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• Here, we investigated the role of auxin distribution in controlling Arabidopsis thaliana late stamen development. • We analysed auxin distribution in anthers by monitoring DR5 activity: at different flower developmental stages; inhibiting auxin transport; in the rpk2-3 and ems1 mutants devoid of middle layer (ML) or tapetum, respectively; and in the auxin biosynthesis yuc6 and perception afb1-3 mutants. We ran a phenotypic, DR5::GUS and gene expression analysis of yuc6rpk2 and afb1rpk2 double mutants, and of 1-N-naphthylphthalamic acid (NPA)-treated flower buds. • We show that an auxin maximum, caused by transport from the tapetum, is established in the ML at the inception of late stamen development. rpk2-3 mutant stamens lacking the ML have an altered auxin distribution with excessive accumulation in adjacent tissues, causing non-functional pollen grains, indehiscent anthers and reduced filament length; the expression of genes controlling stamen development is also altered in rpk2-3 as well as in NPA-treated flower buds. By decreasing auxin biosynthesis or perception in the rpk2-3 background, we eliminated these developmental and gene expression anomalies. • We propose that the auxin maximum in the ML plays a key role in late stamen development, as it ensures correct and coordinated pollen maturation, anther dehiscence and filament elongation. [ABSTRACT FROM AUTHOR]

Self-inhibition of growth has been observed in different organisms, but an underlying common mechanism has not been proposed so far. Recently, extracellular DNA (ex DNA) has been reported as species-specific growth inhibitor in plants and proposed as an explanation of negative plant-soil feedback. In this work the effect of ex DNA was tested on different species to assess the occurrence of such inhibition in organisms other than plants., Bioassays were performed on six species of different taxonomic groups, including bacteria, fungi, algae, plants, protozoa and insects. Treatments consisted in the addition to the growth substrate of conspecific and heterologous DNA at different concentration levels., Results showed that treatments with conspecific DNA always produced a concentration dependent growth inhibition, which instead was not observed in the case of heterologous DNA., Reported evidence suggests the generality of the observed phenomenon which opens new perspectives in the context of self-inhibition processes. Moreover, the existence of a general species-specific biological effect of ex DNA raises interesting questions on its possible involvement in self-recognition mechanisms. Further investigation at molecular level will be required to unravel the specific functioning of the observed inhibitory effects. [ABSTRACT FROM AUTHOR]

Symbiosis is well recognized as a major force in plant ecology and evolution. However, there is considerable uncertainty about the functional, ecological and evolutionary benefits of the very widespread facultative arbuscular mycorrhizal (AM) associations, in which the plants can grow and reproduce whether or not they are colonized by AM fungi. Here we address the significance of new research findings that are overturning conventional views that facultative AM associations can be likened to parasitic fungus–plant associations. Specifically, we address the occurrence and importance of phosphate uptake via AM fungi that does not result in increases in total phosphorus (P) uptake or in plant growth, and possible signalling between AM fungi and plants that can result in plant growth depressions even when fungal colonization remains very low. We conclude that, depending on the individual AM fungi that are present, the role of facultative AM associations in the field, especially in relation to plant competition, may be much more subtle than has been previously envisaged. [ABSTRACT FROM AUTHOR]

• Here, we used phosphorus-32 (32P) labelling in compartmented pots combined with quantitative real-time polymerase chain reaction (PCR) analysis of phosphate (Pi) transporter gene expression to investigate regulation of Pi uptake pathways in barley ( Hordeum vulgare), an arbuscular mycorrhizal (AM) plant that does not show strong positive growth responses to colonization. • Barley was colonized well by Glomus intraradices and poorly by Glomus geosporum, but both fungi induced significant and similar growth depressions compared with nonmycorrhizal controls. The lack of correlation between per cent colonization and extent of growth depression suggests that the latter is not related to carbon drain to the fungus • The contribution of the AM Pi uptake pathway for the two fungi was, in general, related to per cent colonization and expression of the AM-inducible Pi transporter gene, HvPT8, but not to plant responsiveness. Glomus intraradices contributed 48% of total plant P whereas G. geosporum contributed very little. • The growth depression in plants where the AM uptake pathway was functional suggests that the contribution of the direct Pi uptake pathway via root hairs and epidermis was decreased. This decrease was not correlated with downregulation of the epidermal-expressed Pi transporter genes, HvPT1 and HvPT2. We hypothesize post-transcriptional or post-translational control of this transport process by AM colonization. [ABSTRACT FROM AUTHOR]

Presents information on a study which examined the effect of aluminum on the surface potential and the plasma membrane in wheat Triticum aestivum lines. Role of plasma membrane in aluminum tolerance; Growth inhibition of aluminum and aluminum content in root apex; Localization of plasma membrane hydrogen-adenosine triphosphatase in root apex.

