A Study On Al-Induced Secretion Of Organic Acids From Roots Of Both Stylo And Rye And Correspond Regulation Mechanism

As an important forage legume, Stylo (Stylosanthes spp) has been widely planted in acid soil areas. However, there is still no study on aluminum-tolerance of stylo and its tolerance mechanism at present. The present thesis showed that root elongation of alfalfa (Medicago sativa L.) during a 24-h period was inhibited by 80% by the exposure to 5 umol L-1 Al and its roots was obviously stained by eriochrome cyanine R (ER); however, the roots of stylo need to be exposure to 30umol L-1 Al in order to get obviously stained with its root elongation was inhibited by 68%, which shows, for stylo, its ability of tolerance to aluminum is strong. According to analysis of root exudates by HPLC, aluminum induced roots of stylo to secret citrate and its secretion increased with Al concentration treated (0, 10, 20, 50 umol L-1) and the period of exposure to Al (6, 12, 18, 24 h), which indicated that Al-induced secretion of citrate is an important mechanism for stylo to resist the toxicity of aluminum.On the other hand, although in recent years more and more researches concluded that Al-induced secretion of organic acids from roots is a main mechanism for some Al-tolerance plants, so far in field of study the knowledge of the mechanism responsible for Al-induced secretion of organic acids is still very limited. In present study, taking rye (Secale cereale L.) which can secreted citrate and malate as study object, I explored the regulation of organic acid secretion from roots . Secretion of citrate and malate was obviously inhibited by anion channel inhibitors such as niflumic acid and phenlglyoxal. Five umol L-1 salicylic acid (SA) evidently promoted Al-induced secretion of citrate but inhibited secretion of malate. Ca2+ channel inhibitors (La3+, verapamil), greatly inhibited the secretion, while K+ channel inhibitors (CsCl2, tetraethylammonium chloride) has no obviously inhibit to the secretion. As a special chelator of Ca2+, EGTA of 250, 500umol L-1 inhibited secretion of citrate clearly, while had no distinct inhibition to malate secretion. All the above experimental evidence shows that anion channel involve in Al-induced secretion of organic acid from rye roots. Salicylic acid and Ca2+ seem to involve in the process, while K+ has no direct regulation to the secretion of organic acids.