Effect Of Boron On Cell Wall,ROS And Intracellular PH In Citrus Rootstock Under Acid Environment

The citrus industry in the south of China is developing rapidly,and raising the income level of local farmers.However,citrus orchards in southern China are mostly located in acid red soil areas where available B is deficient or seriously deficient in soil.In recent years,high-intensity cultivation have accelerated the process of soil acidification,and the pH value of farmland soil has been constantly decreasing to the lowest.Soil pH and B have become the main factors limiting the quality of citrus production.In addition,In many citrus planting areas,the main cultivars are rootstocks of Poncirus trifoliate(L)Raf.In this study,the effects of B application on cell wall,ROS and intracellular pH of rootstocks of trifoliate orange in acidic condition were studied in a nutrient culture solution(different pH and different concentrations of B).The main results are as follows:(1)When B was added,plant height decreased with the decrease of pH value,while root length decreased by 22.3% and 29.3% compared with pH 5 and 6 at pH4.Under B deficiency,plant height and root length were significantly reduced by16.2% and 20.4% under pH 4 compared with that under pH6.The results showed that strong acid environment inhibited the growth of roots and plant height enormously,whether B was applied or not.Regardless of B deficiency or application,the MDA content in roots at pH 4 was 3.5 times higher than that at pH 6.The doubling of malondialdehyde causes an increase in root cytotoxin and severe damage to the root system.The root of the anvil will increase the soluble protein content and proline content,regulate the osmotic pressure,and change the body’s resistance to resist low acid damage.Compared with leaves,B and pH have a great influence on the contents of K,Ca,Fe and Mn in stems and roots.Under low-acid conditions,the addition of B can also increase the content of elements such as K,Ca,Mg,Fe,Mn,and promote their absorption.(2)Using the anvil seed germination test to raise seedlings,the roots were clustered when pH and B were treated.In addition,The content of B in roots treated with B were decreased with the decrease of pH,but increased with B deficiency.When B was added,the proportions of protoplast B and free B to underground B was decreased at pH 4;under B deficient condition,the proportions of protoplast B to underground B was increased at pH 4,but there was no significant change in free B as compared with pH 6.Explain that more boron is involved in the synthesis of cell walls.At B application,the cellulose content of cell wall was decreased with the decrease of pH value;the chelated pectin and alkali-soluble content in cell wall at pH4 were lower than that of pH 6.The content of B in alkali-soluble pectin(Alk-B)at pH 4 with B was the highest,which was 2.1 and 1.9 times higher than that of pH 5and pH 6 respectively.Most B was bound to pectin,and the proportion of Alk-B was larger than Chel-B.In addition,irrespective of B addition,the ratio of Alk-B and Cel-B was increased at pH 4.The cell wall of root tip cells treated with P4B0 was thicker,and the integrity of cell wall was mostly destroyed with signs of damages compared with P6B0.The decrease of pH value aggravated the destruction of cell wall structure of the root under B deficiency.Therefore,boron is applied in a strongly acidic environment,or the roots are subjected to severe oxidative damage and no effective absorption of boron,or the absorbed boron is mainly used for root clustering without transporting to the leaves,resulting in the occurrence of boron deficiency symptoms.(3)At pH 4,the main root length of the roots of boron-added anvil increased significantly by 27.0% compared with boron deficiency,and the total length of roots increased by 22.5%.However,the root length of the boron-added roots increased significantly by 40.5% and the total length of the roots increased by 17.6% at pH 6.When B was added in strong acid environment,the increase of main root length was less than that of suitable acid,but the increase of total root length was greater than that of suitable acid.This indicated that B application in strong acid environment mainly promoted root uptake of nutrients by changing the total root length.Analysis of roots of different diameters revealed that roots were resistant to rooting by double rooting.FDA-PI staining showed that the root surface cells were loosened and broken,and the root cap was shedding under-B treatment in strong acid environment.However,lateral roots had already occurred in + B treatment.When the pH is suitable,the root "cone" structure is not damaged whether B is added or not and in the absence of boron,the root tip is swollen.At pH 4 and boron deficiency treatment,the SOD and CAT activities were significantly increased to eliminate the accumulation of excess ROS,and the effect was remarkable.DAPI staining showed that the number of apoptosis treated by P4B10 was less than that of P6B10 treatment.At P6B10,the δof vacuoles in root cells of trifoliate was 0.74±0.03,and the pH value was 5.74 ±0.05,showing weak acidity.At pH 4,the vacuole pH of root cells treated with B was increased from 5.54 to 5.71.With addition of B,the decrease of pH value regulated the activities of phosphoenolpyruvate carboxykinase(PEPC)and NADP malic enzyme(NADP-ME)and increased the cytoplasm pH.The stability of intracellular pH ensured the normal metabolism of apical cells.