Arabidopsis SMALL AUXIN UP RNA63 promotes hypocotyl and stamen filament elongation

Auxin regulates plant growth and development in part by activating gene expression. Arabidopsis thaliana SMALL AUXIN UP RNAs (SAURs) are a family of early auxin-responsive genes with unknown functionality. Here, we show that transgenic plant lines expressing artificial microRNA constructs (aMIR-SAUR-A or -B) that target a SAUR subfamily (SAUR61-SAUR68 and SAUR75) had slightly reduced hypocotyl and stamen filament elongation. In contrast, transgenic plants expressing SAUR63:GFP or SAUR63:GUS fusions had long hypocotyls, petals and stamen filaments, suggesting that these protein fusions caused a gain of function. SAUR63:GFP and SAUR63:GUS seedlings also accumulated a higher level of basipetally transported auxin in the hypocotyl than did wild-type seedlings, and had wavy hypocotyls and twisted inflorescence stems. Mutations in auxin efflux carriers could partially suppress some SAUR63:GUS phenotypes. In contrast, SAUR63:HA plants had wild-type elongation and auxin transport. SAUR63:GFP protein had a longer half-life than SAUR63:HA. Fluorescence imaging and microsomal fractionation studies revealed that SAUR63:GFP was localized mainly in the plasma membrane, whereas SAUR63:HA was present in both soluble and membrane fractions. Low light conditions increased SAUR63:HA protein turnover rate. These results indicate that membrane-associated Arabidopsis SAUR63 promotes auxin-stimulated organ elongation.     

The chromatin remodeling complex imitation of switch controls stamen filament elongation by promoting jasmonic acid biosynthesis in Arabidopsis

Plant reproduction requires the coordinated development of both male and female reproductive organs.Jasmonic acid(JA) plays an essential role in stamen filament elongation. However, the mechanism by which the JA biosynthesis genes are regulated to promote stamen elongation remains unclear. Here, we show that the chromatin remodeling complex Imitation of Switch(ISWI) promotes stamen filament elongation by regulating JA biosynthesis. We show that AT-Rich Interacting Domain 5(ARID5) interacts with CHR11,CHR17, and RLT1, several known subunits of ISWI. Mutations in ARID5 and RLTs caused a reduced seed set due to greatly shortened stamen filaments. RNA-seq analyses reveal that the expression of key genes responsible for JA biosynthesis is significantly down-regulated in the arid5 and rlt mutants. Consistently, the JA levels are drastically decreased in both arid5 and rlt mutants. Chromatin immunoprecipitationquantitative PCR analyses further show that ARID5 is recruited to the chromatin of JA biosynthesis genes. Importantly, exogenous JA treatments can fully rescue the defects of stamen filament elongation in both arid5 and rlt mutants, leading to the partial recovery of fertility. Our results provide a clue how JA biosynthesisis positively regulated by the chromatin remodeling complex ISWI, thereby promoting stamen filament elongation in Arabidopsis.     

植物生长调节物质的研究进展

述评了近几年国内外在植物激素与植物体内信使的传递、植物激素与基因诱导和表达、植物生长物质的复合使用、新型植物生长物质的开发及植物激素对提高植物抗逆性的作用等方面的研究进展,并展望了植物生长物质的发展趋势。     

Novel natural substances acting in plant growth regulation

This review includes novel natural products of microbial and plant origin reported to exert plant growth-regulating activities. The well-known classic plant hormones are excluded. The substances described with their biological activities are restricted to those that have been isolated from microbial or plant sources later than 1990 or that have been intensively investigated during the last few years, such as jasmonic acid and brassinosteroids.     

How do plant growth substances work?

Abstract. Despite intensive research effort, the role of growth substances in the life of the intact growing plant is far from clear. Two reasons are suggested which may account for the lack of progress. The first is the failure to recognize the unique aspects of plant development. These which are expressed by the regenerative, organizational and developmental plasticity of the meristem probably result from the possession of growth substances. The second is the concept of growth substances as hormones. This represents the main conceptual thrust of research and is considered critically, starting with the historical system, the coleoptile and dealing with other major growth substance systems in turn. It is concluded that a hormonal concept which includes control by changes in growth substance concentration fails to explain the developmental phenomena under examination. A role for growth substances as integrating agents is suggested and the notion of quantitative tissue sensitivity variation is developed to explain the major growth patterns of developing shoots.     

