Western white pine (Pinus monticola Dougl.) reproduction: I. Gametophyte development

Male and female gametophyte development are described from light and transmission electron microscope preparations of ovules from first and second year Pinus monticola Dougl. seed cones. In the first year of development, pollen tubes penetrate about one-third the distance through the nucellus. The generative cell and tube nucleus move into the pollen tube. The megagametophyte undergoes early free nuclear division. First-year seed cones and pollen tubes become dormant in mid-July. In the second year, seed cones and pollen tubes resume development in April and the pollen tubes grow to the megagametophyte by mid-June. Early in June the generative cell undergoes mitosis, forming two equal-size sperm nuclei that remain within the generative cell cytoplasm. The generative cell has many extensions and abundant mitochondria and plastids. The megagametophyte resumes free nuclear division, then cell wall formation begins in early July. Cell wall formation and megagametophyte development follow the pattern found in other Pinaceae. Three to five archegonial initials form. The primary neck cell divides, forming one tier of neck cells. Jacket cells differentiate around each central cell. The central cell enlarges and becomes vacuolate; then vacuoles decrease in size and the cell divides, forming a small ventral canal cell and a large egg. Plastids in the central cell engulf large amounts of cytoplasm and enlarge. This process continues in the egg, and the peripheral cytoplasm of the egg becomes filled with transformed plastids. Mitochondria migrate around the nucleus, forming a perinuclear zone. The wide area of egg cytoplasm between these two zones has few organelles. A modified terminology for cells involved in microgametophyte development is recommended. Received: 9 December 1999 / Revision accepted: 30 April 2000     

矮沙冬青小孢子发生和雄配子体发育的观察

对矮沙冬青（Ammopiptanthus nanus）小孢子发生及雄配子体发育过程进行了观察,结果表明：花约具4个花粉囊,花药壁发育为基本型,由表皮、药室内壁、中层（2—3层）和绒毡层组成,绒毡层为腺质型。小孢子母细胞减数分裂后胞质分裂为同时型,四分体为四面体型排列,成熟的花粉粒为二细胞型。在矮沙冬青小孢子发生及雄配子体发育过程中没有发现异常现象,认为矮沙冬青濒危不存在雄性生殖结构与发育过程异常的内在因素。     

Microgametophytic plastid nucleoid content and reproductive and life history traits of tribeTrifolieae (Fabaceae)

Microgametophytic plastid nucleoids were quantified for 18 species representing the four core genera of the tribeTrifolieae (Fabaceae),Medicago, Melilotus, Trigonella, andTrifolium. Generative cells of all taxa contained nucleoids, establishing that biparental plastid inheritance is common in theTrifolieae. Nucleoid number and volumes of pollen grains and generative cell nuclei differed among taxa. Nucleoid number was positively correlated with pollen grain and generative cell nuclear volumes, flower size and style length. These relationships disappeared after adjusting nucleoid number for pollen grain and generative cell nuclear volumes. Adjusted nucleoid numbers provided no evidence to support hypotheses that plastid content is associated with ploidy level, mating system, perenniality or size of the reproductive apparatus.     

七筋姑的大小孢子发生雌雄配子体发育及多糖物质的动态

七筋姑(Clintonia udensis Trautv. et Mey)具倒生胚珠、双珠被、薄珠心、单个孢原。大孢子母细胞减数分裂后形成1 3排列,合点端三核退化,珠孔端有功能的大孢子核进行两次有丝分裂。成熟胚囊具5核或6核,即1组卵器、1上极核、合点端的1个或2个退化核。胚囊发育为四孢子、高度退化的贝母型。花药壁由表皮、药室内壁、两层中间层及绒毡层组成,发育属单子叶型。绒毡层解体方式为分泌型。小孢子母细胞减数分裂时胞质分裂为连续型。二轴对称式四分体,2-细胞成熟花粉粒。组织化学表明:大小孢子发生及雌雄配子体形成过程中的不溶性多糖颗粒的分布呈现规律性变化。     

Effects of pollen competitive environment on pollen performance in Mirabilis jalapa (Nyctaginaceae)

 We examined the influence of pollen competitive environment on pollen performance in Mirabilis jalapa. We used the number of pollen grains and the number of pollen tubes per pistil as measures of pollen competition. Pollen germination, pollen tube penetration into the style, and pollen tube growth rates were used as measures of pollen performance. All three measures of pollen performance were affected by the competitive environment. Pollen germination was greatest at intermediate pollen load sizes. The percentage of germinated pollen grains that penetrated the stigma and grew into the style decreased with pollen load size. Pollen tube growth rate in the style was greater and more variable with larger numbers of pollen tubes in the style. Controlling for the degree of selection at the stigma indicated that pollen-pollen or pollen-style interactions were the likely causes of increased growth rates. Received: 28 October 1996 / Revision accepted: 24 January 1997     

Effects of pollen selection on progeny vigor in a Cucurbita pepo x C. texana hybrid

We examined the effects of pollen selection for rapid pollen-tube growth on progeny vigor. First, we crossed a wild gourd (Cucurbita texana) to a cultivated zucchini (Cucurbita pepo cv Black Beauty) to produce an F₁ and then an F₂ generation. Half of the F₁ seeds were produced by depositing small loads of C. texana pollen onto the stigmas of C. pepo. These small pollen loads were insufficient to produce a full complement of seeds and, consequently, both the fast- and the slow-growing pollen tubes were permitted to achieve fertilization. An F₂ generation was then produced by depositing small loads of F₁ pollen onto stigmas of F₁ plants. The F₂ seeds resulting from two generations of small pollen loads are termed the non-selected line because there was little or no selection for pollen-tube growth rate on these plants. The other half of the F₁ and F₂ seeds were produced by depositing large pollen loads (>10 000 pollen grains) onto stigmas and then allowing only the first 1% or so of the pollen tubes that entered the ovary to fertilize the ovules. We did this by excising the styles at the ovary at 12–15 h after pollination. The resulting F₂ seeds are termed the selected line because they were produced by two generations of selection for only the fastest growing pollen tubes. Small pollen loads from the F₂plants, both the selected and the non-selected lines, were then deposited onto stigmas of different C. pepo flowers, and the vigor of the resulting seeds was compared under greenhouse and field conditions. The results showed that the seeds fertilized by pollen from the selected line had greater vegetative vigor as seedlings and greater flower and fruit production as mature plants than the seeds fertilized by pollen from the non-selected line. This study demonstrates that selection for fast pollen-tube growth (selection on the microgametophyte) leads to a correlated increase in sporophyte (progeny) vigor.     

Stage-related expression of mRNAs during pollen development in lily and tobacco

Homogeneous populations of developing microspores and pollen from anthers of lily (Lilium longiflorum Thumb.) and tobacco (Nicotiana tabacum L.) show a continuous production of biomass, reaching a maximum in young pollen. The rate of RNA synthesis was 460 fg · h^–1 in young binucleate cells, 138 fg · h^–1 in late binucleate cells and 56 fg · h^–1 in microspores. The mRNA population in developing pollen can be separated into three groups. In the first group, certain types of mRNAs are present at a constant level during all stages of development. A second group is characteristic of young pollen and increases quantitatively until anthesis. A third group is seen transiently; to this belong mRNAs present only before mitosis or at a distinct cell stage after mitosis. Some of the translation products of this latter group of mRNAs showed similarities between lily and tobacco on two-dimensional gels in respect of molecular weight and isolectric point, indicating that those mRNAs and proteins play a role in the regulation of pollen development.Abbreviations cDNA copy DNA - pI isolectric point To whom correspondence should be addressed.