Effects Of Plant Growth Regulators(PGRs) On The Growth And Physiology Of Tropical Seagrasses

Seagrass beds are one of the most productive marine ecosystems and possess high ecological and economic value.It is also an important component of blue carbon.However,under the dual pressure of human activities and climate change,the seagrass bed ecosystem area is substantially degraded globally.Different exogenous promoting nutrients also differ on the growth and physiological facto rs of seagrasses,and exogenous nutrients are important for the physiological metabolism and ecological functions of seagrasses,and have important reference values for seagrass transplantation as well as seagrass bed restoration.In this paper,we investigated the growth rate,photosynthetic pigment content（chlorophyll a,chlorophyll b and carotenoids）,chlorophyll fluorescence parameters,antioxidant enzymes,and basal substance content of leaves of Thalassia hemprichii and Enhalus acoroides seedlings by analyzing typical plant growth regulators(IAA,GA3 and PP₃₃₃)during seagrass stress using the plant growth regulators（PGRs）technique.The changes in growth rate,photosynthetic pigment content（chlorophyll a,chlorophyll b and carotenoids）,chloroph yll fluorescence parameters,antioxidant enzyme activity,and basal substance content of PGRs were investigated.The following conclusions were obtained by exploring and analyzing the patterns of growth-promoting effects of PGRs on seagrasses.Under laboratory conditions,changes in the physiological and biochemical characteristics of T.hemprichii were significant（P<0.05）when PGRs were applied to both T.hemprichii plants（with/without root tip meristem zone）in culture.When IAA and GA3 were applied,the photosynthetic pigment content,chlorophyll fluorescence parameters,and basal substance content of T.hemprichii were significantly（P<0.05）higher than those of the control,and when PP₃₃₃was applied,the photosynthetic pigment content,chlorophyll fluorescence parameters,and basal substance content of T.hemprichii were significantly（P<0.05）lower than those of the control;after PGRs were applied to T.hemprichii with/without apical meristem zone,the photosynthetic pigment content,chlorophyll fluorescence parameters,and basal substance content of T.hemprichii with meristem zone The photosynthetic pigment content,chlorophyll fluorescence parameters and basal material content were significantly（P<0.05）higher in T.hemprichii with/without apical meristem than in the control.In addition,when GA3 was applied,the leaf tissue of T.hemprichii significantly（P<0.05）promoted the narrowing of leaf width.The growth indexes,photosynthetic pigment content,chlorophyll fluorescence parameters,antioxidant enzyme activity,and basal substance content of E.acoroides seedlings were measured after growing seedlings in the laboratory using IAA,GA3,and PP₃₃₃ for seed soaking and sediment injection treatments,chlorophyll fluorescence parameters,antioxidant enzyme activity,and basic substance content were significantly（P<0.05）higher than those of the sediment-injected treated group,while no significant differences（P>0.05）existed in the physiological indices of seedlings treated with IAA and GA3;the seedlings of E.acoroides treated with PP₃₃₃ were significantly（P<0.05）lower than those treated with IAA and GA3.After applying different concentration gradients of IAA and GA3 to the seagrass plants,the photosynthetic pigment content and chlorophyll fluorescence parameters of seagrass increased and then decreased,the antioxidant enzyme activity decreased and then increased,and proline（Pro）also showed a trend of decreasing and then increasing with increasing IAA concentration.Significant differences（P<0.05）were found among the different concentration treatments,with IB(0.01 g·L^-1)significantly promoting the growth of seagrass and ID(0.04g·L^-1)significantly inhibiting the growth of seagrass.After the application of GA3,the leaf width of T.hemprichii was significantly（P<0.05）reduced with the increase of GA3 concentration after incubation;secondly,the growth of T.hemprichii was stressed with the increase of concentration,which inhibited the growth of leaves and roots.In general,the application of PGRs is beneficial to the growth of tropical seagrasses,but attention should be paid to the application method,type and concentration.In this study,when 0.01 g·L^-1 of IAA was applied by immersion,the photosynthetic pigment content and antioxidant enzyme activity of T.hemprichii increased,and the physiological functions of T.hemprichii were enhanced.The growth function was promoted after the application of IAA and GA3 to E.acoroides seedlings.