Effects Of The Endocytosis Initiated By Exogenous Lanthanum On The Accumulation Of Cadmium In Plant Pavement Cells

The massive mining,production and application of rare earth elements?REEs?lead to their accumulation in the environment,and the impact on ecosystems,especially their primary producers—plants cannot be underestimated.Studies have found that REEs can break the endocytosis inertness formed by the long-term evolution of leaf cells and activate the endocytosis of leaf pavement cells.This effect may provide a channel for other pollutants in the environment such as heavy metals to enter the plant body.Cadmium?Cd?is one of the highly toxic heavy metals in the environment,and the inevitable overlap between REEs and Cd???polluted areas.Then,does La???exposure initiate the endocytosis of leaf cells enhance the intracellular Cd???accumulation and the toxic effect?In this paper,we selected the model plants wild-type Arabidopsis thaliana Col-0 and Venus-CANTH transgenic plants[after induced by dexamethasone?DEX?,blocking clathrin-mediated endocytosis].The lanthanum[La???]and the heavy metal element Cd???,which are common in the environment,are the representatives of REEs and heavy metal elements,respectively.In the three growth stages of Arabidopsis thaliana?seedling stage,vegetative stage,reproduction stage?to study exogenous La???exposure effect of induced leaf endocytosis on intracellular Cd???accumulation.And evaluate the cumulative toxic effects of Cd???from the perspective of photosynthesis,and provide a reference for scientific evaluation of environmental risks of REEs.The main results are as follows:?1?The effect of leaf endocytosis initiated by exogenous La???exposure on intracellular Cd???accumulation:La???can initiate Col-0 leaf pavement cell endocytosis,enhance Col-0 root cell endocytosis[80?M La???>30?M La???],cannot initiate endocytosis of DEX-induced Venus-CANTH transgenic plant leaf pavement cells.It can be proved that La???initiates clathrin-mediated endocytosis.And found that La???affects plant endocytosis is related to DNA methylation.A single Cd???could not initiate the endocytosis of Col-0 leaf pavement cells.In the presence of La???,Cd???can enter the Col-0 leaf cell by endocytose of La???initiated.However,the amount of Cd???in the leaf pavement cells of the Venus-CANTH transgenic strain induced by DEX was significantly less than that of Col-0.This indicates that Cd???will enter the plant leaf pavement cells through the clathrin-mediated endocytosis initiated by La???.In addition,the effect of exogenous La???exposure on leaf endocytosis of different growth stages on the accumulation of intracellular Cd???plants showed the following rules:seedling stage>vegetative period>reproduction period.?2?Evaluate the toxic effects of La???exposure induced intracellular Cd??? accumulation from the perspective of photosynthesis:30?M La???exposure increases Col-0 net photosynthetic rate?P_n?,stomatal factors[stomata opening and intercellular CO₂ concentration?C_i?],non-stomatal factors[apparent sightseeing quantum efficiency?AQY?and Rubisco enzyme activity],80?M La???exposure decreased Col-0 above indicators.Single Cd???exposure reduces Col-0 P_n,stomata opening,C_i,AQY and Rubisco enzyme activity.In the presence of La???,the effect of Cd???exposure on Col-0 P_n,stomatal opening,C_i,AQY and Rubisco activity was stronger than that of Cd???alone.After the DEX-induced Venus-CANTH transgenic plants inhibited clathrin-mediated endocytosis,the above changes were significantly reduced.The above results indicate that in the presence of La???,the inhibition of photosynthesis by Cd???is significantly enhanced,which is due to the accumulation of Cd???induced by La???induced clathrin-mediated endocytosis,And the inhibition of photosynthesis by Cd???is achieved through the synergistic effect of stomatal and non-stomatal factors.The effect of exogenous La???exposure-induced intracellular Cd???accumulation on leaf endocytosis has an overall effect on the different growth stages of the above indicators:seedling stage>vegetative stage>reproduction period.?3?To explore the effect of intracellular Cd???accumulation on leaf endocytosis induced by exogenous La???exposure on photosynthesis from the perspective of chlorophyll fluorescence:30?M La???exposure increases Col-0 chlorophyll content,initial fluorescence yield,maximum fluorescence yield,PS? maximum photochemical quantum yield,PS? actual photochemical quantum yield,apparent electron transfer rate,potential photosynthetic activity,light adaptation to photochemical quenching at steady state and non-photochemical quenching at steady state,while 80?M La???exposure reduced Col-0 above indicators.Cd???exposure reduces Col-0 above indicators.In the presence of La???,Cd???exposure has a stronger inhibitory effect on Col-0 than the above indicators.After the DEX-induced Venus-CANTH transgenic plant inhibited clathrin-mediated endocytosis,in the presence of La???,the degree of Cd???exposure on the above indicators decreased.The above results show that in the presence of La???,the inhibitory effect of Cd???on photosynthetic pigments and PS? reaction centers is significantly enhanced,the enhancement effect stems from La???initiating clathrin-mediated endocytosis that induces Cd???accumulation,and Cd???inhibition of photosynthesis is achieved by reducing photosynthetic pigments and destroying the PS? reaction center.The effect of exogenous La???exposure-induced intracellular Cd???accumulation on leaf endocytosis has an overall effect on the different growth stages of the above indicators:seedling stage>vegetative stage>reproduction period.In summary:La???initiates leaf pavement cell endocytosis and internalizes Cd???in the environment,provide channels for Cd???to enter plant leaf pavement cells,enhance Cd???inhibition of plant photosynthesis damage through stomatal factors,non-stomatal factors,photosynthetic pigment content and PS?.This discovery provides a reference for scientific evaluation of the environmental exposure risk of REEs and the research on the mechanism of exogenous REEs on plants.