Characterization of the tolerance to iron chlorosis in different peach rootstocks grown in nutrient solution

Iron chlorosis is an important problem in peach trees, but differences exist between peach rootstocks in their tolerance to Fe chlorosis in calcareous soils. The purpose of this investigation was to characterize the tolerance of different rootstocks to Fe chlorosis induced by bicarbonate in nutrient solution. The rootstocks studied included peach (Nemaguard), plums (Brompton, San Julian A and Puebla de Soto 101) and almond × peach hybrids (Adafuel and GF677). Young plants obtained from rooted cuttings or from in vitro culture techniques were grown individually, under controlled conditions, in flasks with 700 mL of aerated nutrient solution low in iron and with or without 10 mM bicarbonate or 10 mM phosphate. Susceptiblity to bicarbonate-induced chlorosis was inversely correlated with both the Fe content in young leaves and the reducing capacity of roots, but not with the phosphorus content in young leaves. The plum Puebla de Soto 101 and the hybrid GF677 showed the lowest degree of chlorosis and the highest reducing capacity. Phosphate did not induce chlorosis.     

Variability of sunflower inbred lines to iron deficiency stress

Sunflower (Helianthus annuus L.) has been classified as a Fe-efficient species; however differences have been reported in susceptibility to Fe deficiency stress among cultivars and inbred lines. This paper reports research on responses of inbred lines to Fe deficiency stress (release of protons and root capacity to reduce Fe). When plants were grown individually in aerated nutrient solution without Fe the new selected inbred lines were classified as: a) Lines with good Fe deficiency stress response (RHA 271, RHA 273 and RHA 274); b) Lines that did not lower root external pH (HA 89 and RHA 299), one with very low reducing capacity (HA 89) and the other with reducing capacity (RHA 299); and c) One segregating line (RHA 276) from which two sister lines were selected. When a buffer (5 mM MES, 2-(N- morpholino) ethanesulfonic acid) was added to the root nutrient solution without Fe during growth, the reducing capacity of Fe-inefficient lines was higher for buffered than for unbuffered roots. Therefore, differences among lines for reducing capacity depend on experimental conditions.     

Plasmalemma redox activity and h extrusion in roots of fe-deficient cucumber plants

Cucumber plants (Cucumis sativus L.) with incipient Fe deficiency showed increased root capacity to reduce chelated Fe³⁺ compared to Fe-sufficient plants. When Fe-ethylenediaminete-traacetate was added to the root medium of the Fe-deficient plants, the reductase activity was associated with acidification of the medium and an increase in the net apparent K⁺ efflux. In the presence of the H⁺-ATPase inhibitor N,N′-dicyclohexylcarbodiimide the net apparent H⁺ efflux was completely suppressed, though some reductase activity was preserved, and the net apparent K⁺ efflux was significantly increased. The inhibition of the reductase activity by N,N′-dicyclohexylcarbodiimide was similar whether the pH of the medium was buffered or not. Anoxia and the protonophore carbonyl cyanide m-chlorophenyl hydrazone also caused a similar inhibition of the reductase activity. It is proposed that this redox system transports electrons only and that its activity is inhibited by plasmamembrane depolarization and anoxia. The H⁺ and K⁺ efflux associated with the reductase activity may be a result of the plasmamembrane depolarization it causes.     

Effect of gibberellic acid on K+ (Rb+) uptake and transport in sunflower roots

Four-week-old sunflower plants ( Helianthus annuus L. cv. Halcón), grown in different nutrient solutions, were used to study the effects of gibberellic acid (GA₃) on K⁺ (Rb⁺) uptake by roots or transport to the shoot. Gibberellic acid application to the nutrient solution did not affect the exudation process of excised roots. When GA₃ was sprayed on leaves 2 to 6 days before excising the roots, the rate of exudation and the K⁺ flux increased. When the exudation study was done keeping the roots in a nutrient solution in which Rb⁺ replaced K⁺, the GA₃ effects were evident also on Rb⁺ uptake and transport. In intact plants, GA₃ increased the Rb⁺ transported to the shoot but did not affect Rb⁺ accumulation in the root. It is suggested that these GA₃ effects can be explained if it is assumed that GA₃ acts on the transport of ions to the xylem vessels.     

