Boron — Key element in the actions of phytochrome and gravity?

Hypocotyl sections from dark-grown mung bean (Vigna radiata (L.) Wilczek) seedlings grown without boron exhibit little or no increase in the translocation of fluorescein in phloem cells following gravitational stimulation or red irradiation. In contrast, pretreatment of the hypocotyl sections with low concentrations of boric acid before red irradiation or gravitational stimulation results in a rapid increase in fluorescein movement. Mung bean root tips without boron fail to remain attached to a negativelycharged glass surface after several minutes of red irradiation. A low boron concentration in the solution induces tip attachment. The suggestion is made that boron is required to stabilize a positive electrostatic charge in the plasma membrane that is generated by the actions of phytochrome and gravity.     

Regulation of enzyme levels by phytochrome in mustard cotyledons: Multiple mechanisms?

Phytochrome controls the appearance of many enzymes in the mustard (Sinapis alba L.) cotyledons. The problem has been whether the effect of phytochrome on the appearance of enzymes in this organ is due to a common initial action of P_fr, e.g. due to the liberation of a second messenger. We have compared the modulation by light (phytochrome) of the appearance of phenylalanine ammonia lyase (PAL)⁺ and ribulosebisphosphate carboxylase (Carboxylase)⁺. PAL becomes detectable in the mustard cotyledons at 27 h after sowing while Carboxylase starts to appear only at 42 h after sowing (starting points, 25° C). The starting points cannot be shifted by light. As a major result, in the case of PAL the inductive effect of continuous red light (given from the time of sowing) remains fully reversible by 756 nm-light up to the starting point (27 h after sowing) while with Carboxylase full reversibility in continuous red light is lost at approximately 15 h after sowing. While the induction of Carboxylase is already saturated at a very low level of P_fr (e.g. continuous 756 nm-light saturates the response) and does not depend on irradiance (e.g. continuous 675 mW m^-2 red light and 67.5 mW m^-2 red light lead to the same time course), PAL induction is a graded response over a wide range of P_fr doses and depends strongly on the fluence rate (high irradiance response, HIR). It is concluded that PAL induction and Carboxylase induction are not only separated in time but differ in every regard except that both responses are mediated by phytochrome.The present data support the previous conclusion that the specification of the temporal and spatial pattern of development is independent of phytochrome even though the realization of the pattern of development can only occur in the presence of phytochrome (P_fr). It seems that there is no feedback from pattern realization to pattern specification.Abbreviations P_fr the far-red absorbing, physiologically active form of phytochrome - P_r the red absorbing physiologically inactive form of phytochrome - P_total [P_r]+[P_fr] - PAL phenylalanine ammonia-lyase (EC 4.3.1.5) - Carboxylase ribulosebisphosphate carboxylase (EC 4.1.1.39)     

Temperature- and seed-batch-related variation in the kinetic behaviour of phytochrome under ‘high-irradiance-response’ conditions

The characteristics of the high-irradiance response (HIR) of plant photomorphogenesis are thought to be the result of the interaction of both the light and dark reactions of phytochrome. Thus any variation in the rates of the dark reactions may be expected to lead to variation in the characteristics of the HIR. We report here substantial differences in the rates of the dark reactions between different seed batches of a single species (Sinapis alba L.), and also between different organs of seedlings from each of the batches of seed. Calculations of phytochrome dynamics from the measured dark-reaction rates show that the behaviour of Pfr under HIR conditions will vary considerably according to seed batch and seedling organ. Much larger differences in dark-reaction rates, and the resulting phytochrome dynamics, were found between 25° and 10° C. These lead to the prediction that the HIR will be much reduced at the lower temperature, and may be absent in some cases.Abbreviations and symbols HIR high-irradiance response - Pfr far-red-absorbing form of phytochrome - Pr red-absorbing form of phytochrome - Ptot total phytochrome, Pr+Pfr - _ss Pfr/Ptot ratio which immediately establishes the phytochrome steady state     

Bacteriophytochromes – from informative model systems of phytochrome function to powerful tools in cell biology

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Etude du phytochrome des graines de Pinus nigra Arn par spectrophotométrie bichromatique in vivo

Summary Phytochrome photoconversions P_rP_fr and P_frP_r can be measured by differential spectrophotometry in dry seeds (6% water content) of Pinus nigra Arn. A red light irradiation given before imbibition induces germination when the seeds are subsequently wetted and kept in darkness.In continuous darkness the phytochrome content shows a drastic increase at the beginning of moistening.The detectable pigment is entirely in the P_r form. The normal P_frP_r dark reversion is observed. P_fr destruction does not take place.     

Viola ambigua W. K. in Niederösterreich undViola Thomasiana Perr. et Song. in Tirol

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Clonal Differences in Photosynthesis in Hevea Brasiliensis Müll. Arg.

