Response Of Plant Leaf Structure And Electrophysiology To Short-term Dehydration

Drought is the main limiting factor for plant growth and one of the important factors restricting the development of agriculture and forestry.Since the water supply and drought tolerance of plants are often the key factors limiting the normal growth of plants and the formation of forests,a rapid understanding of the water transportation and utilization mechanism of plant leaves under water stress can help the timely assessment of drought resistance and maximize the realization of the rapid anchoring of arid areas and suitable plants.It can not only ensure the yield of crops,but also improve the efficiency of ecological restoration.Therefore,in this paper,Broussonetia papyrifera(L.)Vent.,Morus alba L.,Parthenocissus tricuspidata,Lonicera japonica Thunb.,Orychophragmus violaceus L.and Brassica napus L.were used as materials,the vitro leaves were subjected to rapid water loss treatments,and the anatomical structure parameters,mechanical parameters,leaf moisture status,electrophysiological parameters,leaf density and chlorophyll fluorescence parameters were measured,in order to analyze the leaf structure,mechanical and electrophysiological response traits,explore the leaf water availability,finally to assess the plant dehydration resistance,which could provide theoretical bases for the rapid determination of the plant drought reisitance.The experimental results showed as follows:(1)The leaf anatomical structures of the six types of plants responded differently to rapid dehydration.Leaf thickness and mesophyll cells of B.papyrifera responded quickly,by increasing the thickness of the palisade tissue and the palisade-sponge ratio and reducing the thickness of the sponge tissue to reduce the water dissipation,and improve the water transport efficiency,expand the mesophyll cell surface area,and maintain photosynthesis effectiveness;Leaf thickness of M.alba decreased significantly,and the palisade-sponge ratio increased slightly to maintain photosynthetic efficiency.After 3 hours of water loss,leaf anatomical structure was greatly affected by dehydration,and there was no significant change in those parameters.L.japonica maintained a relatively stable palisade-sponge ratio,and the overall anatomical structure of the leaves was less affected by dehydration.In the later period of water loss,the palisade-sponge ratio and tightness degree of leaf tissue structure of the P.tricuspidata decreased,and the water retention of the leaves decreased.The leaves of O.violaceus decreased transpiration dissipation and retained water by increasing the palisade-sponge ratio and reducing the thickness of spongy tissue and lower epidermis,while maintaining photosynthetic efficiency.After 3 hours,the leaves had no significant change in structural because of the excessive water loss;the leaves of B.napus showed better water retention,and its anatomical structure was relatively less affected by dehydration.The palisade-sponge ratio of woody plants and liana was generally higher than that of herbaceous plants,and their resistance to dehydration was relatively good.(2)Influenced by the thickness of palisade tissue,the palisade-sponge ratio and tightness degree of leaf tissue structure,leaf mechanical strength of B.papyrifera and L.japonica was enhanced under dehydration.M.alba leaves can maintain a low rate of water loss within 3 hours of water loss.P.tricuspidata leaves had poor internal structure adjustment capabilities and slight variation in mechanical properties.From the 2nd hours,the leaf elasticity of O.violaceus decreased because of water loss.After 3 hours of water loss,the water loss gradually increased,and the accumulated energy of leaves under external pressure decreased significantly,the decline range of B.napus was relatively small.Within 5 hours of water loss,the leaves of B.papyrifera,L.japonica and B.napus showed better water retention than those of M.alba,P.tricuspidata and O.violaceus.(3)To maintain leaf internal water translocation and intracellular water availability during rapid dehydration,different species of plants respond differently by changing leaf internal structure and intracellular composition.B.papyrifera quickly changed the leaf internal structure to adapt to dehydration stress.The intracellular water availability of M.alba was more sensitive than B.papyrifera.B.papyrifera adapted to dehydration stress by shrinking its mesophyll cells to offset the water loss,or triggering water regulation mechanism caused by enzymes,such as carbonic anhydrase.M.alba maintained intracellular water availability just by changing the leaf structure.The offset effects through shrinking cells differed between B.papyrifera and M.alba,because the elastic-plastic of their leaves and cells were different.The 3 hours might be a dehydration tolerance threshold for M.alba.P.tricuspidata and L.japonica leaves themselves lost water relatively slowly,and the internal structure changes were relatively small.P.tricuspidata mainly adjusted the water availability through the contraction of the leaf structure,while L.japonica adjusted its internal water availability through the better elasticity of the cell wall.The increase of the palisade-sponge ratio and the water retention of O.violaceus stabilized the value of leaf density(LD)and water availability.In the later period,because of excessive water loss,leaf internal structure lost its ability to adjust,and the large loss of water caused leaf shrinkage.B.napus exhibited good water retention.Leaf internal structure was relatively less affected by dehydration.The LD can maintain a more stable value throughout the dehydration process and the water availability was maintained.(4)Compared with B.papyrifera,the electron transfer rate of M.alba was more significantly inhibited by water loss,the excess light energy was mainly used for the thermal dissipation,and the damage of photosynthetic structure was more severe than that of B.papyrifera.B.papyrifera began to be significantly affected at 2 hours.After 3 hours of water loss,the photosynthetic potential of P.tricuspidata decreased,the electron transfer was inhibited,the actual photochemical efficiency decreased,and the photosynthetic structure was damaged more seriously.After 4 hours of water loss,the photosynthetic structure of O.violaceus suffered more serious damage,and the actual photosynthetic efficiency decreased significantly.However,B.napus showed a more stable electron transfer rate and actual photochemical efficiency after 2 hours of water loss,and had better photosynthetic adaptability to water loss.B.papyrifera,L.japonica and B.napus showed better photosynthetic ability than M.alba,P.tricuspidata and O.violaceus.The results are consistent with the above conclusion on the leaves dehydration resistance by analysing the leaf structure,leaf mechanics and electrophysiology.(5)The anatomical structure of plant leaves responded to rapid water loss,and their mechanical characteristics corresponded differently.Leaf mechanical properties and electrophysiology can represent the changes of internal structure and intracellular components of leaves,which can be used to analyze the water effectiveness in the process of photosynthesis and respresent the dehydration resistance of plant.It is important for the theoretical researches on plant drought resistance and has practical values in the ecological restoration engineering.