Abstract
Plants deal with resource management during all their life. During the day they feed on photosynthetic carbon, sucrose, while storing a part into starch for night use. Careful control of carbon partitioning, starch degradation, and sucrose export rates is crucial to avoid carbon starvation, insuring optimal growth whatever the photoperiod. Efficient regulation of these key metabolic rates can give an evolutionary advantage to plants. Here we propose a model of adaptive starch metabolism in response to various photoperiods. We assume the three key metabolic rates to be circadian regulated in leaves and that their phases of oscillations are shifted in response to sucrose starvation. We performed gradient descents for various photoperiod conditions to find the corresponding optimal sets of phase shifts that minimize starvation. Results at convergence were all consistent with experimental data: (1) diurnal starch profile showed linear increase during the day and linear decrease at night; (2) shorter photoperiod tended to increase starch synthesis speed while decreasing its degradation speed during the longer night; (3) sudden early dusk showed slower starch degradation during the longer night. Profiles that best explained observations corresponded to circadian regulation of all rates. This theoretical study would establish a framework for future research on feedback between starch metabolism and circadian clock as well as plant productivity.
Highlights
Plants have to deal with resource management to avoid starvation in the dark
When endogenous dawn does not match the actual L/D cycle, growth rate is significantly reduced due to sucrose starvation at the end of the night (Graf et al, 2010) or lower rates of photosynthesis (Dodd et al, 2005). These results indicate that appropriate anticipation of dawn by the circadian clock is essential for optimal growth, resulting in continuous degradation of starch over the course of the night with no symptoms of carbon starvation (Stitt and Zeeman, 2012)
We assume that the rate of starch synthesis γ(t) and sucrose export η(t) are governed by the internal circadian clock with period τ, which is formalized as: FIGURE 2 | Scheme of phase shift for starch metabolism and sucrose export driven by carbon starvation
Summary
Plants have to deal with resource management to avoid starvation in the dark. During the day they feed on carbohydrates from photosynthesis but need to store substantial amount of photosynthate to sustain metabolism and growth during night. Some modeling studies exploring sucrose and starch patterns (Rasse and Tocquin, 2006) or circadian clock (Edwards et al, 2010) exist, but so far, control of carbon partitioning in plants is not well-known.
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