The objective of the present investigation was to examine the extent of variations in single leaf net photosynthetic rate (P_N) and its relative dependence on stomatal conductance (g_s) and the mesophyll capacity to fix carbon in 12 clones of the natural rubber plant. There were significant variations in P_N measured at low and saturating photon flux density (PFD); the extent of variation was larger at low than at saturating PFD. The compensation irradiance (CI) and apparent quantum yield of CO₂ assimilation (φ_c) calculated from the P_N/PFD response curves showed significant variations among the clones. P_N at low irradiance was positively correlated with φ_c. Thus a clone with large P_N at low irradiance, high φ_c, and low CI may tolerate shade better and thus produce a high tree stand per hectare. A strong positive correlation existed between P_N saturated with radiant energy (P_sat) and carboxylation efficiency (CE) estimated from the response curves of P_N on intercellular CO₂ concentration (C_i), but g_s showed a poor correlation with P_sat High CO₂ compensation concentration (Γ) led to low CE in Hevea clones. A clone with large P_sat, high CE, low g_s, and low Γ is the one in which photosynthesis is more dependent on the mesophyll factors than stomata. Such a clone may produce relatively high biomass and maintain high water use efficiency. This revised version was published online in September 2006 with corrections to the Cover Date.     

CP3 is involved in negative regulation of phytochrome A signalling in <Emphasis Type="Italic">Arabidopsis</Emphasis>

Several mutants with altered phytochrome A (phyA) signalling have been identified in screenings under continuous far-red light (FR). The latter protocol could preclude the identification of mutants affected in the signalling pathway that operates even under transient phyA activation, compared to the high-irradiance response (HIR) pathway that requires continuous FR. Since some photomorphogenic mutants show shoot-height phenotypes, the screening was conducted on dwarf mutants of Arabidopsis thaliana (L.) Heynh. from the ABRC stocks grown under hourly FR pulses. The dwarf mutant cp3 (compacta 3) showed normal hypocotyl length and folded cotyledons in darkness but enhanced hypocotyl-growth inhibition and cotyledon unfolding under pulsed FR. The HIR and the response mediated by phyB were not affected. Under pulsed FR, seed germination and blocking of greening upon transfer to white light were enhanced in cp3. PHYA levels were normal in cp3. The phenotype under pulsed FR but not the adult phenotype required phyA. We propose that CP3 is involved in the negative regulation of the signalling pathway that saturates with transient activation of phyA.     

Light-stimulated respiration in the green algaDunaliella tertiolecta: Involvement of the ultraviolet/blue-light photoreceptor(s) and phytochrome?

Starch breakdown and respiratory O₂ uptake in the green algaDunaliella tertiolecta (Butcher) are stimulated not only by blue, but also by red light. In the present study, attempts are described to identify the photoreceptor(s) involved. Fluence rate-response curves with different slopes in the ultraviolet (UV)/blue and in the red spectral region as well as differences in the kinetics and in the unfluence of dark pre-incubation on the stimulation of respiratory O₂ uptake by blue and red light strongly indicate the action of two photoreceptors. Since the effect of red light shows some far-red reversibility, and since simultaneous irradiation with red and far-red light decreases the effectiveness of red light, the involvement of phytochrome — in addition to the UV/blue photoreceptor(s) — is suggested in the light-stimulated respiration inDunaliella.Abbreviation UV ultraviolet     

hAT element population genetics in Anopheles gambiae s.l. in Mozambique

Herves is a functional Class II transposable element in Anopheles gambiae belonging to the hAT superfamily of elements. Class II transposable elements are used as gene vectors in this species and are also being considered as genetic drive agents for spreading desirable genes through natural populations as part of an effort to control malaria transmission. In this study, Herves was investigated in populations of Anopheles gambiae s.s., Anopheles arabiensis and Anopheles merus in Mozambique over a period of 2 years. The copy number of Herves within these three species was approximately 5 copies per diploid genome and did not differ among species or between years. Based on the insertion-site occupancy-frequency distribution and existing models of transposable element dynamics, Herves appears to be transpositionally active currently or, at least recently, in all species tested. Ninety-five percent of the individuals within the populations of the three species tested contained intact elements with complete Herves transposase genes and this is consistent with the idea that these elements are currently active.     

Genetics of esterases in Drosophila. V. Characteristics of the “pupal” esterase in D. virilis

From analysis of the properties of the pupal esterase (p-esterase) in Drosophila virilis, it is concluded that it is heat stable, its electrophoretic detection depends on culture density, its expression is stage specific, and it is not a variant of esterase 2. It was also demonstrated that p-esterase, like esterase 6, is activated by injections of the juvenile hormone into larvae. Heat treatment of heat-resistant D. virilis stocks led to decreased activities of the juvenile hormone dependent esterases but did not affect those of the heat-sensitive stocks. It is suggested that heat resistance in D. virilis is related to some functional features of the system of modifier genes controlling the phenotypic expression of esterases.     

Dreissigste Ausstellung der k. k. österr. Gartenbaugesellschaft in Wien

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