The phylogenetic identity and temperature effects on the photochemical efficiency of the edible green alga “Hitoegusa” (Gayralia spp., referred to as Monostroma nitidum in Japan) from Kagoshima and Okinawa, Japan
摘要
The green alga “Hitoegusa” (commonly referred to as Monostroma nitidum in Japan) is an important edible resource in Kagoshima and Okinawa. To clarify its phylogenetic relationships in these regions, we conducted molecular analyses. Furthermore, to identify the optimal and critical temperatures for sustainable cultivation, we examined the effects of temperature on the photochemical efficiency of samples collected from Kagoshima City (Kagoshima) and Naha City (Okinawa) using a pulse-amplitude modulation (PAM) chlorophyll fluorometer. Molecular phylogenetic analysis of the nuclear rDNA ITS1–5.8S–ITS2 region tufA sequences revealed that the samples from the two locations belonged to different clades. The samples from Kagoshima City were identical to Gayralia kuroshiensis, whereas the samples from Naha, Okinawa formed a clade with other specimens from the Ryukyu and Ogasawara Islands, Chiba and China. The temperature response of the macroscopic stage from both locations showed that the effective quantum yields (ΔF/Fm') were well maintained between 8 °C and 20 °C, with maxima at 14.5 °C for the Kagoshima sample and 15.4 °C for the Okinawa sample, indicating similar thermal responses between the two populations. Additionally, the optimal temperature ranges at both locations encompassed the lowest winter temperatures at their respective study sites (Kagoshima: 15 °C; Okinawa: 20 °C). The alga has a heteromorphic life cycle, with the macroscopic stage declining above 24 °C, whereas the microscopic stage may be adapted to higher temperatures. The results suggest that the edible alga known as “Hitoegusa” in Japan comprises at least two distinct genetic lineages, with the Okinawa population forming a distinct group separate from that of Kagoshima.