Response And Its Physiological Mechanism Of The Three Citrus Rootstocks To Zinc Or Iron Stress

Zinc and iron nutrition have been an important factor of the limitation of yield and quality in orange trees. In order to discuss response and its physiological mechanism of different citrus rootstocks to zinc or iron stress, trifoliate orange(Poncirus trifoliate Raf.), sour orange (Citrus aurantium L.), and red tangerine (Citrus reticulata Blanco)seedlings were as experimental materials with hydroponics. Investigated absorption and transportation of zinc and iron, and the effects of zinc or iron stress on growth, physiological character and the ultrastructural in leaf cell of citrus rootstock.(1)In order to investigate effects of Zinc stress on growth of citrus rootstocks, changes relatively physiological indexes, zinc contents in different parts of trifoliate orange, sour orange and red tangerine and leaf ultrastructure of trifoliate orange were determined under 0mg·L^-1(zinc deficiency), 0.005 mg·L^-1(low zinc), 0.05 mg·L^-1(optimal zinc) and 0.5 mg·L^-1( zinc excess) with hydroponics. The results showed that zinc stress remarkably inhibited the growth of trifoliate orange and sour orange, whereas had little influcence on growth of red tangerine, POD activities in roots of trifoliate orange and sour orange were significantly lower under zinc deficiency and low zinc treatments than under optimal zinc treatment, while CAT activities in roots of red tangerine had no significant difference among Zn treatments; Pro content in leaves and roots of the three citrus rootstocks were notably higher under zinc stress than under optimal zinc treatment, leaf MDA and root Pro content of trifoliate orange were relatively lower than those of sour orange and red tangerine under Zn treatments. Zn contents in roots,stems and leaves of the three citrus rootstocks increased with increasing supply of Zn, Zn contents in roots were higher than other parts on the same Zn treatment, the ratio of leaf/root, stem/root and leaf/stem of zinc translocation coefficient under zinc excess were significantly lower than those of other Zn treatments. The ultrastructure of chloroplast of mesphyll cell of trifoliate orange showed that in the condition of Zn deficiency the structure of chloroplast changed, thylakoid lamella of the chloroplast was loosely distributed with less lamella, but platoglobuli number was decreased Under Zn deficiency, thylakoid lamella of the chloroplast was loosely distributed with less lamella, but platoglobuli number was decreased, vacuolization appeared in the chloroplast. Under Zn excess, starch grain and platoglobuli number in the chloroplast drastic increased. It's suggested that there exist differential response in relation to Zn stress among the three citrus rootstocks. (2)The three citrus rootstocks seedlings such as trifoliate orange, sour orange and red tangerine were taken as experimental material, the effects of iron stress on the growth, physiological character and iron distribution of the three rootstocks were investigated with hydroponics. The results showed that the growth index and concentrations of photosynthetic pigments in leaves of the three rootstocks were significantly lower in the iron deficiency(0μmol·L^-1)than in the treatments of low iron(5μmol·L^-1)and optimal iron(50μmol·L^-1), the activities POD, CAT in leaves and roots decreased and the Pro content in roots increased significantly under the iron deficiency treatment, and the activities of SOD in leaves and roots of the three rootstocks changed irregularly. Under the treatments of iron deficiency and low iron, iron contents in roots showed no difference among the three rootstocks, but were significantly lower than those of optimal iron treatment, respectively. The leaf/root and the stem/root of Fe translocation coefficient in the three rootstocks decreased with increasing supply of Fe, whereas no significant difference was found in the leaf/stem of Fe translocation coefficient.(3) In this research, we investigated physiological responses of young trifoliate orange (Poncirus trifoliata Raf.) seedlings to zinc(Zn) or iron(Fe) deficiency in a potting experiment with nutrition solution culture. Plant biomass and root viability were notably reduced, whereas SOD activitiy were in the leaf and root was induced. Activity of POD in the leaf and root was significantly increased under Zn deficiency, but decreased under Fe deficiency. CAT activity in the root was significantly increased under zinc deficiency, while no difference was observed upon Fe deficiency treatment. Contents of potassium(K), magnesium(Mg) and phosphorus(P) in the root and K in the shoot were significantly decreased under Fe and Zn deficiency,respectively. However, Zn and Cu contents in the root and shoot were enhanced under Fe deficiency, while Zn deficiency caused remarkable increase of root Fe level and Mn level of both root and shoot.Ultrastructural observation of leaf structure and chloroplast showed that organelles were seriously damaged under Fe deficiency, such as revealed by vacuolization of chloroplast and mitochondria, vague chloroplast membrane and thylakoid lamella, drastic increase of platoglobuli number, and absence of starch grain in the chloroplast. Under Zn deficiency, thylakoid lamella of the chloroplast was loosely distributed with less lamella, but platoglobuli number was decreased.