| Calcium oxalate crystals are common plant biominerals with biological functions such as calcium regulation,light regulation,interference with feeding objects,plant defense,and enhanced stress resistance.Previous studies have shown that ascorbic acid may be an important precursor of oxalic acid production,and there are differences in the accumulation of calcium oxalate crystals under different drought conditions.However,the relationship between ascorbic acid and calcium oxalate,the relationship between calcium oxalate crystals and drought resistance is not clear.In this study,36 plant species grown in karst mountainous areas of Guizhou were selected.The morphology and distribution of calcium oxalate crystals were observed.The contents of ascorbic acid and calcium oxalate in leaves were determined,and the correlation between calcium oxalate and ascorbic acid was analyzed.Finally,the Viola verecumda was selected for indoor control experiments to further explore the relationship between calcium oxalate crystals and drought tolerance,in order to reveal the role of calcium oxalate crystals in plant drought tolerance.This research provides a certain theoretical basis for drought adaptation of plants in karst areas.Mainly get the following results:(1)Relationship between calcium oxalate content and ascorbic acid in leaves of karst plantsIn order to analyze the main forms and distribution characteristics of calcium oxalate crystals in karst plant leaves,the correlation between calcium oxalate and ascorbic acid in plant leaves was analyzed.The experiment used optical microscopy,HPLC high performance liquid chromatography and spectrophotometry.Among the leaves of 36 plants,calcium oxalate crystals mainly exist in the form of druses and prisms,which are distributed in mesophyll cells and vein tissue.In 27 plants,leaf ascorbic acid(ASA)was positively correlated with calcium oxalate(r=0.6355),and dehydroascorbic acid(DHA)was positively correlated with calcium oxalate(r=0.3543);in herb,shrub and arbor plants,ASA has a positive correlation with calcium oxalate(r=0.5870;r=0.5558;r=0.5087),however,the relationship between DHA and calcium oxalate was positively correlated(r=0.6108),irrelevant(r=0.2852)and irrelevant(r=0.0262),respectively.The ascorbic acid in the leaves of calcium oxalate accumulating plants is maintained at a high level,which contributes to the synthesis of oxalic acid.(2)Relationship between calcium oxalate crystals and drought tolerance in plants grown on karst areaThe drying parameters and optical microscopic observation methods were used to analyze the changes of leaf water parameters,photosynthetic characteristics and calcium oxalate crystal characteristics during the drought process of V.verecumda.The relationship between calcium oxalate crystals and drought resistance was investigated.In the natural drought conditions of the soil,the amaranth maintains the intracellular water balance mainly by converting the bound water into free water.In the later stages of the drought,some of the free water in the cells may combine with calcium oxalate crystals to form bound water.In addition,the density and bound water content of calcium oxalate crystals have an extremely significant positive correlation linear regression relationship(r = 0.8253,P < 0.0001).The results indicate that calcium oxalate crystals may be an important medium for binding water in cells.It plays an important role in the maintenance of intracellular water.In summary,ascorbic acid can be maintained at a high level in the leaves of calcium oxalate-accumulating plants,presumably contributing to both the synthesis of oxalic acid and the ability to confer antioxidant stress.During the natural drought process,the degradation of calcium oxalate crystals in the leaves of amaranth leaves changes the water state in the cells,thereby maintaining the water homeostasis in the cells,and is also beneficial to the plant tolerant to drought stress. |
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