Relationship Between Polyamines Metabolism and Cell Death in Roots of Malus hupehensis Rehd. Under Cadmium Stress

The free putrescine （Put） content, the hydrogen peroxide （H202） content and the polyamine oxidase （PAO） activity in roots of Malus hupehensis Rehd. var. pinyiensis Jiang （PYTC） were significantly increased, and reached its peak at 1, 2 and 6 h, respectively, under cadmium treatment. The free spermine （Spin） and spermidine （Spd） contents were dramatically decreased, and reached the minimum value at 4-6 h, then remained relatively stable. The change in total free polyammes （PAs） content was consistent with that of free Put. The number of root dead cells was gradually increased after treatment for 24 h, and the typical characteristics of programmed cell death （PCD） were displayed at 48 h. Throughout the Cd treatment process, changes in PAs metabolism appeared to be prior to cell death increase, and the H2O2 content was always maintained at a high level. These results indicated that polyamines could initiate cell death by generating H2O2 in roots of Malus hupehensis Rehd. under CdSO4 stress.

Transepithelial transport of putrescine across monolayers of the human intestinal epithelial cell line, Caco-2

AIM To study the transepithelial transport characteristics of the polyamine putrescine in human intestinal Caco-2 cell monolayers to elucidate the mechanisms of the putrescine intestinal absorption.METHODS The transepithelial transport and the cellular accumulation of putrescine was measured using Caco 2 cell monolayers grown on permeable filters.RESULTS Transepithelial transport of putrescine in physiological concentrations (>0.5 mM)from the apical to basolateral side was linear. Intracellular accumulation of putrescine was higher in confluent than in fully differentiated Caco-2 cells, but still negligible (less than 0.5%) of the overall transport across the monolayers in apical-to-basolateral direction. EGF enhanced putrescine accumulation in Caco-2 cells by four-fold, as well as putrescine conversion to spermidine and spermine by enhancing the activity of Sadenosylmethionine decarboxylase. However,EGF did not have any significant influence on putrescine flux across the Caco-2 cell monolayers. Excretion of putrescine from Caco-2cells into the basolateral medium did not exceed 50 picomoles, while putrescine passive flux from the apical to the basolateral chamber,contributed hundreds of micromoles polyamines to the basolateral chamber.CONCLUSION Transepithelial transport of putrescine across Caco-2 cell monolayers occurs in passive diffusion, and is not influenced when epithelial cells are stimulated to proliferate by a potent mitogen such as EGF.

Improvement of plant abiotic stress tolerance through modulation of the polyamine pathway

Polyamines （mainly putrescine （Put）, spermidine （Spd）, and spermine （Spin）） have been widely found in a range of physiological processes and in almost all diverse environ- mental stresses. In various plant species, abiotic stresses modulated the accumulation of polyamines and related gene expression. Studies using loss-of-function mutants and transgenic overexpression plants modulating polyamine metabolic pathways confirmed protective roles of polyamines during plant abiotic stress responses, and indicated the possibility to improve plant tolerance through genetic manipulation of the polyamine pathway. Additionally, puta- tive mechanisms of polyamines involved in plant abiotic stress tolerance were thoroughly discussed and crosstalks among polyamine, abscisic acid, and nitric oxide in plant responses to abiotic stress were emphasized. Special attention was paid to the interaction between polyamine and reactive oxygen species, ion channels, amino acid and carbon metabolism, and other adaptive responses. Further studies are needed to elucidate the polyamine signaling pathway, especially polyamine-regulated downstream tar- gets and the connections between polyamines and other stress responsive molecules.

Regulatory role of L-proline in fetal pig growth and intestinal epithelial cell proliferation

L-proline(Pro)is a precursor of ornithine,which is converted into polyamines via ornithine decarboxylase(ODC).Polyamines plays a key role in the proliferation of intestinal epithelial cells.The study investigated the effect of Pro on polyamine metabolism and cell proliferation on porcine enterocytes in vivo and in vitro.Twenty-four Huanjiang mini-pigs were randomly assigned into 1 of 3 groups and fed a basal diet that contained 0.77%alanine(Ala,iso-nitrogenous control),1%Pro or 1%Pro+0.0167%α-difluoromethylornithine(DFMO)from d 15 to 70 of gestation.The fetal body weight and number of fetuses per litter were determined,and the small and large intestines were obtained on d 70±1.78 of gestation.The in vitro study was performed in intestinal porcine epithelial(IPEC-J2)cells cultured in Dulbecco’s modified Eagle medium-high glucose(DMEM-H)containing 0μmol/L Pro,400μmol/L Pro,or400μmol/L Pro+10 mmol/L DFMO for 4 d.The results showed that maternal dietary supplementation with 1%Pro increased fetal weight;the protein and DNA concentrations of the fetal small intestine;and mRNA levels for potassium voltage-gated channel,shaker-related subfamily,member 1(Kv1.1)in the fetal small and large intestines(P<0.05).Supplementing Pro to either gilts or IPEC-J2 cells increased ODC protein abundances and polyamine concentrations in the fetal intestines and IPEC-J2 cells(P<0.05).In comparison with the Pro group,the combined administration of Pro and DFMO reduced the expression of ODC protein and spermine concentration in the fetal intestine,as well as the concentrations of putrescine,spermidine and spermine in IPEC-J2 cells(P<0.05).Meanwhile,the percentage of cells in the S-phase and the mRNA levels of proto-oncogenes c-fos and c-myc were increased in response to Pro supplementation,whereas depletion of cellular polyamines with DFMO increased tumor protein p53(p53)mRNA levels(P<0.05).Taken together,dietary supplementation with Pro improved fetal pig growth and intestinal epithelial cell proliferation via enhancing polyamine synthesis.