Stunted, misshapen, necrotic hypocotyls of tomato seedlings (Lycopersicon esculentum L.) germinated on caesium cations in continuous red or white light indicated caesium-associated hypocotyl photo-injury. Continuous, far red irradiation inhibited seedling germination in control and caesium treatments but was reversed by continuous white light. Hypocotyl photoinjury also occurred in far red pretreated seedlings germinated on caesium in continuous white light. Except for suppressed elongation, hypocotyls of caesium-treated seedlings were normal in appearance. Etiolated caesium-treated seedlings placed in continuous white light also exhibited hypocotyl photo-injury. The effects of caesium cations were reversed by potassium cations but not by cations of other alkali metals. [ABSTRACT FROM AUTHOR]

A field exposure system designed for the controlled release of sulphur dioxide (SO[sub2]) was used in two contrasting seasons to expose commercial crops of winter barley (Hordeum vulgare L.) to SO[sub2] concentrations ranging from 40 to 200 pph [parts per billion (10[sup9]) by volume] above ambient. During winter and early spring, growth of the plants was depressed at high SO[sub2] concentrations hut later recovered; in spring and summer, low concentrations stimulated growth above that of controls, but there was no corresponding increase in grain yield. Yield depression is discussed in relation to SO[sub2] concentration and dose. [ABSTRACT FROM AUTHOR]

Photoinhibition of photosynthesis in natural populations of phytoplankton has been investigated in situ in Windermere, English Lake District, and Llyn Padarn, North Wales. The extent of inhibition was found to be directly related to irradiance and to increase with time of exposure. Inhibition was increased when the ultra-violet component of sunlight was not removed by enclosure of samples in glass bottles. Supersaturation with oxygen to the extent likely to occur in the surface waters of lakes did not appear to be an important factor increasing photoinhibition. Experiments on the effect of nutrient deficiency were inconclusive. It was demonstrated that populations could recover from severe photoinhibition within periods of less than 24 h and that when the water column is stable the population in the surface water adapts to become more resistant to photoinhibition. [ABSTRACT FROM AUTHOR]

Lolium perenne L. was grown in a sealed glass chamber force-ventilated with ambient SO2- polluted air and the yield compared with that of control plants grown in a second chamber receiving filtered air free of SO2, und suspended particulates, Whole plant dry weight of L. perenne cv. S23 grown either on a nutrient-rich sand culture or an unfertilized field soil was depressed by up to 36% in polluted air containing mean SO2, concentrations of less than 100 μg m&sup-3;. When detailed growth analyses of S23 L. perenne in unfiltered air and of a clone of wild L. perenne previously reported to be resistant to SO2 pollution were compared, there were distinct differences between the two strains in response to SO2,-polluted air but both were less productive in the latter treatment. Sulphur dioxide was strongly implicated as the factor responsible for the reduced dry matter production of plants raised in polluted air but there was a poor positive correlation between loss of yield and long term mean SO2 concentration within the unfiltered air chamber. The results are discussed with regard to probable mechanisms of growth inhibition and the possibility that experimental conditions either enhanced or confounded the effect of SO2 pollution on plant growth. [ABSTRACT FROM AUTHOR]

Water-soluble compounds isolated from Laminaria digitata and Ascophyllum nodosum caused marked inhibition of lettuce hypocotyl growth. GLC analysis of these substances showed, in one case, properties similar to ABA (abscisic acid) but definite information on this must be deferred until the chemical nature of the seaweed compound is verified. The possible role of these compounds in seaweed growth and their possible significance as ectocrines in the sea, are discussed. [ABSTRACT FROM AUTHOR]

A growth inhibiting substance has been extracted from mature tissues of Eucalyptus obliqua in which apical dominance occurs, but is absent in juvenile tissues of very young seedlings which show weak apical dominance. Sprouting from lignotubers in decapitated E. obliqua seedlings is correlated with a reduction in the level of inhibitory properties. Reapplied inhibitory substance, but not abscisic acid, reduced sprouting. The inhibitory substance has been partially purified and some of its properties tested, suggesting that it is not abscisic acid. [ABSTRACT FROM AUTHOR]