Physiological Response To Programmed Cell Death Of Phaeocystis Globosa Under Environmental Stress

Since 2011,Phaeocystis globosa blooms have frequently occurred in the Beibu Gulf waters of Guangxi,endangering the marine ecosystem and safety of fishery production and blocking the cooling water intake system of nuclear power plants,posing serious safety risks.At present,the research on harmful algal blooms mainly focuses on the occurrence,harm,and prevention processes,while the research on the decay process is relatively less.Based on this,this study explores the physiological and biochemical responses and programmed cell death(PCD)process of P.globosa under different environmental stresses by setting temperature stress and nutrient stress conditions to provide a new scientific basis for exploring the life and death process of P.globosa blooms and its prevention and control ideas.The key to the outbreak of P.globosa blooms is the transition process from free single cells to colonies in its life history.Under the temperature change and nutrient limitation conditions set,P.globosa can still form a large number of colonies.From the different existing forms of P.globosa,we further explore the influence of environmental stress on the growth and physiological and biochemical characteristics changes of P.globosa and then elaborate on the PCD process and its physiological response mechanism in cells.The main results are as follows:(1)The activity of Caspase-3 enzyme which regulates apoptotic behavior in phaeocystis globosa cells under oxidative stress caused by environmental stress was significantly increased,followed by a rapid and irreversible PCD process in algal cells with increased cell membrane permeability,the appearance of cell PS flip-flop,cell contraction,and plasma membrane separation from cell wall phenomena.(2)Low-temperature stress inhibited the normal growth and reproduction of P.globosa cells and did not activate its PCD response process.High-temperature stress caused an oxidative stress response in P.globosa cells,leading to its PCD response,which mainly manifested as a significant increase in SOD and CAT enzyme activity,and algal cells showed an Annexin-FITC positive reaction,confirming that P.globosa cells entered apoptosis under hightemperature stress.(3)P.globosa did not undergo the PCD process under nutrient limitation.Nitrogen limitation inhibited the growth of free single cells of P.globosa,forming colony cells with a larger diameter but fewer single cells distributed on the surface.The colony production capacity dropped sharply.Phosphorus limitation did not affect the growth of free single cells of P.globosa;colony cells had smaller diameters but significantly more single cells distributed on the surface than normal,which could help limited algal cells greatly improve their light conversion ability,increase productivity,and supply energy for themselves.