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One of the longest standing theories and, therein-based, regulation-model of plant root development, posits the inhibitory action of auxin (IAA, indolylacetic acid) on elongation growth of root cells. This effect, as induced by exogenously supplied IAA, served as the foundation stone for root growth regulation. For decades, auxin ruled the day and only allowed hormonal side players to be somehow involved, or in some way affected. However, this copiously reiterated, apparent cardinal role of auxin only applies in roots immersed in solutions; it vanishes as soon as IAA-supplied roots are not surrounded by liquid. When roots grow in humid air, exogenous IAA has no inhibitory effect on elongation growth of maize roots, regardless of whether it is applied basipetally from the top of the root or to the entire residual seedling immersed in IAA solution. Nevertheless, such treatment leads to pronounced root-borne ethylene emission and lateral rooting, illustrating and confirming thereby induced auxin presence and its effect on the root — yet, not on root cell elongation. Based on these findings, a new root growth regulatory model is proposed. In this model, it is not IAA, but IAA-triggered ethylene which plays the cardinal regulatory role — taking effect, or not — depending on the external circumstances. In this model, in water- or solution-incubated roots, IAA-dependent ethylene acts due to its accumulation within the root proper by inhibited/restrained diffusion into the liquid phase. In roots exposed to moist air or gas, there is no effect on cell elongation, since IAA-triggered ethylene diffuses out of the root without an impact on growth.

Snow roots are a very special type of roots that counteract geotropism to grow upward into long-lasting snow fields. They develop under snow at near 0oC, a phenomenon that had previously only been reported from plant shoots (Korner et al. 2019). Up to now, this intriguing and spectacular looking plant structure has been discovered and studied in only a single species, i.e. the vernal forb, Corydalis conorhiza Ledeb. (poppy family, Papaveraceae) at an elevation of almost 3 km in the mountains of the northern Caucasus, Russia by Onipchenko et al. (2009a, 2014), who reported results from a snow-field labeling experiment with the natural nitrogen (N) isotope 15 N, accompanied with anatomical and structural root trait measurements.

Genetic factors determine how local and systemic nitrogen signals shape root system architecture in higher plants., Among all essential mineral elements, nitrogen (N) is required in the largest amounts and thus is often a limiting factor for plant growth. N is taken up by plant roots in the form of water-soluble nitrate, ammonium, and, depending on abundance, low-molecular weight organic N. In soils, the availability and composition of these N forms can vary over space and time, which exposes roots to various local N signals that regulate root system architecture in combination with systemic signals reflecting the N nutritional status of the shoot. Uncovering the molecular mechanisms underlying N-dependent signaling provides great potential to optimize root system architecture for the sake of higher N uptake efficiency in crop breeding. In this review, we summarize prominent signaling mechanisms and their underlying molecular players that derive from external N forms or the internal N nutritional status and modulate root development including root hair formation and gravitropism. We also compare the current state of knowledge of these pathways between Arabidopsis and graminaceous plant species.

An important adaptation during colonization of land by plants is gravitropic growth of roots, which enabled roots to reach water and nutrients, and firmly anchor plants in the ground. Here we provide insights into the evolution of an efficient root gravitropic mechanism in the seed plants. Architectural innovation, with gravity perception constrained in the root tips along with a shootward transport route for the phytohormone auxin, appeared only upon the emergence of seed plants. Interspecies complementation and protein domain swapping revealed functional innovations within the PIN family of auxin transporters leading to the evolution of gravitropism-specific PINs. The unique apical/shootward subcellular localization of PIN proteins is the major evolutionary innovation that connected the anatomically separated sites of gravity perception and growth response via the mobile auxin signal. We conclude that the crucial anatomical and functional components emerged hand-in-hand to facilitate the evolution of fast gravitropic response, which is one of the major adaptations of seed plants to dry land., Root gravitropism anchors land plants to the ground and enables water uptake. Here, Zhang et al. define polar targeting of PIN2-like proteins as a major evolutionary innovation promoting shootward auxin transport and faster gravitropic responses of seed plants compared to basal vascular relatives.

