The physiological dormancy of sunflower (Helianthus annuus) embryos can be overcome during dry storage (after-ripening) or by applying exogenous ethylene or hydrogen cyanide (HCN) during imbibition. The aim of this work was to provide a comprehensive model, based on oxidative signaling by reactive oxygen species (ROS), for explaining the cellular mode of action of HCN in dormancy alleviation. Beneficial HCN effect on germination of dormant embryos is associated with a marked increase in hydrogen peroxide and superoxide anion generation in the embryonic axes. It is mimicked by the ROS-generating compounds methylviologen and menadione but suppressed by ROS scavengers. This increase results from an inhibition of catalase and superoxide dismutase activities and also involves activation of NADPH oxidase. However, it is not related to lipid reserve degradation or gluconeogenesis and not associated with marked changes in the cellular redox status controlled by the glutathione/glutathione disulfide couple. The expression of genes related to ROS production (NADPHox, POX, AO1, and AO2) and signaling (MAPK6, Ser/ThrPK, CaM, and PTP) is differentially affected by dormancy alleviation either during afterripening or by HCN treatment, and the effect of cyanide on gene expression is likely to be mediated by ROS. It is also demonstrated that HCN and ROS both activate similarly ERF1, a component of the ethylene signaling pathway. We propose that ROS play a key role in the control of sunflower seed germination and are second messengers of cyanide in seed dormancy release.
De part ment of Plant Phys i ol ogy, War saw Ag ri cul tural Uni ver sity, Ab stractAllelopathy is de fined as mech a nism of plant-plant, plant-micro or gan isms, plant-vi rus, plant-in sect, and plant -soil-plant in ter ac tions me di ated by plant-or mi cro or ga n ism-pro duced chem i cals re leased to the en vi ron ment. The ma jor ity of allelochemicals are sec ond ary me tab o lites and among oth ers be long to terpenoids, phe no lic com pounds, or ganic cyanides and longchain fatty ac ids. The ac tion of allelo chemicals in tar get plant is di verse and af fects a large num ber of bio chem i cal re actions re sult ing in mod i fi ca tions of dif fer ent phys i o log i cal func tions. Thus the re sults of allelochemical ac tion can be detected at dif fer ent lev els of plant or ga ni za tion: mo lec u lar, struc tural, bio chem i cal, phys i o log i cal and eco log i cal. En zyme ac tiv i ties, cell di vi sion and ultrastructure, mem brane per meabil ity, ion up take and as a con se quence plant growth and devel op ment are mod i fied by allelochemicals. Sig nif i cant effects on pho to syn the sis and res pi ra tion are the best-char ac terized re sults of allelopathic in ter ac tions. More over allelopathic com pounds seem to in duce a sec ond ary ox i da tive stress expressed as en hanced free rad i cal pro duc tion and in duc tion of cel lu lar an ti ox i dant sys tem. Plant sur vival un der allelopathy stress con di tions de pends on plant de fense lead ing to allelochemical detoxication, the pro cess which may go on in par al lel to cell defense re ac tion to ox i da tive stress.The ar ti cle pres ents some as pects of the cur rent knowl edge regard ing mech a nisms of the allelopathy phe nom e non. The allelopathy is a com plex prob lem, thus com pre hen sive un derstand ing of allelochemical mode of ac tion re quires fur ther inves ti ga tion and still re mains an open ques tion.
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