| Glycinebetaine is one of the most important osmotic-regulating chemicals in higher plants and is considered to be involved in plant response. The study was carried out systematically compare the varying characters of multi-index under drought stress and scientifically determine the reasonableness of the index for use. Also, this research can provide some basic data for further studying the biological water saving techniques of citus.Compared with the treament of serving with plantiful water, leaves of trifoliate orange (Poncirus trifoliata (L.) Raf.) and tangerine (Citrus tangerine Hort. ex Tanaka) seedlings were sprayed with water, 100mg·l-1 glycinebetaine resolution, 250mg·l-1 glycinebetaine resolution and 500mg·l-1 glycinebetaine resolution respectively before experiment beginging. The results suggested that, foliar-applied glycinebetaine could decrease osmotic potential and improve the capability of water absorbency as a compatible solute. With decreasing soil moisture, exogenous glycinebetaine sprayed on leaves in Citrus seedlings was able to improve glycinebetaine content. The results of this experiment showed that a low concentration (100mg·l-1) exogenous giycinebetaine is the bestest one.The results showed that exogenous giycinebetaine was able to mentain higher photosythesis ability of leaves under mild and moderate water stress. With decreasing soil moisture, exogenous glycinebetaine sprayed on leaves in Citrus seedlings was able to improve proline and carbohydrate content, improve soluble sugar and proline contents, improve glucose, fructose and sucrose contents, improve photosynthetic pigment content, improve dry matter, decrease H2O2, O2- and MDA content, and reduce membrane damage under water stress. The results of this experiment also showed that a low concentration (100mg·l-1) exogenous glycinebetaine has better effect than high concentration (250mg·l-1) and concentration (500mg·l-1) exogenous glycinebetaine.
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