The forkhead-associated domain 2 (FHA2) in Arabidopsis plays a role in plant fertility by regulating stamen development

The forkhead-associated (FHA) domain is involved in protein–protein interaction by recognizing a phosphothreonine epitope on target proteins. In this study, we investigated in planta functions of the Arabidopsis FHA domain 2. AtFHA2 was mainly localized in the nucleus. Arabidopsis fha2 null mutants grew normally during the vegetative stage, but had severely reduced fertility during reproductive stage. The reduced fertility was mainly caused by defective stamen filament elongation, while female flower parts of the mutants were fertile. Additionally, the mutants had fewer stamens than the wild type and the vegetative organs of the mutants, such as cotyledons and leaves, had increased ploidy. These results suggest that AtFHA2 may play a role in a signaling pathway for the control of plant organ development.     

How do plant growth substances work? II

Abstract. This article continues the discussion on sensitivity prompted by the publication of an earlier paper by the author in 1981. It is indicated that appropriate measurements of sensitivity can help uncover the function of growth substances in development. The experimental constraints which are necessary for unambiguous measurements of sensitivity are outlined and it is shown that a specific sensitivity measurement, termed control strength, would most readily clarify function and help obviate controversy. Methods for measuring control strength which deal with the problem of compartmentalization are considered and it is suggested that stochastic variation in single cell biochemistry might provide a constraint on the accuracy of control strength determinations.     

Effects of gall midge infestation on plant growth and growth regulating substances

The biological association between plant and gall-inducing insects can be characterized by growth and developmental abnormalities of the plant tissues caused by the feeding activities of the insects. The relationship between Wachtliella persicariae L. (Diptera: Cecidomyiidae) and Polygonum amphibium L. has been studied.The gall-making larvae settle only on the undifferentiated parts of the leaf and prevent the normal unfolding of the lamina; and there is a close developmental synchronization between the two organisms.The essential reaction of the leaf tissue to the continuous feeding activity of the larvae is primarily a disturbance of the normal development, characterized by an imbalance in growth-regulating substances. Bioassays showed greater amounts of auxin-like substances in the galled tissues. The way in which feeding behaviour, feeding activity and nutritional physiology possibly interfere with the growth-regulating factors of the leaf is discussed.The resulting abnormal leaf growth and development is essential for the normal growth and development of the larvae.

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Zusammenfassung Die biologische Verbindung zwischen Pflanzen und gallenerzeugenden Insekten kann durch Wachstums-und Entwicklungsabnormalitäten der Pflanzengewebe gekennzeichnet werden, welche durch die Fraßtätigkeit der Insekten hervorgerufen werden. Hier wurde die Beziehung zwischen Wachtliella persicariae (Diptera: Cecidomyiidae) und Polygonum amphibium untersucht.Die gallenerzeugende Larve siedelt sich nur auf undifferenzierten Teilen des Blattes an und verhindert die normale Entfaltung der Lamina; es besteht eine enge Synchronisation der Entwicklung beider Organismen.Die wesentliche Reaktion des Blattgewebes auf die fortdauernde Fraßaktivität der Larve stellt zunächst eine Störung der normalen Entwicklung dar, die durch ein Ungleichgewicht der Stoffe charakterisiert ist, die das Pflanzenwachstum kontrollieren. Biotests ergaben in den vergallten Geweven größere Beträge auxinartiger Stoffe. Der Weg, auf dem Fraßverhalten, Fraßaktivität und Ernährungsphysiologie mit den wachstumkontrollierenden Faktoren des Blattes ineinandergreifen, wird diskutiert.Das entstehende anomale Blattwachstum und seine Entwicklung sind für das normale Wachstum und die Ontogenese der Larve wesentlich.

     

Vitamin D and related compounds as plant growth substances

Vitamin D and related compounds (hydroxylated derivatives and glycosides) occur naturally in certain plants. The metabolism of vitamin D₃ in Solanum malacoxylon Sendtn. is similar in certain respects to that in animal systems. There is also evidence that vitamin D₃, plays a role in processes regulated by Ca²⁺ in plants. Vitamin D₃ possesses plant growth substance activities and in particular enhances adventitious root formation.     

