Q28 - Boron-Sugar Complexes and Pollen Tube Growth

Theoretical 1 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Boron (B) is an essential micronutrient for plants. Its uptake, transport, and function in plants appear to be dependent on the formation of B complexes with sugars, such as sorbitol in phloem sap (Fig. 1) and a specific dimerised form of pectin in growing cell walls. Yokota and Konishi (1999) studied the effect of various exogenously supplied sugars including sucrose, glucose, and fructose on promotion of pollen tube growth by formation of sugar-borate complexes. Pollens were cultivated at different concentrations of B for 20 hours. Effect of sugars on the pH of the media is shown in Table 1, and the length of pollen tubes incubated with the various sugars is shown in Fig. 2. Figure 1. Boron-Sorbitol complex Table 1. Changes of the pH values of the pollen culture media containing different sugars after adding boric acid at different concentrations (first row).

Boron-Sorbitol complex Table 1. Changes of the pH values of the pollen culture media containing different sugars after adding boric acid at different concentrations (first row). Boron-Sorbitol complex Table 1. Changes of the pH values of the pollen culture media containing different sugars after adding boric acid at different concentrations (first row).

Figure 2. Figure 2.

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

A. Growth inhibition of pollen tubes by high concentrations of B is more pronounced in medium containing sucrose as compared to fructose.

B. At low B concentrations (5 mM), growth inhibition of pollen tubes was more pronounced in medium containing glucose as compared to the other sugars.

C. Inhibitory effects of fructose on pollen tube growth increased with increasing concentrations of B.

D. Based on effects of sugar on pH of the media, relative levels of sugar-B complex formation is as follows: Sucrose < Glucose < Fructose.

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Question reproduced from IBO 2018, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)