| Rice(Oryza sativa) is the main food crop in China. Zinc(Zn) and iron(Fe) are the essential micronutrients for rice growth and development. Higher content of zinc or iron in rice seeds plays an important role in improving people’s health. In this study, a popular rice varieties, Liangyoupeijiu, grew under both the long term- and short term-zinc or iron or both deficient conditions. The growth phenotype, nutrient content, physiological and biochemical parameters were analyzed to understand how rice response to the deficiency of zinc or iron or both as well as the zinc and iron interaction in rice. In addition, 98 rice varieties were used to screen and identify the high- and low-zinc or iron seed accumulated rice varieties. The differences of nutrient absorption, transporting and translocation were analyzed between these two type of rice varieties to find out the key element of high zinc or iron accumulation in rice seed. The main results were as follows.The growth phenotype, nutrient content and physiological indicators of Liangyoupeijiu were analyzed under different treatments of zinc deficiency. The results are as follows.(1) Under the short-term Zn deficiency, no significant changes were observed in the rice growth when compared with the normal treatment. The Zn concentration in root increased firstly and later decreased. It increased to 2-foldat the third day and significantly decreased at the 14 th day after Zn deficiency. Meanwhile, the absorption of phosphorus(P) was suppressed in root, while the contents of nitrogen(N) and potassium(K) were not affected.(2) Under the long time Zn deficiency, the bottom leaves became brown and dark, the plants became small, and biomass declined significantly. The Zn concentration declined significantly in roots and shoots, by 38% and 55%, respectively. The N concentration increased significantly in shoot, and gradually returned to normal level after Zn resupplying. The P concentration also increased significantly in shoot, as Zn promoted P transportation from root to shoot. However, he K concentration was not influenced by Zn deficiency. The SOD activity in root, sheath and leaves decreased significantly after long time Zn deficiency. The POD activity significantly decreased in root, but significantly increased in the sheath after resupplying of Zn. The chlorophyll content in flag leaf was affected by the long time Zn deficiency. When compared with the normal Zn treatment, chlorophyll a + b increased by 40%, while the chlorophyll a / b decreased by 5/6.(3) Under low Zn treatment during the whole growth period, when compared with the normal zinc treatment, the root and shoot dry weight significantly reduced. The maximum difference was at the mature stage, and the biomass decreased by 21% and 54%. However, the Zn concentration in each tissue and organ increased at each growth stage, as the biomass decreased significantly. Meanwhile, the low Zn treatment affected the distribution of N, P and K in plant. The allocation of N and P to the spike was inhibited by low Zn treatment. More N was allocated to the stem and leaf sheaths and more P was allocated to the leaves under low Zn treatment. The low zinc level in the environment promoted the absorption of K in root and the accumulation of Kin new leaf.The growth phenotype, nutrient content and physiological indicators of Liangyoupeijiu were analyzed under different treatments of iron deficiency. The results are as follows.(1) Under the short-term Fe deficiency, no significant changes were observed in the rice growth when compared with the normal treatment. The Fe concentration decreased significantly in root, while the N concentration increased significantly, and both gradually returned to the normal level after Fe resupplying. However, the absorptions of P and K were not affected by the short-term Fe deficiency.(2) Under the short-term Fe deficiency, the number of root tips significantly reduced, while the total root surface area, root length and root volume were increased significantly. The leaf area also increased, while the root and shoot biomass decreased. Compared with the normal Fe treatment, the Fe concentration in roots and shoots severely reduced, by 81% and 87%, respectively. The absorption of P was also significantly inhibited, while the N and K concentrations in root and shoot were not significantly affected by the long-term Fe deficiency. The SOD activity in root, leaf sheath and leaves significantly decreased, POD and CAT activities also decreased significantly. The carotenoid and chlorophyll contents in flag leaves also decreased.(3) Under the low Fe treatment during the whole growth period, when compared with the normal Fe treatment, the leaf area significantly increased, while the effective tiller number, root and shoot dry weight significantly decreased. The Fe concentration in each tissue and organ reduced at each growth stage. Meanwhile, the low Fe treatment could affect the distribution of N, P and K in plant. Low Fe inhibited the allocation of N and P to the spike. More N was allocated to the root, and more P was allocated to the sheath. The low Fe treatment also promoted the absorption of K in root and the accumulation of K in root and stem.The interaction effect between zinc and iron was analyzed under the alternative zinc and iron deficiency. The results are as follows.(1) Under the short-term Zn deficiency, the Fe concentration in root significantly reduced, while the Fe concentration in shoot has not been influenced. Under the long-term Zn deficiency, the Fe concentration in root and shoot has not been significantly influenced. However, the Fe concentration in root increased by 40% after Zn resupplying. Under the low Fe treatment during the whole growth period, the Fe concentrations in old leaves and stems increased while the Fe concentrations in spikes and spike-stems reduced significantly.(2) Under the short-term Fe deficiency, the Zn concentration significantly increased, and back to the normal level after Fe resupplying. Under the long-term Fe deficiency, the Zn concentration significantly increased in root. Under the low Fe treatment during the whole growth period, the Zn concentration increased in old leaves, new leaves, sheaths and spike-stem. When compared to the normal Fe treatment, the Zn concentration in spike significantly reduced at the reproductive growth stage.(3) Under the short-term both Zn and Fe deficiency, the Zn concentration increased firstly and later decreased. Under the long-term both Zn and Fe deficiency, both the Zn and Fe concentration in root and shoot significantly reduced. The Fe concentration gradually returned to the normal level after Zn and Fe resupplying, and the Zn concentration was 40% higher than the normal treatment at the 9th day after Zn and Fe resupplying.The Zn and Fe concentrations in husk and brown rice of different varieties were analyzed. The result showed that a wide genetic variation of Zn or Fe concentration in husk and brown rice was existed in different rice varieties. Generally, the Zn concentration in brown rice was higher than it in husk, the Fe concentration in brown rice was lower than it in husk. The highest Zn concentration in husk was 46 mg / kg higher than the lowest one, the highest Zn concentration in brown rice is 27 mg / kg higher than the lowest one, the highest Fe concentration in husk was 160 mg / kg higher than the lowest one, and the highest Fe concentration in brown rice is 47 mg / kg higher than the lowest one. There was a significantly positive correlation in zinc and iron concentrations between the husk and brown rice. For example, both the Zn and Fe concentrations were lower in the husk of Yixiang 1577 and Zhenzhuai, both the Zn and Fe concentrations were lower in the brown rice of 02428, both the Zn and Fe concentrations were higher in the husk and brown rice of Liangyoupeijiu. The allocation of Zn in different tissues and organs was analyzed between the husk and brown rice Zn high- and low-accumulated varieties. Results showed that more Zn was distributed to the spike at the booting stage and less Zn was distributed to the stem at the mature stage in the husk Zn high-accumulated variety. Therefore, the Zn accumulation in the spike at the booting stage and the ability of Zn transportation from the stem to the spike at the mature stage were the main reasons of the high accumulation of Zn in rice seed. Additionally, the allocation of Fe in different tissues and organs was analyzed between the husk and brown rice Fe high- and low-accumulated varieties. Results showed that the high accumulation of Fe in the spike before the mature stage and the ability of Fe transportation from the stem to the spike at the mature stage were the main reasons of the high accumulation of Fe in rice seed. |
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