| Boron(B) is an essential trace e lement which plays an important role in plants, but B is difficult to move in plants, and the lack of B soil is widely distributed which leads to B deficiency very serious. Recently, leaf chlorosis a symptom of B deficiency occurs in the main local cultivar citrus, the fruit dropped rapidly after fruit set, and it affects fruit yield and quality. Rootstocks play an important role in the growth and development of citrus. At present, the mainly B type is inorganic borate and the way is soil fertilization. Boric acid is easy to be fixed in the soil and the effect of plant absorption is not good. Therefore, it is necessary to study the new type B and the scientific B way.We selected trifoliate orange [C.siinensis(L.)Osb.×Poncirus trifoliata(L.)Raf.] as materials to study through solution culture. We observed the changes of the structure of leaves and roots, cell internal structure when boron deficiency. We investigated the effects of different boron fertilizer and different types on citrange boron supplement. The main results were as following:1) Boron deficiency inhibited the plants’ growth, reduced dry matter accumulation and also significantly reduced the boron contents in leaves. The new leaves dropped in 39.5%-49.1% and the old leaves were 33.3%-39.4%. Boron deficiency when potassium(K) content in trifoliate orange seedling tips in B deficiency significantly reduced by 18% than normal boron treatments; Calcium(Ca) content in trifoliate orange seedling tips in boron deficiency fell 12%-49% and 11%-13% down in new leaves; Magnesium(Mg) content had a tendency to rice in boron deficiency. The content of nitrate and soluble protein showed significantly reduced due to boron deficiency.2) Boron deficiency caused the number of cortical parenchyma cells of root decreased and loosely arranged disorder, the cell ruptures and the intercellular space increased; Besides, cytoplasm collapsed and some organelles disappeared, the cell wall thickness increased significantly. Boron deficiency inhibited the development of root vascular severely, made the differentiation was not obvious and the cell volume was small. The leaves of boron deficiency was thickened and uneven, the spongy tissue cells were deformation, the number and volume of cells increased, that made the spongy tissue increased in the mesophyll obviously. At the same time, the B deficiency leads to an accumulation of many starch grains in leaf cells, the content of soluble sugar and starch were increased by 35.3% and 66.7% than B respectively. The area of the vascular b undle in the leaves of B deficiency was reduced, the number of catheters were reduced and the parenchyma cells were misshapen. Boron deficiency inhibited the development of root and vascular bundle in leaves of the rootstock; it affects the cell volume of spongy tissue in leaves and made the cell abnormal proliferation; it destroyed the internal structure of the cells, made the cell wall thickening, and led to the accumulation of starch grains in the cel s of leaves.3) We studied the influence of different wa ys of applying boron on agronomic traits of trifoliate orange, dry matter accumulation, the content of B, K, Ca, Mg in different parts, as well as the sugar, malondialdehyde(MDA), proline(Pro) and the injured rate in the leaves. The results showed that different fertilization methods lead to quite different results. Foliar B significantly increased dry weight of stem and leaf of trifoliate orange seedling, total dry weight and height, and promoted the growth of root; boron concentration in leaves increased by 126.5%, there were 1.3% B in stems metastasis and accumulation. However, foliar applied boron caused B content decreased by 11.1% in trifoliate citrange roots. Foliar boron caused K and Ca and Mg content in leaves were significantly higher than CK; elements content were significantly higher by root giving boron than by foliar boron(except leaf); the content of sugar, MDA, Pro and injury rates in leaves were declining after B. Therefore, foliar B had a good effect in maintaining the balance of the elements in leaves, carbohydrate synthesis and improving the stress resistance of leaves, but it can reduce the boron content in root, aggravated boron deficiency.4) Both two B fertilizers [sorbitol-boric acid(SB) and boric acid(BA)] can increase the fresh and dry weight and plant height of various parts of the rootstock seedling, and SB played an important role in underground growth. SB significantly increased dry weight 126.8% of underground, BA was only 74.0%, the shoot ratio of SB was 55.6% more than BA’s. The transfer of SB in blades or other parts of the ground in was easier than BA. There was no significant difference between the B content of SB and BA in root and stem, but the leaves B content and B accumulation were significantly higher than BA, and the total B content proportion was significantly higher than BA. Various parts of potassium, calcium and magnesium content in SB were higher than that in CK, while the content of element in different parts of BA was higher than SB. Boron deficiency can lead to carbohydrate accumulation in leaves, and SB was more effective than BA in promoting the transport of polysaccharide substance in leaves. The soluble sugar content in SB treatment were decreased by 26.3%, 1.8% than in CK and BA treatment, and the starch content decreased by 43.5%, 26.1%. SB was better than BA in raising resistance ability. Two B fertilizers were significantly lower than the control in Pro and the damage rate of leaves, SB and BA treatment were decreased by 20.6%, 19.6% than CK, and the damage rate was decreased by 13.3% and 16.5%, leaves MDA content of SB significantly decreased by 19.4% than BA. SB was better than BA in improving the growth and development of root of trifoliate orange rootstock. Besides, SB can effectively reduce the content of carbohydrates in leaves, and help the transfer of photosynthetic products. But they had the same effect with B acid in reducing the accumulation of harmful substances, protecting the leaves plasma membrane. |
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