Dynamics of growth and the content of endogenous phytohormones during kidney bean scoto-and photomorphogenesis

The dynamics of growth and the contents of free and bound endogenous IAA, gibberellins (GA), cytokinins (zeatin and its riboside), and ABA in kidney bean plants (Phaseolus vulgaris L., cv. Belozernaya) grown in darkness or in the light was studied. Phytohormones were quantified in 5–15-day-old plants by the ELISA technique. Plant growth and phytohormone content were shown to depend on plant age and the conditions of illumination. During scotomorphogenesis, changes in the biomass and hypocotyl length were highly correlated with the content of GA, whereas during photomorphogeneses, these parameters were correlated with the content of zeatin. In darkness, epicotyl growth displayed a positive correlation with the content of GA, whereas in the light, the correlation was negative. Growth characteristics of the primary leaves were shown to correlate with IAA in darkness and with GA and zeatin in the light. At a low concentration of cytokinins in illuminated leaves, cell divisions occurred, whereas, at the higher cytokinin concentrations, cell expansion occurred. The highest content of GA was characteristic of leaves in the period of growth cessation. ABA accumulated during active leaf and root elongation and biomass increment in the light and during hypocotyl growth in darkness. After plant illumination, the ratio of auxins to cytokinins increased in bean roots and decreased in their epicotyls. Thus, light changed the developmental programs of bean plants, which was manifested in the changed rate and duration of growth of various organs (root, hypocotyl, epicotyl, and leaf). Some mechanisms of light action depended on the contents of IAA, ABA, GA, and cytokinins and the ratios between these phytohormones. Differences between scotonorphogenesis of mono-and dicotyledonous plants are discussed in relation to the levels of phytohormones in them.     

Identification and quantification of indole-3-acetic acid in the kelp Laminaria japonica Areschoug and its effect on growth of marine microalgae

A method was established for the identification and quantification of indole-3-acetic acid (IAA) in extracts of the kelp Laminaria japonica. An IAA content of 90–95 μg kg⁻¹ fresh weight in kelp extract was determined by high performance liquid chromatography (HPLC). IAA identification was based on a combination of co-chromatography and comparative chromatography with a standard, analysis of UV spectra, and atmospheric pressure electrospray mass spectrometry (APESI-MS). IAA was isolated by silica gel chromatography and HPLC. The effect on the growth of four marine microalgae of the pure IAA isolated from kelp extract was investigated. Exogenously added IAA from kelp enhanced the growth of Chlorella sp., Dunaliella salina and Porphyridium cruentum, but not that of Chaetoceros muelleri. IAA from kelp significantly inhibited the accumulation of soluble cellular proteins in Chlorella sp. and P. cruentum, and had a very significant effect on chlorophyll biosynthesis in Chlorella sp. However, there was no obvious effect of IAA on the regulation of biosynthesis of cellular polysaccharides in these four marine microalgae.     

Basipetal auxin versus acropetal cytokinin transport,and their interaction with NO3 fertilisation in cotyledon senescence and sink:source relationships in cucumber (Cucumis sativus L.)

The paramount role of cytokinins (CKs) in initiation, as well as prevention, of senescence is well established. In recent years, experimental methods have become available to raise and lower the CK concentration and experimentally manipulate senescence. Decapitating the apical shoot and adding the synthetic auxin naphthylacetic acid to the cut stem reduced endogenous CKs to low levels. Conversely, if no auxin was applied, xylem and leaf CK levels increased dramatically, indicating that basipolar auxin transport is a key determinant in the synthesis of CKs and is potentially more important than NO₃. Manipulating the concentration of applied NO₃ caused considerable variation in leaf CK levels and concomitant changes in senescence. These and other results suggest that the frequently discussed decrease in nitrogen use efficiency (NUE) may be more highly regulated by CKs than by NO₃. Analysis of the re‐metabolisation and re‐allocation of chlorophyll, proteins, amino acids and starch in three different cucumber cultivars indirectly showed that these metabolites were significantly affected by the concentration of CKs in the leaves. Further research in this area may allow leaf senescence and plant yield to be more efficiently regulated by manipulating CKs and/or basipolar auxin transport instead of nitrate.     

