Q17 - Phenolics from Oak Galls Protect Auxin from Oxidation

Theoretical A Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Plant Hormones Plant Stress Physiology & Defense

Dame Ottoline Leyser (1965-present) showed that auxin is a plant hormone with roles in environment- development interactions. For example, English oak (Quercus robur) is attacked by gall wasp larvae (Cynipidae), which cause tumorous galls to grow. Auxin can cause tumour growth, but auxin is degraded by oxidation (1). Plants use the enzyme PPO to control oxidation of phenolic chemicals (2), but auxin is not a phenolic compound. Different chemical fractions (based on mass) were taken from galls and mixed with auxin and an oxidising agent. Auxin oxidation rate was then measured. Only fractions 6 and 17 contained mostly phenolic compounds (3).

Figure for Q17: Phenolics from Oak Galls Protect Auxin from Oxidation

Using the information and data, determine which of the statements are true or which are false.

A. Auxin activity is high in galls.

B. Compounds in fractions 6 and 17 are oxidised more easily than auxin.

C. Phenolic compounds are responsible for oxidising auxin in galls.

D. Secretion of auxin-like compounds by these gall wasp larvae is necessary to drive gall formation.

E. An upregulation of PPO in galls, compared to healthy tissue, could explain these results.

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Question reproduced from IBO 2017, Theoretical Exam A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Official answer key & worked solutions