Strigolactones as small molecule communicators

Originally identified as an allelochemical involved in plant host-parasite interactions, strigolactones have more recently been shown to have much broader communication roles. Strigolactones function as a symbiotic communicator in plants and mycorrhizal fungi interactions and have also been shown to have hormonal roles in higher plants. This ability to act as both an exogenous and an endogenous signal has interesting implications with respect to the constraints on strigolactone structures. Probing the hormonal function of strigolactones using chemical biology and genetics is beginning to provide clues as to how strigolactones were co-opted as an allelochemical signal by parasitic plants.     

独脚金内酯信号感知揭示配体-受体作用新机制

植物激素在调控细胞与细胞及细胞与环境的相互作用中起着至关重要的作用。作为一种信号分子, 植物激素如何被植物细胞感知一直是植物生物学研究的热点。与底物-酶相互作用的结果不同, 激素分子与受体结合后会触发信号转导, 但激素分子一般不会被受体修饰, 信号转导起始后激素分子通常会从复合体中释放出来被重新利用或降解。近期, 我国科学家通过对独脚金内酯及其受体复合体(AtD14-D3-ASK1)的结构学解析, 发现独脚金内酯的生物活性分子CLIM (covalently linked intermediate molecule)是独脚金内酯被其受体水解后得到的中间分子。研究表明, CLIM与受体AtD14的催化中心以共价键相结合, 进而激活其信号转导。该研究揭示了一种全新的“底物-酶-活性分子-受体”激素识别机制。这种配体-受体作用新机制的发现为植物激素研究开拓了新的视野。     

Sugarcane Straw and its Phytochemicals as Growth Regulators of Weed and Crop Plants

The present study investigates the effect of soil amended with sugarcane straw leachate and its constituents on root elongation of weed and crop plants. The influence of soil biotic and abiotic factors on plant growth were also evaluated through assays in both autoclaved soil and sand. In unsterile soil, straw leachates stimulated root growth of some test plants at 6 g dry straw ls⁻¹ and inhibited root elongation at higher concentrations. A bioassay guided process of the bioactive leachate constituents led to the isolation of vanillic, syringic and ferulic acids. These compounds were also assayed on the test plants in the three mentioned substrates. In unsterile soil, phenolics stimulated the growth of some species at 19 mg l⁻¹. Higher phenolics concentrations were inhibitory. The concentration needed to inhibit 25% root elongation (EC₂₅) was calculated from the dose–response curves. The concentration of phenolics in the leachate (64 g dry straw l⁻¹) was estimated to be 187 mg l⁻¹ (ferulic acid), 131 mg l⁻¹ (vanillic acid) and 20 mg l⁻¹ (Syringic acid). In general, these concentrations were below the EC₂₅ values determined in unsterile soil indicating that these compounds cannot completely explain the strong inhibitory activity of sugarcane straw leachates. The role of soil factors on phytotoxicity of sugarcane straw leachate and its identified growth regulators is also discussed.     

Phytotoxic Diterpenoids from Plants and Microorganisms

Phytotoxic natural products with either unique or various structures are one of the most abundant sources for the discovery of potential allelochemicals, natural herbicides, and plant growth regulators. Phytotoxic diterpenoids, a relatively large class of natural products, play an important role in the plant‐plant or plant‐microorganism interactions. This article argues that the phytotoxic diterpenoids isolated from the plants and microorganisms can either inhibit the seed germination and the growth of plant seedlings or lead to some disease symptoms on the tested plant tissues and plant seedlings.     

Airborne Microorganisms in Broiler Processing Plants

Concentrations of total aerobic bacteria, molds, yeasts, coliforms, enterococci, and psychrophiles were determined in the air of two poultry processing plants with Andersen samplers and a mobile power supply. Total aerobic bacterial counts were highest in the dressing room, with diminishing numbers in the shackling, eviscerating, and holding rooms, when sampling was carried out during plant operation. The average counts per ft³ of air in these four rooms were 2,200; 560; 230; and 62, respectively. (Each value is the average of 36 observations.) The number of organisms increased in the shackling and dressing rooms once processing was begun. Average total aerobic bacterial counts increased from 70 to 870 to 3,000 in the shackling room and from 310 to 4,900 to 7,000 in the dressing room when sampling was carried out at 5:00 am (before plant operations), 9:00 am, and 2:00 pm, respectively. (Each value is the mean of 12 observations.) Airborne molds might originate from a source other than the poultry being processed.     

