Plant development from protoplasts of members of Bryophyta, Pteridophyta and Spermatophyta under identical conditions

Organized development from isolated protoplasts using a single protocol has been obtained with two bryophyte species, one fern species, and 34 dicotyledonous species. Regeneration is described here for the first time with the dicotyledonous species Cyphomandra betacea, Euphorbia pulcherrima, Linum catharticum , and Senecio fuchsii . In co-cultures with a Solanum hybrid, interfamilial and even interdivisional support was observed acting at different developmental steps. The results are discussed with respect to standardization of culture conditions, variety of morphogenic pathways, and interspecific correlations such as tolerance, allelopathy and nursery/feeding in unrelated systems.     

'Inconstant males' and the maintenance of labile sex expression in subdioecious plants

* Here, we evaluate the role of pollen limitation and selfing in the maintenance of labile sex expression in subdioecious plant species. * We used a literature survey to explore which factors correlated with a significant occurrence of hermaphrodites in dioecious species. We developed models to explore the selective maintenance of labile sex expression. The models had similar ecological assumptions but differed in the genetic basis of sex lability. * We found that a significant frequency of hermaphrodites was associated with animal pollination, and that hermaphrodites were 'inconstant' males with perfect flowers, suggesting evolution through the gynodioecious pathway. Models showed that a modifier converting pure males into inconstant males could be maintained under a wide range of reduction in both male and female fitness. Pollen limitation and self-fertilization facilitated invasion of the modifier. Depending on the genetics of sex determination, we found pure dioecy, stable subdioecy (trioecy), and situations where inconstant males coexisted with either pure females or pure males. Under selfing and pollen limitation, certain conditions selected for inconstant males which will drive populations to extinction. * We discuss our results in relation to the evolution towards, and the breakdown of, dioecy, and the ecological and evolutionary implications of labile sex expression.     

The role of roots in sex expression in hemp plants

When the shoots of young hemp (Cannabis sativa L.) plants were cut off the roots, cultured as cuttings, and regenerating (adventitious) roots were removed as soon as appearing, ca. 80–90% of the plants became male (had staminate flowers) whereas if the roots were allowed to develop a similar percentage became female (pistillate flowers). Treatment of de-rooted cuttings with 6-benzylaminopurine (15 mg/l) restored the percent of female plants to ca. 80. It is suggested that the root system plays an essential role in sex expression in hemp and that this role is related to cytokinin synthesis in the root.     

Pathogens and sex in plants

Summary Extant theories that attribute the evolution of sex to pathogen attack depend on the assumption that pathogens are narrowly specialized, so that high fitness on one host genotype results in poor fitness on hosts with other allele combinations. This assumption is necessary in order for frequency-dependent selection to produce sustained cycling of gametic disequilibrium across the host's disease resistance loci, which makes recombination advantageous. However, a review of numerous genetic studies on plant disease resistance failed to uncover a single example consistent with this assumption. Instead, the empirical results provide strong support for a different pattern of pathogen specificity, in which adaptation by pathogens to one resistance allele does not preclude high fitness on alternate host genotypes lacking that allele. Modification of traditional models for pathogen-mediated evolution of sex showed that for conditions close to the empirical pattern of genotypic specificity, sex is almost never favoured. For plants, these results cast doubt on current theories arguing that pathogens are the primary selective agent responsible for sexual reproduction.     

