Fernando Migliaccio

Circumnutation as an autonomous root movement in plants

Although publications on circumnutation of the aerial parts of flowering plants are numerous and primarily from the time between Darwin (1880) and the 1950s, reports on circumnutation of roots are scarce. With the introduction of modern molecular biology techniques, many topics in the plant sciences have been revitalized; among these is root circumnutation. The most important research in this area has been done on Arabidopsis thaliana, which has roots that behave differently from those of many other plants; roots grown on inclined agar dishes produce a pattern of half waves slanted to one side. When grown instead on horizontally set dishes, the roots grow in loops or in tight right-handed coils that are characterized by a tight torsion to the left-hand. The roots of the few plants that differ from Arabidopsis and have been similarly tested do not present such patterns, because even if they circumnutate generally in a helical pattern, they subsequently straighten. Research on plants in space or on a clinostat has allowed the testing of these roots in a habitat lacking gravity or simulating the lack. Recently, molecular geneticists have started to connect various root behaviors to specific groups of genes. For example, anomalies in auxin responses caused by some genes can be overcome by complementation with wild-type genes. Such important studies contribute to understanding the mechanisms of growth and elongation, processes that are only superficially understood.

Arabidopsis root growth movements and their symmetry: progress and problems arising from recent work.

Over the last fifteen years, an increasing number of plant scientists have become interested in the Arabidopsis root growth pattern that is produced on the surface of an agar plate, inclined from the vertical. In this situation, the roots wave intensely and slant preferentially towards one side, showing torsions in the epidermal cell files alternately right-and left handed. In addition, the pattern switches to the formation of large or strict coils when the plate is set horizontally. After this finding, different hypotheses were advanced attempting to explain the forces that shape these patterns. These basically appear to be gravitropism, circumnutation, and negative thigmotropism. With regard to the symmetry, the coils and the slanting in the wild-type are essentially right-handed, but mutants were also reported which show a left-handed symmetry, while some do not show a regular growth pattern at all. This review article discusses the earlier as well as the most recent findings on the topic, and investigates the possibility of describing the different mechanisms shaping the root growth patterns via unifying hypothesis.

Neutron irradiation affects the expression of genes involved in the response to auxin, senescence and oxidative stress in Arabidopsis

We report, in Arabidopsis thaliana plants, the effect of neutron irradiation on the transcription of a set of genes belonging to different physiological groups: auxin action, senescence, oxidative stress, and some aspects of photosynthesis. The results indicated that, in the wild-types, the effect on the ARF1, ARF2, and 19 genes was of down-regulation, whereas of the tested AUX/IAA only AUX/IAA7 showed up-regulation. Different results were obtained as regards the irradiation of the auxin transport mutants aux1 and eir1, because in these cases the ARF genes were up-regulated, whereas AUX/IAA7 was down-regulated in eir1. On the other hand, the senescence activated genes SAG12 and SAG13, and those connected to oxidative stress were up-regulated in the wild-type, but down-regulated in aux1. The gene CAB1, connected to photosynthesis, was also down-regulated in the wild-type, but up-regulated in aux1. Gene expression recovered in many cases almost to the initial condition in a time lapse of 24 hours, even though some effect persisted for a longer time. In particular, the state of juvenility of arf2 was extended by irradiation, whereas, in all the other cases, senescence was accelerated. The research indicates that through mutant selection or genetic engineering a true possibility exists of producing organism more suitable for life in space.

Effect of ABA and kinetin on fluxes of chloride and sulphate in excised maize roots

Abstract Measurements were made on the fluxes of chloride and sulphate in excised maize roots as affected by ABA or kinetin at final concentrations 10−5 M. It was shown that addition of ABA stimulates the translocation of chloride and sulphate at 22 °C not only during the first hours of incubation, but also up to 24 hours. Kinetin on the contrary inhibits it, but mainly after the 6th hours. Moreover, ABA inhibits accumulation and efflux of chloride slowly, while kinetin has no effect on both. These data are interpreted as further support to the hypothesis that the principal action of ABA is the stimulation of ion release in xylem, while the principal action of kinetin is its inibition. The action of hormones appears similar either on chloride or sulphate ions, in spite of their different metabolic significance. These results may demonstrate that the effect of the hormons here considered is unspecific.

Expression of Aux/IAA genes during development of sylleptic and proleptic buds in white poplar

Abstract In this study, the genes of theAux/IAA family were used as functional markers to characterise bud break stages in a white poplar clone. In the first experiment, under greenhouse conditions, the sprouting of repressed sylleptic buds was obtained by pruning the shoot tip during growing season. Buds were collected at 0, 6, 24 and 48 h after pruning for molecular analyses. A decrease in transcript level ofIAA4 andIAA8 genes was observed in the first and second bud below the cut after 6 and 24 h, respectively. In the second experiment, bud break of post-dormant proleptic buds was induced by forcing in climatic chamber. The first 6 and the following 6 buds below the apical one were sampled every 48 h during forcing. Anatomical studies were also carried out on buds and plants were equipped with stem and bud radial growth sensors to check their swelling. In both experiments, gene expression patterns showed a decrease and a successive increase in expression ofIAA4 andIAA8 genes during bud break. The transient down-regulation of these genes was observed only in buds that formed new branches. Thus, similar molecular mechanisms are involved in bud break of both sylleptic and proleptic buds.

