THE INFLUENCE OF GROWTH SUBSTANCES ON THE INDUCTION OF APOGAMY IN PTERIDIUM GAMETOPHYTES

Experiments employing sequences of three media demonstrated the effect of growth substances on the induction of apogamy. The most effective sequence was 4% sucrose 1–14 days, 4% sucrose plus growth substance 15–28 days, and 0.1% sucrose 29–56 days. In this sequence concentrations of NAA, IAA, and GA promoted apogamous shoot formation. A higher NAA concentration than optimal for shoot formation stimulated apogamous root formation in all medium sequences. Kinetin was without effect or inhibitory to apogamy. Combination of kinetin/GA or GA/NAA concentrations did not increase the apogamous response. One combination of the kinetin/NAA concentrations had a synergistic effect on the apogamous shoot formation. Additions of GA to the synergistic kinetin/NAA combination had an antagonistic effect on the apogamous response.     

THE INFLUENCE OF CULTURAL CONDITIONS ON THE INDUCTION OF APOGAMY IN PTERIDIUM GAMETOPHYTES

Apogamous sporophytes formed on Pteridium gametophytes in response to concentrations of certain sugars which supported gametophytic growth. High osmotic concentration of the medium inhibited apogamy, while variations in the basic medium were not stimulatory. Agar, autoclaving, the ammonium ion, and dry media were not required for apogamy. Renewing the medium during an experiment enhanced the apogamous response. Changing the medium at set intervals facilitated the separation of apogamous plant development into gametophytic, initiative, and developmental phases, thus enabling testing of various factors at each of these stages. Apogamy was light-initiated, while the actual development of apogamous sporophytes was caused by light, succinic acid or sugar.     

FORMATION OF 2N MEGAGAMETOPHYTES IN DIPLOID TUBER-BEARING SOLANUMS

Development of megaspores and megagametophytes was analyzed for several diploid potato clones (Solanum spp.) that exhibit either high (HI) or low (LO) seed set when crossed as female with the tetraploid cultivated potato S. tuberosum Group Tuberosa. The objectives were to determine the relationship between ploidy and diam of nuclei and nucleoli, and to determine the mechanism(s) and frequencies of 2n megagametophyte formation. Sizes of nuclei and nucleoli were found to depend on ploidy. For HI clones, the distributions of sizes indicated that doubling occurred during meiosis, and that 30 to 50% of the megaspores and megagametophytes were 2n rather than haploid. Omission of the second meiotic division led to formation of second division restitution (SDR) 2n megagametophytes. Only one HI clone had abnormal meiosis I, in addition to omission of meiosis II in some meiocytes; this clone seemed to produce not only 1n and 2n, but also 4n megagametophytes. The results indicated that high crossability of the HI clones as female with tetraploids largely was due to formation of SDR 2n megagametophytes, a finding strongly supporting the hypothesis that sexual polyploidization is the driving force behind polyploidization of Solanums. The results contribute to increasing evidence that meiotic mutants and abnormalities play an important role in angiosperm evolution.     

THE INITIATION OF SPOROPHYTES BY OBLIGATE APOGAMY IN CHEILANTHES CASTANEA

The initiation of apogamous sporophytes in Cheilanthes castanea was recorded by daily photography of individual gametophytes. Whereas an ordinary embryo arises from a zygote, apogamous embryos of C. castanea originate from one to three initial cells which occur just behind the apical region of the prothallus. The initial (or initials) produce cells with small chloroplasts behind the sinus of the gametophyte. The appearance of cells with smaller chloroplasts than those normally found in gametophytes is the first indication that apogamy is occurring. The cells with small plastids produce a group of densely-cytoplasmic meristematic cells. The size of the meristematic mass increases until shoot and root apices of the apogamous embryo are organized.     

TRANSLOCATION OF 14C IN MACROCYSTIS INTEGRIFOLIA (PHAEOPHYCEAE)1,2

Translocation patterns in the giant kelp, Macrocystis integrifolia Bory, were investigated in situ using ¹⁴C tracer; sources and sinks were identified. Export was first detected after 4 h of labeling; experiments were routinely 24 h continuous ¹⁴C application. Mature blades exported ¹⁴C to young blades on the same frond and on younger fronds, as well as to sporophylls and frond initials at the bases of the fronds. Blades <0.3 m from the apex imported and did not export; this distance did not change seasonally. In spring export from blades 0.3–1.25 m from the apex was exclusively upwards; older blades also exported downwards. In fall downward export began 0.5 m from the apex, and blades >2 m from the apex exported exclusively downwards. Carbon imported by frond initials, young fronds, and sporophylls in fall may partly be stored for growth in early spring. No translocation was seen in very young plants until one blade (secondary frond initial) bad been freed from the apical blade; this blade exported to the apical blade for a time, but imported when it began to develop into a frond. The second and third formed blades on the primary fronds (sporophylls also exported when <0.3 m from the apex, and later stopped. Frond initials and sporophylls on later-formed fronds did not export at all. The translocation pattern in M. integrifolia differs from that previously reported in M. pyrifera in seasonal change and in distances from the apex at which the changes take place.     

