to quantify changes in the metabolic profiles of seven rice varieties known to vary in their water stress response; and (2) to assess whether these metabolite changes were correlated with yield. Metabolites were evaluated at pre-heading for 29 markers among a suite of carbohydrates, amino acids and organic acids. Generally, four clustered groups were observed in response to diminished water reserves in all seven varieties; amino acids increased while organic acids and carbohydrates were mixed in their response. Rice varieties whose stomatal aperture, photosynthetic CO2 assimilation rates, and water use efficiency responded to reduced soil water content, i.e., PI 312777 and Teqing, showed less response in osmoprotectants, such as fructose, glucose, myo-inositol, and trehalose. However, Saber, a variety that was non-responsive to photosynthetic adjustment, accumulated osmoprotectants when stressed and also had less yield loss in response to reduced soil water content. These data suggest genetic variation in regulation of osmoprotectants during water stress which is an indicator of yield differences under varying irrigation levels.