Accumulation and translocation of sulphate in excised maize roots as affected by different saline concentrations in the outer medium

Abstract Accumulation and translocation of sulphate in excised maize roots, submerged in rising saline concentrations, were investigated. It was shown that the accumulation of sulphate is not depressed by concentrations from 1 to 50 mM of NaCl or KCl, it is weakly increased by concentrations of the same salts 100 mM and it is gradually lowered by concentrations from 1 to 100 mM of MgCl2. On the contrary the translocation is gradually inhibited by rising concentrations of NaCl, KCl and MgCl2. A 100 mM NaCl concentration considerably loweres the translocation in 24 hours, but does not affect accumulation. Accumulation and translocation are strongly depressed by the inhibitors of oxydative phosphorylation (2,4 DNP or CCCP) and by 200 mM NaCl, KCl or MgCl2 concentrations. It is concluded that accumulation and translocation are active processes as they are reduced by 2,4 DNP or CCCP; that the small increase in accumulation observed by 100 mM NaCl or KCl concentration is due probably to the discharging action o...

Rha1, a new mutant of Arabidopsis disturbed in root slanting, gravitropism and auxin physiology.

A new Arabidopsis mutant is characterized (rha1) that shows, in the roots, reduced right-handed slanting, reduced gravitropism, and resistance to 2,4-D, TIBA, NPA and ethylene. It also shows reduced length in the shoot and root, reduced number of lateral roots and shorter siliques. The gene was cloned through TAIL-PCR and resulted in a HSF. Because none of the known gravitropic and auxinic mutants result from damage in a HSF, rha1 seems to belong to a new class of this group of mutants. Quantitative PCR analysis showed that the expression of the gene is increased by heat and cold shock, and by presence of 2,4-D in the media. Study of the expression through the GUS reporter gene revealed increased expression in clinostated and gravistimulated plants, but only in adult tissues, and not in the apical meristems of shoots and roots. Addendum to: Fortunati A, Piconese S, Tassone P, Ferrari S, Migliaccio F. A new mutant of Arabidopsis disturbed in its roots right-handed slanting and gravitropism, defines a gene that encodes a heat-shock factor. J Exper Bot 2008; In press.

Osmotic and saline effects of different solutes on chloride fluxes and accumulation in excised maize roots.

Abstract The effect of different saline or non saline solutes (i.e. K2SO4, Na2SO4, MgSO4 and mannitol) on fluxes and accumulation of chloride occurring in excised maize roots were studied adopting the method of compartmental analysis. A stimulation of chloride fluxes outer medium-cytoplasm and symplasm-xylem was induced by solutions of K2SO4 and Na2SO4 at osmotic potential between –1.5 and –3.0 bars. A sharp decrease of the same fluxes was noted with solutions of K2SO4 at –5.7 bars, while the effect was lower when Na+ ions were substituted for the K+ ions. The flux cytoplasm-outer medium was generally stimulated by the decrease of osmotic potential in solutions of electrolytes, but not in solutions of mannitol. The effect on fluxes occurring at tonoplast was clearly lower than the effect on fluxes occurring at plasmalemma. Chloride retention in apparent free space was not significantly modified by a decrease of osmotic potential in every case. Chloride accumulation in cytoplasm was stimulated by solutions...

Licheni Nuovi O Interessanti Delle Coste Italiane

Abstract New or interesting Lichens of italian coasts. — The autor describes a lichen new to Italy, Acarospora microcarpa (Nyl) Wedd, a mediterranean species, found in southern France only hitherto. The lichen was gathered on the tufs rocks of the Isle of Procida; so the species is classed among the cryptogamic flora of phlegrean tufs. The presence of Acarospora trachytica Jatta on the isle of Procida is therefore indicated, a species that is somewhat rare and known so far only on the Island of Ischia and Vesuvius. Some new places for the marine lichen, Verrucaria symbalana Nyl. are reported, and the particular ecological interest of the species and its full geographical placement considered. Finally, new places for Lichina confinis Ag., in Italy are given. This is a marine species of considerable ecological interest.

Contributo Allo Studio Sistematico ed Ecologico Della Luzula Calabra Ten. dell'Altipiano Silano

Abstract Contribution to the systematics and ecology of LUZULA CALABRA Ten. of the Silan highland (Calabria, Southern Italy). — The Luzula calabra Ten. represents a known type endemic to the Silan highland. Some authors regard it as a species in itself, others include it as a variety in the Luzula campestris Lam. et DC. cycle. Therefore, in view of the fact that the systematic value of this entity has not yet been well defined and that it is not always easy to succeed in attributing isolated specimens to the Luzula calabra Ten., and all the more because information relating to the environment in wich the plant lives is scant and not always reliable, the intention of this work has been to specify, by biometric analysis, the fundamental characteristic of the Luzula calabra Ten., and furthermore to give and adequate picture of the environment in wich the plant lives. The resultats of statistical analysis and the diagrams ottained show how the Luzula calabra Ten. offers a particular physiognomy of its own and...