| Banana (Musa. Spp.) is an important herbaceous fruit tree in many tropical and subtropical countries. Shoot-tips micropropagation, cryopreservation by vitrification, ultrastructure of cryopreserved cells and genetic stability of three banana cultivars: "Baxi" (AAA), "Guangdong 2"(AAA), "Guangdong 1"(ABB) were studies in this experiment to investigate primary influencing factors.The main results are as follow:1. Medium for banana shoot-tips culture was optimized and selected. The cluster buds were proliferated preferably and subcultured on the proliferation medium containing 3.0~5.0mg/LBA and 0.1mg/LNAA. Additionally, the buds were rooted normally on half-strengthened root-inducing medium containing KT0.2mg/L and NAA0.1mg/L, and the plantlets could normally root and survive after transplantation.2. Shoot tips excised from healthy in vitro plants of three Banana cultivars were successfully cryopreserved with the vitrification technique. A suitable procedure was established as follows:3~4 weeks after subculture, shoot tips about 2~3cm in length were precultured for 2 days at (25±2) ℃on MS medium supplemented with 0.4mol/L sucrose. Dissected shoot apices about 1.0-1.5mm in length with one or two leaf primordium were loaded with a mixture of 2mol/L glycerol plus 0.4mol/L sucrose for 20~30 min at room temperature. These excised shoot tips were sufficiently dehydrated in a highly concentrated vitrification solution for 40 min at 0℃. And then plunged directly into liquid nitrogen and conserved for at least 1h. After rapid thawing in water at 40℃ for 90s, the tips were rinsed in a 1.2mol/L sucrose solution for 20min at room temperature and then plated on a solidified culture medium supplemented with 0.5 mg/LBA. The cryopreserved materials were cultured in darkness for one week so that they could grow quickly. Successfully vitrified shoot tips resumed growth within 10d of plating and developed shoots within 1 month without intermediary callus formation. This simple protocol was successfully applied to the three cultivars belonging to two genomic groups of banana. The survival rate of shoot tips was 75.9%, 40.0%, 69.6%,respectively,and regrowth rate reached 63.4%, 35.0%, 63.4% respectively. Almost all the shoot tips formed roots and were successfully transferred to soil in pots. The plantlets could normally root and survive after transplantation.3. In vitro cultured bananas were used to study on genetic stability aftercryopreservation, including morphology, cytology and molecular biology. Results showed that on the one hand, there are no significance about leaf area, leaf color, leaf figure, plant height and stem diameter between the treated plantlet and its control. Secondly, chromosome numbers did not alter and were the same as control. On the other hand, DNA polymorphism was not different by AFLP. So we could conclude that genetic stability of banana was not altered after cryopreservation.4. infrastructure of cryopreserved cells was observed by using electron micryoscopy (TEM). The results showed that the plasmolysis became more and more severe during induced dehydration of banana shoot-tips. Most cell protoplasts condensed, and cell walls, cell membranes and nucleus envelopes were lethally injured after freezing conservation. But there were also a few cells located in the periphery of the meristematic dome, which were basically similar to that of control material. They could survive and regenerate plantlets after cryopreservation process.
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