| Spermine (Spm), spermidine (Spd) and their diamine obligate precursor putrescine (Put) are micro molecular aliphatic polycations that are ubiquitous in all plant cells, participate in a wide range of physiological and biochemical processes. Nitric oxide (NO) is a physiologically reactive substance, as a plant cell signaling molecule, it play an important role in plant root growth and other physiological processes. Our previous results suggest that both polyamines and NO promote the seed germination and the development of lateral roots in lettuce, and that polyamines can induce NO production in plant tissues. However, there is no report about what changes the seed storage substances and corresponding hydrolases are in seed germination after treatments with exogenous polyamines and NO ? In this study we choose a normal breed of lettuce seed (Lactuca sativa L. cv. Guasihong) as an experimental material to investigate the role of polyamine and NO in the process of lettuce seed germination. The results are as follows:Treatments with exogenous polyamines at low concentrations promoted early germination of lettuce seed. Spm was more effective than Put, but less than Spd. The detection of time course of seed germination showed that the promoting effect of polyamines disappeared after 48 h. In addition, treatment with 0-0.1 mM SNP markedly promoted seed germination with optimal concentration at 0.1 mM, whereas 0.2 mM SNP failed to increase germination. The detection of time course of seed germination showed that the promoting effect of 0.1 mM SNP on the germination of lettuce seed was obvious in 36 h after treatment, and this effect disappeared in 48 h.The detection of reserve changes showed that the protein, crude fat and starch contents decreased and soluble sugar increased gradually with seed germination. In contrast with the control, the protein, crude fat and starch contents significantly declined after treatments with 0.5 mM polyamines. The differences between polyamine treatments were not observed and only 0.5 mM Spd had strong effects on the decline of starch content and the increment of soluble sugar. Treatments with polyamine synthetic inhibitors (MGBG and CHA) could retard the decreases of the protein and starch contents in various degrees, whereas the crude fat content was inhibited by MGBG.The imbibition with NO donor SNP could obviously reduce starch content and increase soluble content, and 0.05 mM SNP had significant effects. The detection of time course showed that the contents of the protein, crude fat and starch declined and the soluble sugar increased gradually. After treatments with 0.1 mM SNP, the protein and crude fat contents further decreased, but no differences occurred in contrast with the control. Conversely, only starch content decreased and the soluble sugar increased rapidly, the differences after treatments for 24 h were obvious as contrast with the control. The similar effects of the biosynthetic inhibitor of nitric oxide (1.0 mM tunsgate and 0.2 mM L-NAME) on seed reserves were observed. They both had a certain retarding effect on the decline of the protein and the crude fat contents though with no differences as contrast to the control, while the starch degradation was strongly inhibited and the soluble sugar content reduced only after treatment for 36 h.The determination of the activities of various hydrolases during seed germination showed that the activities ofα-amylase, nitrate reductase and lipase increased gradually with lettuce seed germination, andβ-amylase activity declined after its activity reached the peak at 36 h. The imbibition with exogenous polyamines at different concentrations could significantly enhancedα-amylase andβ-amylase activities with optimal concentration at 0.5 mM, and Spd was most effective. Lipase activity was also increased but the polyamine concentrations over 0.5 mM were needed, while nitrate reductase activity reduced. In addition, different kinds of polyamines showed different effects, the promoting effects of Spd and Put onα-amylase,β-amylase and lipase activities were more effective than Spm.In agreement with these results, treatments with the polyamine biosynthetic inhibitors, CHA and MGBG, could significantly inhibit the activities ofα-amylase andβ-amylase activities. The inhibitory effect of CHA onβ-amylase activities was more obvious and better than MGBG. Similarly nitrate reductase activity was also strongly retarded by CHA and MGBG at different concentrations. Unlike with CHA, MGBG imbibition could slightly promote lipase activity though with no difference as contrast with the control.The results caused by NO donor SNP treatment showed that the activities ofα-amylase andβ-amylase in lettuce seeds were promoted by low SNP, but inhibited by high SNP concentration. The nitrate reductase activity was also improved with optimal concentration at 0.1 mM SNP. The concentration exceeding 0.1 mM SNP exhibited a promotive effect on lipase activity. The detection of time course showed that the activities ofα-amylase, nitrate reductase and lipase increased with lettuce seed germination, and significantly enhanced by 0.1 mM SNP treatment.β-amylase activity declined after it reached the peak at 36 h and also improved by SNP.After treatments with NO biosynthetic inhibitor tunsgate and L-NAME, the nitrate reductase and lipase activities strongly reduced, the effects occurred only at 12 h after inhibitor treatments. There was difference of inhibitory effect ofα-amylase on acting time between tunsgate and L-NAME,. Tunsgate showed its inhibitory effect at 12 h after seed germination, while L-NAME behaved at 36 h.β-amylase activity decreased only at 24h after L-NAME treatment.Altogether, Polyamines and nitric oxide may regulate the germination of lettuce seeds through manipulating the activities ofα-amylase,β-amylase, nitrate reductase and lipase and affecting reserve degradation. Treatment with polyamine and nitric oxide mainly caused starch degradation and soluble sugar increment. |
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