Cytoplasmic Inheritance Of Section Leuce In Populus And Their Triploid Hybrid Clones

Cytoplasmic inheritance is a form of extranuclear inheritance,which includes plastid and mitochondria inheritance.So far there are no comprehensive and systematic reports on cytoplasmic inheritance of section Leuce in Populus at home and abroad.The research on cytoplasmic inheritance has theoretical and practical significance in the fields of phylogenetic evolution,genetic diversity,resistance research, genetic improvement and cross breeding of Populus.Sixteen species and clones in section Leuce, including P.tomentosa,P.bolleana,P.alba,P.davidiana,P.adenopoda,P.tomentosa×P.bolleana, P.alba×P.glandulosa,P.alba×P.tomentosa and their triploid hybrid clones were selected as samples.The plastids,mitochondria and their DNAs in the pollen development of section Leuce were studied by a combination of cytological detection of pollen development,pollen nuclease detection and PCR-RFLP analysis.Moreover,the chloroplast traits of triploid clones of Populus tomentosa from different hybrid parents were analyzed to measure genetic effects of the cytoplasm.By these experiments,the obtained major results and conclusions are described as follows:1) The observations of electron microscopic and DAPI-DiOC fluorescence microscopic have demonstrated that the formed generative cells were free of plastids because of extremely unequal distribution of plastids in the first microspore mitosis.The fluorescence observation of DNA showed that cytoplasmic(plastid and mitochondria) nucleoids gradually degenerated and disappeared during pollen development,but a certain amount of mitochondrion with complete structure still were present. These results provide precise cytological evidences of plastid and mitochondria maternal inheritance in section Leuce.At the meantime,relatively later eliminattion or degeneration of some plastid and their DNAs was founded in P.alba×P.glandulosa.2) High activity of pollen nuclease was found in P.tomentosa,triploid clone of P.tomentosa,P. davidiana and P.tomentosa×P.bolleana by DNA-SDS-PAGE method.Three Ca²⁺ dependent pollen nucleases(17,21,33 KD) and one Zn²⁺ dependent pollen nuclease(26 KD) were detected in P. tomentosa and triploid clone of P.tomentosa.Two Ca²⁺ dependent pollen nucleases(17,21 KD) and one Zn²⁺ dependent pollen nuclease(26 KD) were found in P.davidiana and P.tomentosa×P. bolleana.These results show that the activity of pollen nuclease may induce the selective degradation of organelle DNA.3) The inheritance of chloroplast and mitochondria DNA of 16 species and clones belonging to the section Leuce and their F₁ progenies was analyzed by PCR-RFLP analysis.Restriction fragment length polymorphism(RFLP) analysis has revealed that the chloroplast DNA in 22 F₁ hybrid individuals including(P.tomentosa×P.bolleana)×P.tomentosa),(P.tomentosa×P.bolleana)×(P.alba×P. glandulosa) is maternal inheritance.This supports the result of cytological analysis in plastid.Moreover, there was no variation among these 22 hybrids in the PCR amplification pattern and the restriction pattern,indicating that mitochondrial genes are highly conserved in section Leuce.These results provide direct evidences of maternal chloroplast in P.tomentosa,P.bolleana,P.davidiana,P.adenopoda,P. tomentosa×P.bolleana,P.alba×P.glandulosa and P.alba×P.tomentosa.4) The size,number,DNA content of chloroplast were measured in seven triploid clones of Populus tomentosa clones from different hybrid parents and three diploid Populus tomentosa clones.Results show that variations of chloroplast traits before and after the chromosome doubling incompletely increase with polyploidy increasing,are diversity and closely related with their parents' characteristics.more detail as follows:there is an unobvious difference in chloroplast size between most triploid clones of Populus tomentosa and their diploid parents,while the chloroplast number increased with chromosome doubling.Especially the triploid Populus tomentosa clones from female gamete doubling reached the very significant level.Variations in chloroplast DNA content per unit volume or per cell in triploid clones of Populus tomentosa from male gamete doubling were more significant than those from female one.Chloroplast size was negatively related to chloroplast number per unit volume, Chloroplast DNA content per unit volume was not closely correlated with size and number per unit volume of chloroplast.