| Spirodela polyrhiza (L.) Schleiden is an aquatic floating plant in Lemnaceae. It distributes in temperate and tropical zone worldwidely. Spirodela polyrhiza is used as animal feed due to several features: rapid growth, high starch and protein contents, and easy to collect etc. It grows in wastewater to remove nitrogen, phosphorus and heavy metals to purify the water. It can also be used as a medicinal plant. Spirodela polyrhiza has multiple benefits as fodder, wastewater purifier, biomass energy and Chinese herbology.Spirodela polyrhiza is usually used as an energy plant because of it’s high starch content.The germplasm resources usually preserved as frond cultures, which needs periodical replacement with fresh medium. Spirodela polyrhiza can form a kind of dormant bud called turion. Turion has high starch content of nearly 60% in dry weight and is able to survive in harsh environment. The main purpose of this experiment is to develop a highly efficient protol to induce turion formation and germination, to provide improved starch content and preserve Spirodela polyrhiza germplasm in the form of turion.Spirodela polyrhiza strain DW2501-4 that was collected from Hainan was used to study turion-mediated reproduction. Paraffin sections of the fronds, turion-like fronds,and turions were prepared to observe their tissue structure. Strains HB0301 that was collected from Hubei and DW2501-4 were used in turion production and germination study in the laboratory conditions and outdoors. Turions were prepreserved under different conditions before they were induced to germinate. The main results were as follows:(1) New fronds of DW2501-4 reproduced continuosly in half strength Hoagland’s solution until the nutrition was scarce, turion was then formed. The turions were collected and cold-treated for one week at 40C, and were transfered in half strength Hoagland’s solid medium with 1% sucrose, and incubated at 24℃. The turions germinated in 3 days.Paraffin sections of the fronds, turion-like fronds, and turions were prepared to observe their tissue structure. Results indicated that fronds had several veins and a small amount of starch grains in the cells, it was full of air chambers in the tissue, and air chambers in the upper layer were small while air chambers in the bottom layer were big. Turion-like frond contained a few veins and some small air chambers, its cells contained a lot of starch grains. Veins and air chambers were not observed in turion. A lot of starch grains were observed in turion cells, some tannin cells were also observed in turions. During germination, the starch grains were digested and became smaller and smaller, and roots and new fronds were formed.(2) Four inducing factors of turion formation were investigated using a single factor design and orthogonal design: nutritional deficiency, abscisic acid (ABA) concentration,temperature, illumination time. Results showed that: ①The nitrogen deficiency could quickly and efficiently induce turion formation than phosphorus deficiency and sulfur deficiency.②ABA(concentration above 0.05 μg/mL) inhibited the growth of fronds,and the optimum ABA concentrations were 0.005 μg/mL and 0.01 μg/mL for turion induction in DW2501-4 and HB0301,respectively.③At 20 ℃ to 320C, lower temperature were favorable for the formation of turion, whereas, higher temperature were advantageous to the frond reproduction. ④DW2501-4 and HB03 formed more turions and fronds at 16 h and 24 h of light than 8 h of light. Long illumination time were good for turion formation and frond reproduction. ⑤The optimum conditions of turion formation was half strength Hoagland’s medium supplemented with 0.005 μg/mL ABA, at 24℃, 16 h/8 h (day/night)photoperiod.③ HB0301 and DW2501-4 were cultured under outdoor natural illumination.①Cultured in August 2015, the amount of turion and starch content of DW2501-4 were significantly higher when cultured in both tap water and half strength Hoagland’s liquid medium without nitrogen, the amount of turion was significantly higher when HB0301 were cultured in tap water and the medium without nitrogen, starch content of HB0301 was significantly higher when cultured in the medium without phosphorus. The lack of nitrogen and phosphorus could promote the formation of turion and starch accumulation.④Turions of DW2501-4 and HB0301 had the highest germination potential and produced more fronds under 24 h and 16 h of light. The germination rate had no significant difference between the three light condition, but turion germination time were shorten by long-day illumination. ④The optimum condition of turion germination was cultured in half strength Hoagland’s solid medium supplemented with 1% sugar and 0.1 μg/mL GA3,at 28 ℃, 16 h/8 h (day/night) photoperiod.(5) Tutions of DW2501-4 and HB0301 had higher germination rate that preserved at 4℃than preserved at the room temperature. After preserved at 4℃ for 270 days, the turion germination rate were 38.3% and 40.0%, respectively. |
