Effects of Different Zn Supply Levels on Physiological Parameters, Seed Zn Concentration and Root Cell Ultrastructure in three Different Genotypes of Brassica Species

Abstract

Crop Zn content is different between various crop species. The purpose of the present study was to determine Zn response in seed of three species of Brassica (B. napus, B. juncea and B. campestris) when exposed to different Zn supply levels (0, 1, 5, 10 and 20 mg kg -1 ) in pot experiment. The results showed that the activities of antioxidant enzymes, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) in leaf, and dry weights of plant, straw, leaf and seed increased at CZn 2+ ≤5 mg kg -1 . The highest seed dry weight of three species were observed in 5 mg kg -1 Zn treatment, increased by 37.7%, 82.6% and 18.0% compared to the controls, respectively. The ultrastructural damage was found in the root tip cells for B. napus and YR in the presence of 20 mg kg -1 Zn, while intact structure of the root tip cells was observed in B. campestris. The total amino acid content of root exudates in B. juncea and B. napus was significantly higher than that of B. campestris in the presence of 1 and 20 mg kg -1 Zn. High supply level of Zn 2+ (20 mg kg -1 ) could promote the secretion of amino acids in root exudates. Dry weight (stem, leaf and seed) of B. napus reveal a decreasing trend when Zn supplied at levels above 10 mg kg -1 . As the increase of Zn supply level, the concentrations of Zn in seed of rape revealed an increasing trend. The best Zn supply level for having more biomass and more Zn in seeds of rape without toxic effects was observed at 10 mg kg -1 . The highest of Zn concentration in seed were observed in B. napus may be due to due to more root exudates. Zinc concentration in Zn-highefficiency species is related to the absorption capacity of the plant's roots and the ability to change soil Zn availability