Metabolic Acclimation to Anoxia Induced by Low (2-4 kPa Partial Pressure) Oxygen Pretreatment (Hypoxia) in Root Tips of Zea mays

Young intact plants of maize (Zea mays L. cv INRA 508) were exposed to 2 to 4 kilopascals partial pressure oxygen (hypoxic pretreatment) for 18 hours before excision of the 5 millimeter root apex and treatment with strictly anaerobic conditions (anoxia). Hypoxic acclimation gave rise to larger amounts of ATP, to larger ATP/ADP and adenylate energy charge ratios, and to higher rates of ethanol production when excised root tips were subsequently made anaerobic, compared with root tips transferred directly from aerobic to anaerobic media. Improved energy metabolism following hypoxic pretreatment was associated with increased activity of alcohol dehydrogenase (ADH), and induction of ADH-2 isozymes. Roots of Adh1⁻ mutant plants lacked constitutive ADH and only slowly produced ethanol when made anaerobic. Those that were hypoxically pretreated acclimated to anoxia with induction of ADH2 and a higher energy metabolism, and a rate of ethanol production comparable to that of nonmutants. All these responses were insensitive to the presence or absence of NO₃⁻. Additionally, the rate of ethanol production was about 50 times greater than the rate of reduction of NO₃⁻ to NO₂⁻. These results indicate that nitrate reductase does not compete effectively with ADH for NADH, or contribute to energy metabolism during anaerobic respiration in this tissue through nitrate reduction. Unacclimated root tips of wild type and Adhl⁻ mutants appeared not to survive more than 8 to 9 hours in strict anoxia; when hypoxically pretreated they tolerated periods under anoxia in excess of 22 hours.     

Effect of path or sink anoxia on sugar translocation in roots of maize seedlings

The subcellular and developmental distribution of β-cyanoalanine synthase (EC 4.4.1.9), which catalyzes the reaction between cysteine and HCN to form β-cyanoalanine and H₂S, were investigated in barley (Hordeum vulgare) leaves. Total leaf activity was 1.1 micromoles per minute per gram fresh weight. Sucrose density gradients of lysed mesophyll protoplasts of barley revealed the exclusive or predominant localization of β-cyanoalanine synthase in the mitochondria. The enzyme was absent from both vacuole and chloroplast fractions.

β-Cyanoalanine synthase activity was distributed over the entire length of the barley leaf. Activity was dependent on the developmental stage, with a 3.5-fold higher activity in the oldest (apical) compared to the youngest (basal) parts of the leaf. The corresponding difference in activity for mesophyll protoplasts isolated from these parts was 7.5-fold. In younger leaf seagments, the nonchlorophyllous tissues accounted for up to 70% of the total β-cyanoalanine synthase activity. These results are discussed with reference to the formation of HCN as a substrate in barley leaves.

     

Larger adenylate energy charge and ATP/ADP ratios in aerenchymatous roots of Zea mays in anaerobic media as a consequence of improved internal oxygen transport

Internal transport of O₂ from the aerial tissues along the adventitious roots of intact maize plants was estimated by measuring the concentrations of adenine nucleotides in various zones along the root under an oxygen-free atmosphere. Young maize plants were grown in nutrient solution under conditions that either stimulated or prevented the formation of a lysigenous aerenchyma, and the roots (up to 210 mm long) were then exposed to an anaerobic (oxygen-free) nutrient solution. Aerenchymatous roots showed higher values than non-aerenchymatous ones for ATP content, adenylate energy charge and ATP/ADP ratios. We conclude that the lysigenous cortical gas spaces help maintain a high respiration rate in the tissues along the root, and in the apical zone, by improving internal transport of oxygen over distances of at least 210 mm. This contrasted sharply with the low energy status (poor O₂ transport) in non-aerenchymatous roots.Abbreviation AEC adenylate energy charge     

Oxygen Transport and Root Respiration of Maize Seedlings: A Quantitative Approach Using the Correlation between ATP/ADP and the Respiration Rate Controlled by Oxygen Tension

Oxygen uptake and ATP/ADP ratio were simultaneously monitored during incubation of excised maize (Zea mays L. INRA 508) root tips under varying O₂ partial pressure. Both variables were independent of O₂ tension until a critical O₂ pressure was reached. Below this pressure, ATP/ADP ratio and respiratory rate declined. However, in tissues having a high glycolytic capacity, the correlation between the ATP/ADP ratio and the respiratory rate breaks down as O₂ tension decreases, due to the increasing contribution of fermentative processes.

In presence of 2 millimolar NaF, the ATP/ADP ratio varied solely as a function of the O₂ tension, without interference by fermentative activity, and a close correlation links the ATP/ADP ratio and the respiratory rate of excised maize root tips over the whole range of O₂ tensions tested.

Using this correlation, a method is proposed for the quantitative determination of the relative cellular respiratory rate permitted by O₂ transport from the aerial part of young maize seedlings along the seminal root placed in an anoxic environment.

Data are presented which demonstrate the preeminent part played by the cortical air spaces in O₂ transport. Their contribution to respiration was high in the first few centimeters nearest the seed and decreased rapidly as the distance from the aerated source increased. It is concluded that O₂ transport might contribute to the survival or to adaptive responses of root tissues in flooded soils but that the ventilation of the apical growing zone was inadequate to sustain the growth.

