MODELING CARBON METABOLISM IN THE DEVELOPING STORAGE ROOTS OF RAYONG 9 CASSAVA VARIETY UNDER DIFFERENT WATER CONDITIONS

Global climate changes alter seasonal period and cause unusual variation in daily temperature and humidity. The circumstance directly affects water availability for crop growth and subsequently reduces final production. Studies in cassava show that irrigated plantation could alleviate the impact of the variable environmental exposures and could also rise storage root (SR) yield under a favorable condition. It demonstrates a closed link of water availability condition to plant carbon metabolism and biomass production. As hypothesized, we here investigated carbon assimilation and carbon conversion in developing storage roots of Rayong 9 cassava variety grown under the different water regimes (WR), relatively drier (WR1) and wetter (WR2) conditions based on soil matric potential. Constraint-based metabolic model was developed to simulate carbon conversion towards root biomass biosynthesis in responsible of the higher yield of SR dry weight and starch content in WR2 condition. Simulation showed that carbon flux partitioning in root metabolism at 8-month-old plants differed between water conditions. Plants in WR2 condition showed higher total photosynthesis which yielded more amounts of sucrose for storage root development. The simulated results also showed the difference in balance of apoplasmic (via invertase) and symplasmic (via sucrose synthase) sucrose transports in these conditions. The more active carbon flux through sucrose synthase reaction at the late stage of SR development observed in WR1 may reflect the response of carbon metabolism to the relatively dry condition. This insightful understanding of metabolic response to water conditions has moved another step forward to the optimized irrigation practice in cassava precision farming.