The reduced availability of nitrogen sources in seawater leads to discoloration of the edible red seaweed Pyropia yezoensis and induces the expression of genes encoding ammonium, nitrate and urea transporters. In the present study, we demonstrate that low temperatures can also cause discoloration of this economically important seaweed. Thus, we addressed regulatory mechanisms of cold-inducible discoloration. When P. yezoensis thalli were incubated at 0, 5 and 10°C, the thalli exhibited retarded growth and discoloration, along with reduced phycoerythrin contents. Fertilization with nitrogen sources did not recover this discoloration at 0°C, suggesting that defects in nitrogen absorption cause low temperature-induced discoloration. The expression levels of many nitrogen transporter genes were reduced at low temperature. We propose that low temperature-mediated repression of ammonium, nitrate and urea transporter gene expression promotes the reduced absorption of nitrogen sources in P. yezoensis, thereby leading to discoloration. This process is different from the well-known mechanism underlying discoloration in P. yezoensis under nitrogen-deficient conditions at normal culture temperature.

海水中氮源的可用性降低导致可食用的红海藻斑节菜变色，并诱导编码铵，硝酸盐和尿素转运蛋白的基因表达。在本研究中，我们证明了低温也可能导致这种经济上重要的海藻变色。因此，我们讨论了冷诱导的变色的调节机制。当在0、5和10 °C孵育yezoensis拟南芥时，该拟南芥显示出生长迟缓和变色，同时藻红蛋白含量降低。氮源施肥无法在0 °C时恢复这种变色，表明氮吸收缺陷会导致低温引起的变色。低温下许多氮转运蛋白基因的表达水平降低。我们建议低温介导的氨，硝酸盐和尿素转运蛋白基因表达的压制促进野牛假单胞菌氮源吸收减少，从而导致变色。此过程不同于众所周知的机制，即在正常培养温度下在缺氮条件下，紫叶假单胞菌会发生变色。