Genetics of sex determination in flowering plants

Most flowering plant species are hermaphroditic, but a small number of species in most plant families are unisexual (i.e., an individ-ual will produce only male or female gametes). Because species with unisexual flowers have evolved repeatedly from hermaphroditic progenitors, the mechanisms controlling sex determination in flowering plants are extremely diverse. Sex is most strongly determined by genotype in all species but the mechanisms range from a single controlling locus to sex chromosomes bearing several linked locirequired for sex determination. Plant hormones also influence sex expression with variable effects from species to species. Here, we review the genetic control of sex determination from a number of plant species to illustrate the variety of extant mechanisms. We emphasize species that are now used as models to investigate the molecular biology of sex determination. We also present our own investigations of the structure of plant sex chromosomes of white campion (Silene latifolia - Melan-drium album). The cytogenetic basis of sex determination in white campion is similar to mammals in that it has a male-specific Y-chromosome that carries dominant male determining genes. If one copy of this chromosome is in the genome, the plant is male. Otherwise it is female. Like mammalian Y-chromosomes, the white campion Y-chromosome is rich in repetitive DNA. We isolated repetitive sequences from microdissected Y-chromosomes of white campion to study the distribution of homologous repeated sequences on the Y-chromosome and the other chromosomes. We found the Y to be especially rich in repetitive sequences that were generally dispersed over all the white campion chromosomes. Despite its repetitive character, the Y-chromosome is mainly euchromatic. This may be due to the relatively recent evolution of the white campion sex chromosomes compared to the sex chromosomes of animals. © 1994 Wiley-Liss, Inc.     

How geitonogamous selfing affects sex allocation in hermaphrodite plants

Does the mode of self-pollination affect the evolutionarily stable allocation to male vs. female function? We distinguish the following scenarios. (1) An ‘autogamous’ species, in which selfing occurs within the flower prior to opening. The pollen used in selfing is a constant fraction of all pollen grains produced. (2) A species with ‘abiotic pollination’, in which selfing occurs when pollen dispersed in one flower lands on the stigma of a nearby flower on the same plant (geitonogamy). The selfing rate increases with male allocation but a higher selfing rate does not mean a reduced export of pollen. (3) An ‘animal-pollinated’ species with geitonogamous selfing. Here the selfing rate also increases with male allocation, but pollen export to other plants in the population is a decelerating function of the number of simultaneously open flowers. In all three models selfing selects for increased female allocation. For model 3 this contradicts the general opinion that geitonogamous selfing does not affect evolutionarily stable allocations. In all models, the parent benefits more from a female-biased allocation than any other individual in the population. In addition, in models 2 and 3, greater male allocation results in more local mate competition. In model 3 and in model 2 with low levels of inbreeding depression, hermaphroditism is evolutionarily stable. In model 2 with high inbreeding depression, the population converges to a fitness minimum for the relative allocation to male function. In this case the fitness set is bowed inwards, corresponding with accelerating fitness gain curves. If the selfing rate increases with plant size, this is a sufficient condition for size-dependent sex allocation (more allocation towards seeds in large plants) to evolve. We discuss our results in relation to size-dependent sex allocation in plants and in relation to the evolution of dioecy.     

Sex choice in plants: facultative adjustment of the sex ratio in the perennial herb Begonia gracilis

Sex allocation theory predicts that reproducing individuals will increase their fitness by facultatively adjusting their relative investment towards the rarer sex in response to population shifts in operational sex ratio (OSR). The evolution of facultative manipulation of sex ratio depends on the ability of the parents to track the conditions favouring skewed sex allocation and on the mechanism controlling sex allocation. In animals, which have well-developed sensorial mechanisms, facultative adjustment of sex ratios has been demonstrated on many occasions. In this paper, we show that plants have mechanisms that allow them to evaluate the population OSR. We simulated three different conditions of population OSR by manipulating the amount of pollen received by the female flowers of a monoecious herb, and examined the effect of this treatment on the allocation to male vs. female flowers. A shortage of pollen on the stigmas resulted in a more male-skewed sex allocation, whereas plants that experienced a relatively pollen rich environment tended to produce a more female-skewed sex allocation pattern. Our results for Begonia gracilis demonstrate that the individuals of this species are able to respond to the levels of pollination intensity experienced by their female flowers and adjust their patterns of sex allocation in accordance to the expectations of sex allocation theory.     

Gametophyte Regeneration and Apospory from Archegoniate Protoplasts Under Conditions Devised for Higher Plants*

Developmental pathways from isolated protoplasts were investigated with the moss Funaria hygrometrica, the liverwort Anthoceros crispulus, and the fern Anogramma leptophylla. Gametophytic protoplasts regenerated gametophytes. Apospory was obtained with sporophytic protoplasts of the moss and the fern. The archegoniates also grew in interdivisional co-cultures with solanaceous species.     