杨树试管苗嫩茎生根过程中内源IAA的免疫金银定位

生长素类物质在木本植物生根过程中发挥重要作用。杨树生根与生长素的关系及生根过程中内源激素的变化已有大量报道,而生根过程中生长素的组织定位分析则尚未见报道。该文应用免疫化学分析方法对741杨（Populus alba×（P.davidiana×P.simonii）×P.tomentosa）嫩茎生根过程中内源IAA在组织中的分布进行了研究。结果显示,741杨的嫩茎在无外源激素的1/2MS培养基上诱导10天后可生根,14天后生根率达100%。诱导前,嫩茎基部组织中几乎没有IAA信号;诱导8天后,嫩茎基部维管组织中有大量的IAA积累,而且中部的维管组织中也有明显的IAA信号（主要分布在韧皮部和维管形成层）;10天后,形成不定根原基,此时IAA主要分布在根原基;12天后,根原基分化成不定根并突破表皮,IAA在不定根中的分布主要集中在根尖和中柱。该文对741杨的嫩茎生根过程中IAA的组织分布特点及运输途径进行了讨论。     

Auxin-induced leaf blade expansion in Arabidopsis requires both wounding and detachment

Elevation of leaf auxin (indole-3-acetic acid; IAA) levels in intact plants has been consistently found to inhibit leaf expansion whereas excised leaf strips grow faster when treated with IAA. Here we test two hypothetical explanations for this difference in growth sensitivity to IAA by expanding leaf tissues in vivo versus in vitro. We asked if, in Arabidopsis, IAA-induced growth of excised leaf strips results from the wounding required to excise tissue and/or results from detachment from the plant and thus loss of some shoot or root derived growth controlling factors. We tested the effect of a range of exogenous IAA concentrations on the growth of intact attached, wounded attached, detached intact, detached wounded as well as excised leaf strips. After 24 h, the growth of intact attached, wounded attached, and detached intact leaves was inhibited by IAA concentrations as little as 1 µM in some experiments. Growth of detached wounded leaves and leaf strips was induced by IAA concentrations as low as 10 µM. Stress, in the form of high light, increased the growth response to IAA by leaf strips and reduced growth inhibition response by intact detached leaves. Endogenous free IAA content of intact attached leaves and excised leaf strips was found not to change over the course of 24 h. Together these results indicate growth induction of Arabidopsis leaf blade tissue by IAA requires both substantial wounding as well as detachment from the plant and suggests in vivo that IAA induces parallel pathways leading to growth inhibition.     

Optimization of medium for indole-3-acetic acid production using Pantoea agglomerans strain PVM

Aims: To optimize the medium components for the production of indole‐3‐acetic acid (IAA) by isolated bacterium Pantoea agglomerans strain PVM. Methods and Results: Present study deals with the production of an essential plant hormone IAA by a bacterial isolate P. agglomerans strain PVM identified by 16S rRNA gene sequence analysis. The medium containing 8 g l^?1 of meat extract and 1 g l^?1 of l ‐tryptophan (precursor) at optimum pH 7, 30°C and 48‐h incubation gave the maximum production of IAA (2·191 g l^?1). Effect of IAA synthesized on in vitro root induction in Nicotiana tobacum (leaf) explants was compared with that of control. IAA was characterized by high‐performance thin‐layer chromatography, high‐performance liquid chromatography and gas chromatography–mass spectroscopy. Conclusions: Pantoea agglomerans strain PVM was a good candidate for the inexpensive and utmost production of IAA in short period, as it requires simple medium (meat extract and l ‐tryptophan). Significance and Impact of the Study: The present report first time showed the rapid, cost‐effective and maximum production of IAA. No reports are available on the optimization of particular medium components for the production of IAA. This study demonstrates a novel approach for in vitro root induction in N. tobacum (leaf) explants.     