Strigolactones as mediators of plant growth responses to environmental conditions

Strigolactones (SLs) have been recently identified as a new group of plant hormones or their derivatives thereof, shown to play a role in plant development. Evolutionary forces have driven the development of mechanisms in plants that allow adaptive adjustments to a variety of different habitats by employing plasticity in shoot and root growth and development. The ability of SLs to regulate both shoot and root development suggests a role in the plant''s response to its growth environment. To play this role, SL pathways need to be responsive to plant growth conditions, and affect plant growth toward increased adaptive adjustment. Here, the effects of SLs on shoot and root development are presented, and possible feedback loops between SLs and two environmental cues, light and nutrient status, are discussed; these might suggest a role for SLs in plants'' adaptive adjustment to growth conditions.Key words: strigolactones, light, nutrient status, root, shoot, branching, lateral roots, root hairsStrigolactones (SLs) are carotenoid-derived terpenoid lactones suggested to stem from the carotenoid pathway¹ via the activity of various oxygenases.^2,3 SLs production has been demonstrated in both monocotyledons and eudicotyledons (reviewed in ref. ⁴), suggesting their presence in many plant species.⁵ SLs are synthesized mainly in the roots and in some parts of the stem and then move towards the shoot apex (reviewed ref. ⁷).^6,8,9SLs were first characterized more than 40 years ago as germination stimulants of the parasitic plants Striga and Orobanche and later, as stimulants of arbuscular mycorrhiza hyphal branching as well (reviewed in ref. ^{4, 10–13}). Recently, SLs or derivatives thereof, have been identified as a new group of plant hormones, shown to play a role in inhibition of shoot branching,^2,3,8,9 thereby affecting shoot architecture; more recently they have also been shown to affect root growth by affecting auxin efflux.¹⁴Plants have developed mechanisms that allow adaptive adjustments to a variety of different habitats by employing plasticity in their growth and development.¹⁵ Shoot architecture is affected by environmental cues, such as light quality and quantity and nutrient status.^16–19 Root-system architecture and development are affected by environmental conditions such as nutrient availability (reviewed in ref. ^{20, 21}). At the same time, plant hormones are known to be involved in the regulation of plant growth, development and architecture (reviewed in ref. ^22–24) and to be mediators of the effects of environmental cues on plant development; one classic example is auxin''s role in the plant''s shade-avoidance response (reviewed in ref. ²⁵).The ability of SLs to regulate shoot and root development suggests that these phytohormones also have a role in the plant''s growth response to its environment. To play this putative role, SL pathways need to be responsive to plant growth conditions, and affect plant growth toward enhancing its adaptive adjustment. The present review examines the SLs'' possible role in adaptive adjustment of the plant''s response to growth conditions, by discussing their effect on plant development and the possible associations and feedback loops between SLs and two environmental cues: light and nutrient status.     

microRNAs as Developmental Regulators

The field of miRNA biology is relatively young, but its impact on our understanding of the regulation of a wide array of cell functions is far-reaching. The importance of miRNAs in development has become nearly ubiquitous, with miRNAs contributing to development of most cells and organs. Although miRNAs are clearly interwoven into known regulatory networks that control cell development, the specific modalities by which they intersect are often quite distinct and cleverly achieved. The frequently emerging theme of feed-back and feed-forward loops to either counterbalance or reinforce the gene programs that they influence is a common thread. Many of these examples of miRNAs as developmental regulators are presently found in organs with different miRNAs and targets, whereas novel, unexpected themes emerge in the context of mouse development as we learn more about this rapidly developing area of biology.     

