Role of basipetal auxin transport and lateral auxin movement in rooting and growth of etiolated lupin hypocotyls

The involvement of polar auxin transport (PAT) on the growth of light-grown seedlings and rooting is generally accepted, while the role of auxin and PAT on the growth of dark-grown seedlings is subject to controversy. To further investigate this question, we have firstly studied the influence of NPA, a known inhibitor of PAT, on the rooting and growth of etiolated Lupinus albus hypocotyls. Rooting was inhibited when the basal ends of de-rooted seedlings were immersed in 100 micro m NPA but was partially restored after immersion in NPA + auxin. However, NPA applied to de-rooted seedlings or the roots of intact seedlings did not inhibit hypocotyl growth. It was taken up and distributed along the organ, and actually inhibited the basipetal transport of ((3)H)-IAA applied to isolated hypocotyl sections. Since the apex is the presumed auxin source for hypocotyl growth and rooting, and the epidermis is considered the limiting factor in auxin-induced growth, the basipetal and lateral auxin movement (LAM) after application of ((3)H)-IAA to decapitated seedlings were studied, in an attempt to evaluate the role of PAT and LAM in the provision of auxin to competent cells for growth and rooting. Local application of ((3)H)-IAA to the stele led to the basipetal transport of auxin in this tissue, but the process was drastically reduced when roots were immersed in NPA since no radioactivity was detected below the apical elongation region of the hypocotyl. LAM from the stele to the cortex and the epidermis occurred during basipetal transport, since radioactivity in these tissues increased as transport time progressed. Radioactivity on a per FW basis in the epidermis was 2-4 times higher than in the cortex, which suggests that epidermal cells acted as a sink for LAM. NPA did not inhibit LAM along the elongation region. These results suggest that while PAT was essential for rooting, LAM from the PAT pathway to the auxin-sensitive epidermal cells could play a key role in supplying auxin for hypocotyl elongation in etiolated lupin seedlings.     

Endogenous auxin levels in terminal stem cuttings of Chrysanthemum morifolium during adventitious rooting

Free and ester-bound IAA were determined in Chrysanthemum morifolium Ramat cv. 'Yellow Galaxy' by means of a solid phase enzyme immunoassay. In shoots, free auxin decreases basipetally whereas ester IAA reaches a maximum in the middle part. After making the cuttings, a strong increase in both free and ester IAA (or total IAA, respectively) is found up to the time when the first adventitious roots become visible. Only prolonged irradiance of stock plants at high light intensities (40 W m⁻²) delays this increase in the cuttings, concomitantly with a lower number of roots compared to the controls (4.5 W m⁻²), although root growth as determined by measuring root length or fresh weight is not affected. A distinct relation is found between IAA content of stock plants at the time when cuttings are taken and the number of adventitious roots formed by the cuttings 20 days later.     

Early changes in auxin and ethylene production in vine cuttings before adventitious rooting

Node cuttings of in vitro cultured grapevine were rooted in absence of any growth regulator, before the onset of the axillary bud. There were two peaks of ethylene production at 2 and 10–12 h, well marked in the top and bottom portions of the cuttings for the former. The level of IAA increased in the basal portions of the cuttings only, from the 4th hour, and culminated at the 24th hour. The wound ethylene of the first rise might be initiating the sequence of reactions leading to root formation. The second ethylene rise might result from the beginning of the increase of the IAA level.     

Unraveling the evolution of auxin signaling

Auxin signaling is central to plant growth and development, yet hardly anything is known about its evolutionary origin. While the presence of key players in auxin signaling has been analyzed in various land plant species, similar analyses in the green algal lineages are lacking. Here, we survey the key players in auxin biology in the available genomes of Chlorophyta species. We found that the genetic potential for auxin biosynthesis and AUXIN1 (AUX1)/LIKE AUX1- and P-GLYCOPROTEIN/ATP-BINDING CASSETTE subfamily B-dependent transport is already present in several single-celled and colony-forming Chlorophyta species. In addition, our analysis of expressed sequence tag libraries from Coleochaete orbicularis and Spirogyra pratensis, green algae of the Streptophyta clade that are evolutionarily closer to the land plants than those of the Chlorophyta clade, revealed the presence of partial AUXIN RESPONSE FACTORs and/or AUXIN/INDOLE-3-ACETIC ACID proteins (the key factors in auxin signaling) and PIN-FORMED-like proteins (the best-characterized auxin-efflux carriers). While the identification of these possible AUXIN RESPONSE FACTOR- and AUXIN/INDOLE-3-ACETIC ACID precursors and putative PIN-FORMED orthologs calls for a deeper investigation of their evolution after sequencing more intermediate genomes, it emphasizes that the canonical auxin response machinery and auxin transport mechanisms were, at least in part, already present before plants "moved" to land habitats.     

