Damage changes the optimal light color for growth and reproduction of Arabidopsis thaliana

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Shira M. Sasson and Daniel R. Scholes, University of Indianapolis

Background/Question/Methods
Tissue removal by mammalian herbivores is a common and often intense stressor for plants to mitigate. Damaged plants typically exhibit substantially altered regrowth patterns relative to undamaged growth, and different plant genotypes can vary considerably in their regrowth and reproductive success when damaged. Arabidopsis thaliana genotypes display a wide range of natural growth patterns and reproductive success, as well as a variety of tolerance outcomes. An aspect that is not readily testable under natural conditions however is the role of light in influencing patterns of growth, reproduction, and damage tolerance. Specifically, different wavelengths of light are known to cue development—blue light typically promotes vegetative growth while red light stimulates flowering. Using Columbia-4 (Col-4), Landsberg erecta (Ler), and two Col-4×Ler offspring genotypes grown in red, blue, and white light (as a control), we determined whether light interacts with genotype to influence undamaged growth and reproduction. We measured the total length of all stems as a measure of growth and estimated seed yield as a measure of reproduction. Further, half of the plants of each genotype×light group were clipped during growth, and their regrowth and reproduction were compared to unclipped plants to determine the effect of light color on damage tolerance.

Results/Conclusions
Relative to plants in white light, unclipped Col-4 and Ler experienced increases in total stem length and seed yield when grown under blue light and decreases in these measures in red light. The Col-4×Ler offspring genotypes experienced decreased total stem length and seed yield under both experimental light conditions relative to white light. Col-4 and Ler both experienced an increase in growth and reproduction when damaged relative to when undamaged under white light, but experienced lower tolerance ability for stem length and seed yield when damaged under blue and red light. Both offspring genotypes however experienced reduced stem length and seed yield when damaged under white light, greater damage tolerance under red light (though still with a decrease when damaged), and a substantial increase in growth and reproduction when damaged relative to when undamaged under blue light. Overall, genotypes that grow and reproduce best under blue light (Col-4 and Ler) tolerate damage least under blue light, whereas those that inherently grow worst under blue light relative to other light conditions (the offspring) tolerate damage best under blue light. These results support the reported tradeoff between undamaged fitness and damage tolerance and indicate a role for blue light in this pattern.