水稻多卵卵器的起源

被子植物的卵器中通常只有１ 个卵细胞。在水稻（Ｏｒｙｚａ ｓａｔｉｖａ）多胚品系胚囊中观察到二卵卵器和三卵卵器。对其大孢子和胚囊发生进行了观察,首次揭示了被子植物多卵卵器的起源。该品系大孢子发生正常。大孢子母细胞进行正常的减数分裂形成４ 个大孢子。靠近合点端的大孢子发育,其它３ 个退化。功能大孢子第一次有丝分裂后,两个子核被一中央大液泡分隔在胚囊珠孔端和合点端。紧接着发生第二次有丝分裂,合点端核分裂时纺锤丝与胚囊纵轴平行,而珠孔端核分裂时纺锤丝与胚囊纵轴成４５°夹角。由此产生的四核胚囊中,合点端１核向胚囊中部或中上部（胚囊珠孔端）迁移。四核胚囊再经１ 次有丝分裂形成两种类型的核分布偏离蓼型的八核胚囊。一种类型是珠孔端４个核,中部与合点各２ 个核,在胚囊细胞化过程中,珠孔端４ 核分化成四细胞卵器,其中卵细胞和助细胞各２ 个,中部的２ 核分化成２ 极核中央细胞,合点端的２ 核形成反足细胞。另一种类型是珠孔端６ 个核,合点端２ 个核,在胚囊细胞化过程中,两端各１ 核向中部迁移分化成２ 极核中央细胞,珠孔端剩余的５ 核分化成５ 细胞卵器,其中卵细胞３ 个,助细胞２ 个,合点端的１ 核迅速分裂形成反足细胞     

APOGAMY AND SOMATIC RESTITUTION IN THE FERN CERATOPTERIS

A mutant stock of the fern Ceratopteris has been derived from an inbreeding study following an interspecific hybridization between two diploid species. The mutant is characterized by gametophytes that produce non-functional spermatozoids and are incapable of selfing. Sporophytes develop apogamously from the mutant gametophytes and, although they are initially haploid and sterile, portions of the fronds later become doubled somatically and behave like tissues of sexually derived homozygous sporophytes. The mutant segregates from sporophytes in a 1:1 ratio when crosses are made with wild type gametophytes. Certain aspects of the behavior are similar to those seen in some naturally occurring apomictic ferns.     

INDUCTION OF ANTHERIDIA IN ASCOBOLUS STERCORARIUS

Sexual organs develop in the hermaphroditic, heterothallic ascomycete Ascobolus stercorarius only when strains of opposite mating-type are paired under appropriate conditions. A previous study of the two reciprocal compatible interactions, A-antheridial/a-ascogonial and a-antheridial/A-ascogonial, revealed several differences between them. The present study of the induction of antheridia has uncovered several other differences. Such induction occurred on severed hyphae, non-germinated oidia and germinated oidia of mating-type A but not of a under two different sets of conditions: (1) when such elements were placed on an agar medium containing only the secretions of a compatible mycelium, and (2) when they were in close proximity to a second group of compatible non-germinated or germinating oidia on an agar surface. This tendency for vegetative elements of A to differentiate as male structures more readily than those of a is consistent with the previous observation that the interaction of A-antheridial/a-ascogonial is generally the more vigorous one. It may also be responsible for a condition approaching functional sexual dimorphism in many mixed (A + a) mycelial cultures.     

VARIATION IN LEAFLET MORPHOLOGY AMONG POPULATIONS OF CARIBBEAN CYCADS (ZAMIA)

Caribbean cycads (Zamia L.) are well known for variation in leaflet morphology. Here, I examine the variation in leaflet morphology among five populations of Zamia in Florida. Variables measured were leaflet length and width, leaflet length: width ratio, leaflet surface area, rachis and petiole lengths, number of leaflets per leaf, and total leaf area. In addition to comparisons among the Florida populations, these populations are compared with three previously studied populations in Puerto Rico (Newell, 1986). For the most part, the populations exhibited significant differences in all variables. In spite of the extensive morphological variation in this group of plants, leaflet morphology has long been important in Zamia taxonomy. The Florida populations would be considered by some to be either one, two, or three different species. The Florida and Puerto Rico populations together might be considered as few as one species or as many as five species. Based upon the data presented here, the five Florida populations appear to represent a single species; and the three Puerto Rico populations appear to represent two additional species. Further clarification of the taxonomy of Caribbean Zamia will require additional characters such as cone morphology and protein or DNA patterns.     

哺乳动物卵母细胞减数分裂恢复的诱导

促使哺乳动物卵母细胞减数分裂恢复的机制尚不十分清楚。有腔卵泡中发育充分的卵母细胞被减数分裂抑制因子阻滞在生发泡（GV）期,环一磷酸腺苷（cAMP)是研究得最为清楚的减数分裂抑制因子。然而,其它因子也参与了卵母细胞减数分裂的阻滞。虽然排卵前的促黄体素（LH）峰诱导卵母细胞减数分裂恢复已成定论,但是参与该事件的各种过程非常复杂,因而还没有完全确定。目前,有两种主要但并不互相排斥的假说。第一种假说认为,LH对颗粒细胞的刺激作用终止减数分裂抑制因子流向卵母细胞,从而使卵母细胞膈离这些抑制因子并进而促使减数分裂恢复,第二种假设认为LH刺激颗粒细胞产生一种减数分裂诱导信号,该信号进而克服或者破坏减数分裂抑制因子的作用。权衡这两种假说,目前的证据倾向于支持阳性信号假说,而且最近的研究暗示,该种阳性信号的产生发生在颗粒细胞中LH诱导的cAMP水平上升和MAPK激酶激活之后。     

水稻子房培养中助细胞无配子生殖的稳定性及其发育条件的探讨

通过本文的实验研究,表明助细胞无配子生殖是水稻未传粉子房培养中不易受培养条件影响的一个稳定特性。无配子生殖原胚的诱导不完全依赖外源激素,不一定必需子房直接接触培养基,对有无光照也没有严格要求;但原胚的继续生长发育则需要在适当的外源激素,子房的液体漂浮培养和黑暗条件下才能顺利进行。