During the whole history of their life on Earth, higher plants evolved under the constant gravity stimulus. Therefore, plants developed efficient mechanisms of gravity perception, underlying their ability to adjust the direction of growth to the gravity vector, i.e. the phenomenon of gravitropism. In this context, alterations in the magnitude and vector of the gravity field might compromise plant growth and development. This aspect was successfully addressed in gravity fields of low intensity (microgravity). On the other hand, microgravity can be simulated on the Earth by clinorotation, i.e. rotation of the experimental plant along one or several axes. This approach is routinely used for studies of gravity-related responses of crop plants, although the effect of simulated microgravity on the most sensitive ontogenetic stages — germination and seedling development — is still not sufficiently characterized. Recently, we addressed the effects of clinorotation on the proteome of germinating oilseed rape (Brassica napus) seeds. Here we extend this study to the seedling primary metabolome and address its changes in the presence of 3D-clinorotation. GC-MS analysis revealed essential alterations in patterns of sugars and sugar phosphates (specifically glucose-6-phosphate), methionine and glycerol. Thereby, abundances of individual metabolites showed high dispersion, indicating high lability and plasticity of the seedling metabolome.

Background Branch angle is a pivotal component of tea plant architecture. Tea plant architecture not only affects tea quality and yield but also influences the efficiency of automatic tea plant pruning. However, the molecular mechanism controlling the branch angle, which is an important aspect of plant architecture, is poorly understood in tea plants. Results In the present study, three CsLAZY genes were identified from tea plant genome data through sequence homology analysis. Phylogenetic tree displayed that the CsLAZY genes had high sequence similarity with LAZY genes from other plant species, especially those in woody plants. The expression patterns of the three CsLAZYs were surveyed in eight tissues. We further verified the expression levels of the key CsLAZY1 transcript in different tissues among eight tea cultivars and found that CsLAZY1 was highly expressed in stem. Subcellular localization analysis showed that the CsLAZY1 protein was localized in the plasma membrane. CsLAZY1 was transferred into Arabidopsis thaliana to investigate its potential role in regulating shoot development. Remarkably, the CsLAZY1 overexpressed plants responded more effectively than the wild-type plants to a gravity inversion treatment under light and dark conditions. The results indicate that CsLAZY1 plays an important role in regulating shoot gravitropism in tea plants. Conclusions The results provide important evidence for understanding the functions of CsLAZY1 in regulating shoot gravitropism and influencing the stem branch angle in tea plants. This report identifies CsLAZY1 as a promising gene resource for the improvement of tea plant architecture.

Summary • An in vitro targeted inoculation technique has been developed for studying the earliest stages of arbuscular endomycorrhizal (AM) infection of Medicago truncatula roots, and in particular the spatio-temporal expression of the early nodulin gene MtENOD11. • Agrobacterium rhizogenes transformed root explants were derived either from Myc +M. truncatula or from the infection-defective Myc − mutant TR26 ( dmi2–2 ), both expressing the pMtENOD11-gusA fusion. The normal positive geotropism of these roots, coupled with the negative geotropism of Gigaspora germ tubes allowed oriented growth of the two symbiotic partners, facilitating the identification of initial fungal/root contacts. • Early infection events at the stage of appressoria and/or internal hyphae could be observed for over 50% of the inoculated explants, revealing that MtENOD11 is expressed transiently in both epidermal and cortical cells at sites of hyphal penetration in Myc + roots, but not in epidermal cells in contact with appressoria in Myc − roots. • We propose that a direct link exists between MtENOD11 gene expression and cellular events required for fungal penetration, thereby extending analogies between rhizobial and AM host root infection processes.

The mutation Ageotropic (Agt) results in defective development of the surface pellicle which overlies the young epidermal cells of mesocotyl and nodal roots of maize. In roots of plants of the parent, cv. Kys, pellicle development is normal. This structure forms a coherent, smooth covering, up to ∼ 13/μm thick, over the epidermal cells distal to the elongation zone. This pellicle is external to the helicoidal outer wall of the epidermal cells and is composed of a thick inner layer with close-packed, longitudinally oriented fibrils, and a thin outer layer with less regularly oriented fibrils. Both layers of the normal pellicle and the underlying epidermal wall are strongly stained by the periodic acid-Schiff's (PAS) reaction. In Agt plants, the pellicle is irregular and diffuse, lacks definition of the two layers and is largely amorphous with occasional wisps of fibrils. Neither this mutant pellicle nor the underlying epidermal wall are PAS-positive. Mesocotyl and nodal roots of Agt are sensitive to gravity but grow crookedly through soil. It is proposed that a normal pellicle maintains the smooth outer contour of young roots and provides stiffness in the region distal to the zone of elongation. When the pellicle is defective, the root tip is more compliant and bends result when the tip encounters small air spaces and barriers in the soil.

