Effects Of Different Nitrogen Levels On Root Development Of Wheat With Different Quality Traits And Studies On Special Root Hairs

The studies were carried out in the Scientific & Educational Park of Henan Agricultural University in 2005~2007. Pot and field experiments were employed to study root developmental characteristics under conditions of high, medium and low (CK) nitrogen application rates and with strong-gluten, weak-gluten and medium-gluten wheat (Triticum aestivum L.) cultivars. Root samples for measurement of morphological, quantitative and physiological traits were obtained at growing stages just before wintering, wintering, jointing, flag leaf expansion, grain formation, middle grain filling, and late waxy ripeness (late dough stage). After harvest, main quality indices such as content of protein, soluble sugars and starch in grains were determined. On the medium nitrogen application level and with Yunong 949, a medium-gluten cultivar, special root hairs on nodal roots were systematically studied in the field experiment. The root samples with special root hairs on them were dug out from the filed at jointing stage, at 7, 14, 21, 28, 35, 42, 49, 56, 63 and 72 d after jointing, and at late dough stage, respectively. By a common dissecting microscope, carefully determine forming site, density and length of special root hairs on a nodal root and observe morphology and structure of the root hairs.The main results are as follows:(1) Effects of nitrogen in different application levels on the morphological, quantitative and physiological traits of the root system were made clear. Root-shoot ratio was the highest and content of total nitrogen in roots was the lowest in control. However, under the medium nitrogen application level, the number of nodal roots per culm and per plant and dry root weight per plant significantly increased (α=0.05) as compared with those in either high nitrogen application level or CK. Difference in root volume per plant between medium nitrogen application level and either high nitrogen application level or CK was extremely significant (α=0.01) at grain formation stage. Under the high nitrogen application level, content of total nitrogen in roots was the highest and root-shoot ratio was the lowest. These data indicated that overdue nitrogen application (high nitrogen level) did not mean improving morphological, quantitative and physiological traits of roots under conditions of the current studies.(2) Difference in morphological, quantitative and physiological traits of the root system among cultivars of different quality types was observed. Comparatively, morphological, quantitative and physiological traits of roots of the strong-gluten cultivars Yumai 34 and Zhengmai 9023 were somewhat inferior to those either of the medium-gluten cultivar Yunong 949 or the weak-gluten cultivar GS Zhengmai 004. However, content of total nitrogen in roots of Zhengmai 9023 was higher than that of any of the other three cultivars. With regards the medium-gluten cultivar Yunong 949, morphological, quantitative and physiological traits of roots were superior to those of the strong-gluten cultivar. Difference in dry root weight per plant between Yunong 949 and Zhengmai 9023 was extremely significant both at flag leaf expansion stage and grain formation stage. As for the weak-gluten cultivar, main morphological, quantitative and physiological traits of the root system were better than those of any of the other experimental cultivars. Root vigor of GS Zhengmai 004 was extremely stronger than that of any of the other cultivars at wintering and before wintering. These data showed that difference existed in root development of cultivars of different quality types and that the experimental conditions in the particular studies gave special favor to the root system of the weak-gluten cultivar.(3) Correlations between root traits and grain quality traits were analyzed among cultivars of different quality types. Positive correlations between content of total nitrogen in roots of strong-gluten cultivars Yumai 34 and Zhengmai 9023 in early growing period and content of protein in grains were significant. In the weak-gluten cultivar GS Zhengmai 004, significant positive correlations existed not only between root vigor and content of total nitrogen in roots in early growing period and content of protein in grains, but also between root volume per plant, dry root weight per plant and root-shoot ratio and starch content in grains. The data indicated that it might be feasible to improve grain quality by regulating root development in the production practice due to the significant correlations existing between root traits and grain quality traits.(4) Regular occurrence patterns, morphology and structure of special root hairs on nodal roots were preliminarily studied. The results showed that special root hairs occurred commonly on nodal roots after jointing. On the basal portion of a nodal root, special root hairs unevenly distributed, assuming a gradual decreasing trend from the basal end downwards. Length of the concentrated and the moderate forming segments decreased but that of the sparse segment increased with advance in growing period. Density of the special root hairs also decreased with advance in growing period. Protruding or branching of special root hair cells was observed to be a common phenomenon. In late growing period, thickening of secondary walls of the special root hair occurred, which might be some of a mechanism of special root hairs to defend environmental stresses such as diseases and drought.