Objectives Phosphate (Pi) deficiency affects the growth and production of wheat. Many contrasting Pi-efficient wheat genotypes have been developed for improving yield in low-Pi soils. They are also important to sustainable agricultural systems. This study compares the response of seedlings of high and low Pi-efficient wheat cultivars to Pi deficiency.
Methods A high Pi-efficient wheat genotype ‘Xiaoyan 54’ (XY) and a low Pi-efficient genotype ‘Chinese Spring’ (CS), were selected for a hydroponic experiment. The treatments were sufficient Pi (+P), Pi deficiency (−P), and the resupply of Pi after its deprivation (RP). The time-course response of the wheat seedlings to Pi deficiency was analyzed at morphological and physiological levels. Further, the expression of Pi-starvation responsive genes in wheat seedlings of the two contrasting Pi-efficient genotypes was recorded.
Results The shoot biomass in XY was lower than in CS, while the root biomass showed no significant difference between the two genotypes regardless of Pi supply. Correspondingly, the root-shoot ratio in XY was higher than in CS. Although Pi and total P concentrations in the roots and shoots of wheat seedlings gradually decreased with Pi starvation, no significant difference was observed between the two genotypes. When Pi was resupplied, its concentration in the Pi-starved seedlings immediately increased. The Pi concentration in the roots and shoots of XY was higher than in CS. TaIPS1 and TaSPX3 – the sensors to Pi-starvation response in plants – were highly induced at the transcriptional level in tandem with the reduction of Pi concentration in the plants. However, the expression of these genes declined when Pi was resupplied in the Pi-starved seedlings. At the early stage of Pi starvation, the expression of these genes in CS was higher than in XY. This was reversed due to long-term Pi depletion, suggesting that the low Pi-efficient genotype was more sensitive to Pi starvation. In contrast, the expression levels of TaPHT1.1/9 and TaPHT1.10 were inhibited at the initial stage of Pi deprivation but highly induced under long-term Pi starvation. The resupply of Pi more highly induced the expression levels of two TaPHT1 genes than Pi sufficient and deficient treatments. Concerning the two different genotypes, the expression of TaPHT1.1/9 was (P < 0.05) higher in XY than CS in the long-term Pi starvation treatment, while the transcripts of TaPHT1.10 showed no significant (P > 0.05) difference between them. In addition, Pi starvation (P < 0.05) accelerated the Fe accumulation on the root surface of CS but showed a minimal effect on XY.
Conclusions The high Pi-efficient genotype (XY) had a larger root-shoot ratio and stronger Pi uptake. In contrast, the low Pi-efficient genotype (CS) accumulated more Fe on the root surface under Pi starvation. Therefore, it is valuable to explore further how Fe accumulation on the root surface affects the efficiency of uptake and utilization of Pi.
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