20 p.-6 fig., Clinorotation was the first method designed to simulate microgravity on ground and it remains the most common and accessible simulation procedure. However, different experimental settings, namely angular velocity, sample orientation, and distance to the rotation center produce different responses in seedlings. Here, we compare A. thaliana root responses to the two most commonly used velocities, as examples of slow and fast clinorotation, and to vertical and horizontal clinorotation. We investigate their impact on the three stages of gravitropism: statolith sedimentation, asymmetrical auxin distribution, and differential elongation. We also investigate the statocyte ultrastructure by electron microscopy. Horizontal slow clinorotation induces changes in the statocyte ultrastructure related to a stress response and internalization of the PIN-FORMED 2 (PIN2) auxin transporter in the lower endodermis, probably due to enhanced mechano-stimulation. Additionally, fast clinorotation, as predicted, is only suitable within a very limited radius from the clinorotation center and triggers directional root growth according to the direction of the centrifugal force. Our study provides a full morphological picture of the stages of graviresponse in the root tip, and it is a valuable contribution to the field of microgravity simulation by clarifying the limitations of 2D-clinostats and proposing a proper use., This research was funded by Agencia Estatal de Investigación of the Spanish Ministry of Science and Innovation, Grants #ESP2015-64323-R and #RTI2018-099309-B-I00 (co-funded by EU-ERDF), awarded to FJM. The clinostat was obtained by a Grant of the United Nations Zero-Gravity Instrument Project (ZGIP), second and third cycle calls 2014/2018 (UNOOSA), awarded to RH and FJM. AV is a recipient of a contract of the Spanish National Program for Young Researchers Training (BES-2016-077976).

Tropisms are among the most important growth responses for plant adaptation to the surrounding environment. One of the most common tropisms is root gravitropism. Root gravitropism enables the plant to anchor securely to the soil enabling the absorption of water and nutrients. Most of the knowledge related to the plant gravitropism has been acquired from the flowering plants, due to limited research in non-seed plants. Limited research on non-seed plants is due in large part to the lack of standard research methods. Here, we describe the experimental methods to evaluate gravitropism in representative non-seed plant species, including the non-vascular plant moss Physcomitrium patens, the early diverging extant vascular plant lycophyte Selaginella moellendorffii and fern Ceratopteris richardii. In addition, we introduce the methods used for statistical analysis of the root gravitropism in non-seed plant species.

Roots typically grow downward into the soil where they anchor the plant and take up water and nutrients necessary for plant growth and development. While the primary roots usually grow vertically downward, laterals often follow a gravity set point angle that allows them to explore the surrounding environment. These responses can be modified by developmental and environmental cues. This review discusses the molecular mechanisms that govern root gravitropism in flowering plant roots. In this system, the primary site of gravity sensing within the root cap is physically separated from the site of curvature response at the elongation zone. Gravity sensing involves the sedimentation of starch-filled plastids (statoliths) within the columella cells of the root cap (the statocytes), which triggers a relocalization of plasma membrane-associated PIN auxin efflux facilitators to the lower side of the cell. This process is associated with the recruitment of RLD regulators of vesicular trafficking to the lower membrane by LAZY proteins. PIN relocalization leads to the formation of a lateral gradient of auxin across the root cap. Upon transmission to the elongation zone, this auxin gradient triggers a downward curvature. We review the molecular mechanisms that control this process in primary roots and discuss recent insights into the regulation of oblique growth in lateral roots and its impact on root-system architecture, soil exploration and plant adaptation to stressful environments.

