菠菜硝态氮累积和还原与植株生长的关系

通过盆栽试验,以两个硝态氮含量差异显著的菠菜品种为供试材料,在不同生长时期,测定了叶柄、叶片干重、水分含量、硝态氮含量及叶片内源和外源硝酸还原酶活性,研究菠菜硝态氮累积和硝酸还原酶活性的动态变化及其与植株生长变化的关系。结果表明,随生长期后移,叶柄、叶片及地上部干重和水分含量先增加而后降低,硝态氮含量则持续降低,低硝态氮累积品种S9的下降更为明显,出苗后52d和62d地上部分别降低了100%和89.7%;叶片内源和外源酶活性则随植株生长量增加而增加,高硝态氮累积品种S4增加（379%和199%）更明显,之后该品种酶活性随植株生长量降低而显著下降,品种S9却显著增加,分别为121%和288%。生长前期,品种S4硝态氮含量、干重增长速率及内源、外源酶活性均显著高于品种S9,内源/外源酶活性比值却明显低于后者;生长后期,除外源酶活性和内源/外源酶活性比值外,品种间差异均不明显。因此,生长前期高累积品种硝态氮含量降低较少,主要原因可能是其内源/外源酶活性比值（70.7%）较低,生长后期该品种的内源/外源酶活性比值（98.2%）显著增加后,硝态氮含量迅速下降进一步证明了这一推测。综合上述结果可知,内源/外源酶活性比值更能揭示植株生长变化引起的品种间硝态氮含量变化差异。

Nitrate Accumulation and Reduction in Spinach and Their Relations to Plant Growth

Previous research indicates that nitrate accumulation in plants changed with plant growth,but mechanisms behind those changes are unknown.Understanding these mechanisms will benefit adopting appropriate strategies to decrease the nitrate content in plants since high nitrate accumulation in leafy vegetables is potentially toxic to human health.A pot experiment was carried out to investigate the dry weight,water content,and nitrate-N concentrations of petioles and leaf blades,and in vivo and in vitro nitrate reductase activity（NRA） in leaf blades of two spinach cultivars at different growth stages.The objective was to study the dynamic changes of nitrate-N concentrations and NRA of two spinach cultivars,and their relations to plant growth.The results showed that the dry weights and water contents of petioles,leaf blades,and shoot for both cultivars increased with the increase of plant biomass and then declined with the decrease of plant growth.However,the nitrate-N concentrations of both cultivars decreased with plant growth,and the decrease for cultivar S9 with lower nitrate-N concentration was more significantly than that for cultivar S4 with higher nitrate-N concentration.During the early growth stage,in vivo and in vitro NRA increased with plant growth,and these for cultivar S4 increased by 379% and 199% which were significantly higher than that for cultivar S9,but they were decreased for cultivar S4 and increased for cultivar S9 at later growth stage.The increase of dry weight and water content,nitrate-N concentrations,in vivo and in vitro NRA of cultivar S4 were significantly higher,but the ratio of in vivo /in vitro NRA was lower than those of cultivar S9 on days 40 and 52 after germination.These differences between spinach cultivars were not significant at later growth stage.This indicated that the nitrate decrease of cultivar S4 was more slowly than that of cultivar S9 should be due to its lower ratio of in vivo /in vitro NRA,and this hypothesis was proved by the fact that the nitrate-N concentration of cultivar S4 decreased significantly with the increase of in vivo /in vitro NRA ratio at late stage.This suggested that the variations of nitrate-N concentration for both cultivars be closely related to the ratio of in vivo /in vitro NRA at different growth stages.