The Adaptable Responses Of Different Cultivars Of Pigeon Pea And Corresponding Mechanisms Under P-deficiency Stress And Al-toxicity Stress

Phosphorus (P) deficiency and aluminum (Al) toxicity are major factors limiting plant growth in acid soils, and the two factors always occur together. It is considered that pigeon pea is one of potential crops growing in acid soils. In present study, Al-tolerance of seven pigeon pea cultivars (MD1, MD2, MD3, MD4, MD5, MD6 and MD7) was investigated. The result showed that there was great genetic variation in Al tolerance among different cultivars of pigeon pea. Al-tolerance in MD7 and MD2 was showed to be the most, followed by that in MD6, MD1, MD3, MD4 and MD5 in order. So MD7, MD2 and MD5 were chosen for the studies on the reactions and corresponding mechanisms of pigeon pea in response to P deficiency and Al toxicity in hydroponics system. The results indicated as follows.Under low P condition, root morphology of pigeon pea occurred to transfigure. Total root length, lateral root growth and root biomass were increased, as well as root shoot ratio. Activities of acid phosphatase (APA) in the root apices and that secreted from the root apices were greater under Pdeficiency than those under P sufficiency. And activities of APA of different pigeon pea cultivars had positive correlations to those biomass and phosphorus uptake. P-deficiency stress induced malic acid exudation from pigeon pea roots. Mucilage attached to the root apices played an effective role in alleviating Al toxicity to root apices. And Al-toxicity stress induced roots of pigeon pea to secrete citric acid specifically. The higher Al concentration (0, 20, 30, 50 umol L-1) , the more citric acid exuded. Under both low-P and Al-toxicity stress, activity of APA in root apices was decreased obviously, but that secreted from root apices was enhanced slightly. And organic acid exudation was increased significantly.MD7 had the highest total biomass and phosphorus uptake under low P condition, implied that MD7 was a P-efficiency genotype. Correspondingly, root biomass, activities of APA, and ability of absorbing and utilizing P in MD7 were largest. On the contrary, those of MD5 were lowest, which suggested MD5 belonged to P-inefficiency genotype. And MD2 stayed in the middle of P efficiency.MD7 and MD2, whose root apices were stained with hematoxylin after Al treatment, were showed to be Al-tolerance genotypes, while MD5 belonged to intermediate Al-tolerance genotype. After the removal of the mucilage attached to the root apices, the elongation of MD2 roots was subjected to the most critical inhibition. Under 50 umol L-1 Al stress, citric acid exudation from roots of MD2 was larger than that of MD5 and MD7. So the alleviativeeffects of mucilage and citric acid to Al toxicity might be important mechanisms for MD2 to deal with Al toxicity. Under both P-deficiency and Al-toxicity stress, the increased exudations of citric acid and oxalic acid from MD7 roots were larger than those from others.In conclusion, MD7 was a cultivar of tolerating both P deficiency and Al toxicity well, which could adapt to acid soils mostly. MD5 was the lowest tolerant cultivar among them, while MD2 was a intermediate P-efficiency and Al-tolerance cultivar.