Endomorphins were recently identified as endogenous ligands with high selectivity for mu opioid receptors. We have characterized the ability of endomorphins to bind to and functionally activate the cloned human mu opioid receptor. Both endomorphin-1 and endomorphin-2 exhibited binding selectivity for the mu opioid receptor over the delta and kappa opioid receptors. Both agonists inhibited forskolin-stimulated increase of cAMP in a dose-dependent fashion. When the mu opioid receptor was coexpressed in Xenopus oocytes with G proteinactivated K + channels, application of either endomorphin activated an inward K + current. This activation was dosedependent and blocked by naloxone. Both endomorphins acted as full agonists with efficacy similar to that of [D-Ala P ,N-MePhe R ,Gly-ol S ]enkephalin (DAMGO). These data indicate that endomorphins act as full agonists at the human mu opioid receptor, capable of stimulating the receptor to inhibit the cAMP/adenylyl cyclase pathway and activate G-protein-activated inwardly rectifying potassium (GIRK) channels.z 1998 Federation of European Biochemical Societies.

Biochar, as a soil conditioner, has been widely used to promote the growth of maize, but most of the current research is short-term experiments, which limits the research on the long-term effects of biochar, especially the physiological mechanism of biochar on maize growth in aeolian sandy soil is still unclear. Here, we set up two groups of pot experiments, respectively after the new biochar application and one-time biochar application seven years ago (CK: 0 t ha-1, C1: 15.75 t ha-1, C2: 31.50 t ha-1, C3: 63.00 t ha-1, C4: 126.00 t ha-1), and planted with maize. Subsequently, samples were collected at different periods to explore the effect of biochar on maize growth physiology and its after-effect. Results showed that the plant height, biomass, and yield of maize showed the highest rates of increase at the application rate of 31.50 t ha-1 biochar, with 22.22% increase in biomass and 8.46% increase in yield compared with control under the new application treatment. Meanwhile, the plant height and biomass of maize increased gradually with the increase of biochar application under the one-time biochar application seven years ago treatment (increased by 4.13%-14.91% and 13.83%-58.39% compared with control). Interestingly, the changes in SPAD value (leaf greenness), soluble sugar and soluble protein contents in maize leaves corresponded with the trend of maize growth. Conversely, the changes of malondialdehyde (MDA), proline (PRO), catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) manifested an opposite trend to the growth of maize. In conclusion, 31.50 t ha-1 biochar application can promote the growth of maize by inducing changes in its physiological and biochemical characteristics, but excessive biochar application rates ranging from 63.00-126.00 t ha-1 inhibited the growth of maize. After seven years of field aging, the inhibitory effect of 63.00-126.00 t ha-1 biochar amount on maize growth disappeared and changed to promoting effect.

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Conditioning alkaline soil with acidic phosphorus-rich biochar might contribute to achieving sustainable phosphorus (P) use and residue management. In this study, acidic phosphorus-rich biochar was prepared from halophyte species biochar (HBC) by the modification of H3PO4 (P-HBC) and H4P2O7 (PA-HBC). The P combination method and fractions in biochars were characterized, and the effects of biochars on P fractions in different types of alkaline soil were examined with incubation experiments. The results showed that the pH values of P-HBC (3.31) and PA-HBC (2.17) decreased significantly, and the total P content increased to 4.66 g·kg− 1 and 5.24 g·kg− 1, respectively. The spectral analysis confirmed the doping of P and acid groups in biochar. The addition of modified biochars in alkaline soils will makes the soil tend to be neutral. Sequential extraction of soil P confirmed that biochars application facilitated the transformation of stable P into active fractions, with greater effects from modified biochars than HBC. Activation mechanism of biochar to soil P fractions varies from soil types. Overall, acidic phosphorus-rich biochars can be employed to improve alkaline soil properties and increase P activity.

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