Figure 4.
Effects of an extended night on the rate of starch synthesis, and differences in primary metabolites between wild-type and GlgC-TM plants. A, Effect on the rate of starch synthesis of a single extended night. Rates were estimated from measurements (means of values from six plants) at the beginning and end of the day in plants in 12:12 conditions and plants grown in these conditions but subjected to a 4-h extension of the night prior to the day of measurement. At least three separate experiments were performed for each type of plant (independent symbols) with six biological replicates in each. Plants were the wild type (Col-0), GlgC-TM transgenic lines (GlgC), transgenic lines expressing a constitutively redox activated form of AGPase (redox), the adg2 mutant, and transgenic lines expressing a form of AGPase with altered sensitivity to allosteric modification (TLUp3). For GlgC-TM, constitutively redox activated, and TLUp3 plants, two independent lines were used (white and black symbols). Values are the percentage change in the rate of starch synthesis between the end of a normal night and the end of an extended night. For each genotype, the central bar is the mean and the top and bottom bars the sd of the means across all experiments. Means indicated with a different letter (a–c) are statistically significantly different (Newman-Keuls multiple comparison test, P < 0.05). The range of rates of starch synthesis (mg h–1 g–1 fresh weight [FW]) across all experiments following a normal night and an extended night were: Col-0, 0.51 to 0.81 and 0.74 to 1.29; GlgC-TM, 0.27 to 0.43 and 0.20 to 0.35; redox, 0.55 to 0.91 and 0.83 to 1.28; adg2, 0.59 to 0.64 and 0.69 to 0.74; and TLUp3, 0.88 to 1.08 and 1.07 to 1.42. B, ADP-Glc contents of wild-type (Col-0) plants, APS1 control line N2, and GlgC-TM lines C3 and C4. Plants were grown in 12:12 conditions and harvested at 3 h (white) and 15 h (black) after dawn. Values are means ± sd of measurements on six plants. C, Glc 1-P contents of plants as in C grown in 12:12 conditions and harvested at ZT3 (white) or ZT15 (black) or grown in 6:18 conditions and harvested at ZT3 (light gray) or ZT9 (dark gray). Values are means ± sd of measurements on five plants. D, Glc content over 24 h of plants grown in 6:18 conditions. Black circle indicates the wild type (Col-0), black rectangle indicates APS1 control line N2, white triangle indicates GlgC-TM line C3, white rectangle indicates GlgC-TM line C4, and white circle indicates adg1 mutant. The Glc content of transgenic lines C3 and C4 at 6 h after dawn was significantly higher than that of the wild type and the N2 control line but significantly lower than in the adg1 mutant in both 12:12 and 6:18 conditions (in 12:12: the wild type = 0.089 ± 0.03, N2 = 0.12 ± 0.04, C3 = 0.26 ± 0.03 [P < 0.05 versus the wild type or N2, Student’s t test], C4 = 0.44 ± 0.09 [P < 0.01], and adg1-1 = 1.30 ± 0.05 [P < 0.01 versus C3 or C4]; in 6:18: the wild type = 0.39 ± 0.08, N2 = 0.16 ± 0.02, C3 = 0.89 ± 0.10 [P < 0.01 versus the wild type or N2], C4 = 1.11 ± 0.05 [P < 0.01], and adg1-1 = 1.90 ± 0.29 [P < 0.05 versus C3 or C4]). Values are means ± se of measurements on six plants. Where not visible, error bars are smaller than symbols.