Exploring the evolution of environmental sex determination, especially in reptiles

Environmental sex determination has been documented in a variety of organisms for many decades and the adaptive significance of this unusual sex-determining mechanism has been clarified empirically in most cases. In contrast, temperature-dependent sex determination (TSD) in amniote vertebrates, first noted 40 years ago in a lizard, has defied a general satisfactory evolutionary explanation despite considerable research effort. After briefly reviewing relevant theory and prior empirical work, we draw attention to recent comparative analyses that illuminate the evolutionary history of TSD in amniote vertebrates and point to clear avenues for future research on this challenging topic. To that end, we then highlight the latest empirical findings in lizards and turtles, as well as promising experimental results from a model organism, that portend an exciting future of progress in finally elucidating the evolutionary cause(s) and significance of TSD.     

Diurnal Lhc gene expression is present in many but not all species of the plant kingdom

The diurnal and circadian expression of light-harvesting genes (Lhc) is well documented for many plant species of the Angiospermae division. Here we present the diurnal mRNA levels of species of the Gymnospermae, Pteridophyta, Bryophyta and Phycophyta divisions. Except for four Coniferophytina species, diurnal Lhc mRNA accumulation is detected in fern, moss and algae, supporting the idea that the concept of circadian clock-controlled gene expression is an ancient process. Possible reasons why plants need the circadian clock control mechanism are discussed.Dedicated to Dr H. W. Heldt on the occasion of his 60th birthday.     

Evolution of the pathways of sex differentiation in plants

The stages of formulating the theory of sex evolution, determination, and expression in plants were briefly reviewed. The role of phytohormones in sex differentiation in dioecious and monoecious plants was analyzed.     

Evolution of habitat-dependent sex allocation in plants: superficially similar to, but intrinsically different from animals

Because pollen disperses and ovules do not, a basic difference in dispersal abilities of male and female gametes exists in plants. With an analytical model, we show that the combination of such sex-biased dispersal of gametes and variation of habitat quality results in two opposite selective forces acting on the evolution of sex allocation in plants: (i) a plant should overproduce pollen in good patches and overproduce ovules in poor patches in order to equilibrate secondary sex ratios of gametes after pollen dispersal; (ii) a plant should overproduce ovules in good patches and overproduce pollen in poor patches in order to increase the likelihood that its progeny establishes in good patches. Our theoretical results indicate that the evolution of habitat-dependent sex allocation should be favoured in plants, in a direction that depends on the relative dispersal ability of pollen and seeds. We also show that superficially similar predictions obtained for habitat-dependent evolutionarily stable sex allocation in animals actually result from a completely different balance between the two underlying evolutionary forces.     

A re-evaluation of plants referred to as Pteridiutn herediae (Colmeiro) Love & Kjellqvist

SHEFFIELD, E., WOLF, P. G., HAUFLER, C. H., RANKER, T. A. & JERMY, A. C, 1989. Are-evaluation of plants referred to as Pteridiutn herediae (Colmeiro) Love & Kjellqvist. Based on perceived differences in morphology, chromosome number and habitat, specimens of Pteridiutn from southern Spain have been segregated by previous authors as a species distinct from Pteridium aquilinum , and called Pteridium herediae. However, type specimens of this taxon cannot be found. New collections of Pteridium from similar habitats in the area were examined and analysed in the present study and the results compared with those from British plants (P. aquilinum). The Spanish plants were not found to differ significantly from P. aquilinum morphologically, and all yielded chromosome counts (sporophytes, 104; gametophytes, 52) considered typical for the genus. Genotype frequency data obtained from isozyme electrophoresis of Spanish and British Pteridium yielded a genetic identity of 0.86; well within intraspecific distances found in other ferns.
These data indicate that there are currently no grounds for accepting that a form of Pteridium , distinguishable from P. aquilinum on the basis of differences in morphology, chromosome number, habitat or biochemistry, exists on the limestone soils of the Sierra de Cazorla region of southern Spain.     