CD8 T cells expressing NK associated receptors are increased in melanoma patients and display an effector phenotype

CD8⁺ T cells can express NK-associated receptors (NKRs) that may regulate their cytolytic function. We have characterized the expression of several NKRs on peripheral blood CD8⁺ T cells from melanoma patients and compared them to age-matched healthy donors. The analysis performed includes HLA class I specific receptors (KIRs, LILRB1 and CD94/NKG2) and other NK receptors like CD57, CD56 and CD16. Melanoma patients showed a higher variability in the expression of NKRs on circulating CD8⁺ T cells than age-matched healthy donors. NKR expression on CD8⁺ T cells from melanoma patients showed a significant increase of KIR2DL2/L3/S2 (mAb gl183), CD244, CD57, CD56 and CD16. We have also found an increase of CD8⁺ CD28^– CD27^– T cells in melanoma patients. This subset represents terminally differentiated effector cells expressing CD244 and high levels of perforin. The expression of NKRs was also mainly restricted to this T cell subset. Altogether, circulating CD8⁺ T cells from melanoma patients display a distinct phenotype characterized by downregulation of costimulatory molecules and higher expression of NKRs. We suggest that the increased expression of NKRs on T cells may contribute to the final outcome of the immune response against melanoma both stimulating or inhibiting activation and differentiation to effector cells. Blocking inhibitory receptor function and enhancing activating receptors may represent new strategies with therapeutic potential against melanoma.     

Crosstalk between ABA and auxin signaling pathways in roots of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> (L.) Heynh.

Studies of abscisic acid (ABA) and auxin have revealed that these pathways impinge on each other. The Daucus carota (L.) Dc3 promoter: uidA (-glucuronidase: GUS) chimaeric reporter (ProDc3:GUS) is induced by ABA, osmoticum, and the auxin indole-3-acetic acid (IAA) in vegetative tissues of transgenic Arabidopsis thaliana (L.) Heynh. Here, we describe the root tissue-specific expression of ProDc3:GUS in the ABA-insensitive-2 (abi2-1), auxin-insensitive-1 (aux1), auxin-resistant-4 (axr4), and rooty (rty1) mutants of Arabidopsis in response to ABA, IAA and synthetic auxins naphthalene acetic acid (NAA), and 2, 4-(dichlorophenoxy) acetic acid. Quantitative analysis of ProDc3:GUS expression showed that the abi2-1 mutant had reduced GUS activity in response to ABA, IAA, or 2, 4-d, but not to NAA. Similarly, chromogenic staining of ProDc3:GUS activity showed that the aux1 and axr4 mutants gave predictable hypomorphic ProDc3:GUS expression phenotypes in roots treated with IAA or 2, 4-d, but not the diffusible auxin NAA. Likewise the rty mutant, which accumulates auxin, showed elevated ProDc3:GUS expression in the absence or presence of hormones relative to wild type. Interestingly, the aux1 and axr4 mutants showed a hypomorphic effect on ABA-inducible ProDc3:GUS expression, demonstrating that ABA and IAA signaling pathways interact in roots. Possible mechanisms of crosstalk between ABA and auxin signaling are discussed.     

Cholodny–Went revisited: a role for jasmonate in gravitropism of rice coleoptiles

Gravitropism is explained by the Cholodny–Went hypothesis: the basipetal flow of auxin is diverted laterally. The resulting lateral auxin gradient triggers asymmetric growth. However, the Cholodny–Went hypothesis has been questioned repeatedly because the internal auxin gradient is too small to account for the observed growth asymmetry. Therefore, an additional gradient in indolyl-3-acetic acid (IAA) sensitivity has been suggested (Brauner and Hager in Planta 51:115–147, 1958). We challenged the Cholodny–Went hypothesis for gravitropism of rice coleoptiles (Oryza sativa L.) and found it to be essentially true. However, we observed, additionally, that the two halves of gravitropically stimulated coleoptiles responded differentially to the same amount of exogenous auxin: the auxin response is reduced in the upper flank but normal in the lower flank. This indicates that the auxin-gradient is amplified by a gradient of auxin responsiveness. Hormone contents were measured across the coleoptile by a GC-MS/MS technique and a gradient of jasmonate was detected opposing the auxin gradient. Furthermore, the total content of jasmonate increased during the gravitropic response. Jasmonate gradient and increase persist even when the lateral IAA gradient is inhibited by 1-N-naphtylphtalamic acid. Flooding with jasmonate delays the onset of gravitropic bending. Moreover, a jasmonate-deficient rice mutant bends more slowly and later than the wild type. We discuss a role of jasmonate as modulator of auxin responsiveness in gravitropism.