Physiological responses to nitrogen deficiency and resupply in different blade portions of Pyropia yezoensis f. narawaensis (Bangiales, Rhodophyta)

Abstract

This study examines the physiological differences in growth, progress of bleaching, recovery of pigmentation, and nitrogen uptake rate between the lower and upper blade portions of Pyropia yezoensis (Ueda) M.S. Hwang et H.G. Choi f. narawaensis Miura (formerly Porphyra yezoensis Ueda f. narawaensis Miura), which is the predominant cultivar currently used in Japan, due to its large elongated blade. In an experimentally induced nitrogen deficient condition, the rate of blade length increase was significantly higher in the upper portion than in the lower portion because of the faster cell division. The color and pigment contents of the upper portion reduced more rapidly than those of the lower portion. These results demonstrate that the more rapid bleaching in the upper portion is caused by faster cell division and more nitrogen deficiency to synthesize the new pigments in comparison with the lower portion. On the other hand, when nitrogen was resupplied, the upper portion synthesizes photosynthetic pigments more actively compared with the lower portion, despite the faster cell division in the upper portion. In blades affected by bleaching, after nitrogen resupply NH4+ uptake rate per area was significantly higher in the upper portion than in the lower portion. Thus, the higher uptake rate supports faster cell division, higher pigmentation, and faster recovery from bleaching in the upper portion.