High temperature treatment induced production of unreduced 2n pollen in Camellia oleifera

Unreduced gametes through chromosome doubling play a major role in the process of plant polyploidization.Our previous work confirmed that Camellia oleifera can produce natural 2n pollen,and it is possible to induce the 2n pollen formation by high temperature treatment.This study focused on the optimization of the 2n pollen induction technique and the mechanisms of high temperature-induced2n pollen formation in C.oleifera.We found that the optimal protocol for inducing 2n pollen via high temperature was to perform 45℃with4 h at the prophaseⅠstage of the pollen mother cells(PMCs).Meanwhile,high temperature significantly decreased the yield and fertility of2n pollen.Through the observation of meiosis,abnormal chromosome and cytological behaviour was discovered under high-temperature treatment,and we confirmed that the formation of 2n pollen is caused by abnormal cell plate.Based on weighted gene co-expression network analysis,fifteen hub genes related to cell cycle control were identified.After male flower buds were exposed to heat shock,polygalacturonase gene(CoPGX3)was significantly upregulated.We inferred that high temperature causes the CoPGX3 gene to be overexpressed and that CoPGX3 is redistributed into the cytosol where it degrades cytoplasmic pectin,which leads to an abnormal cell plate.Furthermore,abnormal cytokinesis resulted in the formation of dyads and triads,and PMCs divided to produce 2n pollen.Our findings provide new insights into the mechanism of 2n pollen induced by high temperature in a woody plant and lay a foundation for further ploidy breeding of C.oleifera.

Cytology of 2n Pollen Formation in Nonastringent Persimmon

Cytological mechanisms of 2n pollen formation in ' Zenjimaru' nonastringent persimmon (Diospyros kaki L.f.) were studied. The following abnormalities in meiosis were found to be responsible for the production of 2n pollens: (1) disoriented spindles, including parallel, fused and tripolar spindles, were formed at metaphase II and anaphase II; (2) the nuclei at telophase II were arranged to two poles, each of which contained two nuclei, or to three poles, one of which contained two nuclei, the other two contained one nucleus respectively; (3) dyads and triads were produced at the tetrad stage. The dyad would develop into two 2n pollens, and the triad would develop into one 2n and two n pollens. The 2n pollens produced by this mechanism were genetically equivalent to FDR (first division restitution) gametes, thus providing a potential value for sexual polyploidization.

The Potential Breeding Value of Two Newly Developed 2N Pollen Producing Diploid Hybrids in Potato

Diploid hybrid derived from dihaploid Neo-tuberosum × Solanum phurejaand progeny of the diploid hybrid backcrossed to dihaploid Neo-tuberosum,which could produce 2n pollen, were crossed as male to S.tuberosumssp. tubersumc.v. NEA303. The performance of the 4x hybrids obtained from 4x × 2x cross was investigated for yield and yield components in the first year clonal generation. The 4x hybrids shown a drastic heterosis in plant height. Marketable yield/plant for the 4x hybrid was no better than that for the 4x cultivar, but the best hybrid individual of the two hybrid populations exceeded the best individual of the cultivar by 260 g/plant and 60 g/plant, respectively. Total yield/plant for the 4x hybrids performed drastic heterosis, however tuber number/plant was high and mean tuber weight low. These limit the use of 4x × 2x hybrids in potato breeding programs and need to be improved in near future.

Study on Pollen Chromosome Doubling in Zenjimaru Persimmon

The factors influencing pollen chromosome doubling in Zenjimaru persimmon were studied, based on the knowledge of meiosis process of pollen mother cells. The results showed: (1) the suitable concentration of colchicine was 0.3-0. 5%; (2) the best doubling effect could be obtained during the period from the diplotene stage to the diakinasis stage, and the highest proportion was up to 40.6%; (3) considering giant pollen ratio and proportion of staminate-flower collection, the better treating frequency was 3 times; (4) giant pollen, which formed mainly from dyad and had bigger cell nucleus volume, was unreduced and hexaploid.

Evaluation of some Newly Developed Diploid Hybrids and their Breeding Value in 4x-2x Crosses

The narrow genetic base in potato (Solanum tuberosum L.) limits the progress in cultivar development.The rich diploid germplasm in the origin center of potato provide a unique resource for improvement of tetraploid potatoes.Seven newly developed diploid hybrids with 2n pollen production,all of which have S. phureja background,were developed and evaluated for their value in potato breeding.They were crossed as male parnets to six tetraploid Solanum tuberosum cultivars,and seeds in large quantity from eleven crosses were obtained.Main agronomic traits,such as tuber yield,tuber number,mean tuber weight,tuber shape,eye depth,skin smoothness,flesh color,and specific gravity,were measured for 4x 2x tetraploid progenies in seedling generation,and their parents as well.All of the diploid hybrids had some merit for specific traits and the DH39 was more promising;high specific gravity trait in some diploid hybrids was successfully introgressed into tetroploid progenies via 4x 2x crosses.These diploid hybrids have potential value in potato breeding.

Cytological Studies on Unreduced Gamete Formation of Strawberries (Fragaria)

A diploid strawberry (Fragaria vesca L.) which can naturally produce unreduced gametes (2n pollen) and doubled-unreduced gametes (4n pollen) was used to study the cytological mechanism of 2n and 4n gamete formation. The result showed that the formation of 2n gamete was mainly due to the abnormal orientation of spindles at metaphase II. The normal orientation of two spindles at metaphase I was perpendicular to each other, which led to tetrad formation at the end of meiosis. Two kinds of abnormal orientation of metaphase II spindles, i. e. parallel spindles and triangle spindles, were observed. Of the parallel spindles, the 4 group chromosomes were distributed to 2 poles and formed a dyad which formed two 2n pollen grains further-ly. Of the triangle spindles, the 4 group chromosomes were distributed to 3 poles and formed a triad which formed one 2n pollen grain and two n pollen grains. In addition, a few very big pollen grains (4n pollen) which probably due to the fusion of the tetrad were found.

不同倍性香石竹杂交花粉管生长荧光显微观察及结实研究

以香石竹四倍体材料‘紫蝴蝶’(2n=4x=60)为母本,二倍体材料‘珍珠粉’和‘NH6’(2n=2x=30)为父本,利用荧光显微镜观察其授粉后花粉管生长情况,统计其座果率、亲和指数及种子萌发率,并对杂交后代进行倍性鉴定。结果表明,在‘紫蝴蝶’柱头上,‘珍珠粉’和‘NH6’的花粉2h开始萌发,花粉管多处出现胼胝质塞,且花柱组织出现胼胝质反应,4h花粉管到达柱头中部并出现胼胝质塞,6h花粉管到达柱头基部,17h柱头基部的花粉管增多,花粉管进入子房组织且子房组织出现胼胝质反应,17～24h花粉管能与胚珠结合,但结合率低;‘紫蝴蝶’ב珍珠粉’杂交未获得植株,‘紫蝴蝶’בNH6’杂交获得3株植株,染色体倍性鉴定表明3株植株均为四倍体,这可能是‘NH6’产生2n配子的缘故。

亚洲百合花粉染色体加倍的研究

以亚洲百合俄维侬幼嫩花蕾为材料，采用不同浓度秋水仙碱溶液处理幼嫩花蕾来得到染色体加倍的2n花粉。观察花粉母细胞减数分裂过程，探讨其减数分裂过程与花蕾大小的对应关系，确定诱导2n花粉的有效时期。结果表明：花蕾长度为1．0～2．4cm时是2n花粉的有效诱导时期，以0．1％的秋水仙碱溶液连续注射处理3d，效果最佳，诱导率高达33．2％。