Guoxin Shi

Regulation of exogenous spermidine on the reactive oxygen species level and polyamine metabolism in Alternanthera philoxeroides (Mart.) Griseb under copper stress

Effects of exogenous spermidine (Spd) on the reactive oxygen species level and polyamine metabolism against copper (Cu) stress in Alternanthera philoxeroides (Mart.) Griseb leaves were investigated. Cu treatment induced a marked accumulation of Cu and enhanced contents of malondialdehyde (MDA), hydrogen peroxide (H2O2) and the generation rate of O2·−. It also significantly increased putrescine (Put) levels but lowered spermidine (Spd) and spermine (Spm) levels. The activities of arginine decarboxylase (ADC), ornithine decarboxylase (ODC) and polyamine oxidase (PAO) were all elevated with the increase of Cu concentration. However, application of exogenous Spd effectively decreased H2O2 content and the generation rate of O2·−, prevented Cu-induced lipid peroxidation and reduced Cu accumulation. Moreover, it declined level of endogenous Put and increased levels of Spd and Spm. Activities of ADC, ODC and PAO were all inhibited by exogenous Spd. The results indicated that application of exogenous Spd could enhance the tolerance of A. philoxeroides to Cu stress by reducing the reactive oxygen level and balancing polyamine metabolism.

Lead tolerance mechanism in sterilized seedlings of Potamogeton crispus L.: Subcellular distribution, polyamines and proline

The effects of increasing concentrations of lead (Pb) on malondialdehyde (MDA) content, soluble protein, Pb accumulation, nutrients, polyamines (PAs) and proline metabolism were investigated in sterilized seedlings of Potamogeton crispus L. after 5d exposure. Significant oxidative stress was not caused, indicated by a little induction of MDA content and soluble proteins. Pb accumulation increased in a concentration-dependent manner and most of Pb was stored in the cell wall. Total P, Mg, Na and Zn rose and total Fe fell; total Ca increased at 25 μM Pb but then declined. The nutrients in cell wall fraction changed in the same pattern as total nutrients, whereas those in soluble and organelle fraction declined. Total putrescine (Put) decreased markedly, while total spermidine (Spd), spermine (Spm) and (Spd+Spm)/Put ratio increased progressively but then declined. The trends for free, perchloric acid soluble conjugated (PS-conjugated) and perchloric acid insoluble bound (PIS-bound) PAs were similar to those on total PAs, except that PIS-bound Spm increased significantly. Arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) activities rose gradually, while diamine oxidase (DAO) initially increased but then declined. Proline content increased initially only to decline later, due to the increase of r-glutamyl kinase (GK) activity. Meanwhile, ornithine-d-aminotransferase (OAT) activity gradually reduced, while no significant change was observed in proline dehydrogenase (PDH) activity. Our results indicated that the tolerance of P. crispus to Pb stress was based on cell wall compartmentalization combined with increase of nutrients, alterations of PAs, and induction of proline.

Polyamine metabolism and physiological responses of Potamogeton crispus leaves under lead stress

Aquatic macrophytes were found to be the potential scavengers of heavy metals from aquatic environment. In this study, influences of ladder concentration of lead (Pb) on the leaves of Potamogeton crispus Linn were studied after 7 days of treatment. The accumulation of Pb, nutrient element contents, the generation rate of superoxide radical (O2·−), MDA, proline, and polyamine (PAs) contents, as well as the activities of diamine oxidases (DAO), polyamine oxidases (PAO), arginine decarboxylase (ADC), and ornithine decarboxylase (ODC) in P. crispus leaves were investigated. The result indicated that Pb treatment decreased the activity of DAO, whereas the proline content, MDA content, the generation rate of O2·− and the activity of ODC increased in different degrees. Meantime, Pb treatment significantly increased the free putrescine (Put) level and made other PAs levels dynamic changes. The activities of PAO and ADC were declined firstly and then enhanced with the increase in the Pb concentration.

Exogenous spermidine enhances Hydrocharis dubia cadmium tolerance

The effects of exogenous spermidine (Spd) on arginine decarboxylase (ADC), ornithine decarboxylase (ODC), polyamine oxidase (PAO), and diamine oxidase (DAO) activities, the rate of superoxide radical (O2·−) generation and polyamine (PA), malondialdehyde (MDA), and H2O2 contents in Hydrocharis dubia (Bl.) Backer leaves under cadmium (Cd) toxicity were studied after 6-day treatment. Cd stress increased putrescine (Put) level and lowered spermidine (Spd) and spermine (Spm) levels. In addition, the activities of ADC, DAO, and PAO were increased, while that of ODC was decreased. Exogenous application of Spd markedly reversed these Cd-induced effects. It also significantly reduced the generation of O2·− and H2O2 and prevented lipid peroxidation. These results suggest that exogenous Spd can enhance the tolerance of H. dubia to Cd. The maintenance of PA homeostasis was necessary for plant metal tolerance.

Exogenous spermidine and spermine enhance cadmium tolerance of Potamogeton malaianus

In order to investigate the effects of spermidine (Spd) and spermine (Spm) on cadmium stress, the content of chlorophyll, hydrogen peroxide (H2O2), malondialdehyde (MDA), soluble protein and proline, the rate of O2·− generation, and activities of antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR)) in Potamogeton malaianus Miq. were measured. Exogenous application of Spd or Spm significantly enhanced the level of proline, retarded the loss of chlorophyll, enhanced photosynthesis, decreased the rate of O2·− generation and H2O2 content, and prevented Cd-induced lipid peroxidation. Spd and Spm also effectively maintained the balance of antioxidant enzyme activities under Cd stress; however, GR activity was found to increase only slightly in response to polyamines (PAs). The antioxidant systems, which were modified by PAs, were able to moderate the radical-scavenging system and to lessen in this way the oxidative stress. These results suggest that both Spd and Spm can enhance Cd tolerance of P. malaianus.