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Q67 - Gibberellin Signaling and Root/Shoot Allocation in Transgenic Poplar

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

Scientists constructed gibberellic acid (GA)-deficient and GA-insensitive transgenic lines of poplar plants. They measured concentration of phytohormones, including GA1 and GA4 and IAA, in the leaves and roots of transgenic and wildtype plants (Table Q.67). They also measured the growth of plants in greenhouse and in vitro conditions (Figure Q.67).

Table Q.67 Phytohormone concentrations (ng/g dry weight, mean ± SD) in leaves and roots of the wild type and the two transgenic types. Asterisks (* p<0.05, ** p<0.01) mark values significantly different from wild type.

Organ Plant type GA1 GA4 IAA
Leaf Wild-type 58.1 ± 15.4 6.64 ± 3.18 22.5 ± 3.1
Leaf GA-deficient 19.9 ± 9.4** 5.53 ± 2.33* 21.1 ± 5.9
Leaf GA-insensitive 139.6 ± 21.9** 12.2 ± 3.6** 19.6 ± 3.7
Root Wild-type 77.1 ± 29.3 2.24 ± 0.74 61.4 ± 4.1
Root GA-deficient 48.8 ± 9.6** 1.15 ± 0.62** 72.9 ± 5.2*
Root GA-insensitive 97.7 ± 31.5** 3.93 ± 0.68** 69.1 ± 9.7*

Fig.Q.67 A-D: Root and shoot biomass under greenhouse conditions. Top panel shows the fresh biomass of shoots and roots in GA-deficient (A) and GA-insensitive (B) transgenics. Bottom is the shoot/root ratio in GA-deficient (C) and GA-insensitive (D) transgenics. E-J: Root development (lateral and primary root length/density) in GA-deficient and GA-insensitive transgenic lines grown in vitro, compared to wild type.

Figure 1. Figure 1.

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

A. Greenhouse-grown dwarf plants of both transgenic types display a significant reduction in aerial biomass and an increase in belowground biomass, leading to a significant reduction in the shoot-to-root ratio relative to the wild-type control.
B. The most severely dwarfed plants have more, as well as longer, lateral roots than the wild-type control.
C. The degree of dwarfism in both GA-insensitive and GA-deficient lines is positively correlated with the extent of primary and lateral root formation and elongation.
D. In poplar plants, gibberellins negatively affect lateral root formation, and there may be an interaction between gibberellins and auxin that regulates lateral root formation.
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Question reproduced from IBO 2016, Theoretical Paper B, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)