| Waterlogging is one of the most disastrous natural calamities all over the world,hence understanding waterlogging responses of plants is now thought to be one of themost important topics in plant science. Plants have evolved a number of adaptationmechanisms to cope with the anaerobiosis due to waterlogging. These mechanismsinclude anatomic and morphological and physiological modifications, such asaerenchyma and adventitious root formation which are responsible for thetransportation of oxygen to under water organs to boost their survival rate.Suaeda salsa L.(Chenopodiaceae) is suggested to be a good use in thephytoremediation of saline soils as well as a significant pioneer plant due to itscharacteristics. As a euhylophyte, S. salsa develops numerous adventitious roots andaerenchyma when suffering from waterlogging. The investigation of these responseswould be an avenue for further elucidation of the salt-waterlogging cross-responsivepathways for this stress and also play a pivotal role in keep ecological balance inYellow River Delta.It has been widely demonstrated that nitric oxide (NO) served as a regulatorysignal molecule in plant growth and development and adaptive responses to biotic andabiotic stresses. However, it is still far from clear whether NO is involved inadventitious root formation under waterlogging treatment. On the other hand,although there is a universal cognition that auxin is responsible for adventitious rootformation and there is accumulating evidence of the interaction between NO andauxin in this process, the mechanisms behind this interplay referring to theadventitious root formation under waterlogging still remain elusive.In the present study,60day-old S. salsa seedlings were used to evaluate theeffects of a nitric oxide (NO) donor (sodium nitroprusside, SNP), a NO scavenger theNO scavenger2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-1-oxyl-3-oxide(cPTIO), naphthyl acetic acid (NAA) on adventitious root formation underwaterlogging. The effects of these treatments on endogenous NO levels inadventitious root tip cells were investigated using a NO-specific fluorescent probe,4,5-diaminofluorescein diacetate (DAF-2DA) in association with a fluorescence microscopy.The main results are as following:1. SNP was an appropriate NO donor and contributed to the growth andadventitious root formation of S. salsa seedlings under waterlogging treatment withthe concentration of0.08mmol·L-1. The beneficial effect of SNP would be slight withthe concentration lower than0.08mmol·L-1, and a detrimental effect would occurwith the concentration higher than0.08mmol·L-1.2. Appropriate dose of SNP treatment contributed to the plant growth,adventitious root formation and growth (root number, root length, root activity etc.) aswell as NO content in adventitious root tips of S. salsa seedlings under waterlogging.Moreover, SNP treatments decreased nitrate reductase activity while increased NOSactivity in adventitious roots, which suggested that it was NOS pathway that might beassociated with endogenous NO production. In addition, results showed that SNPenhanced aerenchyma formation in adventitious roots.3. It was shown that NAA was an appropriate auxin donor and contributed to thegrowth and adventitious root formation of S. salsa seedlings under waterloggingtreatment with the concentration of0.5mg·L-1. The beneficial effect of NAA wouldbe slight with the concentration lower than0.5mg·L-1, and a detrimental effect wouldshow up with the concentration higher than0.5mg·L-1.4. With appropriate dose of SNP and NAA treatment, there was an enhancementof plant growth, adventitious root formation and growth (root number, root length,root activity etc.) as well as NO content in adventitious root tips of S. salsa seedlingsunder waterlogging. Furthermore, the application of NO scavenger led to a markedreduction of both NAA and SNP, which indicated that NO could be considered as adownstream effector of auxin signalling in adventitious root formation, which mighthave an essential role in auxin transportion. |
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