The Role Of Exogenous Nitric Oxide In Modulating Aluminum-Induced Oxidative Stress In Cassia Tora L.

Nitric oxide (NO) is a bioactive molecule firstly described in mammals as a major messenger in the cardiovascular, immune and nervous system. NO has also been suggested a putative role as an anti-stress molecule in plants by reason of its ability to reduce the oxidative injury produced by biotic and abiotic stress such as pathogen attack, drought, salty, UV-B radiation and heavy metal. In the present study, we evaluated a putative role of NO in modulating aluminum (Al)-induced oxidative stress in the root of C. tora.Al treatment caused the root growth inhibition and induced the high level of H2O2, malondialdehyde (MDA) and membrane permeability in roots of C. tora, suggesting that the oxidative stress in plants was trigged by Al. Pretreatment with 0.4 mmol/L NO donor sodium nitroprusside (SNP) before Al exposure reduced the Al-induced root growth inhibition. However, this effect could be cancelled by a nitric oxide scavenger cPTIO [2-(4-carboxy-2-phenyl-4,4,5,5 -tetramethylinidazoline-l-oxyl-3-oxide)]. SNP also reduced H2O2 and MDA contents, suggesting a protective ability of NO against oxidative damage. Pretreatment with SNP reduced Al accumulation in roots of C. tora, suggesting that NO confered Al tolerance by reducing lipid peroxidation and plasma membrane damage.To further understand the putative role of NO in protecting against Al-induced oxidative damage, we measured the activities of several antioxidant enzymes and observed that Al induced increases in CAT, SOD and POD activities. However, pretreatment with 0.4 mmol/L SNP caused a decrease in Al-induced SOD and CAT activities but an increase in POD activity. In this case, NO probably reduced the oxidative injury by enhancing POD activity for removal of H2O2.We also measured the activity of lipoxygenase (LOX) and found that treatment with 20 μmol/L Al caused an increase in LOX activity. However, pre-application of NO donor SNP had a negative effect on the activity. These results indicated that NO inhibited Al-induced LOX activity and reduced lipid peroxidation catalyzed by LOX, and thereby, reduced oxidative damage.NO interaction with Al-induced oxidative stress in C. tora might be described as following process: NO enhanced POD activity, decreased LOX activity, and resulted in improved capacity for scavenging H2O2 and thus reduced lipid peroxidation.