Effect of morphactin on certain plant growth substances in bean roots

The effect of morphactin (methyl-2-chloro-9-hydroxyfluorene-9-carboxylate) on the content of several plant growth substances in bean roots was determined. Beans (Phaseolus vulgaris L. cv. Spartan) were soaked in aqueous solutions of morphactin, 1 x 10^-4, 1 x 10^-5, and 1 x 10^-6M and grown in moist vermiculite. As controls were used beans grown in water-moistened vermiculite either intact or having the root tips removed (decapped). The roots, morphactin-treated, controls, and the decapped ones were analyzed for indol-3-yl acetic acid (IAA), indol-3-yl acrylic acid (IAcA), indol-3-yl pyruvic acid (IPyA), indol-3-yl lactic acid (1LA), abscisic acid (ABA), gibberellins GA₁, GA₃, GA₄, and GA₉ using gas-liquid chromatographic methods. Morphactin, while affecting the geotropical responses, changed also the growth substance content of roots. IAA, ABA, GA₁, and GA₉ contents decreased, IPyA, IAeA, GA₃, and GA₄ contents were not affected and ILA content increased slightly with increasing dosages of morphactin. Growth substance pattern of decapped roots resembled that of the roots treated with the highest dose, 1 x 10^-4M, of morphactin.     

Role of plant growth regulators in host-pathogen relationships

The effect of indol-3-ylacetic acid, gibberellie acid, kinetin, abscisic acid and Ethrel on the growth of mycelium, sporulation and germination of spores ofFusarium culmorum of different pathogenicity to wheat seedlings was studied. The production of gibberellins, auxins, cytokinins, ethylene and growth inhibitors by these isolates was determined as well. It has been found that most pronounced and explicit effect on growth and development in fungi was produced by Ethrel which strongly inhibited these processes. ABA proved to be a strong growth and development stimulator, though to a different extent in different isolates. GA₃ strongly stimulated sporulation and spore germination in some isolates. The effect of IAA and K on growth and development in fungi was slight. More sensitive to growth regulators were the fungi in earlier stages of growth. No correlation between the pathogenicity of the isolates and their ability to produce growth regulators as well as between their susceptibility to exogenous growth substances in the processes of fungal growth and development was stated. Presented at the International Symposium “Plant Growth Regulators” held on June 18–22, 1984 at Liblice, Czechoslovakia.     

Production of buds and plantlets from the stamen’s filament ofLilium regale cultivatedin vitro

Excised stamens ofLilium regale were grownin vitro. From the cut end of the filament a callus is produced and from it several buds and plantlets arise.     

Role of growth regulators in the senescence of Arabidopsis thaliana leaves

A homozygous, dominant, C₂H₄-resistant line of Arabidopsis thaliana (L.) Heynh (cv. Columbia; er ) was selected from ethylmethylsulfonate-mutagenized seed, and used to test the role of C₂H₄ and other growth regulators in senescence of mature leaves. Chlorophyll (Chl) loss from disks excised from leaves of er was much slower than that from wild-type (WT) disks, whether they were held in the light or in the dark. C₂H₄ accelerated Che loss from WT disks but had no effect on the yellowing of mutant disks. C₂H₄ biosynthesis was higher in disks from the mutant plants, particularly in the light. In the dark, treatment with the cytokinin, 6-benzyladenine (BA), reduced Chl loss from wild-type disks, but had no effect on mutant disks. In the light, BA treatment stimulated chlorophyll breakdown in both wild type and mutant disks. Treatment with abscisic acid (ABA) stimulated chlorophyll loss in wild-type and mutant disks, whether they were held in the light or the dark. C₂H₄ production was stimulated in ABA-treated disks, but they still yellowed even when C₂H₄ production was inhibited by application of aminooxyacetic acid (AOA). These data indicate that C₂H₄ is only one of the factors involved in leaf senescence, and that the promotion of senescence by ABA is not mediated through its stimulation of C₂H₄ production.