The Response Mechanisms Of Lateral Roots And Stomata To Elevated Carbon Dioxide

The atmospheric concentration of carbon dioxide (CO2) has increased markedly since the industrial revolution as a result of abundant fossil fuel use and deforestation. Elevated CO2 has been shown to enhance photosynthesis, growth and development of roots, while induce stomatal closure of leaves. Lateral roots (LRs) play an important role in nutrient uptake, and thus alleviate the nutrient limitation to plant growth under elevated CO2. On the other hand, elevated CO2 has been shown to induce stomatal closure of leaves. Stomatal closure significantly decreases plant transpiration, and contributes to enhanced water use efficiency and resistance to water stress. Several lines of evidence suggest that nitric oxide (NO) plays an important role in diverse physiological processes, including plant growth and development, stomata movement, and resistance to biotic and abiotic stresses. This paper examined the response mechanisms of lateral roots and stomata to elevated CO2 and the role of NO in CO2 elevation-induced lateral root formation and stomatal closure.In Conviron E7/2 growth chambers, CO2 treatments were initiated by treating with a concentration of either 350 or 800 μL L-1. Then, the number of lateral roots, stomatal aperture, NO levels and enzyme activity were measured. The levels of NO were determined using the cell NO-specific fluorescent probe (DAF-FM DA). The role of nitric oxide synthase (NOS, indicated like NOS or NOS-like in the paper) and nitrate reductase (NR) in the CO2 elevation-induced NO accumulation was explored by application of NOS inhibitor L-NAME and NR inhibitor tungstate, respectively. Tomato, arabidopsis wild type, NOS mutant atnosl and NR mutant nia1nia2 were used as experimental materials to explore the response mechanisms of lateral roots and stomata to elevated CO2.1. Tomato was used to explore the response mechanisms of lateral roots to elevated CO2. We suggest that CO2 elevation-induced NO accumulation was important for lateral root formation. Elevated CO2 significantly increased the activity of NOS in roots, but not NR activity. Moreover, the pharmacological evidence showed that NOS rather than NR was responsible for CO2 elevation-induced NO accumulation. Elevated CO2 enhanced the activity of NOS and promoted production of NO, which was involved in lateral root formation in tomato under elevated CO2.2. The present experiment showed that after 6 hours of elevated CO2 treatment, the stomatal aperture decreased to 2.3μm, which was decreased by 32% in comparison with ambient CO2 treatment. The intensity of green fluorescence showed that the level of NO in guard cells were 88% higher under elevated CO2 than under ambient CO2. CO2 elevation-induced stomatal closure was reversed by treatment with NO scavenger cPTIO, the level of NO in guard cells decreased by 35% and the stomatal aperture increased to 3.2 μm, similar to those under ambient CO2. Under elevated CO2, addition of 200μM L-NAME increased the stomatal aperture by 30% and decreased NO accumulation in guard cells by 33%; while addition of 100μM tungstate increased the stomatal aperture by 35% and decreased NO accumulation in guard cells by 40%. It is showed that elevated CO2 significantly increased the level of NO in guard cells and decreased aperture of stomata compared to ambient CO2. CO2 elevation-induced stomatal closure was reversed by scavenging NO. It indicated that NO plays an important role in stomatal closure of tomato induced by CO2 elevation. The pharmacological evidences that both NOS inhibitor L-NAME and NR inhibitor tungstate significantly decreased NO accumulation in guard cells and inhibited stomatal closure under elevated CO2, indicated that both NOS and NR were involved in CO2 elevation-induced NO accumulation. Therefore, it could be concluded that elevated CO2 promotes the production of NO through both NOS and NR, increases the level of NO in guard cells, which then induces stomatal closure in tomato.3. Arabidopsis wild type, NOS mutant atnosl and NR mutant nia1nia2 were used as experimental materials. In the present study, it is showed that elevated CO2 induced NO accumulation in guard cells by 120% and decreased aperture of stomata by 32% compared to ambient CO2. CO2 elevation-induced stomatal closure was reversed by scavenging NO. Here, we suggested that NO plays an important role in stomatal closure of Arabidopsis induced by elevated CO2. The pharmacological and genetic evidences that both NOS inhibitor L-NAME and NR inhibitor tungstate significantly decreased NO accumulation in guard cells and inhibited stomatal closure, while the stomatal aperture of both atnosl and nia1nia2 mutant decreased slightly under elevated CO2, indicated that both NOS and NR were involved in CO2 elevation-induced NO accumulation. Therefore, we conclude from these findings that elevated CO2 increases the level of NO through both NOS and NR, which then induces stomatal closure in Arabidopsis under elevated CO2.