Role Of Extracellular ATP (eATP) In Wheat Seed Vigor And Germination Rate Regulation And Its Mechanism

Seed viability and germination rate are important indicator of seed quality. Previous studies have shown that extracellular ATP (eATP) not only regulates various plant growth and development processes, but also mediates multiple response of plant to stress stimuli. However, up to data, the role and underlying mechanism of eATP in regulation of seed viability and germination rate remain incomplete clear. In the present study, using wheat (Triticum aestivum L.) seed as materials, the role of eATP and the relationship between eATP and hydrogen dioxide (H2O2) or nitric oxide (NO) in regulation of seed viability and germination rate were investigated. The main results are as follows:1. ATP and 2’(3’)-O-(4-Benzoy(benzoyl) adenosine 5’-triphosphate triethylammonium) (Bz-ATP), a nonhydrolyzable analog of ATP, significantly increased seed vigor and germination rate, whereas β,γ-methyleneadenosine 5’-triphosphate (β,γ-meATP), a competitive inhibitor of eATP, which can excluse eATP from its binding sites, glucose-hexokinase (HK), a cell-impermeant traps, and Suramin, an eATP receptor antagonist, remarkably reduced seed vigor and germination rate. The results clearly indicate that eATP has a vital role in the regulation of seed viability and germination rate.2. Diphenylene iodonium (DPI), which is an inhibitor of NADPH oxidase, largely abolished the inductive effect of Bz-ATP on seed viability, germination rate and H2O2 production in embryo cells, so did ascorbic acid (ASA), an important reducing substrate for H2O2 removal, and catalase (CAT), a H2O2 scavenger enzyme. However, H2O2 restored the inhibitory effect of DPI on seed viability and germination rate, but did not rescue those of ASA and CAT, in the seeds treated with Bz-ATP. The results provide evidence that H2O2 generated by NADPH oxidase is involved in the effect of eATP on seed viability and germination rate.3. NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthase (NOS), sodium tungstate (Na2WO4), an inhibitor of nitrate reductase (NR), and 2-(4-Carboxyphenyl)-4,4,5,5-tetramethy limidazoline-1-oxyl-3-oxide (c-PTIO), a NO scavenger, obviously inhibited the effect of Bz-ATP on seed viability, germination rate and NO generation in embryo cells. However, sodium nitroprusside (SNP), a NO-releasing compound, largely prevented the inhibitory effects of L-NAME and Na2WO4 on seed viability and germination rate, but did not rescue those of c-PTIO, in the seeds treated with Bz-ATP. The results not only show that NO mediates the inductive effect of eATP on seed viability and germination rate, and suggest that both NOS and NR are responsible for eATP-induced NO synthesis.4. SNP rescued the inhibitory effects of DPI, ASA and CAT on seed viability and germination rate, but H2O2 did not restore those of L-NAME, Na2WO4 and c-PTIO, in the seeds treated with Bz-ATP. Similarly, DPI, ASA and CAT significantly inhibited Bz-ATP-induced NO production, but L-NAME, Na2WO4 and c-PTIO had no effect on Bz-ATP-triggered H2O2 production in embryo cells. The results show that H2O2 mediates the effect of eATP on seed viability and germination rate via inducing NO production.