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← Theoretical B

Q36 — CONSTANS, Photoperiod, and Seed Mass

Theoretical B Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Photoperiodism, Vernalization & Flowering

Researchers studied the effect of photoperiod and CONSTANS (CO) protein, a critical mediator of photoperiodic cues, on seed mass and size.

Three-panel figure: panel A shows bar charts comparing days-to-flowering (DGF) and seed mass (SM) under 16-hour-day/8-hour-night versus 12-hour-day/12-hour-night conditions for Lotus japonicus and Vigna umbellata; panel B shows a bar chart of seed size at 2, 4, 6, 8, and 10 days after pollination, comparing control and Dex-treated CO-transgenic seeds, with significance brackets; panel C shows a bar chart comparing mature ovule size between wild-type and CO loss-of-function plants. Figure 1. A The flowering time and seed mass of two plant species grown under 16-hour-day/8-hour-night (16-8) and 12-hour-day/12-hour-night (12-12) conditions, representing long-day and short-day photoperiods (DGF: days between germination and flowering; SM: seed mass). B How CO in seeds affects seed size (mm²) in wild-type (WT) and CO-transgenic (CO-trans) seeds, where CO is only functional upon incubating seeds with the compound Dex (DAP: days after pollination; “s”/“ns” denote significant/non-significant differences). C Mature ovule size (mm²) of wild-type (WT) and CO loss-of-function (CO-LoF) mutants.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. Compared to short-day conditions, long-day conditions enhance flowering and increase seed mass for Vigna umbellata.
B. Disrupting the nighttime right in the middle with a flash of red light should accelerate flowering in Lotus japonicus under 12-hour-day-12-hour-night conditions.
C. The activity of the CO is more crucial in the earlier stages of embryo development than in the later stages.
D. CO regulates seed size both before and after double fertilization.
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Question reproduced from IBO 2024, Theoretical Exam Part B, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF