二·閱讀測驗::
 Phosphorus is an important nutrient for crop productivity. More than 60% of the total phosphorus in cereal crops is finallyallocated into the grains and is therefore removed at harvest. This removal accounts for 85% of the phosphorus fertilizersapplied to the field each year. However, because humans and non-ruminants such as poultry, swine and fish cannot digestphytate, the major form of phosphorus in the grains, the excreted phosphorus causes eutrophication of waterways. A reductionin phosphorus accumulation in the grain would contribute to sustainable and environmentally friendly agriculture. Here wedescribe a rice transporter, SULTR-like phosphorus distribution transporter (SPDT), that controls the allocation of phosphorusto the grain. SPDT is expressed in the xylem region of both enlarged- and diffuse-vascular bundles of the nodes, and encodes aplasma- membrane-localized transporter for phosphorus. Knockout of this gene in rice (Oryza sativa) altered the distribution ofphosphorus, with decreased phosphorus in the grains but increased levels in the leaves. Total phosphorus and phytate in thebrown de-husked rice were 20-30% lower in the knockout lines, whereas yield, seed germination and seedling vigour were notaffected. These results indicate that SPDT functions in the rice node as a switch to allocate phosphorus preferentially to thegrains. This finding provides a potential strategy to reduce the removal of phosphorus from the field and lower the risk ofeutrophication of waterways.
                                                                                        From Yamaji et al. 2017, Nature, 541:92-95.
【題組】16. What happens to the major portion of phosphate fertilizers applied to rice crops?
(A) Phosphate precipitates and becomes unavailable.
(B)Rain provokes the leaching of phosphate into underground water, causing eutrophication.
(C) Rice plants take up and store phosphate it in their grains. It is then removed from the field when the grains are harvesteD.
(D) 85% of the phosphate is not taken up by plants and stays trapped in phytates in the soil.