Selection for phosphorus （P）-efficient genotypes and investigation of physiological mechanisms for P-use efficiency in maize has mainly been conducted at the seedling stage under controlled greenhouse conditions. Few studies have analyzed characteristics of plant growth and yield formation in response to low-P stress over the whore growth period under field conditions. In the present study, two maize inbred lines with contrasting yield performances under low-P stress in the field were used to compare plant growth, P uptake and translocation, and yield formation. Phosphorus accumulation in the P-efficient line 154 was similar to that of line 153 under high-P. Under low-P, however, P uptake in line 154 was three times greater than that in line 153. Correspondingly, P-efficient line 154 had a significantly higher yield than P-inefficient line 153 under low-P conditions （Olsen-P=1.60 mg kg-1）, but not under high-P conditions （Olsen-P=14.98 mg kg-1）. The yield difference was mainly due to differences in the number of ears per m2, that is, P-efficient line 154 formed many more ears under low-P conditions than P-inefficient line 153. Ear abortion rate was 53% in the P-inefficient line 153, while in line 154, it was only 30%. Low-P stress reduced leaf appearance, and delayed anthesis and the silking stage, but increased the anthesis-silking interval （ASI） to a similar extent in both lines. The maximum leaf area per plant at silking stage was higher in P-efficient line 154 than in P-inefficient line 153 under both P conditions. It is concluded that low-P stress causes intense intraspecific competition for limited P resources in the field condition which gives rise to plant-to- plant non-uniformity, resulting in a higher proportion of barren plants. As soon as an ear was formed in the plant, P in the plant is efficiently reutilized for kernel development.
White lupin （Lupinus albus） exhibits strong root morphological and physiological responses to phosphorus （P） deficiency and auxin treatments, but the interactive effects of P and auxin in regulating root morphological and physiological traits are not fully understood. This study aimed to assess white lupin root traits as influenced by P （0 or 250 ~tmol L-1） and auxin （10=8 mol L-1 NAA） in nutrient solution. Both P deficiency and auxin treatments significantly altered root morphological traits, as evi- denced by reduced taproot length, increased number and density of first-order lateral roots, and enhanced cluster-root for- marion. Changes in root physiological traits were also observed, i.e., increased proton, citrate, and acid phosphatase exudation. Exogenous auxin enhanced root responses and sensitivity to P deficiency. A significant interplay exists between P and auxin in the regulation of root morphological and physiological traits. Principal component analysis showed that P availability ex- plained 64.8% and auxin addition 21.3% of the total variation in root trait parameters, indicating that P availability is much more important than auxin in modifying root responses of white lupin. This suggests that white lupin can coordinate root mor- phological and physiological responses to enhance acquisition of P resources, with an optimal trade-off between root morpho- logical and physiological traits regulated by external stimuli such as P availability and auxin.
Protein dephosphorylation mediated by protein phosphatases plays a major role in signal transduction of plant responses to environmental stresses. In this study, two putative protein phosphatases, PvPS2：1 and PvPS2：2 were identified and characterized in bean （Phaseolus vulgaris）. The two PvPS2 members were found to be localized to the plasma membrane and the nucleus by transient expression of PvPS2：GFP in onion epidermal cells. Transcripts of the two PvPS2 genes were significantly increased by phosphate （P1） starvation in the two bean genotypes, G19833 （a P-efficient genotype） and DOR364 （a P-inefficient genotype）. However, G19833 exhibited higher PvPS2：1 expression levels than DOR364 in both leaves and roots during P1 starvation. Increased transcription of PvPS2：1 in response to P1 starvation was further verified through histochemical analysis of PvPS2：I promoter fusion b-glucuronidase （GUS） in transgenic Arabidopsis plants. Analysis of PvPS2：1 overexpression lines in bean hairy roots and Arabidopsis showed that PvS2：1 was involved in root growth and P accumulation. Furthermore, expression levels of two P1 starvation responsive genes were upregulated and the APase activities were enhanced in the overexpressing PvPS2：1 Arabidopsis lines. Taken together, our results strongly suggested that PvPS2：1 positively regulated plant responses to P1 starvation, and could be further targeted as a candidate gene to improve crop P efficiency.
