| Under P deficiency stress, a series of physiological and biochemical changes have been studied, such as plant secreted organic acid from roots to activate the unavailable inorganic phosphorus into the available form, some special enzyme and protein which was important to absorb, activate, transport and utilize the phosphorus was induced.This paper studied the growth changes in wheat and barley under P deficiency stress to comparative the variant physiological and biochemical response. And the possible action of endogenous hormones was studied to discuss the initiative mechanism of barley and wheat to adapt low P stress. It can supply some information for the study of enhancing the ability of P deficiency stress tolerance and absorbing valid phosphorus of wheat and barley. The main results were as follows:1.Under P deficiency stress the roots system configuration changes in wheat and barley were studied. The results showed that P deficiency stress induced the roots length elongating, the roots surface area augmenting, the root dry weight and activity of root dehydrogenase increasing. And the root/shoot ratios of wheat and barley were distinct higher than control's. From the study, it was found that the root/shoot ratio and roots length of wheat increased at the early stage of low P stress, but the barley's showed little variation.2.Under P deficiency stress, the membrane lipid peroxidation in wheat and barley was studied. The results showed that the MDA content of barley was far higher than control's at late stage of P deficiency stress, however the wheat's showed little variation. With the same P concentration, SOD activity in wheat and barley was enhanced with the duration of P stress. It could be concluded that P deficiency stress could increase the membrane lipid peroxidation in barley, it affect little the membrane in wheat. The above results probably indicate that thechange of protective enzyme(SOD) activity and the ability of scavenging O were one of the physiological mechanism of deficiency phosphorus tolerance.3.Under P deficiency stress, the changes of protein content and enzyme activity in wheat and barley were studied. The results showed that the soluble protein content was enhanced at the early stage of P deficiency stress, and then decreased. It may because the soluble secretory protein content increased at some stage of P deficiency stress. The ACP activity in wheat and barley enhanced during the P deficiency stress, which could decompose the remanent organic phosphorus in plant to decrease the P deficiency stress. The results of ACP isozyme zymogram analysis showed that P deficiency stress induced barley producing several special bands, but wheat producing only one. With the decrease in P concentration in medium, the ACP isozyume bands activity presented fortified trend.4.Under P deficiency stress, the other changes in barley and wheat were studied. The results showed that the Pro content change was wavy, during the P deficiency stress. The chlorophyll content in wheat increased, but changed very little in barley at late stage of P deficiency stress. P deficiency induced the organic acid accumulating in barley and wheat, which could help plants to secrete organic acid out of roots. Analysis of soluble sugar content indicated that P deficiency stress changed the distribution of carbohydrate between roots and shoots in barley and wheat.5.Under P deficiency stress, the changes of endogenous hormones in barley and wheat were studied. The results showed that different phosphorus stress induced IAA content increasing and it decreased with the increase in P concentration in medium, however the iPA content changes were reverse to IAA. The ABA content changes showed little variation but GA3 concentration increased considerably at the early stage of P deficiency stress. It's probably the part reason of other reaction which could induce the roots system configuration changing. The analysis of different hormones ratio showed that barley and wheat adjust the balance of hormones to adapt...
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