Cybernetic modeling and regulation of metabolic pathways in multiple steady states of hybridoma cells

Hybridoma cells utilize a pair of complementary and partially substitutable substrates, glucose and glutamine, for growth. It has been shown that cellular metabolism shifts under different culture conditions. When those cultures at different metabolic states are switched to a continuous mode, they reach different steady states under the same operating conditions. A cybernetic model was constructed to describe the complementary and partial substitutable nature of substrate utilization. The model successfully predicted the metabolic shift and multiple steady-state behavior. The results are consistent with the experimental observation that the history of the culture affects the resulting steady state.     

Increased localization of APP‐C99 in mitochondria‐associated ER membranes causes mitochondrial dysfunction in Alzheimer disease

In the amyloidogenic pathway associated with Alzheimer disease (AD), the amyloid precursor protein (APP) is cleaved by β‐secretase to generate a 99‐aa C‐terminal fragment (C99) that is then cleaved by γ‐secretase to generate the β‐amyloid (Aβ) found in senile plaques. In previous reports, we and others have shown that γ‐secretase activity is enriched in mitochondria‐associated endoplasmic reticulum (ER) membranes (MAM) and that ER–mitochondrial connectivity and MAM function are upregulated in AD. We now show that C99, in addition to its localization in endosomes, can also be found in MAM, where it is normally processed rapidly by γ‐secretase. In cell models of AD, however, the concentration of unprocessed C99 increases in MAM regions, resulting in elevated sphingolipid turnover and an altered lipid composition of both MAM and mitochondrial membranes. In turn, this change in mitochondrial membrane composition interferes with the proper assembly and activity of mitochondrial respiratory supercomplexes, thereby likely contributing to the bioenergetic defects characteristic of AD.     

BORC coordinates encounter and fusion of lysosomes with autophagosomes

Whereas the mechanisms involved in autophagosome formation have been extensively studied for the past 2 decades, those responsible for autophagosome-lysosome fusion have only recently begun to garner attention. In this study, we report that the multisubunit BORC complex, previously implicated in kinesin-dependent movement of lysosomes toward the cell periphery, is required for efficient autophagosome-lysosome fusion. Knockout (KO) of BORC subunits causes not only juxtanuclear clustering of lysosomes, but also increased levels of the autophagy protein LC3B-II and the receptor SQSTM1. Increases in LC3B-II occur without changes in basal MTORC1 activity and autophagy initiation. Instead, LC3B-II accumulation largely results from decreased lysosomal degradation. Further experiments show that BORC KO impairs both the encounter and fusion of autophagosomes with lysosomes. Reduced encounters result from an inability of lysosomes to move toward the peripheral cytoplasm, where many autophagosomes are formed. However, BORC KO also reduces the recruitment of the HOPS tethering complex to lysosomes and assembly of the STX17-VAMP8-SNAP29 trans-SNARE complex involved in autophagosome-lysosome fusion. Through these dual roles, BORC integrates the kinesin-dependent movement of lysosomes toward autophagosomes with HOPS-dependent autophagosome-lysosome fusion. These findings reveal a requirement for lysosome dispersal in autophagy that is independent of changes in MTORC1 signaling, and identify BORC as a novel regulator of autophagosome-lysosome fusion.     

Dynamic behavior of hepatitis C virus quasispecies in patients undergoing orthotopic liver transplantation.

We have studied the distribution of viral sequences from the 5' noncoding region and from a fragment of the E2/NS2 region of the hepatitis C virus (HCV) genome in samples obtained before and after liver transplantation in two patients with HCV cirrhosis. The population of viral sequences in both regions were established by sequencing cloned PCR products. In both cases, the complexity of the viral quasispecies decreased after transplantation, although the consensus nucleotide and amino acid sequences remained unchanged. It is suggested that both positive and negative selection and random sampling events contribute substantially in shaping the genetic composition of HCV quasispecies and that recurrence of HCV infection may occur under equilibrium conditions.