Vegetative Proliferation of Floral Spikelets in British Grasses

Proliferation of spikelets in grasses other than those raceswhich are habitually viviparous is reviewed, and the factorsinducing proliferation experimentally in Cynosurus cristatusand other species are discussed. It is concluded that the evidencefavours the hypothesis that in the viviparous races a considerablygreater minimal concentration of the putative flowering hormoneis required for flower induction than for culm initiation, whereasin the seminiferous races this difference is not so great. Inthe viviparous races, the threshold for flower initiation israrely exceeded so that perfect flowers appear only occasionally,whilst in the normally seminiferous races, the conditions ariseonly rarely where an amount of hormone is produced sufficientto initiate culms but insufficient to promote flowering.     

The Extended Synthesis: Something Old, Something New

The eclipse of Darwinism began to end in the 1980s and hangs in the balance today. We need an Extended Synthesis, using “extension” metaphorically. We must extend back in time to recover important aspects of Darwinism that were set aside, and then lost during neo-Darwinism, then move forward beyond neo-Darwinism to encompass new data and concepts. The most comprehensive framework for the Extended Synthesis is the Major Transitions in Evolution. The Extended Synthesis rests comfortably within a philosophical perspective in which biology does not need to be connected with other areas of science in order to justify itself. I am attracted to an older concept in which biology needs a covering law to connect it with the rest of the natural sciences. Darwin implicated a “higher law,” but did not specify it. If we can elucidate that law, the Extended Synthesis will become the Unified Theory of Biology called for by Brooks and Wiley 25 years ago.     

Dual Floral Induction Requirements in Phleum alpinum

Flowering requirements of four Norwegian populations of Phleumalpinum were studied in controlled environments. A dual inductionrequirement was demonstrated in all populations. Inflorescenceinitiation had an obligatory requirement for short days (SD)and/or low temperature, while culm elongation and heading wereenhanced by long days (LD) and higher temperatures. At 3 and6 °C primary induction was almost independent of photoperiod,whereas SD was more effective than LD at higher temperatures.The critical temperature for primary induction was about 15°C in SD and 12 °C in LD. Saturation of induction required12 weeks of exposure to inductive conditions, although someheading and flowering took place with 6 weeks exposure to optimalconditions (9 °C/SD). Inflorescence development also tookplace in 8 h SD although it was delayed and culm elongationwas strongly inhibited compared with LD conditions. Only smalldifferences in flowering response were found between the populations. Phleum alpinum L., alpine timothy, dual floral induction, flowering, photoperiod, temperature     

Floral Induction of Xanthium strumarium in Long Days

An efficient method of inducing flowering in the normally strictshort-day plant, Xanthium strumarium L., in long days is described.Plants were grown in 16-h long days and subjected to two thermocycleswith a root application of gibberellic acid at the 8th h ofthe light period. A thermocycle was defined as follows. Forthe first 8 h of the 24-h cycle, the temperature was 4 °C;for the remaining 16 h, it was 23 °C. The light was on forthe first 16 h and off for the remaining 8 h. Xanthium strumarium L., floral induction, thermoperiod, gibberellic acid     

Focus on Metabolism: Something Old,Something New: Conserved Enzymes and the Evolution of Novelty in Plant Specialized Metabolism

Plants produce hundreds of thousands of small molecules known as specialized metabolites, many of which are of economic and ecological importance. This remarkable variety is a consequence of the diversity and rapid evolution of specialized metabolic pathways. These novel biosynthetic pathways originate via gene duplication or by functional divergence of existing genes, and they subsequently evolve through selection and/or drift. Studies over the past two decades revealed that diverse specialized metabolic pathways have resulted from the incorporation of primary metabolic enzymes. We discuss examples of enzyme recruitment from primary metabolism and the variety of paths taken by duplicated primary metabolic enzymes toward integration into specialized metabolism. These examples provide insight into processes by which plant specialized metabolic pathways evolve and suggest approaches to discover enzymes of previously uncharacterized metabolic networks.The plant kingdom collectively produces hundreds of thousands of low molecular weight organic molecules traditionally known as secondary metabolites, some of which have been shown to play roles in abiotic and biotic stress responses (e.g. herbivory defense), beneficial insect interactions (e.g. pollinator attraction), and communication with other plant and nonplant species (e.g. allelopathy and legume-rhizobia interactions; Saito and Matsuda, 2010; Pichersky and Lewinsohn, 2011; Wink, 2011). These metabolites have been widely used throughout the course of human history as medicines, spices, perfumes, cosmetics, and pest-control agents as well as in religious and cultural rituals. For the past 150 years, there has been a strong focus on documenting the chemical diversity of secondary metabolites in the plant kingdom, leading to the discovery of diverse classes of compounds such as terpenes, flavonoids, alkaloids, phenylpropanoids, glucosinolates, and polyketides. These secondary compounds were historically differentiated from products of primary metabolism, such as sugars, amino acids, nucleic acids, and fatty acids, as being nonessential for plant survival (Sachs, 1874; Kossel, 1891; Hartmann, 2008). However, by the 1980s, important functional roles began to be elucidated for metabolites previously classified as secondary, such as the phenolics (e.g. plant-microbe interactions and UV-B light protection; Bolton et al., 1986; Peters et al., 1986; Li et al., 1993; Landry et al., 1995), alkaloids (defense against herbivory; Steppuhn et al., 2004), and terpenes (defense against herbivory, antimicrobial activities, and volatile pollinator attractants; Papadopoulou et al., 1999; Schiestl and Ayasse, 2001; Erbilgin et al., 2006; Nieuwenhuizen et al., 2009). This change in our understanding of their roles has led to the coining of a new term, specialized metabolites, for these compounds, both to acknowledge their importance and to reflect the fact that many of them are phylogenetically restricted (Pichersky et al., 2006; Pichersky and Lewinsohn, 2011).Although the structural diversity of specialized metabolites far exceeds that of primary metabolites, all specialized metabolite classes are ultimately derived from primary metabolic precursors (Wink, 2011). For example, phenylpropanoids are derived from the amino acid Phe (Vogt, 2010), while the biosynthetic blocks of terpenes, isopentenyl diphosphate and dimethylallyl diphosphate, originate from mevalonate, a sterol precursor, and alternatively from methylerythritol phosphate, which is derived from glycolytic pathway precursors (Kirby and Keasling, 2009). Nitrogen-containing alkaloids are derived from a variety of primary metabolites, including amino acids and purine nucleosides (Facchini, 2001). Over the past 20 years, an increasing number of specialized metabolic enzymes have also been found to have their origins in primary metabolic pathways (Weng, 2014). Such shifts in enzyme function are made possible primarily by the process of gene duplication, which is very common in plants.     