Symbiotrophy of lignophytes and fungi: Its terminological and conceptual deficiencies

The authors suggest a replacement of the terms ectotrophic, endotrophic, and peritrophic mycorrhizae byectocellular, endocellular, andperipheral mycorrhizae. The termrhizoclena (root mantle) is advanced for superficial rootadherent fungal mycelia. The two principal varieties of rhizoclenae are:mycochlamydes, lanose fungal mantles enveloping the roots;mycoplasts, grumose fungal mantles consisting of sapropellous clusters of soil, root sloughings, and fungal hyphae agglutinated by microbial excretions. Emphasis is placed on nutritional importance of the epirhizal root auxiliaries. These constituents of the rhizosphere by virtue of their chelating processes convert raw organic and mineral sources of nutrients into available form. A tree or other lignophyte removed from the soil is only a part of the whole plant surgically separated from its rhizospheric digestive organ. In consequence, suggestion is made to recognize obvious orphanero-symbiosis, detectable by ocular or microtome examination, and concealed orcrypto-symbiosis, effected by juxtaposed mycelia. A scarcity or entire absence of ectocellular mycorrhizal short roots of seedlings naturally reproduced under the canopy of mother stands indicated the minor nutritional importance of these root-fungus organs. The abundance of short roots, common to greenhouse and nursery cultures, is attributed to the exposure of trees to full sunlight and excessive production of carbohydrates. Preservation of the termpseudomycorrhizae may be justified in application to mycelia-free forked short roots produced in sterile nutrient solutions, especially those enriched in growth-promoting hormones.     

Plant Growth Regulators and Induction of Leaf Senescence in Nitrogen-Deprived Wheat Plants

The sequence of events and the signals that regulate the remobilization of nitrogen (N) reserves during senescence induced by N starvation were studied in leaf 3, the last fully expanded leaf, in 17-day-old wheat (Triticum aestivum L.) plants. The first event observed was a rapid decrease in the isopentenyl adenosine (iPA) concentration during the first 24 h of N starvation. No differences in t-zeatin riboside and dihydrozeatin riboside concentrations were observed until the end of the assay. During the following 6 days, a decrease in soluble amino acids, chlorophyll, and protein, as well as an increase in soluble sugar concentration and endoproteolytic activity, could be observed. At day 3 of the experiment, the abscisic acid (ABA) concentration in the leaves of N-deprived plants started to increase. After 6 days of N deprivation there was a rise in oxidative stress, as indicated by the increase in malondialdehyde concentration, as well as a decrease in the activities of antioxidant enzymes catalase and ascorbate peroxidase. To analyze interactions with leaf development, the first, second, third, and fourth leaves were studied. iPA concentration decreased in all the leaf stages, including leaf 4, which was not fully expanded. A linear correlation between iPA and protein concentration was determined. These results suggest that the sharp fall in iPA could be the earliest event that induces protein degradation during the development of senescence induced by N deficiency, and that only later is ABA accumulated and oxidative stress developed.     

Germination Promotant for Plants Seed,produced by Microorganisms

The culture filtrate of the Streptomyces sp. S-580 showed strong activity in promoting the germination of rice plant seeds. The culture conditions of the strain and fractionation of the active principles from the culture filtrate were investigated. The active crude syrup (A.C.S.) obtained is effective at the dilution of 10^?5 ~ 10^?8 for the germination of rice plant seeds, 10^?5~10^? for barley and oats seeds.     

Phospholipids as Plant Growth Regulators

In this paper the potential to use phospholipids and lysophospholipids as plant growth regulators is discussed. Recent evidence shows that phospholipids and phospholipases play an important signalling role in the normal course of plant development and in the response of plants to abiotic and biotic stress. It is apparent that phospholipase A (PLA), C (PLC) and D (PLD), lysophospholipids, and phosphatidic acid (PA) are key components of plant lipid signalling pathways. By comparison, there is very little information available on the effect of exogenously applied phospholipids on plant growth and development. This paper serves to introduce phospholipids as a novel class of plant growth regulator for use in commercial plant production. The biochemistry and physiology of phospholipids is discussed in relation to studies in which phospholipids and lysophospholipids have been applied to plants and plant parts. Implicit in the observations is that phospholipids impact the hypersensitive response and systemic acquired resistance in plants to improve crop performance and product quality. Based on published data, a scheme outlining a possible mode of action of exogenously applied phospholipids is proposed.     

Effects of Some Growth Regulators on Young Iron Deficient Maize Plants

Young maize plants, grown hydroponically, were supplied with 1/10 the optimal amount of iron (0.75 mg dm^–3). Foliar treatments with solutions, containing N⁶-benzyladenine (BA), indole-3-acetic acid (IAA) or (2-chloroethyl)-trimethylammoniumchloride (CCC) were conducted after chlorosis had been well manifested. Changes in growth, chlorophyll content, rate of photosynthesis, catalase and peroxidase activities in leaves, and the contents of Fe, Cu, Zn, Mn, and P in leaves were recorded. Growth regulators improved (CCC, IAA) or aggravated (BA) the physiological state of chlorotic plants. Their effect might be explained by changes in Fe transport towards the leaves, by increased efficiency of Fe utilization, and by effects on plant metabolism not involving Fe.     