The actual effect of ethylene on shoot gravitropic response has been controversial. To elucidate the role of ethylene in the modulation of shoot gravitropic response, Arabidopsis inflorescences and light-grown seedlings were pretreated with 0.1-10 -1 of ethylene for either a long (12-48 h) or short term (0.5 h). When the gravicurvature was measured either in air or in ethylene, it was found that prolonged exposure to various levels of ethylene stimulated both inflorescence stem and hypocotyl gravicurvature in air, while the continued presence of ethylene immediately following reorientation of plant tissues inhibited gravicurvature of both tissues. Both stimulatory and inhibitory effects existed in inflorescence stems and hypocotyls when the plant tissues were exposed to a chosen concentration of ethylene. Stimulation by ethylene was stronger than its inhibition in inflorescence stems, while the reverse was true for the hypocotyls. Therefore, the continued presence of high levels of naturally produced ethylene in eto1-1 did not suppress the faster gravicurvature of inflorescence stems, whereas the removal of exogenously applied ethylene was necessary to observe faster gravicurvature of both the wild-type and eto1-1 hypocotyls. Both effects acted through the known ethylene receptor complex. These results strongly suggest that ethylene of a chosen concentration has opposing effects on the negative gravitropic responses of both inflorescence stems and hypocotyls. The ultimate negatively gravitropic behaviour of a plant tissue, when exposed to ethylene, depends on the dynamic interplay between these two opposing effects.

European species of Nuphar are amongthe most accessible members of the basal angiosperm grade, but detailed studies using scanning electron microscopy are lacking. We provide such data and discuss them in the evolutionary context. Dorsiventral monopodial rhizomes of Nuphar bear foliage leaves and non-axillary reproductive units (RUs) arranged in a Fibonacci spiral. The direction of the phyllotaxis spiral is established in seedlings apparently environmentally and maintained through all rhizome branching events. The RUs can be located on dorsal, ventral or lateral side of the rhizome. There is no seasonality in timing of their initiation. The RUs usually form pairs in positions N and N + 2 along the ontogenetic spiral. New rhizomes appear on lateral sides of the mother rhizome. A lateral rhizome is subtended by a foliage leaf (N) and is accompanied by a RU in the position N + 2. We hypothesize a two-step process of regulation of RU/branch initiation, with the second step possibly involving environmental factors such as gravitropism. Each RU has a short stalk, 1-2 scale-like phyllomes and a long-pedicellate flower. We support a theory that the flower is lateral to the RU axis. The five sepals initiate successively and form two whorls as 3 + 2. The sepal arrangement is not ‘intermediate’ between whorled and spiral. Mechanisms of phyllotaxis establishment differ between flowers and lateral rhizomes. Petal, stamen and carpel numbers are not precisely fixed. Petals are smaller than sepals and form a whorl. They appear first in the sectors of the outer whorl sepals. The stamen arrangement is whorled to chaotic. The merism of the androecium tends to be the same as in the corolla. Flowers with odd numbers of stamen orthostichies are found. These are interpreted as having a non-integer merism of the androecium (e.g., 14.5). Carpels form a whorl in N. lutea and normally alternate with inner whorl stamens. Sterile second whorl carpel(s) are found in some flowers of N. pumila.

Background Shoot orientation is important for plant architecture formation, and zigzag-shaped shoots are a special trait found in many plants. Zigzag-shaped shoots have been selected and thoroughly studied in Arabidopsis; however, the regulatory mechanism underlying zigzag-shaped shoot development in other plants, especially woody plants, is largely unknown. Results In this study, tea plants with zigzag-shaped shoots, namely, Qiqu (QQ) and Lianyuanqiqu (LYQQ), were investigated and compared with the erect-shoot tea plant Meizhan (MZ) in an attempt to reveal the regulation of zigzag-shaped shoot formation. Tissue section observation showed that the cell arrangement and shape of zigzag-shaped stems were aberrant compared with those of normal shoots. Moreover, a total of 2175 differentially expressed genes (DEGs) were identified from the zigzag-shaped shoots of the tea plants QQ and LYQQ compared to the shoots of MZ using transcriptome sequencing, and the DEGs involved in the “Plant-pathogen interaction”, “Phenylpropanoid biosynthesis”, “Flavonoid biosynthesis” and “Linoleic acid metabolism” pathways were significantly enriched. Additionally, the DEGs associated with cell expansion, vesicular trafficking, phytohormones, and transcription factors were identified and analysed. Metabolomic analysis showed that 13 metabolites overlapped and were significantly changed in the shoots of QQ and LYQQ compared to MZ. Conclusions Our results suggest that zigzag-shaped shoot formation might be associated with the gravitropism response and polar auxin transport in tea plants. This study provides a valuable foundation for further understanding the regulation of plant architecture formation and for the cultivation and application of horticultural plants in the future.

