Cross talk between phytohormones, nitric oxide (NO), and auxin has been implicated in the control of plant growth and development. Two recent reports indicate that NO promoted auxin signaling but inhibited auxin transport probably through S-nitrosylation. However, genetic evidence for the effect of S-nitrosylation on auxin physiology has been lacking. In this study, we used a genetic approach to understand the broader role of S-nitrosylation in auxin physiology in Arabidopsis. We compared auxin signaling and transport in Col-0 and gsnor1-3, a loss-of-function GSNOR1 mutant defective in protein de-nitrosylation. Our results showed that auxin signaling was impaired in the gsnor1-3 mutant as revealed by significantly reduced DR5-GUS/DR5-GFP accumulation and compromised degradation of AXR3NT-GUS, a useful reporter in interrogating auxin-mediated degradation of Aux/IAA by auxin receptors. In addition, polar auxin transport was compromised in gsnor1-3, which was correlated with universally reduced levels of PIN or GFP-PIN proteins in the roots of the mutant in a manner independent of transcription and 26S proteasome degradation. Our results suggest that S-nitrosylation and GSNOR1-mediated de-nitrosylation contribute to auxin physiology, and impaired auxin signaling and compromised auxin transport are responsible for the auxin-related morphological phenotypes displayed by the gsnor1-3 mutant.
Water deficits are a common limiting factor of plant growth. Many studies have looked at the effects of drought, but few have compared the independent and interactive effects of multiple dimensions of changing precipitation patterns (e.g., reduced rainfall frequency and reduced rainfall volume) on overall plant growth of individuals with snapshots of growth-related plant performance. Methodology. In this greenhouse experiment, we investigated responses of the legume Lupinus perennis and the C 3 grass Agropyron repens to a factorial combination of 50% reductions in watering frequency and watering volume. Watering treatments were designed based on 10-yr climate records from where these species co-occur. For both species, we measured leaf senescence, above-and belowground biomass accumulation, leaf net photosynthesis, and stomatal conductance. The leaf water potential and the proportion of N derived from symbiotic N 2 fixation of L. perennis were also measured. Pivotal results. Reduced watering frequency had similar effects on both A. repens and L. perennis, including a 21% reduction in total biomass. However, effects of the reduced-volume treatment were largely species specific. For example, total biomass accumulation decreased and leaf senescence increased only in L. perennis. The proportion of N from symbiotic fixation in L. perennis was reduced only when water volume was also reduced, but overall leaf N remained constant in all treatments. Instantaneous prewatering gas exchange measurements showed that species maintained leaf net photosynthesis but with reduced stomatal conductance across all water availability manipulations. Conclusions. This study provides new insights into differential and species-specific effects of changes in water frequency and volume. Moreover, it suggests that trying to understand plant responses to changing or heterogeneous precipitation regimes based solely on a single parameter of water availability (often mean annual rainfall) might mask important dynamics governing these phenomena.
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