The development of technique of decrease in nitrate accumulation in vegetables by controlling environmental conditions and nitrate reduction in leaf

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The purpose of this study is to establish a technique that would decrease the nitrate concentration in vegetables, especially spinach by using continuous lighting method treated just before harvest (CLM). CLM for 24 hr simultaneously caused a significant decrease in nitrate and increases in ascorbic acid and carotene contents in spinach leaf On the other hands, oxalate which is harmful component content in leaf slightly decreased by CLM Then CLM did not affect an oxalate metabolism in spinach leaf. Therefore, we examined the effects of the combination treatment of CML and carbon dioxide enrichment (CDE) to decrease in nitrate and oxalate simultaneously. Photosynthetic rate of spinach leaf in CLM+CDE condition was 1.6 times higher than in only CLM condition. While, photorespiration rate was almost zero in CLM+CDE condition. This suggests that oxalate metabolism may be seriously inhibited in CLM+CDE condition Nitrate content in spinach leaf decreased by both CLM and CLM+CDE conditions, but the decrease was more pronounced in CLM+CDE than in CLM. CLM treatment did not affect oxalate content in spinach leaf. However, CLM+CDE treatment caused a significant decrease in oxalate content in leaf. The result indicate that combination treatments of continuous lighting and carbon dioxide enrichment treated just before harvest induce simultaneously decrease in harmful components in spinach such as nitrate and oxalate.