Effects Of Auxin On Adventitious Roots Of Suaeda Salsa Under Waterlogging

As the global climate changes, sea level rises. These make the coastal beach landface the threat of flooding. And extreme weather, such as storm and floods, isthreatening the survival of the plants. There is a large area of the coastal beach land inChina, so how to make good use of tidal flats and develop pioneer plants, is significatto improve the land utilization and the development of economy. For most plantsgrown on the beach, the main threat is flooding. Plants under flooding stress develop aseries of physiological, biochemical and morphological changes, to cope with thestress on plant growth. The main harm of waterlogging is anoxia. For most of theplants, when flooding stress occurs, flooded parts of the plants produce adventitiousroots to alleviate the roots anoxic condition. And the formation of adventitious roots ismainly regulated by auxin. Therefore, in this article, Suaeda salsa was used to explorethe effects of auxin on formation of adventitious roots under waterlogging, thechanges of the activity of antioxidant protection system and the changes ofendogenous hormone level. These results will provide certain evidences why plantsgrown on the beach can survive.The main results were as followings:1. Flooding significantly inhibited the growth of Suaeda salsa, while applicationof a certain concentration of NAA or IBA alleviated the suppression of flooding stresson the growth of Suaeda salsa. In a certain concentration range, the dry and freshweight, height and branch number of Suaeda salsa was increased with the rising ofauxin concentration. With0.5mg·L–1NAA or0.4mg·L–1IBA treatment, Suaeda salsagrowth was the best. When the concentration of NAA and IBA continued to increase,the dry and fresh weight, height and branch number of plant began to decline. So0.5mg·L–1NAA and0.4mg·L–1IBA treatment had the most significant effect to alleviatethe inhibition of stress on the growth of Suaeda salsa. So we chose these twoconcentrations as the optimum concentration for subsequent experiments. 2. NAA and IBA could promote Suaeda salsa adventitious roots’ growth underwaterlogging. With the increase of hormone concentration, the number of adventitiousroots, weight and diameter were increased. When treated with0.5mg·L–1NAA, thenumber of adventitious roots quality was the heaviest and the diameter was the largest.With NAA concentration increasing, a series of adventitious roots growth indexdecreased. Under0.4mg·L–1IBA treatment, adventitious roots grew better. With theincrease of IBA concentration, adventitious roots growth index was also reduced. Thisshowed that NAA and IBA as auxin analogues had a dual role for adventitious roots:promote the growth of adventitious roots in a lower concentration, while decrease thegrowth in a higher concentration.3. When waterlogging happened, hormones in plant would change significantly.The results showed that the adventitious roots began to appear within thewaterlogging occurred16hours. So we inferred that, Suaeda salsa endogenoushormone adjustment had been completed from the beginning to16hours ofwaterlogging. After the waterlogging stress occurred, Suaeda salsa endogenous IAAcontent increased, and quickly transferred to the flooded area, to ensure theoccurrence of adventitious roots. Our study suggested that JA-Me has negative effecton the formation of adventitious roots. Because JA-Me’s content in Suaeda salsa wasalso increased under waterlogging, but was blocked in the underground part. As themost common form of stress hormones, ABA in flooding stress occurred alsoincreased at first, then reduced. Contrary to JA-Me, ABA mainly accumulated in theshoot. The results indicated that under waterlogging, the endogenous hormoneschanged differently in different parts of the plant, to regulate and participate theresponse to flooding stress.4. Formationof the adventitious roots in Suaeda salsa under waterlogging wasdetected at parenchymal cell of pericycle. Adventitious roots’ formation might be dueto a certain concentration of auxin that could make the parenchyma cells recovermeristematic ability, form the primordium, and then break through the cortex.Different concentrations of auxin regulated adventitious root’s length mainly throughthe influence of the length of the adventitious root elongation area cells. 5. Under waterlogging, the production of reactive oxygen species in plantsincreased significantly. The accumulation of reactive oxygen species made the plantscell membrane lipid peroxidation, and influenced various physiological processes andmetabolism such as growth inhibition. In the early days of flooding, activity of SOD,CAT and APX of S. salsa seedlings increased, then gradually reduced. Application ofcertain concentration of exogenous NAA or IBA significantly alleviated thesuppression of flooding-induced the activity of antioxidant enzymes in Suaeda salsa,for the ROS removal ability of plant was increased. Also the resistance of floodingwas improved. The results showed that auxin could protect enzymatic antioxidantsystem from waterlogging.At the same time, Suaeda salsa activity of nonenzymic antioxidant system hadalso been enhanced. Different from enzymatic antioxidant system, after7daysflooding treatment, the content of GSH and AsA were significantly higher than that ofcontrol, but the content was relatively lower under optimum concentration ofexogenous NAA or IBA treatment. This showed thatSuaeda salsa relied mainly on thenonenzymic antioxidant system to remove excessive ROS at beginning ofwaterlogging. The existence of exogenous auxin protected the enzymatic antioxidantsystem, so that the nonenzymic antioxidant system had not been fully activated.