Study On Physiological Adaptability Of Different Camellia Oleifera Cultivars To Boron Deficiency Stress

Boron is an essential trace mineral element for plant growth and development.Boron is involved in the formation of cell wall and cell membrane structure and the stability of function,after boron deficiency,leaf veins protruding,leaf etiolation,necrosis of shoot and root apical growth points,flower disfigurement,and physiological dysfunction of plant photocontract efficiency,osmotic regulation ability,antioxidant system and so on.China has the largest area of C.oleifera in the world,but most of the distribution area of C.oleifolia is in the southeast of China where boron deficiency is severe,and one of the factors that limit the development of C.oleifolia industry is the problems caused by boron deficiency,such as malnourishment and yield decline.Boron transporters genes play an extremely important role in the uptake and transport of boron by plants,helping plants exhale excess boron when the external boron content is high and efficiently taking up boron when the external boron content is low.However,the study of boron transporters genes in boron transport of C.oleifolia has not been reported.Therefore,screening deficiency boron tolerant cultivars and studying the deficiency boron tolerance mechanism of C.oleifolia can provide an important theoretical basis for solving the boron deficiency problem in C.oleifolia industry.In this study,seven cultivars of C.oleifolia from’Chang Lin’and’Hua Xiang’series were used as materials in Hubei and Hunan province,to explore the differences of different cultivars in boron concentrations（boron deficiency,0μmol/L;low boron,10μmol/L;normal boron,32μmol/L）growth differences and physiological responses in hydroponic environment.Used the membership function value method and the minimum distance method of cluster analysis to evaluate the resistance to deficiency boron of C.oleifolia cultivars,and further preliminary analyzed the molecular mechanism of boron efficient and boron inefficient C.oleifolia cultivars.The main research results are as follows:（1）Under the two boron deficiency conditions,the young leaves of seven C.oleifolia cultivars showed the symptoms of loss of green and yellowing,leaf reverse-rolling,veins bulging and bursting,and leaf brown spots,to evaluate boron deficiency tolerance from leaf phenotype:’Chang Lin 4’>’Chang Lin 3’>’Chang Lin 40’>’Hua Xin’>’Hua Shuo’>’Hua Jin’>’Xiang Lin 210’.After boron deficiency,root apical enlargement and browning,no new roots and lateral roots emerge,or even stop growing,and the root is arbuscular,to evaluate boron deficiency tolerance from root phenotype:’Chang Lin 4’>’Chang Lin 40’>’Chang Lin 3’>’Xiang Lin 210’>’Hua Shuo’>’Hua Xin’>’Hua Jin’.The total biomass,plant height and ground diameter growth,root length,root surface area,root volume,root diameter and root-shoot ratio of’Hua Jin’,’Hua Xin’,’Hua Shuo’and’Xiang Lin 210’were significantly affected by the two boron deficiency stress levels,’Chang Lin 40’and’Chang Lin 3’were significantly affected only under severe boron deficiency,and the growth parameters of’Chang Lin 4’was less significantly affected by the two boron deficiency stresses.（2）The net photosynthetic rate,stomatal conductance,transpiration rate and photosynthetic pigment content of seven C.oleifolia were positively correlated with boron concentration,inter satiety CO₂concentration was negatively correlated.Under the two boron deficiency conditions,’Chang Lin 40’and’Hua Xin’were significantly affected by two boron deficiency stresses in photosynthetic pigments and photosynthetic;’Chang Lin 3’,’Hua Jin’and’Hua Shuo’only photosynthetic efficiency was significantly inhibited;and’Chang Lin 4’and’Xiang Lin 210’photosynthetic pigments,photosynthetic were less significantly affected.（3）The boron content in each part of seven C.oleifolia was positively correlated with the boron concentration;boron content distribution in each part of the plant:old leaf>new leaf>stem>root;reduction of boron content in each part of the plant:new leaf>old leaf>root>stem;boron migration coefficient of each variety in the absence of boron:’Hua Xin’>’Hua Shuo’>’Chang Lin 40’>’Chang Lin 4’>’Chang Lin 3’>’Xiang Lin210’>’Hua Jin’.’Chang Lin 4’boron content in each part was not significantly affected by the two boron deficiencies,’Hua Jin’and’Hua Xin’was significantly affected.（4）By comparing the physiological indexes of seven C.oleifolia cultivars treated with different boron deficiency concentrations,the results showed that there were significant differences in the adaptability of seven C.oleifolia cultivars to the two boron deficiency environments.In this experiment,the three"Chang Lin"cultivars had stronger antioxidant and osmotic response than the four"Hua Xiang"cultivars,so they had stronger tolerance to boron deficiency.（5）Pearson correlation analysis showed that photosynthetic index parameters,root scanning parameters,boron content and physiological parameters were significantly correlated with soluble sugar,soluble protein,SOD,CAT,APX,H₂O₂,O^2-,proline and cellulose,which could be selected as reference indexes in the future screening of boron deficiency tolerance cultivars of C.oleifolia.The membership function value method and cluster analysis minimum distance method were used to evaluate the low boron tolerance of seven C.oleifolia cultivars and the results showed that the tolerance of boron deficiency of each cultivars was as follows:’Chang Lin 4’>’Chang Lin 40’>’Chang Lin3’>’Xiang Lin 210’>’Hua Xin’>’Hua Shuo’>’Hua Jin’,and cluster analysis method shows that’Chang Lin 40’,’Chang Lin 3’,’Chang Lin 4’and’Xiang Lin 210’with strong boron deficiency tolerance were grouped into one group,’Hua Jin’,’Hua Xin’and’Hua Shuo’with poor boron resistance were grouped together,In general,’Chang Lin 4’was the most tolerant Chang Lin cultivars and’Xiang Lin 210’was the most tolerant Hua Xiang cultivars.（6）The boron tolerance of plants is directly related to the expression of boron transporters genes plant internal.Boron deficiency induced four genes Co BOR1,Co BOR1-like,Co BOR2 and Co NIP5-1 up-regulation in a short time and showed the highest expression at 12h,and the gene expression levels in roots of the boron efficient cultivar’Chang Lin 4’were 16.4 times,4.1 times,4.6 times and 10.1 times of those of the inefficient cultivar’Hua Jin’.In the whole period,the expression levels in roots and leaves of the boron efficient cultivar’Chang Lin 4’were much higher than that of the boron inefficient cultivar’Hua Jin’.These results indicated that the main mechanism of tolerance of boron deficient environment in boron efficient cultivar’Chang Lin 4’was（1）by up-regulation of boron transporter genes for a short period of time,（2）highly boron mobility,（3）highly effective antioxidant and osmotic regulation system,（4）highly photosynthetic efficiency,（5）adaptation of roots to boron deficiency,（6）stable cell wall structure.This study revealed the differences in growth,photosynthesis and physiology of seven C.oleifolia under two levels of boron deficiency stress,screened the boron efficient C.oleifolia’Chang Lin 4’,and from the physiological and molecular mechanism level to preliminary analyzed tolerance mechanism,the results provide a basis for the promotion of different C.oleifolia in the production areas with different soil boron content,and to provide basic data for genetic engineering methods to cultivate deficiency boron resistant C.oleifolia.