Iron deficiency in peach trees: effects on leaf chlorophyll and nutrient concentrations in flowers and leaves

The effects of iron deficiency on the leaf chlorophyll concentrations and on the macro- (N, P, K, Ca and Mg) and micro-nutrient (Fe, Mn, Zn and Cu) composition of flowers (at full bloom) and leaves (60 and 120 days after full bloom) of field-grown peach (Prunus persica L. Batsch) trees were investigated. Flowers and leaves were taken and analysed from fifty individual trees. Our data indicate that large decreases in leaf chlorophyll concentration were found at the beginning of the season in control trees, possibly associated to a dilution effect by leaf growth, that were later followed by leaf chlorophyll concentration increases. Leaf Fe chlorosis apparently results from two different processes, the dilution of leaf Chl caused by growth and the subsequent inability to produce and/or stabilize new Chl molecules in the thylakoid membrane. Iron chlorosis did not change the seasonal change patterns of any of the nutrients studied. In Fe-deficient trees the K concentration and the K/Ca ratio were high not only in leaves but also in flowers, indicating that this is a characteristic of Fe-deficient plant tissue in the whole fruit tree growing season. Flower Fe concentrations were well correlated with the degree of chlorosis developed later in the season by the trees, suggesting that flower analysis could be used for the prognosis of Fe deficiency in peach.     

Wave propagation in cardiac tissue and effects of intracellular calcium dynamics (computer simulation study)

Computer simulation using Luo-Rudy I1 model of ventricular myocyte showed that intracellular calcium dynamics become irregular in case of high rate stimulation. This causes the transition from stationary to nonstationary spiral wave and its breakup in 2D model of cardiac tissue. Obtained results suggest how ventricular fibrillation may occur due to the abnormalities of intracellular calcium dynamics. The short review of existing cardiac cell models with calcium dynamics is presented.     

Branch growth of riparian cottonwoods: a hydrologically sensitive dendrochronological tool

 The conservation of riparian (river valley flood plain) forests relies on the provision of instream flows that are sufficient to sustain tree growth. In the present study, annual branch growth increments were investigated as an indicator of environmental favorability for riparian cottonwoods. Trees of three species, Populus angustifolia, P. balsamifera, and P. deltoides, and their natural interspecific hybrids, were studied at five sites along the Oldman and South Saskatchewan rivers in Alberta, Canada. Annual branch growth increments for the interval from 1983 to 1992 were positively correlated with stream flows (r ² = 0.79 at Lethbridge) and slightly negatively correlated with weather variables that contribute to water demand: evaporation, temperature, wind, and/or sunshine. The combination of January to May stream flow (water supply) and June evaporation (water demand) almost entirely accounted for the branch growth variation across years (r ² = 0.91 at Lethbridge). Tree ring increments were also investigated but were less closely correlated than branch increments across trees or with stream flow. Branch growth increments thus provide an accurate but short duration (1 or 2 decades) record of environmental favorability for growth. The close correlation between branch growth and stream flow indicates that water is the principal limitation to growth of these riparian cottonwoods and that these trees obtained their water from a source linked to the stream, the riparian water table. Analyses of branch increments should provide a management tool for (i) determining instream flow needs for riparian cottonwoods and (ii) analyzing impacts of stream flow alterations due to river damming or water diversion. Received: 8 May 1997 / Accepted: 23 September 1997     

The "prismane" protein resolved: X-ray structure at 1.7 Å and multiple spectroscopy of two novel 4Fe clusters

The three-dimensional structure of the native "putative prismane" protein from Desulfovibrio vulgaris (Hildenborough) has been solved by X-ray crystallography to a resolution of 1.72?Å. The molecule does not contain a [6Fe-6S] prismane cluster, but rather two 4Fe clusters some 12?Å apart and situated close to the interfaces formed by the three domains of the protein. Cluster 1 is a conventional [4Fe-4S] cubane bound, however, near the N-terminus by an unusual, sequential arrangement of four cysteine residues (Cys 3, 6, 15, 21). Cluster 2 is a novel 4Fe structure with two μ₂-sulfido bridges, two μ₂-oxo bridges, and a partially occupied, unidentified μ₂ bridge X. The protein ligands of cluster 2 are widely scattered through the second half of the sequence and include three cysteine residues (Cys 312, 434, 459), one persulfido-cysteine (Cys 406), two glutamates (Glu 268, 494), and one histidine (His 244). With this unusual mixture of bridging and external type of ligands, cluster 2 is named the "hybrid" cluster, and its asymmetric, open structure suggests that it could be the site of a catalytic activity. X-ray absorption spectroscopy at the Fe K-edge is readily interpretable in terms of the crystallographic model when allowance is made for volume contraction at 10?K; no Fe··Fe distances beyond 3.1?Å could be identified. EPR, Mössbauer and MCD spectroscopy have been used to define the oxidation states and the magnetism of the clusters in relation to the crystallographic structure. Reduced cluster 1 is a [4Fe-4S]¹⁺ cubane with S?=?3/2; it is the first biological example of a "spin-admixed" iron-sulfur cluster. The hybrid cluster 2 has four oxidation states from (formally) all Fe^III to three Fe^II plus one Fe^III. The four iron ions are exchange coupled resulting in the system spins S?=?0, 9/2, 0 (and 4), 1/2, respectively, for the four redox states. Resonance Raman spectroscopy suggests that the bridging ligand X which could not be identified unambiguously in the crystal structure is a solvent-exchangeable oxygen.