Ⅲ-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 47 (2014)

Effects of heavy-ion beam irradiation on sporophyte survival and growth inUndaria pinnatifida

Y. Sato,*1,*2 T. Hirano,*3 Y. Hayashi,*4 M. Kasahara,*1 N. Fukunishi,*4 T. Abe*3,*4 and S. Kawano*2
Undaria pinnatifida, called wakame in Japanese, is oneof the most popular seaweed in Japan, Korea, and China. It
is the most important cultivated seaweed in Iwate andMiyagi Prefectures in Japan. In recent years, the wakame
yield has been decreasing because of changing environment,
unimproved productivity, and damage due to Tsunami. For
the purpose of yield restoration and sustainable growthmarket of U. pinnatifida, the development of new cultivars
with properties such as high yield or high environmental
adaptability is necessary. We used heavy-ion-beamirradiation to induce mutagenesis in U. pinnatifida for theproduction of new cultivars.1) However, since not enoughstudies have been conducted in the mutagenesis of marine
algae, it is important to produce efficient mutation breedingin U. pinnatifida to assess the relationship between survival
rate after irradiation and mutation frequency. In this study,
we irradiated U. pinnatifida sporophytes with C-ion andAr-ion beam and analyzed the effects on sporophyte
survival and growth in the M1 generation toward successful
mutant screening in M2 generation.
Sporophytes of U. pinnatifida were obtained after
fertilizing the male and female gametes. The sporophytes of
1-mm length were transferred into 15-ml plastic tubes for
C-ion irradiation and hybribags for Ar-ion irradiation, bothcontaining sterilized seawater, and were irradiated at dose
ranges of 0–25 Gy (C ions) or 0–10 Gy (Ar ions). Each tube
or hybribag contained 50 sporophytes. After the irradiation,
the sporophytes were cultivated in 500-ml Erlenmeyer
flasks containing 1/4 PESI medium, 2) with aeration, at
15°C, photoperiod of 12 h/12 h (light/dark), and a lightintensity of 90 μmol photons m−2 s−1. The survival rate wasmeasured after 3 weeks of culture. The plants surviving andreaching 20-mm with in the culture period were further
cultivated in the Rotating and Flowing Land Tank System(PAT.P) at 10°C, photoperiod of 12 h/12 h (light / dark), anda light intensity of 180 μmol photons m−2 s−1 for 8 weeks.
The total length and fresh weights of all the sporophytes
were measured after blotting them dry.
In the flask cultivation after irradiation, dead sporophytes
were observed. Almost all the dead sporophytes had formed
within 1 week of cultivation and had wrinkled leaves (datanot shown). The survival rates after 3 weeks of cultivation
were decreased with increasing irradiation dose (Fig. 1).
The survival rates in sporophytes irradiated using C-ion
beam in sporophytes irradiated using C-ion beam were
almost similar to those in female gametophytes derived
from sporophylls irradiated using C-ion beam.1)

The surviving sporophytes of 20-mm length weretransferred to the land tanks. The total length and individual
weight differed between the doses and ion species. The
sporophytes irradiated with 2 Gy of C-ion beam were thelargest: the maximum length and weight were 75 cm and45.6 g, respectively. These values were approximately twotimes higher than those for the largest sporophytes in thecontrol. The sporophytes irradiated with 25 Gy of C-ion and2.5–10 Gy of Ar-ion remained withered for up to 2 weeks
after culturing in the tanks.
The sporophytes irradiated with 2-12.5 Gy of C-ion and 1
Gy of Ar-ion formed sporophylls after cultivation for 2months. Currently, we have cultured and performed mutant
screening of the sporophytes in the M2 generation. We will
analyze the next generation of the large sporophytes
obtained after C-ion irradiation at 2 Gy to confirm whether
the phenotype is inheritable.

Fig. 1 Survival rates of young sporophytes irradiated withC-ion and Ar-ion beams.

Fig. 2 Total length and individual weight of Undaria
pinnatifida sporophytes measured 8 weeks after theirradiation with C-ion and Ar-ion beams.
References*1

Riken Food Co.,LtdGraduate School of Frontier Sciences, University of Tokyo*3
RIKEN Innovation Center*4
RIKEN Nishina Center

1) Y. Sato et al.: RIKEN Accel. Prog. Rep. 46, 267 (2012)2) M. Tatewaki: Phycologia 6, 62 (1966)*2- 300 -