Potential Momilactones in Rice Stress Tolerance and Health Advantages

The aim of this review was to provide an updated outlook on the relevance of momilactones in rice during the 50 years since their discovery. Momilactones A (MA) and B (MB) were initially extracted from rice husks in 1973 and have since been identified in various parts of the rice plant including leaves, bran, straw, roots, and root exudates. The biosynthesis of these compounds in rice initiates from geranylgeranyl diphosphate (GGDP) and progresses through several cyclization stages. The genes governing the synthesis of MA and MB are located on chromosome 4 within the rice genome. Concentrations of these compounds vary across different parts of the rice plant, ranging from 2 to 157 mu g/g. Notably, Japonica rice varieties tend to have higher levels of MA and MB (157 and 83 mu g/g, respectively) compared to Indica varieties (20.7 and 4.9 mu g/g, respectively). There is a direct correlation between the levels of MA and MB and the increase in antioxidant activity, protein, and amylose content in rice grains. The production of these compounds is enhanced under environmental stresses such as drought, salinity, chilling, and UV exposure, indicating their potential role in rice's tolerance to these conditions. MA and MB also demonstrate allelopathic, antibacterial, and antifungal properties, potentially improving the resilience of rice plants against biotic stressors. Although their antioxidant activity is modest, they effectively inhibit leukemia cells at a concentration of 5 mu M. They also show promise in diabetes management by inhibiting enzymes like alpha-amylase (with IC50 values of 132.56 and 129.02 mg/mL, respectively) and alpha-glucosidase (with IC50 values of 991.95 and 612.03 mg/mL, respectively). The therapeutic qualities of MA and MB suggest that cultivating rice varieties with higher concentrations of these compounds, along with developing their derivatives, could benefit the pharmaceutical industry and enhance treatments for chronic diseases. Consequently, breeding rice cultivars with increased momilactone levels could offer substantial advantages to rice farmers.