Preliminary Illustrate The Physiological And Molecular Mechanism Of Affecting Arabidopsis Primary Root Growth Under UV-B Stress

As an important abiotic stress, ultraviolet B (UV-B) radiation is relatively clear in the study of leaf and stomata, however fewer researches on the root system of plants. Studies show that Arabidopsis thaliana root system can response to UV-B signal and the root tip become up warped under the UV-B treatment. To elucidate the effect of UV-B stress on plant root growth and development, this paper uses model plant Arabidopsis thaliana as study materials to analyze the root growth morphology in seedlings, and the effect of ROS, NO and auxin signal under UV-B stress in Arabidopsis root tip, as well as to discuss the biological significance and so on.The trial uses UV-B to induce 5-days-seedings 3min, then recover the seedlings to normal growth condition of vertical cultivation, and detect to morphology, physiology, biochemistry and molecular index. Through a series of tests, we get the following results:UV-B stress can induce primary root tip up warp in Arabidopsis thaliana seedlings. And the angle of up warped root is changing with the time of exposure to UV-B. According to the statistical analysis of the angle of up warped root, the root tip in Arabidopsis thaliana seedlings is up going. Up to 90 degrees, the root tip begin to stretch forward, and then the root tip grows it back to MS medium after 24h.The starch granules in Arabidopsis root cap are reducing gradually under UV-B stress. Up to 12h, starch granules begin to recover slowly. This suggests that starch granules content in root cap rapid reduce under UV-B stress, resulting root tip geotropism lost, which may be one of the reasons of Arabidopsis root tip up warped.PI staining shows that Arabidopsis primary root tip in both meristematic zones and upwarped section appear obvious cell death under UV-B stress; Further analysis by DAPI and hochest33342 fluorescent staining shows that UV-B stress can cause programmed cell death significantly in root tip meristematic zones. This suggests that under UV-B stress, the root tip can regulate the root development by inducing cell apoptosis to adapt to the adversity stress.Morphology analysis shows that "upwarped root" is due to the cells of root tip elongation zones out of shape, leading to the root tip become up warped from the surface of the MS medium. Using transgenic plant of microtubules marker gene TuA6-GFP, we found that the microtubules in cells of meristematic region happened rearrangement after UV-B stress, then leading to cell morphological changes.Using ROS fluorescent probes and NO fluorescent probe test, we found that UV-B stress induced the outbreak of ROS and NO significantly in root tip of Arabidopsis thaliana seedlings. Further studies showed that there is no relationship between upstream and downstream of ROS and NO, suggesting that they were produced by way of independence under UV-B stress.Using transgenic plants DR5-GUS, we analyzed the change of response to auxin in Arabidopsis taproot under UV-B stress. We found that DR5-GUS staining reduce gradually in Arabidopsis thaliana root tip under UV-B stress, and to 6h, it recovered to normal level gradually. We further analyzed the effect on auxin transport protein of root tip under UV-B stress. Through analysis of transgenic plants that auxin transport protein of fluorescence reporter gene, we found that under UV-B stress AUX1-YFP fluorescence of root tip decreased significantly, 1h to a minimum, then recovered to normal level gradually; PIN2-GFP decreased to a minimum at 2h, then recovered to normal level gradually. These suggested that UV-B stress may be affect the ability of auxin transport in root tip, thus changed auxin levels in root tip, and then affected starch granules content in root cap, resulting in geotropism loss and the appearance of "upwarped root". Using genetics analysis of auxin over-production mutant yucca, we further confirmed that the up warped root was related to the change of auxin content in root tip.With the treatments of ROS scavenger or NO inhibitor, we found that ROS and NO influenced on the response of DR5-GUS obviously in root tip, which indicated that both two signaling molecules may be involved in regulating the content, distribution and response of auxin in root tip under UV-B stress.In this paper, we preliminary illustrates the NO/ROS signal and auxin are involved in regulating signal pathways and molecular mechanism of UV-B stress. These studies are helpful for us to further clarify the signaling pathways UV-B induced in plant root system, and provide the basis for further illuminating the physiological and molecular mechanism of plant root development under UV-B stress.