Evol Ecol Res 12: 457-476 (2010)     Full PDF if your library subscribes.

How anthocyanin mutants respond to stress: the need to distinguish between stress tolerance and maximal vigour

Eric J. von Wettberg1, Maureen L. Stanton2 and Justen B. Whittall3

1Department of Biological Sciences, Florida International University, Miami, Florida, 2Center for Population Biology, University of California, Davis, California and 3Department of Biology, Santa Clara University, Santa Clara, California, USA

Correspondence: E.J. von Wettberg, Department of Biological Sciences, Florida International University, Miami, FL 33199, USA.
e-mail: eric.vonwettberg@fiu.edu


Background: Anthocyanins are produced by plants in response to diverse stresses. Mutants that block the anthocyanin biosynthetic pathway (ABP) at various steps can easily be compared across numerous abiotic stresses.

Hypothesis: Anthocyanins or their precursors are required for stress tolerance. Thus, ABP loss-of-function mutants should have proportionately lower fitness than wildtype plants under stress, compared with benign conditions. In contrast, a decrease in maximal vigour – the general capacity for growth and fecundity – should be most pronounced under benign conditions that allow luxuriant growth by the most vigorous genotypes.

Tests: Determine whether, under stressful conditions, ABP loss-of-function mutants have relatively lower fitness than wildtype plants. Also, test for reduced maximal vigour by determining whether ABP mutants have comparatively decreased fitness under optimal (‘benign’) growing conditions.

Organism: Arabidopsis thaliana loss-of-function mutants (representing all steps in the ABP), as well as wildtype plants, in two genetic backgrounds.

Methods: We grew plants under near-optimal conditions and five stress treatments (UV-B, drought, cold, low Ca : Mg, high Ni). We estimated relative fitness as an individual’s lifetime fertility, relative to the mean wildtype fertility in a given treatment.

Results: Stress treatments significantly reduced lifetime fertility of wildtype and mutant lines. Wildtypes outperformed anthocyanin-deficient mutants under benign conditions, but as the stress increased, the difference between wildtype and mutant fitness diminished. Fitness did not increase with a mutation’s sequential position in the ABP, nor was there an effect of the ability to produce flavonols on fertility.

Conclusions: Mutations in the ABP did not reduce stress tolerance. Rather, the loss of ABP function reduced maximal vigour, most evidently in near-optimal growth conditions.

Keywords: abiotic stress tolerance, anthocyanin biosynthetic pathway, flavonols, mutants, trade-offs, vigour.

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