UC San Diego

Excess soil salinity is a worsening problem for maize agriculture, but recent research into natural compounds that help roots locate water in salty soil may lead to a sustainable solution. Of interest are the apocarotenoid compounds: they regulate root growth, but certain apocarotenoids have not been studied in maize roots yet. In this thesis, maize seeds were exogenously treated with the apocarotenoids anchorene, retinaldehyde, and ꞵ-cyclocitral to characterize 1) their direct effects on root growth and 2) their direct or indirect abilities to mitigate salt stress. We found that the optimal apocarotenoid concentration for growth differs between maize varieties, and that an exogenous application of ꞵ-cyclocitral at 200 µM increases shoot length and lateral root count. In addition, we found that anchorene and retinaldehyde inhibit root growth and that 50 µM of the retinaldehyde inhibitor D15 improves root growth. When maize was subjected to homogenous salt stress, the effects of exogenous ꞵ-cyclocitral and retinaldehyde were negated. Salt distribution in agricultural soil is often distributed heterogeneously, though, so further testing in more agriculturally relevant conditions would better characterize the potential of these compounds in mitigating salt stress in agriculture. Overall, these results indicate that apocarotenoids regulate maize development, and elevating certain apocarotenoid levels may be useful in promoting maize vigor in an agricultural context. In the future, it will be important to delineate the mechanisms of apocarotenoid regulation and examine the role of apocarotenoids with other environmental stressors such as heat, flood, and drought.