| Wild and cultivated populations of Pyropia haitanensis have frequently experienced extremely low pH conditions in the last few decades.This could potentially threaten the development of the aquaculture of this economically important marine crop.Algae generally use CO2 concentrating mechanisms(CCMs)to efficiently obtain inorganic carbon,but knowledge of CCMs of Porphyra haitanensis is still limited.To gain a broader perspective,we investigated the short-term(4 hours)and long-term(7 days)term responses of CO2 concentrating mechanisms(CCMs)of P.haitanensis thalli and conchocelis to large variations in pH.In addition,in order to evaluate the effects of long-term alkalization(high pH/low CO2)on CCMs of P.haitanensis conchocelis,this study analyzed the responses of CCM of conchocelis to low pH/high CO2.Our study found that a pH of 4 and 5,which mimicked the decreased pH caused by acid rain,resulted in decreased photosynthesis and respiration while leading to the death of P.haitanensis thalli.Thus,acid rain would result in a decline in P.haitanensis production and threaten wild seaweed sources.However,a pH of 6 and 7 enhanced the growth of P.haitanensis thalli by more than 30%,mainly because increased CO2 levels favored photosynthesis,while the algae need to effectively maintain intracellular pH homeostasis to support rapid growth rates.this study propose that the CCMs component involved in the movement and metabolism of inorganic carbon may play an important role in pH homeostasis.In addition,pH 9 also led to the death of P.haitanensis thalli,which is consistent with observations of the natural distribution of this algae.This study also found that,the major components of CCM of conchocelis are the extracellular carbonic anhydrase(CA)and intracellular CA,and the HCO3-transporter.Under sustain conditions(pH 9),the extracellular CA photosynthetic rate was 80%.However,in normal seawater(pH 8),the extracellular CA and HCO3-transporter respectively contributed 45%and 31%,and no significant difference was found between them.The decrease of pH from 9 to 8 significantly increased the photosynthesis by 74%,Low pH inhibited the expression of key genes of CCM and carbon fixation.This study showed that there were significant differences in the utilization of inorganic carbon and the ability to maintain cell homeostasis in different generations of P.haitanensis.The present study suggested that the actual variation in pH experienced by marine organisms needs to be considered in the experimental design of related studies.The results of this study can provide a reference for the management and planning of the aquaculture of the economic seaweed. |