     

H Efflux and Hexose Transport under Imposed Energy Status in Maize Root Tips

The relationship between changes in H⁺ flux and sugar transport in maize Zea mays L. DEA root tips have been investigated using two methods for controlling the cellular nucleotide level: (a) incubation in the presence of a glucose analog, the 2-deoxyglucose, which decreased the ATP level to less than 15% of its initial value within 60 minutes without changing the ADP and AMP levels; (b) an hypoxic treatment which also decreased the ATP level but with a concomitant rise in ADP and AMP. In both cases the rate of hexose transport was not modified until ATP had dropped to 70% of its initial value; then it decreased with the cellular ATP level. The residual uptake rate at very low ATP concentrations still represented 50% of the maximum rate with the dGlc treatment but only the diffusion rate in anoxia. H⁺ efflux was abolished in anoxia but not by the 2-deoxyglucose treatment, in spite of a lower cellular ATP concentration. Our results are consistent with an inhibition of H⁺-ATPase activity in anoxia by the high levels of cellular ADP and AMP, and provide in vivo evidence that sugar uptake is dependent upon the proton motive force rather than cellular ATP concentration. The absence of stimulation of H⁺ extrusion by ferricyanide in either normoxic or hypoxic conditions suggests that a redox system does not appear to contribute to H⁺ secretion under the conditions of this investigation.     

The beta-globin gene in Sardinian delta beta 0-thalassemia carries a C----T nonsense mutation at codon 39.

Sardinian delta beta 0-thalassemia is an inherited syndrome characterized by the inactivity of the beta-globin gene and the persistent activity of the fetal gamma-globin genes, particularly the A gamma-globin gene. Previous mapping studies with restriction enzymes failed to show any abnormality in the non-alpha globin gene cluster. We have now examined the possibility that this syndrome might result from a single rather than two different defects. Restriction enzyme polymorphisms linked to the delta beta 0-thalassemic non-alpha globin fragments were defined providing the basis for cloning the delta beta 0-thalassemic beta-globin gene from the DNA of a heterozygous patient. This gene appears to carry a C----T single mutation causing the appearance of a stop codon at amino acid position 39 of the beta-globin gene. This mutation was previously reported in beta 0-thalassemic patients, in linkage with different haplotypes. We conclude that Sardinian delta beta 0-thalassemia is the result of two separate mutations, the former one (unknown) responsible for persistent expression of gamma-globin genes, the latter for beta 0-thalassemia.     

Inhibition of bromodomain and extra‐terminal proteins increases sensitivity to venetoclax in chronic lymphocytic leukaemia

The development of drugs able to target BTK, PI3k‐delta and BCL2 has dramatically improved chronic lymphocytic leukaemia (CLL) therapies. However, drug resistance to these therapies has already been reported due to non‐recurrent changes in oncogenic pathways and genes expression signatures. In this study, we investigated the cooperative role of the BCL2 inhibitor venetoclax and the BRD4 inhibitor JQ1. In particular, we found that JQ1 shows additional activity with venetoclax, in CLL cell lines and in ex vivo isolated primary CD19⁺ lymphocytes, arguing in favour of combination strategies. Lastly, JQ1 is also effective in venetoclax‐resistant CLL cell lines. Together, our findings indicated that the BET inhibitor JQ1 could be a promising therapy in CLL, both as first‐line therapy in combination with venetoclax and as second‐line therapy, after the emergence of venetoclax‐resistant clones.     

Hematopoietic growth factors in autologous transplantation

Hematopoietic growth factors (HGFs) sustain the survival, proliferation and differentiation of hematopoietic stem cells and some functions of mature blood cells. In man several HGFs have been characterised and cloned so far, and this has allowed investigators to confer the rationale for the clinical application of these molecules in hematology and oncology. In particular G-CSF and GM-CSF are currently utilised to abrogate the hematological toxicity of chemotherapy for standard and dose-intensified therapy, neutropenia following bone marrow and peripheral blood stem cell transplantation. Moreover there has recently been great interest in the ex vivo expansion of hematopoietic stem and progenitor cells for a variety of applications, such as in vitro tumor cell purging or for reducing the volume of blood processed by the leukapheresis. Several combinations of HGFs have been described to sustain the ex vivo survival and proliferation of these cells disclosing new opportunities in the field of stem cells transplants.     

Genetic studies on some Nepalese populations

Populations living in two different regions of Nepal have been studied. The first region (the Kali Gandaki valley) is inhabited mainly by Magars, Gurungs, Thakalis and Chetris. It has been found that they exhibit different ABO gene frequencies though living in very close areas and often in the same villages. Thus they are still genetically different entities besides being ethnically distinguishable from each other.The second region examined in the present survey (the Solu Khumbu) is inhabited by Sherpas. They were studied for markers not analysed in a previous research, namely for ABO, UMPK, PGD, GLO and LDH.     

Bone marrow microenvironment: The guardian of leukemia stem cells

Bone marrow microenvironment(BMM) is the main sanctuary of leukemic stem cells(LSCs) and protects these cells against conventional therapies. However, it may open up an opportunity to target LSCs by breaking the close connection between LSCs and the BMM. The elimination of LSCs is of high importance, since they follow cancer stem cell theory as a part of this population. Based on cancer stem cell theory, a cell with stem cell-like features stands at the apex of the hierarchy and produces a heterogeneous population and governs the disease.Secretion of cytokines, chemokines, and extracellular vesicles, whether through autocrine or paracrine mechanisms by activation of downstream signaling pathways in LSCs, favors their persistence and makes the BMM less hospitable for normal stem cells. While all details about the interactions of the BMM and LSCs remain to be elucidated, some clinical trials have been designed to limit these reciprocal interactions to cure leukemia more effectively. In this review, we focus on chronic myeloid leukemia and acute myeloid leukemia LSCs and their milieu in the bone marrow, how to segregate them from the normal compartment, and finally the possible ways to eliminate these cells.