Gibberellins inhibit adventitious rooting in hybrid aspen and Arabidopsis by affecting auxin transport

Knowledge of processes involved in adventitious rooting is important to improve both fundamental understanding of plant physiology and the propagation of numerous plants. Hybrid aspen (Populus tremula × tremuloïdes) plants overexpressing a key gibberellin (GA) biosynthesis gene (AtGA20ox1) grow rapidly but have poor rooting efficiency, which restricts their clonal propagation. Therefore, we investigated the molecular basis of adventitious rooting in Populus and the model plant Arabidopsis. The production of adventitious roots (ARs) in tree cuttings is initiated from the basal stem region, and involves the interplay of several endogenous and exogenous factors. The roles of several hormones in this process have been characterized, but the effects of GAs have not been fully investigated. Here, we show that a GA treatment negatively affects the numbers of ARs produced by wild‐type hybrid aspen cuttings. Furthermore, both hybrid aspen plants and intact Arabidopsis seedlings overexpressing AtGA20ox1, PttGID1.1 or PttGID1.3 genes (with a 35S promoter) produce few ARs, although ARs develop from the basal stem region of hybrid aspen and the hypocotyl of Arabidopsis. In Arabidopsis, auxin and strigolactones are known to affect AR formation. Our data show that the inhibitory effect of GA treatment on adventitious rooting is not mediated by perturbation of the auxin signalling pathway, or of the strigolactone biosynthetic and signalling pathways. Instead, GAs appear to act by perturbing polar auxin transport, in particular auxin efflux in hybrid aspen, and both efflux and influx in Arabidopsis.     

Points of regulation for auxin action

There have been few examples of the application of our growing knowledge of hormone action to crop improvement. In this review we discuss what is known about the critical points regulating auxin action. We examine auxin metabolism, transport, perception and signalling and identify genes and proteins that might be keys to regulation, particularly the rate-limiting steps in various pathways. Certain mutants show that substrate flow in biosynthesis can be limiting. To date there is little information available on the genes and proteins of catabolism. There have been several auxin transport proteins and some elegant transport physiology described recently, and the potential for using transport proteins to manage free indole-3-acetic acid (IAA) concentrations is discussed. Free IAA is very mobile, and so while it may be more practical to control auxin action through managing the receptor and signalling pathways, the candidate genes and proteins through which this can be done remain largely unknown. From the available evidence, it is clear that the reason for so few commercial applications arising from the control of auxin action is that knowledge is still limited.     

Effects of auxin and irradiance on the rooting of cuttings of Pinus sylvestris

Abstract Seedlings of Pinus sylvestris L. were grown under controlled conditions (temperature 20°C, photoperiod 17 h) at two irradiances, 8 or 40 W m^-2. Hypocotyl cuttings were excised and rooted at different irradiances in tap water solutions of indolebutyric acid (IBA). The fastest rooting and highest rooting percentage were obtained with cuttings from stock plants grown at 8 W m^-2 and treated with 10^-5M IBA for 21 days. The concentration of 10^-4M IBA inhibited root formation. In comparable treatments rooting was always better in cuttings from stock plants grown at 8 W m^-2 than in cuttings from stock plants grown at 40 W m^-2. The irradiance during the rooting period had only a minor influence on rooting. When cuttings from plants irradiated with 40 W m^-2 were treated with 10^-5M IBA for 21 days the rooting percentage almost reached the same level as in untreated cuttings from stock plants given 8 W m^-2. In cuttings treated with IBA during the whole rooting period, rooting was depressed in comparison to untreated cuttings. Aeration of the 10^-4M IBA solution increased the rooting percentage, but aeration had no effect on untreated cuttings and on cuttings treated with lower IBA concentrations.     

