Response To Cd Stress Of Different Families Of Hibiscus Hamabo Sieb.et Zucc

Hibiscus hamabo Sieb. et Zucc.is the deciduous arbor, which belongs to Hibiscus, Malvaceae. It is a pioneer tree species and it is always used as bank protection forest and the coastal backbone forest strip because of its saline tolerance, water-out tolerance, protection of sea wind. Some researches had been made and a certain achievements had been got on seedling-raising technique, waterlogging and salt trees of Hibiscus hamabo. There are rear researches on effects of Cd on Hibiscus hamabo families. This paper took 6 families seedlings of Hibiscus hamabo as the materials, used solution culture method to study the physiological and biochemical mechanism for Cd (0,10,20,30 mg/L) and the difference tolerance for Cd among different families. The purpose of this study was to provide useful reference for using woody plants to repair and improve soil (especially beach) polluted by heavy metal Establish comprehensive index system of superior family breeding and provide plant material for building bank protection forest on the southeast coastal through the comparison of different tolerances for Cd among different Hibiscus hamabo families. The results were as follows:(1) Growth and change of physiology of seedlings in Hibiscus hamabo families under Cd stressLong time (60 d) Cd stress decreased the net height and total biomass of seedlings in Hibiscus hamabo families significantly under solution culture. This phenomenon was observed more obviously when the concentration was high. At the early stage of sreess, net height of seedlings incrased fast, the stress time longer, the increasing range became smaller.SPAD, Fv/Fm,φps(?), qP decreased as time of stress went on of seedlings in Hibiscus hamabo families. NPQ gradually increased which decreased the activity of PSⅡ. The decrease of chlorophyll molecule was the main reason of Fm decreasing. At the same time, stress of Cd2+ changed the composition of photosynthetic pigment, the synthesis of Chla was more sensitive to Cd2+ Decreasing content of Car indicated that Cd2+ reduced the ability of antioxidation of non-enzyme systems of Hibiscus hamabo.The activity of SOD, POD and CAT, content of SP in young leaves of seedlings in Hibiscus hamabo family increased first and then decreased under Cd4 stress. The increase reduced the toxicity of Cd2+ in some degree, however, their decrease indicated that there was some limit on protection of membrane system and osmoregulation substances. Change of SOD activity was consistent with CAT activity. Degree of activated of POD and duration of POD activity was longer than SOD and CAT. Time for SP content reached to the peak was shorter than SOD, POD and CAT which indicated that soluble protein in Hibiscus hamabo was more sensitive to Cd2+. Because the duration time was short, the soluble protein was inhibited easily. Content of MDA in seedling leaves increased gradually and the preoxidation activity of membrane lipids aggravated while the concentration of Cd2+ increased and stress time prolonged. (2) Root morphological and physiological pesponses of seedlings in Hibiscus hamabo families to Cd stressLong time Cd2+ stress (10-30 mg/L) decreased the length, surface area, volume, tips and the composition of root in seedlings of Hibiscus hamabo families significantly. Effect of Cd2+ on cross-growth of root (tips and composition of root) was more obvious than longitudinal growth of root (length, surface area and volume of root) which resulted that morphologic structure of root tended to simplification. The root system spatial structure was simpler when the Cd2+ concentration was higher. There was a significant negative correlation between MDA content and morphological parameters (R=0.865, p＜0.05) under Cd2+ stress which could be conjectured that increase content of MDA in seedlings root resulted in the change of root morphologic structure (tend to simplification).Ratio of SOD/POD and SOD/CAT in seedlings root increased while concentra-tion of Cd2+ increased, the increasing range of SOD/POD was more obvious which indicated that the root cell of seedlings had been damaged by oxidation. There was differences among different Hibiscus hamabo families on endurance to Cd. SH3 and S8 had strong durance while C25 and S1 had weak durance. (3) Accumulation of Cd in seedlings and tolerance of seedlings in Hibiscus hamabofamilies under Cd stressStress of Cd+(10-30 mg/L) for 60 d decreased biomass of seedling both above and under ground, increased the ratio of root-shoot, changed the distribution pattern of biomass. Under 10,20,30 mg/L Cd2+ stress, Cd content of root in seelding was 1720. 3410,4780 mg/kg respectively, which showed that Hibiscus hamabo had super ability to accumulate Cd and the enrichment of Cd was observed in root. The amount of Cd accumulation increased while biomass decreased when concentration of Cd increased, which indicated that high biomass of plant and super ability of accumulating Cd could not appear at the same time. High ability of accumulation decreased potential biomass of plant. Cd tolerance index showed that Hibiscus hamabo seedlings had high Cd tolerance (Ti=69.30) when concentration of Cd2+ was 10 mg/L. Tolerance of Cd under 20 and 30 mg/L was medium and the tolerance index was 55.53,35.21 respectively. There were significant difference on Cd accumulation and Cd endurance among different Hibiscus hamabo families under Cd stress.The best two families were SH3 and S8 while the worst family was C25. (4) Comprehensive evaluation on Cd tolerance among Hibiscus hamabo familiesThe height, biomass, SPAD, Fv/Fm,φPSⅡand qP of Hibiscus hamabo decreased when Cd pollution was serious. Cd pollution could increase the activity of POD in order to protect the membrane system of Hibiscus hamabo plant. At the same time, Cd pollution increased NPQ and content of MDA in plant cells significantly.Analysis of principal component showed that the change of growth characters and chlorophyll fluorescence parameters of Hibiscus hamabo seedlings was most obvious under Cd stress. These change had indicative function to contamination degree of soil. The activity of POD could reflect the tolerance of Hibiscus hamabo under Cd stress. Root morphological parameters could also be used to reflect the Cd tolerance of Hibiscus hamabo families.Comprehensive appraisal of characters on Cd tolerance among 6 Hibiscus hamabo families showed that tolerance order to Cd were different when different itms were studied in one family. It was concluded t at the tolerance order was SH3＞C17＞S8＞SH2＞S1＞C25 among 6 Hibiscus hamabo families. Breeding and using Hibiscus hamabo families which had strong tolerance to Cd was benifical to control the pollution of Cd in tidal flats soil and proided valuable plant materal to construction of protection forest in southeast coast.