Partitioning of assimilated carbon between alternative sinks changes in response to both high and low temperature
Measurements of the three major carbon sinks in Arabidopsis leaves - starch, malate, and fumarate - were taken in control conditions, and on the 1st and the 7th day of cold and warm treatment, respectively (Fig. 3). To measure the carbon accumulated during the photoperiod, the beginning of day concentrations were subtracted from the end of day concentrations for each carbon sink. Each of these accumulates in an approximately linear fashion across the 8-hour photoperiod under controlled environment conditions (Dyson et al., 2016). On the 1st day of treatment, diurnal accumulation of malate was unaffected by either cold or warm in Col-0 and C24 plants (Fig. 3a,b; Fig. S5a-c). Fumarate accumulation, however, increased in response to both treatments in these genotypes (Fig. 3c,d; Fig. S5d-f), this response being most pronounced in the cold and in the Col-0 genotype. Consistent with previous published data (Riewe et al ., 2016), C24 accumulated less fumarate than Col-0 in all conditions, however it accumulated similar amounts of malate. The fum2 mutant did not accumulate fumarate but increased its malate accumulation on the 1st day of cold and warm treatment. Organic acid accumulation continued to increase in the cold over the week but not in the warm (Fig. 3; Fig. S6). All three genotypes increased their diurnal starch production in response to cold on the 1st day and maintained that increase on the 7th day (Fig. 3e). In the warm, starch accumulation did not change significantly, except in C24 plants on the 7th day of treatment, where it increased (Fig. 3f).