Changes in auxin protectors and IAA oxidases during the rooting of chestnut shoots in vitro

Auxin protectors and IAA oxidase activity were comparatively analyzed in the upper and the lower parts of shoots of chestnut ( Castanea sativa Mill.) cultivated in vitro with indolebutyric acid (IBA) pretreatment. Rhizogenesis of the shoots is accompanied by an increase in auxin protectors in the lower parts and by a decrease of these protectors in the upper parts. Besides, the IAA oxidase activity declines in the basal parts during the rooting process while it increases in the upper ones. These biochemical events would enhance the IAA level in the rooting region of the shoots. In untreated, non-rooted cuttings, the IAA oxidase activity remains low in the upper parts and high in the basal parts of the shoots. The results thus indicate that the IBA treatment may control the endogenous auxin level of the cuttings, either through a direct regulation of the IAA oxidase system or more indirectly through the transport of auxin protectors.     

Adventitious rooting: examining the role of auxin in an easy- and a difficult-to-root plant

Therooting responses of cuttings of difficult-to-root lilac (Syringavulgaris) and easy-to-root forsythia(Forsythia×intermedia)were compared. The rooting ability of lilac cuttings declined over the growingseason (May–June). There was also a decline in the initial concentrationof free IAA at the base of the cuttings, but there was not a tight relationshipbetween basal IAA concentration and rooting ability. Polar auxin transportability was measured in lilac and forsythia during the period of maximum growthby [³H]IAA application to stem internodal tissue. Transport abilitydeclined in lilac over this time period, particularly in terms of transportintensity and percentage of [³H]IAA transported. In contrast thechanges in polar auxin transport ability in forsythia were less marked. Thisdifference between species was maintained in winter hardwood cuttings, withforsythia tissue showing greater polar auxin transport ability than lilac. Theimportance of polar auxin transport for adventitious rooting was demonstratedinboth lilac and forsythia softwood cuttings by use of the polar transportinhibitor 2,3,5-triiodobenzoic acid (TIBA). Overall the results indicate thatdifferences in polar auxin transport ability between lilac and forsythiacontribute to differences in rooting ability.     

“探索生长素类似物促进插条生根的最适浓度”的教学组织

“探索生长素类似物促进插条生根的最适浓度”的实验探究活动．是引导学生将生物学知识运用于生产实践的好素材,从实验教学内容、学情、教学目标、教学过程的组织和教学建议等几个方面进行了分析和研究,希望通过有效的教学组织提高课堂的高效性,同时用生活化的内容充实课堂教学．为课程改革增添新的活力。     

Sites and regulation of auxin biosynthesis in Arabidopsis roots

Auxin has been shown to be important for many aspects of root development, including initiation and emergence of lateral roots, patterning of the root apical meristem, gravitropism, and root elongation. Auxin biosynthesis occurs in both aerial portions of the plant and in roots; thus, the auxin required for root development could come from either source, or both. To monitor putative internal sites of auxin synthesis in the root, a method for measuring indole-3-acetic acid (IAA) biosynthesis with tissue resolution was developed. We monitored IAA synthesis in 0.5- to 2-mm sections of Arabidopsis thaliana roots and were able to identify an important auxin source in the meristematic region of the primary root tip as well as in the tips of emerged lateral roots. Lower but significant synthesis capacity was observed in tissues upward from the tip, showing that the root contains multiple auxin sources. Root-localized IAA synthesis was diminished in a cyp79B2 cyp79B3 double knockout, suggesting an important role for Trp-dependent IAA synthesis pathways in the root. We present a model for how the primary root is supplied with auxin during early seedling development.     

