The Study Of Anatomical Mechanism Of Trifoliate Orange(Poncirus Trifoliata(L. ) Raf. ) Malformed Root Induced By Boron Deficiency

Boron(B) is an essential micro element nutrient for the normal growth of plants.Boron plays an important role in many metabolic processes in plants. However, B deficiency becomes deepening serious in most citrus orchards. Boron deficiency not only affected the yield and quality of citrus, but also changed the morphology of the plant.Trifoliate orange(Poncirus trifoliata(L.) Raf) is the most widely used rootstock in China and its typical symptom of boron deficiency is the malformed and necrotized of root tip. Therefore, the employment of anatomical method to definite root abnormal anatomical changes in the process of development caused by boron deficiency will provide a better understanding of the mechanism of citrus root development under boron deficiency and has a great significance on solving the problems of boron stress in citrus production. In this study, trifoliate orange seedling was selected as research material. Hydroponic culture system was used to investigate the anatomical mechanisms of B deficiency on root growth and development of trifoliate orange. The main results are as follows:1. Apparent symptoms change process of trifoliate orange root under boron deficiency.The characteristics of boron deficiency at different stages of root: at first the color of root caps changed, and followed by root caps thickened, and then long out of the lateral roots, root cap became "twin peaks",finally the surface of root cracked,finally the color of new lateral root apex changed;Under the conditions of boron deficiency, the growth of primary root was significantly inhibited. The tap root elongation, total root length, root total surface area were mainly limited at the third stage of boron deficiency; Under boron deficiency, the root average diameter significantly increased compared with controls, but when they reached a certain threshold,the quantitative value is not increased.2. The change process of the anatomic structure of trifoliate orange root induced by boron deficiencyFrom the first stage, the root cap cell layer has a significant reduction,and the position of the thickening gradually keep away from the root apex; At the second stage of boron deficiency,apical quiescent center necrosis, root tip cells slowly drop and gradually appeared empty, root cap cells fall off, root surface is uneven, cell deformity; With boron deficiency continued, the root cutting diameter becomes larger,the number, thickness and area of the cortex and vascular tissue were increased. In addition, the quantity of catheter were also increased;The cortical cells were squeezed and deformed and the diameter of cells became smaller.3. The vessels molecular characteristics change process of trifoliate orange root under boron deficiency.With the increasing degree of boron deficiency, the length and width of vessels were reduced. Moreover,the max angle of perforated plated were also decreased;The number of the pitted vessels increased, the number of spiral vessels and annular decreased, but scalariform and reticulate vessels changed not regularly.4. The effects of boron deficiency on different forms of boron in trifoliate orangeThe total boron content in different tissues of the plant was gradually reduced in boron deficiency;The free boron and semi-boron concentration of primary root decreased significantly only at the fifth stage of boron deficiency, bur semi-boron concentration of lateral root decreased significantly only at the first and second stage of boron deficiency; the bound boron in taproot and lateral root decreased significantly only at the fifth stage of boron deficiency.