THE EFFECT OF WATER STRESS ON NITRATE REDUCTASE ACTIVITY AND NITROGEN AND PHOSPHORUS CONTENTS IN CUMINUM CYMINUM L.

Abstract

Cumin (Cuminum cyminum L.) is a plant with great medicinal importance cultivated in many regions such as Iran, India, Indonesia, Afghanistan, Pakistan, Lebanon, Syria and Turkey. In this research, nitrogen and phosphorus concentrations and nitrate reductase enzyme activity were studied in cumin under flooding stress. Cumin plants were cultivated in pots containing garden soil (in 1 cm depth, 15-20°C, 14 h light and 10 h darkness). Germination took place after 2 weeks. Flooding stress was applied 6 weeks after germination on a number of pots according to their field capacity (FC) (2, 3, and 4 fold) for 1 week; a number of pots were also considered as controls with field capacity. Plants were then harvested and chemical analysis of the factors under study was done using roots and shoots of the plants exposed to flooding conditions and the control plants. The experiment had a completely randomized design in which four levels of water in the soil (2FC, 3FC, 4FC) were compared. Analysis of variance was carried out using SPSS software and means were compared by Duncan’s test at [≤0.05 significance level. The results showed that in comparison with control plants, nitrogen and phosphorus concentrations were significantly lower in both shoots and roots of flooded plants. This decrease was more pronounced in treated plants exposed to 4×field capacity conditions. Nitrogen concentration in roots and shoots of treated plants showed a significant decrease in comparison with control plants and this was more noticeable in treated plants exposed to 4×field capacity conditions. Moreover, concentration of nitrite produced from nitrate reduction catalyzed by nitrate reductase enzyme in roots and shoots of treated plants had a significant increase in comparison with control plants. Treated plants exposed to 4×field capacity conditions showed the most increase. Also the study showed that cumin seeds could survive in flooding environment for 14 days. Thus, flooding stress in cumin seeds decreased nitrogen and phosphorus concentrations in roots and shoots. This stress increased the activity of nitrate reductase enzyme in both roots and shoots.