Evolution de l'activité auxines-oxydasique et peroxydasique lors de l'induction photopériodique et de la sexualisation de l'épinard

(Evolution of the auxin-oxidase and peroxidase activity during the spinach's photo-periodic induction and sexualisation) Protein extracts, prepared from spinach leaves, are analysed after a gel chromatography on Sephadex G-100 and SE-Sephadex C-50. The photoperiodic induction seems related with a fall of the auxin-oxidase and peroxidase activities we observe a change in the isozyme number and pattern. The female plants have more isozymes, but the enzymatic activity is higher in the male plants. The destruction of the indole-3-acetic acid, in spinach, is not strictly related to the peroxidase

The Steady State Chlorophyll a Fluorescence Exhibits in Vivo an Optimum as a Function of Light Intensity which Reflects the Physiological State of the Plant

Modulated (690 and 730 nm), as well as direct chlorophyll (Chl) a fluorescence and changes in the concentration of the oxidized P700 were measured under steady state conditions in leaves of higher plants adapted to different light intensities. All the leaf samples exhibit an optimum curve of steady state fluorescence yield (Fs) versus the light intensity but its position with respect to light intensity varies considerably from one species to another or from one sample to other even in the same plant or within the same leaf sample. However, the optimum level of Fs was always at a moderate light intensity. By using the modulated fluorescence technique, the system with all closed (Flm) or open reaction center (Flo) were measured in steady state conditions. Each experimentally measured fluorescence yield was separated into a fluorescence emission of open (Fopen = Flo,(1—Vs)) and closed (Fclosed = (Flm . Vs)) reaction center (RC) of photosystem II where Vs=(Fs - Flo)/(Flm - Flo) is the function of fraction of closed reaction centers. With increasing light intensity, the fraction of open RC decreased while the fraction of closed RC increased. Maximum quantum efficiency (ΦPo) and actual quantum efficiency (ΦP) decreased by increasing light intensity. An optimum level of Fs was observed, when the fraction of closed reaction centers Vs of each sample was about 0.2 showing a common quenching mechanism which determines the fluorescence properties under steady state condition. This explains the apparent phenomenological contradiction that the fluorescence yield under steady state conditions can increase or decrease upon an increase of actinic ligh

Ethylene Production in Spinach Leaves during Floral Induction

Spinach plants were induced to flower by transferring them from short days to continuous light. Their leaf laminae released more ethylene than those from vegetative plants. These leaves also exhibited a greater capacity to convert exogenous ACC into ethylene. Cell wall preparations from the leaves of continuously illuminated plants also converted exogenous ACC into ethylene more readily than extracts from short day plants. These effects and also those previously reported for peroxidases appear very similar to these brought about by various environmental stresses such as pollution and mechanical irritatio

Atomic-force microscopy imaging of plasma membranes purified from spinach leaves

Summary: Plasma membranes purified from spinach leaves by aqueous two-phase partitioning were examined by atomic-force microscopy (AFM) in phosphate buffer, and details on their structure were reported at nanometric scale. Examination of the fresh membrane preparation deposited on mica revealed a complex organization of the surface. It appeared composed of a first layer of material, about 8 nm in thickness, that practically covered all the mica surface and on which stand structures highly heterogeneous in shape and size. High-resolution imaging showed that the surface of the first layer appeared relatively smooth in some regions, whereas different characteristic features were observed in other regions. They consisted of globular-to-elliptical protruding particles of various sizes, from 4-5 nm x-y size for the smallest to 40-70 nm for the largest, and of channel-like structures 25-30 nm in diameter with a central hole. Macromolecular assemblies of protruding particles of various shapes were imaged. Addition of the proteolytic enzyme pronase led to a net roughness decrease in regions covered with particles, indicating their proteinaceous nature. The results open fascinating perspectives in the investigation of membrane surfaces in plant cells with the possibility to get structural information at the nanometric rang

Changing concepts in plant hormone action

Summary: A plant hormone is not, in the classic animal sense, a chemical synthesized in one organ, transported to a second organ to exert a chemical action to control a physiological event. Any phytohormone can be synthesized everywhere and can influence different growth and development processes at different places. The concept of physiological activity under hormonal control cannot be dissociated from changes in concentrations at the site of action, from spatial differences and changes in the tissue's sensitivity to the compound, from its transport and its metabolism, from balances and interactions with the other phytohormones, or in their metabolic relationships, and in their signaling pathways as well. Secondary messengers are also involved. Hormonal involvement in physiological processes can appear through several distinct manifestations (as environmental sensors, homeostatic regulators and spatio-temporal synchronizers, resource allocators, biotime adjusters, etc.), dependent on or integrated with the primary biochemical pathways. The time has also passed for the hypothesized ‘specific' developmental hormones, rhizocaline, canlocaline, and florigen: root, stem, and flower formation result from a sequential control of specific events at the right places through a coordinated control by electrical signals, the known phytohormones and nonspecific molecules of primary and secondary metabolism, and involve both cytoplasmic and apoplastic compartments. These contemporary views are examined in this revie

Apoplast: a sensitive site for assessing some biochemical effects of O3 or SO2 in Norway spruce needles

International audienc

Auxin control of calcium-mediated peroxidase secretion by auxin-dependent and auxin-independent sugarbeet cells

Peroxidase secretion by three sugarbeet cell lines in the absence of Ca2+ was unaffected by the addition of auxins of different chemical structures. The six auxins tested had no effect on the Ca2+ -promoted peroxidase secretion by habituated non-organogenic cells (HNO), but they enhanced the secretion by normal non-organogenic cells (NNO) and three of them inhibited it in the case of the habituated organogenic line. A 5-week subculture of the auxinindependent HNO callus on auxin-containing media increased the sensitivity of cells to Ca2+ and their responsiveness to auxins in suspension cultures. Conversely, subculture of the auxin-requiring NNO callus on auxin-deficient medium induced a decreased sensitivity to Ca2+ and a complete loss of response to auxins. The possible regulation of peroxidase secretion by Ca2+- and auxin-receptors is discussed. © 1983