Effects of low-dose gamma irradiation on artemisinin content and amorpha-4,11-diene synthase activity in Artemisia annua L.
OBJECTIVE
This research work aimed to create in vitro plantlet variants of Artemisia annua through gamma irradiation. The obtained variants were then evaluated for the correlation between their artemisinin content and enzyme activity of amorpha-4,11-diene synthase (ADS), the first enzyme of the artemisinin pathway.


METHODS
Shoot tips from plantlets of A. annua were exposed to gamma rays at a low-dose range and transferred to hormone-free MS medium for in vitro cultivation. A dose-response curve and the value of 50% of lethal dose (LD50) were then obtained. This LD50 dose of gamma rays was used for treating another batch of shoot tips. The surviving plantlets after four subsequent subcultures were evaluated for their ability to accumulate artemisinin in correlation with the enzyme activity of ADS.


RESULTS
The dose-response curve showed that the LD50 value was at 8 Gray (Gy). The surviving irradiated plantlets from this dose treatment had artemisinin content ranging from 0.03-0.70% (w/w) of dry weight, comparing with only 0.18% present in the original non-irradiated samples. Their correlation coefficient between the ADS activity and the artemisinin content appeared to be R2 = 0.090 for all the 18 samples tested, although, selectively, more than half of these (11 samples) showed their R2 value of as high as 0.851.


CONCLUSIONS
There was no correlation between the artemisinin content and ADS activity found in the whole population, but the correlation was observed in the main subpopulation of the irradiated A. annua plantlets.
Koobkokkruad
Thongchai
T
Biomedicinal Chemistry Program, Department of Biochemistry, Chulalongkorn University, Bangkok, Thailand.
Chochai
Araya
A
Kirdmanee
Chalermpol
C
De-Eknamkul
Wanchai
W
D019883:Alkyl and Aryl Transferases / Q000378:metabolism*; D031172:Artemisia annua / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects*; D037621:Artemisinins / Q000378:metabolism*; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays
D037621:Artemisinins; C031327:artemisinin; D019883:Alkyl and Aryl Transferases; C403714:amorpha-4,11-diene synthase