Ethylene Production in Spinach Leaves during Floral Induction

Spinach plants were induced to flower by transferring them fromshort days to continuous light. Their leaf laminae releasedmore ethylene than those from vegetative plants. These leavesalso exhibited a greater capacity to convert exogenous ACC intoethylene. Cell wall preparations from the leaves of continuouslyilluminated plants also converted exogenous ACC into ethylenemore readily than extracts from short day plants. These effectsand also those previously reported for peroxidases appear verysimilar to these brought about by various environmental stressessuch as pollution and mechanical irritation. Key words: Ethylene, floral induction, stress, photoperiod, spinach     

Short-day and Low-temperature Control of Floral Induction in Festuca

The conditions necessary for floral induction to occur in tallfescue (Festuca arundinacea), meadow fescue (Festuca pratensis),and red fescue (Festuca rubra), have been investigated. Onlya Tunisian ecotype of tall fescue produced inflorescences undershort-day conditions when air temperatures were above 8 °C.Under short days with low temperatures nearly all plants ofS. 170 tall fescue and S. 215 meadow fescue produced inflorescencesafter 15 weeks' exposure, but S. 59 red fescue showed only asmall response. Evidence was obtained for the existence in bothtall fescue and meadow fescue of a juvenile stage during whichplants showed a reduced response to inductive conditions. Avariation of 35 days in the required length of exposure to inductiveconditions was demonstrated between families within the S. 170variety of tall fescue, indicating the possibility of selectingfor larger or smaller inductive requirements. A second generationof seed was produced within a 12-month period from inflorescenceswhich had developed in a heated glasshouse during the wintermonths.     

被子植物成花诱导和性别决定机制的研究进展

开花植物具有多样性的生殖系统,其中单性花的形成是促进异交、避免自交衰退、保持遗传多样性的重要途径。单性花物种分布于被子植物不同进化分支上的事实表明,物种的雌雄异花性可能是通过不同的机制进化形成的。本文从花发育、性染色体、植物激素和环境因素四个方面,阐述了被子植物性别分化调控机制的研究进展。     

Floral Induction in Short-Day Lemna paucicostata 6746 by 8-Hydroxyquinoline, under Long Days

Lemna paucicostata 6746 is a short-day duckweed and flowersin response to a single photoinductive cycle. Its critical darkperiod requirement is ca. 10 h. Flowering in this duckweed couldbe induced by 8-hydroxyquinoline (8-HQ) under an otherwise non-inductivelong-day regime of 16 h light and 8 h darkness; the criticaldark period requirement for initiation of flowering was thusreduced by at least 2 h. However, 8-HQ was ineffective in initiatingflowering in strain 6746 under continuous illumination. Atomicabsorption analysis of the plant material revealed that thecontent of both iron and copper is markedly higher in the plantstreated with 8-HQ. A comparison of the effects of 8-HQ and thoseof EDTA and ethylenediamine-di(o-hydroxyphenylacetic acid),on flowering of strain 6746, has also been made. (Received August 23, 1983; Accepted October 18, 1983)     

Floral Diversity and Pollen Transfer Mechanisms in Bird-pollinated Salvia Species

Annals of Botany 100:     

Plant Callus: Mechanisms of Induction and Repression

Plants develop unorganized cell masses like callus and tumors in response to various biotic and abiotic stimuli. Since the historical discovery that the combination of two growth-promoting hormones, auxin and cytokinin, induces callus from plant explants in vitro, this experimental system has been used extensively in both basic research and horticultural applications. The molecular basis of callus formation has long been obscure, but we are finally beginning to understand how unscheduled cell proliferation is suppressed during normal plant development and how genetic and environmental cues override these repressions to induce callus formation. In this review, we will first provide a brief overview of callus development in nature and in vitro and then describe our current knowledge of genetic and epigenetic mechanisms underlying callus formation.