Studies Of Nonenzymatic Nitric Oxide Produced By NO₂^-in Maize Seedlings Resistance To Drought And Cadmium Stress

Nitric oxide （NO） can be synthesized by enzymatic or non-enzymatic means. A largenumber of studies have used sodium nitroprusside （SNP） etc as an external source of NO,which has made great contribution for physiological function and signal transductionmechanisms researches of NO-related. Given NO sourced from nitrite （NO₂^-）under acidicconditions at the existing of reducing agent such as L-ascorbic acid （Vc） or reducedglutathione （GSH）, has a great deal of advantages such as convenient source, low cost,suitable for mass production, the present work will discuss the function of non-enzymaticNO₂^--sourced NO, in maize （Zea mays L.） seedlings resisting to drought deprivation, seedgermination and seedling growth tolerance to heavy metal cadmium （Cd） stress. We intend toprovide theoretical guidance to developing NO product for the field crops.The main researchresults are as follows:1) We found that GSNO which is synthesized by Vc+GSH through enhance antioxidantenzymes activity such as superoxide dismutase （SOD）, catalase （CAT）, ascorbate peroxidase（APX） and glutathione reductases （GR）, which in turn decreased both H₂O₂and O₂^-.levels inmaize leaves, and protect membrane lipids escape from over-oxidation. GSNO also canmaintain chloroplast pigments homeostasis, decreased water-losing of detached leaves,enhanced seedling growth. The feasible GSNO concentration is about500μM.2) NO produced by both of two ways could also promote seeds germination which aretreated with1000μM CdCl₂. But the effects rely on dose, that is low concentrations topromote and after the optimal concentration, the promoting effect gradually reduced. ForNaNO₂, the optimal concentration is2000μM and for GSNO is500μM. NO produced cansignificantly promote the growth of roots and shoots of the seed, to improve the germinationrate, germination potential, germination index, enhanced seed vigor.3) Compared with the control, the synthesis of NO could ease yellowing phenomenonof leaves, improve plant height, and to promote the role of lateral roots development; increasethe chlorophyll content of leaves of maize seedlings; improve the activity of SOD, CAT,APX and GR during stress. And the synthesis of NO could effectively alleviate the content of H₂O₂and O₂^-., then decreased the accumulation of MDA and increase of acid-soluble thiol（TAST）, GSH and phytochelatin （PCs）. The optimal concentration is Vc+3000μM NaNO₂and800μM GSNO.