Auxins function as key hormonal regulators at the intersection between the environmental signals and the response pathways that they trigger. Auxin levels respond to changing conditions both spatially within the plant and temporally, forming complex gradients that appear to be a central component of the hormone’s regulatory activity for plant development. We will define the responses resulting from perturbations in light quantity and quality to gain an understanding of auxin regulation under differing growth conditions.
- Determine the interactions among auxin transport, auxin synthesis, and light. Although light has been shown to affect some aspects of auxin biosynthesis and polar auxin transport in a variety of different plant species, how auxin transport is regulated by light has not been extensively analyzed. We have recently found profound changes in polar auxin transport in hypocotyls of tomato and Arabidopsis following light treatment and now will characterize the response with regard to light quality and duration in wild-type plants as well as in mutants deficient in known photoreceptors.
- Determine the phytohormonal signaling pathways for the shade avoidance response in Arabidopsis. Shade-intolerant plants, including Arabidopsis, when exposed to light with a reduced red/far-red ratio, as encountered from competition under a plant canopy, initiate a suite of responses known as the shade avoidance response. Growth under reduced red/far-red leads to a rapid increase in auxin levels by activation of auxin biosynthesis dependent on TAA1, an aminotransferase that catalyses the formation of indole-3-pyruvate. Thus, an important goal of this proposal is to more fully elucidate the hormonal signaling events of shade avoidance.
- Measure the relationship between light and auxin synthesis in seedlings transitioning from etiolated growth to auxotrophic metabolism. Since many reports in the literature and our data indicate that auxin content does change in response to light, we will compare totally etiolated plants with those receiving a pulse of light and those transferred to continuous light, over brief time periods (min and hrs) and longer time periods (days) and we will also examine the transition not only in de-etiolation but in response to the development of mature chloroplasts. Thus, the effect of light quality on de novo auxin biosynthesis and on auxin levels will be examined in a systematic way, as well as the role of light intensity (fluence) on initiation of auxin biosynthesis and the levels of IAA established.
In summary, this work focuses on the critical evaluation of the links between light and both auxin metabolism and transport.