Climbing Epipremnum aureum plants develop larger leaves than unsupported, hanging plants. This effect may be regarded, in part, as a thigmomorphogenic response, but gravimorphogenetic effect may also be involved, since polar auxin transport is known to be negatively affected in plants with horizontal or hanging stems, which may result in an altered hormone balance at the whole plant level. The present work was aimed at studying how exogenous auxins and cytokinins may influence growth of E. aureum rooted cuttings under different training systems. Rooted cuttings of E. aureum were cultivated either climbing on an upright wooden board or creeping on the glasshouse bench or hanging from a basket. All leaves of each plant were sprayed to run-off at sunset with four indole-3-acetic acid (IAA) doses 7 days after transplanting and one week later, with four benzylaminopurine (BAP) concentrations, rendering 16 hormone combination treatments. The application of IAA or BAP at 50 mg L-1 to creeping and hanging plants significantly promoted growth but, in climbing plants, a negative effect was generally observed. Changes in net assimilation and photosynthetic rates, together with modified allometric coefficients, accounted for these responses. The higher growth promotion by exogenous growth regulators observed in creeping or hanging plants compared to climbing plants, may be interpreted mostly as a gravimorphogenetic response. Plantas trepadeiras (Epipremnum aureum) conduzidas suspensas, desenvolvem folhas maiores em comparação com plantas conduzidas sem suporte (rasteiras). Esse efeito pode ser visto, em parte, como uma resposta thigmomorfogênica; mas o efeito gravimorfogênico também pode estar envolvido, uma vez que o transporte polar de auxinas é afetado negativamente em plantas com hastes horizontais ou pendentes, o que pode resultar em um balanço hormonal alterado, a nível da planta como um todo. O presente trabalho teve como objetivo estudar como as auxinas e citocininas exógenas podem influenciar o crescimento de estacas enraizadas de E. aureum sob diferentes sistemas de condução. Estacas enraizadas de E. aureum foram cultivadas como trepadeiras em uma tábua de madeira vertical ou rasteiras sobre bancada em casa de vegetação ou suspensas em uma cesta. Todas as folhas de cada planta foram pulverizadas até escoamento à tarde, com quatro doses de ácido indol-3-acético (AIA), 7 dias após o transplante e, após uma semana, com quatro concentrações de benzilaminopurina (BAP), resultando em 16 tratamentos combinados com hormônios. A aplicação de IAA ou BAP a 50 mg L-1 em plantas rasteiras e suspensas, promoveu crescimento significativo mas, em plantas trepadeiras, observou-se, em geral, efeito negativo. Mudanças na assimilação líquida e taxas fotossintéticas, juntamente com coeficientes alométricos modificados, foram responsáveis por essas respostas. A maior promoção do crescimento por reguladores de crescimento exógenos, observada em plantas rasteiras ou suspensas em comparação com plantas trepadeiras, pode ser interpretada principalmente como uma resposta gravimorfogênica. Fil: Di Benedetto, Adalberto Hugo. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Universidad de Buenos Aires; Argentina Fil: Galmarini, Claudio Romulo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Mendoza-San Juan. Estación Experimental Agropecuaria La Consulta; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; Argentina. Universidad Nacional de Cuyo; Argentina Fil: Tognetti, Jorge Alberto. Comision de Investigaciones Cientificas de la Provincia de Buenos Aires. Observatorio Medioambiental la Plata. - Universidad Nacional de la Plata. Observatorio Medioambiental la Plata.; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina

