The Production And Signal Mechanism Of NO Molecule In Bidens Pilosa Under Pb Stress

Lead (Pb) is an important pollution source of heavy metals. Exogenous nitric oxide (NO) is a common signal molecule in biology regulating plant growth and it has been shown that it participates in all kinds of plant responses to Pb stress, Bidens pilosa L. is an ideal germplasm resource repairing soils contaminated by Pb. The effects of NO on routes of NO production, the membrane lipid peroxidation, osmotic regulation substances, antioxidant enzyme activities, plant growth, Pb cumulant and active oxygen metabolism in leaves, stems and roots of B. pilosa L. seedlings under Pb (600 ?mol/L lead nitrate) stress for 3 d were studied by determining relative electrical conductivity (REC), contents of malondialdehyde (MDA), hydrogen peroxide (H2O2), superoxide anion (O2O generating rate, contents of proline (Pro), soluble protein (SP), carotenoid (Car), activities of ascorbicacidper oxidase (APX), glutathione reductase (GR), peroxidase (POD), catalase(CAT), super oxidedismutase(SOD), nitric oxide synthase (NOS), nitrate reductase (NR), nitric oxide (NO) levels, nitrite ion(NO2-) contents in the leaves,stems and roots of sixty days old seedlings of B. pilosa pretreated with an exogenous NO donor, a nitric oxide synthase inhibitor (L-NAME), a nitrate reductase inhibitor (NaN3) and a NO scavenger (c-PTIO) to explore the role and mechanism in B. pilosa seedlings under Pb stress, to enhance B. pilosa seedlings resistance to Pb and its better application in Phytoremediation of Pb contaminated soil. The results indicated:(1) 600 mg/L Pb significantly increased NO, NO2- and Car contents, NOS and NR activities of B. pilosa. SNP significantly increased NO contents, SNP also notably enhanced NOS activities in leaves and roots and Car contents in leaves and stems of B. pilosa seedlings, which indicated SNP could be via NOS and Car routes to induce NO production.while c-PTIO could remarkably reduce NO contents, NOS and NR activities and Car contents, which suggested c-PTIO reduced NO contents via NR, NOS and Car routes. NaN3 could significantly lower NR activities, and NaN3 remarkably NO contents in leaves, stems and roots of B. pilosa seedlings; L-NAME could significantly lower NOS activities, and L-NAME remarkably NO contents in leaves, stems and roots of B. pilosa seedlings; which indicated NR and NOS could participate in production of NO of B. pilosa seedlings under Pb stress.(2) 600 mg/L Pb notably enhanced activities of APX, CAT, SOD, GR and POD, remarkably promoted the synthesis of Pro in leaves and roots, SS in stems and roots,800 mg/L Pb remarkably promoted the synthesis of Pro in stems.Those suggested B. pilosa seedlings could generated to adjust the antioxidant enzyme system and promote the synthesis of Pro and SS to resist Pb harm.600 mg/L Pb notably increased fresh weight, dry weight, plant height, main-root length, the maximum lateral root length and lateral root net increase and Pb cumulant of B. pilosa, of which Pb cumulant is 888.77 mg/kg.(3) SNP could lead B. pilosa seedlings to produce NO.300 mol/L SNP significantly promoted the synthesis of Pro, SP and Car. The effects of SNP on activities of antioxidant enzymes in leaves, stems and roots of B. pilosa seedlings was complex.200 ?mol/L SNP significantly enhanced activities of APX in leaves and stems and GR in stems,300 ?mol/L SNP significantly enhanced activities of POD in leaves, and 1000 ?mol/L SNP significantly enhanced activities of CAT in stems and roots and SOD in leaves,300 ?mol/L SNP remarkably reduced REC, contents of MDA, H2O2 and O2- generating rate in leaves, stems and roots, remarkably increased fresh weight, dry weight, plant height, main-root length, the maximum lateral root length, lateral root net increase and Pb cumulant of B. pilosa seedlings under Pb stress. It was shown that appropriate concentration of exogenous NO could effectively protect the membrane system stability and alleviate the harm of Pb stress on B. pilosa seedlings. But the effects of exogenous NO had two sides, namely the low concentration eased and the high damaged, of which mitigation effects of 300 ?mol/L SNP treatment on B. pilosa seedlings under Pb stress was the most remarkable. Pb cumulant is different in leaves, stems and roots, of which roots is greater than stems and stems is greater than leaves.(4) NaN3 and L-name remarkably increased NO contents. NaN3 significantly reduced APX and SOD activities in leaves and stems, CAT activities, POD activities, notably promoted the synthesis of Pro, SP in leaves and roots and Car in stems, remarkably increased REC in stems, contents of MDA in roots and H2O2 in stems, O2- generating rate in leaves and stems, notably reduced fresh weight, dry weight, plant height, main-root length, the maximum lateral root length and lateral root net increase of B. pilosa seedlines under Pb stress. L-NAME significantly reduced CAT activities, SOD activities in leaves and stems, POD activities in stems and roots, notably promoted the synthesis of Pro, SS in stems, remarkably increased contents of H2O2 in leaves, O2- generating rate in leaves, stems and roots, notably reduced fresh weight, dry weight, plant height, main-root length, the maximum lateral root length and lateral root net increase of B. pilosa seedlings under Pb stress. c-PTIO singnificantly reduced APX in leaves and roots, CAT activities, SOD and POD activities in leaves and roots, remarkably restrain Pro contents, SP contents in leaves and roots, SS contents in leaves and stems and Car in stems, notably increased REC in roots, MDA in stems and roots,O2-generating rate, H2O2 contents in leaves and roots, remarkably reduced fresh weight, dry weight and main root length. Those results suggested that NR? NOS and endogenous NO could ease harm of Pb and promote plant growth by adjusting the antioxidant enzyme system and osmotic regulation substances, That NR and NOS participated in resitance of Pb was possible related to them participating to production of NO. In a word, NO could enhance B. pilosa resistance to Pb and NO had well prospect in phvtoremediation of Pb contaminated soil with B.pilosa seedlings.