Environmental conditions affect sex expression in monoecious, but not in male and female plants of Urtica dioica

Urtica dioica is a sub-dioecious plant species, i.e. males and females coexist with monoecious individuals. Under standard conditions, seed sex ratio (SSR, fraction of males) was found to vary significantly among seed samples collected from female plants originating from the same population (0.05–0.76). As a first step, we investigated the extent to which SSR and sex expression of male, female, and monoecious individuals is influenced by external factors. We performed experiments to analyse: (1) whether the environment of a parental plant affects the sex ratio (SR) of its offspring, (2) whether SSR can be affected by environmental conditions before flowering, and (3) whether sex expression of male, female and monoecious plants that have already flowered can be modified by environmental conditions or by application of phyto-hormones. Within the range of our experimental design, SSR was not influenced by external factors, and gender in male and female plants was stable. However, sex expression in monoecious plants was found to be labile: flower sex ratio (FSR, fraction of male flowers) differed considerably between clones from the same individual within treatments, and increased toward 100% maleness under benign conditions. These results provide strong evidence that monoecious individuals are inconstant males, which alter FSR according to environmental circumstances. In contrast, we consider sex expression in male and female individuals to be solely genetically based. The observed variation in SSR between maternal parents cannot be explained by sex-by-environment interactions.     

Tryptamine and related compounds in plants

The occurrence of the tryptamines and related compounds in fungi and higher plants is listed on a taxonomic basis. Several of these amines have considerable physiological activity in higher animals.     

Differences between single cell responses to different components of the sex pheromone in males of the lightbrown apple moth (Epiphyas postvittana)

ABSTRACT. Single cell responses, elicited by each of three components of the pheromone blend of the lightbrown apple moth, Epiphyas postvittana (Walker) (Lepidoptera, Tortricidae), exhibit significant differences in disadaptation rates and effect of stimulation on the spontaneous generation of spikes upon removal of the stimulus. The major component has a disadaptation rate of a few seconds and a sustained effect on the rate of spontaneous spike generation upon removal of the stimulus. Faster disadaptation rates and sharp reduction in the spike rate upon removal of stimulus, were observed for one minor component, 12: Ac, and suggests a likely role in close-range orientation to the female. The second minor component produces two types of response, one of which resembles the major component. The other, more common response, exhibits a very slow rate of disadaptation, of the order of minutes. This characteristic also may have some bearing on search strategies.     

短命植物甘新念珠芥(Neotorularia korolkovii)和宽翅菘蓝(Isatis violascens)的物候与性表达特征

甘新念珠芥（Neotorularia korolkovii）和宽翅菘蓝（lsatis violascens）是两种广泛分布于新疆准噶尔荒漠的十字花科早春短命植物。对其物候与性表达特征研究结果表明：（1）二者种子均在3月下旬萌发,5月下旬和6月上旬果实完全成熟,生活周期分别为62d和71d,其中营养生长期约占1／3、生殖生长期约占2／3。（2）花均为两性,四强雄蕊,单花开放时间较短,长雄蕊的花药开裂早于短雄蕊,但短雄蕊花药中的花粉数较长雄蕊的多。（3）长、短雄蕊花药中花粉可育率均达90％以上,花粉活力的变化曲线基本相同,柱头可授期分别为9．Oh和4．5h,花粉寿命及柱头可授期均短于单花花期,花粉活力最高的时期正是其柱头的最佳授粉期。柱头可授期与花粉活力及寿命在时间上的高度吻合,增加了在不可预测环境中授粉的机会与效率,从而保障生殖成功。（4）二者的P／O（花粉／胚珠）值分别为108．07±17．17、992.10±272．16,属于自交繁育系统;对其传粉过程、套袋实验及荧光显微观察的结果也证明它们主要以白花传粉的方式来进行交配。（5）两种植物从物候、花部性表达以及交配式样上均存在与其严酷荒漠环境相适应的特点,是长期适应准噶尔荒漠特殊生态环境的结果,对于保证繁殖成功并扩大种群具有重要的意义。