Study On Effect Of Lead Stress On Growth Of Rice

Soil is a natural environment to support human life and an important resource for agricultural production. The issues that the world is facing, such as food, resources and environment, are closely related with the soil. With the development of modern industries, industrial "three wastes"discharge, excess mine explorations, heavy metal pollution are becoming increasingly prominent, and the increasing soil pollution has attracted wide attention. In the present study, the effect on photosynthesis, phytohormones, mineral elements, the antioxidant protection system and other physiological and biochemical reactions by lead contamination were studied in rice (Oryza sativa L.), the main results are as follows:1. Effect of lead stress on photosynthesis of riceWith increasing concentration of lead, SPAD value of Xiangzaoxian24 showed a down-up-down trend at tillering and booting stages, increase gradually at maturity stage ;while SPAD value of Baliangyou100 was increased at first and then decreased at tillering and booting stages, there were no significant differences at maturity stage.With increasing concentration of lead, at tillering stage, the net photo-synthetic rate (Pn) and transpiration rate (Tr) of Xiangzaoxian24 showed the trend from early increase to late decrease, and the stomatal conductance (Cond) showed a down-up-down trend. The net photosynthetic rate, stomatal conductance and transpiration rate of Baliangyou100 showed the trend from increasing to decreasing; at booting stage, the net photosynthetic rate, stomatal conductance and transpiration rate of Xiangzaoxian24 showed a down-up-down trend. The net photosynthetic rate of Baliangyou100 showed a down-up-down trend, the stomatal conductance showed the trend from increasing to decreasing, and the transpiration rate from decreasing to increasing; At heading stage, the net photosynthetic rate and stomatal conductance of Xiangzaoxian24 showed a down-up-down trend, the transpiration rate showed the trend from decreasing to increasing, the net photosynthetic rate stomatal conductance of Baliangyou100 showed the trend from early increase to late decrease, and the transpiration rate showed a up-down-up trend. At maturity stage, the net photosynthetic rate of Xiangzaoxian24 showed a increasing trend, the stomatal conductance and transpiration rate showed the trend from early increase to late decrease. The net photosynthetic rate of Baliangyou100 showed the trend from early increase to late decrease, the stomatal conductance showed a increasing trend, and the transpiration rate showed the trend from early decrease to late increase. At 4 growth stages, there were no significant differences of the intercellular CO₂ concentration among the treatments of 2 rice varieties.2. Effect of lead stress on rice leaves antioxidant system and Physiological and Biochemical IndexesSOD,POD and CAT activity of 2 rice varieties changes in the same trend, SOD activity showed a down-up-down trend, POD and CAT activity showed the trend from increasing to decreasing with increasing concentration of lead.With increasing concentration of lead, the Proline concent and permeability of the membrane in Xiangzaoxian 24 leaves showed the trend from decreasing to increasing. While showed a up-down-up trend in Baliangyou100. MDA concent showed the trend from decreasing to increasing, and Root Activity showed the trend from increasing to decreasing.3. Effect of lead stress on the phytohormones content of rice roots and leavesWith the increasing concentration of lead, abscisic acid(ABA)in leaves increased gradually; gibberellins (GA₁) showed the trend from increasing to decreasing. Zeatin(Z) and zeatin riboside(ZR) of had no significant differences. Indole 3-acetic acid (IAA)in leaves of Xiangzaoxian 24 showed a down-up-down trend. while Baliangyou100 showed the trend from increasing to decreasing.With the increasing concentration of lead, GA₁ and IAA in root showed the trend from increasing to decreasing of 2 rice varieties; ZR in root of Xiangzaoxian24 decreased, Z showed the trend from increasing to decreasing. ZR and Z in root of Baliangyou100 showed a down-up-down trend; ABA in root of Xiangzaoxian24 showed a up-down-up trend, while ABA in BaliangyoulOO root showed the trend from decreasing to increasing.4. Effect of lead stress on mineral elements content in rice roots, leaves and seeds.Lead concentration in rice different parts under the lead stress increased with the increase of lead concentration, there were significant differences in different treatment. Lead concentration in rice roots, leaves and seeds were measured by ICP. The results showed that the order of lead content was root> leave>seed.The contents of K, Ca, Mg, Mn and Zn in parts of Xiangzaoxian 24 and Baliangyou 100 were correlated negatively with lead concentration, while contents of Fe and Cu were correlated positively with lead concentration.