Key message Gravitropic movements in angiosperm woody stems are achieved through the action of bark and/or wood motor, depending on the bark and wood fibre anatomy (with trellis structure or not; with G-layers or not). Bark motor is as efficient as wood motor to recover from tilting in young trees of 21 tropical species. Context Angiosperm trees produce tension wood to control their orientation through changes in stem curvature. Tension wood is classified into 3 anatomical groups: with unlignified G-layer, with lignified G-layer and without G-layer. Aims This study aimed at assessing whether this anatomical diversity reflects a diversity in efficiency of gravitropic movement. Methods The study was conducted on tropical seedling from the three anatomical groups. Seedlings were staked and grown tilted. At the end of the experiment, changes in curvature when releasing the stem from the stake and when removing bark were measured. Three parameters were computed to compare the global efficiency of gravitropism (stem gravitropic efficiency) and the specific efficiency of motor mechanism based on wood (maturation strain of tension wood) and bark (standardized debarking curvature). Results The maturation strain of tension wood was similar between species with unlignified and lignified G-layer. Species without G-layer exhibited low maturation strain and large debarking curvature, showing they rely on bark for gravitropism. Bark and wood achieved similar motor efficiency. Conclusion Lignin does not affect the generation of tensile stress in the G-layer. Bark can be as efficient as wood as a motor of gravitropic movements.

Land plants perceive gravity and respond to it in an organ-specific way; shoots typically direct growth upwards, roots typically downwards. Historically, at least with respect to maize plants, this phenomenon is attributed to three sequential processes, namely graviperception, the transduction of the perceived signal, and the graviresponse, resulting in a typical (re)positioning of the organ or entire plant body relative to the gravivector. For decades, sedimentation of starch-containing plastids within the cells of special tissues has been regarded as the primary and initiating process fundamental for gravitropic growth (starch-statolith hypothesis). Based on Popper’s falsification principle, uncompromising experiments were executed. The results indicate that the model of graviperception based on amyloplast sedimentation does not apply to maize seedlings.

Oryza longistaminata, the African wild rice, can propagate vegetatively through rhizomes. Rhizomes elongate horizontally underground as sink organs, however, they undergo a developmental transition that shifts their growth to the surface of the ground to become aerial stems. This particular stage is essential for the establishment of new ramets. While several determinants such as abiotic stimuli and plant hormones have been reported as key factors effecting developmental transition in aerial stem, the cause of this phenomenon in rhizome remains elusive. This study shows that depletion of nutrients, particularly sucrose, is the key stimulus that induces the developmental transition in rhizomes, as indicated by the gradient of sugars from the base to the tip of the rhizome. Sugar treatments revealed that sucrose specifically represses the developmental transition from rhizome to aerial stem by inhibiting the expression of sugar metabolism and hormone synthesis genes at the bending point. Sucrose depletion affected several factors contributing to the developmental transition of rhizome including signal transduction, transcriptional regulation and plant hormone balance. Electronic supplementary material The online version of this article (10.1007/s10265-018-1033-x) contains supplementary material, which is available to authorized users.

In the review, the problem of plant movements (photo- and gravitropism) is discussed. The contemporary data on physiological and molecular mechanisms of tropisms in underground shoots and roots are presented. Special attention is paid to diagravitropism phenomenon in underground shoots (stolons and rhizomes) that grow in perpendicular direction to the Earth's gravitational axis. The role of phytochrome control in maintaining the horizontal growth of stolons and rhizomes is demonstrated, and physiological mechanisms of photo- and diagravitropism are discussed. It is shown that switching of an underground shoot tip from diatropic to ortotropic (vertical) growth is dependent on the carbohydrate and phytohor-mone balance. The perspectives are outlined for further exploratory studies on mechanisms of growth orientation and morphogenesis of underground diagravitropic shoots.

In a recent publication, Edelmann (Protoplasma 2018; 255,1877-1881) refuted the well-established starch-amyloplast hypothesis of gravitropism in plants. Gravitropic curvatures of shoots and roots were still present after amyloplast-containing tissues (in sheath of vascular bundles and root caps) were dissected. Here, we discuss Edelmann's data in the light of Popper's falsification principle.

