Study On The Embryo Development And Seed Germination Of Bletilla Striata

Bletilla striata is the research objective and three aspects were carried out.The differences between sexual reproduction and NAA induced apomixis of B.striata were explored in this study by observing the morphological development of ovules and seeds at different day after pollination.The seeds were used as materials and the nutrition type of B.striata seed germination was determined by methods of the seeds were sterile culture on silica sand substrate（removing organic components）adding MS liquid medium under light,as well as cultured on the peat and leaf substrates under light or in dark.In addition,the effects of different days after pollination（DAP）,plant growth regulators,light intensity and other factors on the germination of B.striata seed are also explored.These provided references for further understanding of the development of B.striata seed embryos and seed germination.The main results are as follows:1.Comparative study between sexual reproduction and apomixis.The results show that:（1）The ovules were limited development at the time of flowering,a large number of ovule primordia were formed on 10 DAP;the archesporial cell developed into embryo-sac mother cell on 25 DAP;the double fertilization was completed on 36-39 DAP;the development of embryo began on 45 DAP and embryos developed completely on 130 DAP;（2）NAA-induced apomixis fruits is small and the rate of seeds with embryo is low.The diameter of fruit and rate of seed with embryo were 0.71 cm and 66.73%on 130 DAP,while those induced by NAA were0.45 cm and 42.47%,respectively.In addition,the results in vitro culture showed that the germination and growth of seeds induced by NAA were slower compared with that of normal pollination and drying treatment also significantly delayed the seed germination;（3）Ovules development in the same ovary was not synchronous under these two treatments.On normal 39DAP,the maximum vertical diameter of ovule was 1.08 mm,and the minimum was only 0.21mm,double fertilization have completed in most embryo sacs,while a few are still developing.On 30 DAP NAA treatment,the maximum vertical diameter of ovule was 0.31 mm and the minimum was only 0.16 mm,while most of the ovules only developed into mononuclear embryo sac and a few developed into 2-nuclear embryo sac.2.Study on the nutrition type of B.striata seed germination.The results showed that:（1）The seeds can germinate normally and grow into autotrophic individuals even on silica sand substrate（removing organic components）adding MS liquid medium under light.The dry weight of protocorm decreased at the early stage of seed germination and increased gradually with the development,it was 3.4μg at 2 d,drop to 1.8μg at 6 d,and increase to 9.2μg on 12 d meanwhile the leaf length was 0.22±0.03 mm;（2）The growth rate of B.striata protocorm on peat substrate was faster than that of leaves,and seedlings can form efficiently.The seeds can germinate and grow normally on the leaf substrate under light.However a large number of embryos stopped growing after seed coat rupture in dark;（3）The protocorms formed on peat and leaf were observed by tissue staining,and the endophytic fungi was not found in protocorms.In other words,seed germination of B.striata is non-fungal heterotrophic type and is different from that of most orchids.3.Influencing factors on B.striata seed germination.The results show that:（1）the different DAP affected germination,with the extension of DAP the time shortened and the rate increased;acid hydrolyzed casein promote germination of seed at 45,50 and 70 DAP,and only the embryo anterior part of immature seeds turned green when the embryos swelled;（2）the effects of four plant growth regulators on germination are that ABA inhibited seed germination and growth but it do not restrain the protocorms turning green;GA₃ promoted the elongation of protocorm and leaves,and length of protocorm in 0.5 mg·L^-1GA₃ can be up to 3.23 mm;6-BA had no significant effect on the germination and growth;NAA faded the green color of protocorm,in addition inhibited growth at high concentration;（3）the influence of three kinds of light intensity on germination and growth is that on the solid medium,the embryo became green after absorbing water under normal light,and formed leaves,adventitious roots and pseudobulbs in turn;The protocorm elongated under weak light;Under dark condition,the germination time was prolonged,and the protocorm continued to elongate,similar to the phenomenon of"etiolation",similar to the effect of GA₃.