Principles of organization and evolution of systems of regulation of functions

Evolution of living organisms is closely connected with evolution of structure of the system of regulations and its mechanisms. The functional ground of regulations is chemical signalization. As early as in unicellular organisms there is a set of signal mechanisms providing their life activity and orientation in space and time. Subsequent evolution of ways of chemical signalization followed the way of development of delivery pathways of chemical signal and development of mechanisms of its regulation. The mechanism of chemical regulation of the signal interaction is discussed by the example of the specialized system of transduction of signal from neuron to neuron, of effect of hormone on the epithelial cell and modulation of this effect. These mechanisms are considered as the most important ways of the fine and precise adaptation of chemical signalization underlying functioning of physiological systems and organs of the living organism     

Metabolic changes during rooting in stem cuttings of Casuarina equisetifolia L.: effects of auxin, the sex and the type of cutting on rooting

Rooting in terminal shoot and lateral shoot cuttings from 10-year-old elite trees of Casuarina equisetifolia L. in different sex groups was achieved after 20 days when the basal ends of the cuttings were dipped for 3 h in 20 ppm indole-3-butyric acid (IBA). Shoots derived from male plants rooted better than their female and monoecious counterparts, and the lateral shoots were more responsive to rooting than the terminal shoots. During rooting, the metabolic activities varied in both lateral shoot and terminal shoot cuttings derived from plants under different sex groups. Peroxidase and polyphenoloxidase activities were high during root initiation and showed a sharp decline thereafter. The polyphenoloxidase activity was higher in the lateral shoot than the terminal shoot cuttings. The rooted plantlets survived and established well in the field.Abbreviations IAA indole-3-acetic acid - IBA indole-3-butyric acid - NAA 1-naphthaleneacetic acid - PVP polyvinylpyrrolidone     

Redox regulation of auxin signaling and plant development in Arabidopsis

Thioredoxin (NTR/TRX) and glutathione (GSH/GRX) are the two major systems that play a key role in the maintenance of cellular redox homeostasis. They are essential for plant development, cell division or the response to environmental stresses. In a recent article,¹ we studied the interplay between the NADP-linked thioredoxin and glutathione systems in auxin signaling genetically, by associating TRX reductase (ntra ntrb) and glutathione biosynthesis (cad2) mutations. We show that these two thiol reduction pathways interfere with developmental processes. This occurs through modulation of auxin activity as shown by genetic analyses of loss of function mutations in a triple ntra ntrb cad2 mutant. The triple mutant develops almost normally at the rosette stage but fails to generate lateral organs from the inflorescence meristem, producing almost naked stems that are reminiscent of mutants affected in PAT (polar auxin transport) or biosynthesis. The triple mutant exhibits other defects in processes regulated by auxin, including a loss of apical dominance, vasculature defects and reduced secondary root production. Furthermore, it has lower auxin (IAA) levels and decreased capacity for PAT, suggesting that the NTR and glutathione pathways influence inflorescence meristem development through regulation of auxin transport and metabolism.Key words: arabidopsis, NTS pathway, NGS pathway, thioredoxin (TRX), glutaredoxine (GRX), polar auxin transport (PAT), auxin biosynthesis, pin-like phenotype, apical dominance, meristematic activityExposure of living organisms to environmental stresses triggers various defense and developmental responses. Redox signaling is involved in many aspects of these responses.^2–6 The key players in these responses are the NADPH-dependent glutathione/glutaredoxin system (NGS) and the NADPH-dependent thioredoxin system (NTS). TRX and GRX play key roles in the maintenance of cellular redox homeostasis.^7–10 Genetic approaches aiming to identify functions of TRX and GRX in knock-out plants have largely been limited by the absence of phenotypes of single mutants, presumably due to functional redundancies among members of the multigene families of TRX and GRX.¹¹ Interplay between NTS and NGS pathways have been studied in different organisms^12–17 and association of mutants involved in these two pathways have recently revealed new functions in several aspects of plant development.^4–6     

Quantum processes in evolution of regulation of living systems (mathematical modeling)

We have developed an imitation model of the appearance of regulation of physiological functions of protocell at initial stages of evolution of living system. It is based on suggestion of the appearance of signal function in spontaneously formed products of partial hydrolysis of the protocell polypeptides, based on which there appear the regulatory molecules—quanta of regulation. For construction of the model, the mathematical apparatus of final automats and of genetic algorithm is used. The model has demonstrated the positive role of involvement of regulatory peptides in the system of regulation of protocell functions to provide its viability under the changing envelopment conditions.