Sound is a fundamental form of energy and it has been suggested that plants can make use of acoustic cues to obtain information regarding their environments and alter and fine-tune their growth and development. Despite an increasing body of evidence indicating that it can influence plant growth and physiology, many questions concerning the effect of sound waves on plant growth and the underlying signalling mechanisms remains unknown. Here we show that in Arabidopsis thaliana , exposure to sound waves (200 Hz) for 2 weeks induced positive phonotropism in roots, which grew towards to sound source. We found that sound waves triggered very quickly (within minutes) an increase in cytosolic Ca 2+ , possibly mediated by an influx through plasma membrane and a release from internal stock. Sound waves likewise elicited rapid reactive oxygen species (ROS) production and K + efflux. Taken together these results suggest that changes in ion fluxes (Ca 2+ and K + ) and an increase in superoxide production are involved in sound perception in plants, as previously established in animals.

著者人数: 15名, Accepted: 2017-05-28, 資料番号: SA1170107000

Existing reports have described a notable fact that 1-naphthylphthalamic acid (NPA) coupled with 1-aminocylopropane-1-carboxylic acid (ACC), a precursor of ethylene, can regulate gravitropism of pea primary root by altering the volume of indole-3-acetic acid (IAA) and gibberellin A3 (GA3) in the root. However, the mechanism behind this is not quite clear. In this study, various concentration setups of NPA and ACC were used during cultivation of pea seeds (exposed to H2O2) to study the effect of NPA and ethylene on contents of IAA and GA3 in curving pea primary roots. Results showed that generally the horizontal bending of pea primary roots induced by H2O2 could be alleviated by NPA and ACC. Alpha-amylase activity in pea primary roots declined gradually with the rise of NPA and ACC concentrations, consequently boosting the content of starch while reducing the content of soluble sugar. ACC instigated the ethylene triple response. In addition, IAA content in primary roots declined gradually with the rise of NPA concentration, but GA3 content did not show any consistent fluctuation. The inhibition of NPA on IAA polar transport in pea was only effective in primary roots, with no effect on the IAA transport from bud to other parts.

Auxin has been identified to play critical roles in regulating plant growth and development. The polar transport of auxin is regulated by auxin transporters. In the present study, an auxin efflux carrier gene MdPIN1 was cloned from Malus×domestic, Royal Gala, and introduced into wild-type Arabidopsis thaliana (Col-0). The transgenic plants exhibited the phenotype of inhibition of primary root (PR) elongation and increased lateral root (LR) number in compared with Col-0. Overexpression of MdPIN1 affected auxin transport, and enhanced phototropic responses and geotropism reaction, whereas had no significant difference in the auxin biosynthesis. These findings suggest that the MdPIN1 gene plays a vital role in auxin transport and root development.

Imaging analysis was carried out during the gravitropic response of etiolated Arabidopsis hypocotyls, using an IAA19 promoter fusion of destabilized luciferase as a probe. From the bright-field images we obtained the local deflection angle to the vertical, A, local curvature, C, and the partial derivative of C with respect to time, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\partial C/\partial t$$\end{document}∂C/∂t. These were determined every 19.9 µm along the curvilinear length of the hypocotyl, at ~10 min intervals over a period of ~6 h after turning hypocotyls through 90° to the horizontal. Similarly from the luminescence images we measured the luminescence intensity of the convex and concave flanks of the hypocotyl as well as along the median of the hypocotyl, to determine differential expression of auxin-inducible IAA19. Comparison of these parameters as a function of time and curvilinear length shows that the gravitropic response is composed of three successive elements: the first and second curving responses and a decurving response (autostraightening). The maximum of the first curving response occurs when A is 76° along the entire length of the hypocotyl, suggesting that A is the sole determinant in this response; in contrast, the decurving response is a function of both A and C, as predicted by the newly-proposed graviproprioception model (Bastien et al., Proc Natl Acad Sci USA 110:755–760, 2013). Further, differential expression of IAA19, with higher expression in the convex flank, is observed at A = 44°, and follows the Sachs’ sine law. This also suggests that IAA19 is not involved in the first curving response. In summary, the gravitropic response of Arabidopsis hypocotyls consists of multiple elements that are each determined by separate principles. Electronic supplementary material The online version of this article (doi:10.1007/s10265-017-0932-6) contains supplementary material, which is available to authorized users.