Regulation Of Plant Growth Substances On The Turions Formation And Germination Of Potamogeton Crispus L.

The formation and germination of turions are two key stages in the life cycle of Potamogeton crispus L.. a typical submerged macrophyte. and have an important impact on the rise and fall of the populations of P. crsipus in natural water. The cultured plant or turions of P. crispus were treated exogenously with hormones-like substances to study the regulation of plant hormone on the formation and germination of turions. The physiological mechanism of turions formation and germination and the responses of turions formation to phosphorous level in water were also investigated. The research provided certain experimental basis for exploring the mechanism of the rise and fall of P. crispus in polluted water and P. crispus revegetation in adversed environment. The main results are as followes:1. The survey result conducted in an pond near Nanhu lake, Wuchang showed that, P. crispus began flowering in late March, then fruiting and a large number of turions generated in mid-Apirl, and when turions began ripeness in early and mid-May, plant began to decline. The chlorophyll a content of plant increased significantly during flowering and then maintained relatively stable, but increased significantly again during the period of plant declining and falling. The contents of chlorophyll b and carotenoid in plant showed a big swing during the propagule formation. The content of soluble protein in plant increased up to the maximum in flowering, and then reduced gradually, but increased again near the period of declining and falling. The content of carbohydrate in plant showed that, the downward trends of the content of starch, soluble sugar and surcose were showed when the turions formed, implied that these substances might be the source of the storage material in turions.2. In the conditon of artificially controlled culture of 0.025～25 mg/L of phosphorus concentratiuon of water, stem and leaf growth and biomass accumultion of plant were little affacted, while Chlorophyll a, chlorophyll b and carotenoid contents of plant reduced along with increasing phosphorus level, as well as the starch content. Reducing sugar and sucrose contents declined when the phosphorus level of water increased to 0.25 mg/L and 2.5 mg/L, respectively. Phosphorus content in plant increased with elevating phosphorus level of water. When the phosphorus level was 0.25 mg/L or higher, decreased nitrogen content and increased soluble protein content in plant were determined, demonstrated that a metabolism adaptatiive ability might exist in P.crispus under certain degree of high-phosphorus stress. With increasing phosphorus level, the dry weight of turion reduced but its water content increased, and the changes reached significant level when phosphorus increased to 2.5 mg/L. The number of turion formation and biomass per plant decreased significantly when phosphorus level increased to 25 mg/L. The contents of soluble sugar, reducing sugar and starch in plant were detected decreased by the increasing phosphorus levels. As a result, we suggested that progagule formation was more sensitive to the phosphorus level of water than the plant growth of P.crispus. It might be one of the mechanisms that P. crispus population declined in eutrophicated lakes.3. From 12 days before propagule formation, we applied 6-BA and GA₃ on cultured plant of P .crsipus. The results showed that, treating with GA₃ or 6-BA could both inhibite the propagules formation. Among treatments once for 4 h every 3 days with GA₃ or 6-BA of 2.5 mg/L and 25 mg/L, only in GA₃ treatment of lower concentration a fewer branch-like turions, which were smaller, slender and were named phylloclade turion. formed. While, in other treatments progagules formation were inhibited thoroughly. There were less difference existed in type, proportion, length and some other morphological types of progagules were observed between 6-BA treatments and control, but more phylloclade turions generated and propagules were longer with more nodes were found in GA₃ treatments than that in control. Physiological and biochemical analysis showed that cytokinin affacted propagule formation mainly through promoting chlorophyll and soluble protein content increased, while gibberellin mainlly through inhibiting carbohydrate accumulation in propagule. Plant growth was more sensitive than propogule formation to the two types of plant growth regulators.4. In the natural condition of winter, 5μmol/L,10μmol/L of abscisic acid (S-ABA, a natural type of ABA) were applied with different ways on cultured separated stems of P. crispus in 1 % Hoagland nutrient solution with controlled nitrogen level of 0.25 mg/L and phosphorus level of 0.025 mg/L to detect the effect of ABA on stem growth and development. The results showed that treating once (4h) with different condcentration of ABA had no significant impact on stem biomass, but decreased branch formation significantly. Treating several times (4 h every 4 days) with different concentrations of ABA slowed down stem biomass accumulation, but increased branching and increased root length, significantly and with a stronger effect in lower concentration treatment. Determination of photosynthetic pigments showed that treating once with two concentrations and several times with higher concertration had little effects on the contents of chlorophyll (Chla and Chlb) and carotenoid, but treating several times with lower concertration of ABA increased chlorophyll contents. The soluble protein content increased by ABA treating once, but decreased by treating several times. In our expermental condtion, no propagule formation was found.5. Dormant turion were treated with 150 mg/L GA₃, 10 mg/L 6-BA, 150 mg/L NAA and 10 mg/L 2,4-D, respectively and was incubated in indoor tap water in summer to detect the mechanisms of turion dormancy release. The results showed that these plant growth substances could release turion dormancy quickly, and made turion germinate more shoots. Among these treatments, 6-BA showed the strongest effect on promting germination and GA₃ promoted young shoot growth mostly. During germinating progress, the turion starch content in vivo reduced significantly and quickly at the initiation, and the contents of reducing sugar and soluble sugar increased after the first drop. It suggested that gowth-promoting plant hormone were involved in regulatiing turion germination through promoting carbohydrate metabolism in turion. 6. The turions treated with the plant growth substances said above were planted in basin using paddy soil as sediment and water as overlying water in summer. The results showed that all treatments increased the plant surviving number significantly. GA₃ treatment promoted primary branch growth, but inhibited root growth, and NAA treatment as well. Meanwhile, GA₃ treatment inhibited secondary branch formation, but promted its growth, and 6-BA treatment as well. More propagules were formed by different substances treatments than that in control, and GA₃ treatment got the most phylloclade turion formation and the highest total biomass both of propagule and plant. Chlorophyll and carotenoids determination in plant showed that all phtosynthetic pigment contents, the ratios of Chla/Chlb and Chl/Car in growth substances treatments were almostly samilar levels as those in control. The plant contained higher nitrogen concertration treated with 2,4-D and NAA, and higher phosphorus concertration with 6-BA and 2,4-D. The inceased pH and transparency, but decreased conductivity occurred in water when P. crsipus restored growth. Our study explored a possible approach to regulate P. crsipus regrowth in summer water.