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Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892

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BuyFindarrow_forward

Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892
Textbook Problem

As Chapter 37 discusses, the plant hormone ABA (abscisic acid) inhibits seed germination, while any of several GAs (gibberellins) stimulate it. For hundreds of plant species, exposure to a substance in wood smoke—one of a family of plant growth regulators called karrikins, or KARs—markedly improves the germination rate. When flames destroy the existing vegetation at a fire scene, more sunlight reaches the ground. In the presence of ample sunlight, KARs apparently promote germination by enhancing the expression of genes that encode GA.

The Figure below summarizes experiments by Australian researchers studying KAR activity in mutant A. thaliana plants (called gal-3), which do not synthesize GA. The graph tracks germination activity after two groups of identical test seeds began imbibing water in a medium that contained the gibberellin GA3. All seeds were exposed to identical levels of a karrikin called KAR1. The red symbols designate seeds of mutant ABA-deficient plants that were supplied with supplementary ABA. The white symbols are ABA-deficient seeds that did not receive the supplement.

Based on this graph:

Comparing the upper and lower data sets, what are the two basic observations you can make about the effects of the seed exposure to differing GA concentrations?

Chapter 36, Problem 3ITD, As Chapter 37 discusses, the plant hormone ABA (abscisic acid) inhibits seed germination, while any

FIGURE ResponseofphytohormonemutantstoKAR1:Germination of A. thaliana ga1-3 mutants in the presence of 1 or 10 µM GA3 6 1 µM KAR1.

Source: David C. Nelson, Julie-Anne Riseborough, Gavin R. Flematti, Jason Stevens, Emilio L. Ghisalberti, Kingsley W. Dixon, and Steven M. Smith. 2009. Karrikins discovered in smoke trigger Arabidopsis seed germination by a mechanism requiring gibberellic acid synthesis and light. Plant Physiology 149:863–873. Plant physiology by AMERICAN SOCIETY OF PLANT PHYSIOLOGISTS. Copyright 2009. Reproduced with permission of AMERICAN SOCIETY OF PLANT BIOLOGISTS in the format Textbook via Copyright Clearance Center.

Summary Introduction

To review:

The effects of seed exposure to different GA (Gibberellic Acid) concentrations by comparing the upper and lower data sets given in the graph.

Biology: The Dynamic Science (MindTap Course List), Chapter 36, Problem 3ITD

Introduction:

The largest class of plant hormones is gibberellins, synthesized in tips of roots, shoot, and young leaves. They help in stimulating fruit growth, triggering elongation of stem, and dormancy break of seed and buds.

Explanation

Gibberellins are known for cell elongation as well as cell division. GA3 has an effect on plant parts, increasing and elongating their size. The plant seeds that were exposed to GA3 start germinating faster as compared to the seeds that were not exposed...

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