Strigolactones,karrikins and beyond

The plant hormones strigolactones are synthesized from carotenoids and signal via the α/β hydrolase DWARF 14 (D14) and the F‐box protein MORE AXILLARY GROWTH 2 (MAX2). Karrikins, molecules produced upon fire, share MAX2 for signalling, but depend on the D14 paralog KARRIKIN INSENSITIVE 2 (KAI2) for perception with strong evidence that the MAX2–KAI2 protein complex might also recognize so far unknown plant‐made karrikin‐like molecules. Thus, the phenotypes of the max2 mutants are the complex consequence of a loss of both D14‐dependent and KAI2‐dependent signalling, hence, the reason why some biological roles, attributed to strigolactones based on max2 phenotypes, could never be observed in d14 or in the strigolactone‐deficient max3 and max4 mutants. Moreover, the broadly used synthetic strigolactone analog rac‐GR24 has been shown to mimic strigolactone as well as karrikin(‐like) signals, providing an extra level of complexity in the distinction of the unique and common roles of both molecules in plant biology. Here, a critical overview is provided of the diverse biological processes regulated by strigolactones and/or karrikins. These two growth regulators are considered beyond their boundaries, and the importance of the yet unknown karrikin‐like molecules is discussed as well.     

不同药用植物根际土壤原核微生物多样性研究

为研究不同药用植物根际土壤中的原核微生物多样性,分别采集白术(Atractylodes macrocephala)、白芍(Paeonia sterniana)、牡丹(Paeonia suffruticosa)、玄参(Scrophularia ningpoensis)四种药用植物的根际土壤以及非种植区的土壤,针对16S rRNA基因的V3～V4区进行测序,分析土壤细菌群落的组成。结果表明,药用植物根际土壤中的细菌群落多样性指数显著高于非种植区土壤。五组样本的优势类群差异不大,总体相对丰度较高的有变形菌门(Proteobacteria)、酸杆菌门(Acidobacteria)、放线菌门(Actinobacteria)、芽单胞菌门(Gemmatimonadetes)、绿弯菌门(Chloroflexi)等,药用植物根际中的放线菌相对丰度高于非种植区。属水平上四种药用植物根际细菌和非种植区的群落结构有较大差异,四种中药材的根际土壤中各自富集了特异性的有益细菌属。药用植物根际土壤中的NMD1、Dongia、Gaiella、Streptomyces等相对丰度高于非种植区,而非种植区土壤中Lysoba...     

Phenotypes of Tobacco Plants Expressing Genes for the Synthesis of Growth Regulators

The expression of genes for synthesis of auxin (iaaM and iaaH) and cytokinins (ipt) was studied in tobacco plants transformed by two Agrobacterium tumefaciens strains C 58 and LBA 4404. The strain LBA 4404 carried binary vector plasmid pCB 1334 (ipt gene) and plasmid pCB 1349 (iaaM, iaaH and ila genes). Both plasmids carried reportered gene for npt II. Obtained plants expressed incorporated genes. New proteins with molecular masses of about 74, 40, 26, 25, 21 and 17 kDa for wild plasmid pTi C58; 60, 36, 31.5, 27, 26 and 17 kDa for binary vector plasmid pCB 1334 and 74, 49, 36, 31.5, 26 and 25 kDa for binary vector plasmid pCB 1349 were found in the patterns of soluble proteins. Significant changes in the content of chlorophylls, especially chlorophyll a, were detected in the plants carrying ipt gene and in plants transformed by the wild strain C58 of A. tumefaciens. Tobacco plants expressing ipt gene and genes from T-DNA of pTi C58 plasmid were dwarf, and in comparison to the controls, they had thicker stems, and the surface of the leaf blades was reduced to 20 - 50 %. Adventitious roots, growing from the stem, were typical for transformants overproducing auxins. Regenerants and transformants expressing genes from T-DNA of plasmid pTi C58 differed in the shape of the flowers and their fertility. This revised version was published online in July 2006 with corrections to the Cover Date.