Abstract
To assess the influence of drought stress on the growth and nitrogen nutrition status of pakchoi (Brassica campestris ssp. Chinensis L.) at different nitrogen (N) levels, the changes in N accumulation and enzyme activities involved in N assimilation were investigated. The drought was induced by adding polyethylene glycol (PEG) under hydroponic culture conditions. Pakchoi seedlings were exposed to a modified nutrient solution with different nitrogen concentration (N1, N2, and N3 represent 2, 9 and 18 mM NaNO3, respectively) and osmotic potential (W1, W2 and W3 represent 0, 60 and 120 g·L−1 PEG 6000) in a full factorial, replicated randomized block design. A short time (seven days) of drought stress caused a significant decline in plant water content, transpiration rate, shoot biomass and shoot nitrogen concentration. Increasing N availability considerably alleviate drought stress by increasing the content of total free amino acids in the roots, promoting the acceleration of root biomass accumulation, and improving the activities of nitrate reductase (NR; EC 1.7.1.1) and glutamine synthetase (GS; EC 6.3.1.2) which would reduce moisture limitations. The results suggested that pakchoi supplied with relative higher N had better growth performance under drought stress.
Highlights
Water and nitrogen (N) are the two main limiting factors for crop growth and productivity, especially those grown under greenhouse conditions
Once taken up by plants, the NO3− is reduced to nitrite (NO2− ) by nitrate reductase (NR; EC 1.7.1.1) to ammonium (NH4+ ) by nitrite reductase (NiR; EC 1.7.2.2)
After seven days of exposure to drought stress, plant water content significantly decreased in the moderate drought group, but there were no differences between mild drought group and blank at three
Summary
Water and nitrogen (N) are the two main limiting factors for crop growth and productivity, especially those grown under greenhouse conditions. Water deficiency depresses N uptake by the root and transport to the aboveground part due to a restricted transpiration rate affecting active transport and membrane permeability [3,4]. N is a critical mineral nutrient for crop growth and involves almost all physiological processes like adenosine triphosphate (ATP) synthesis, photosynthesis and active defense mechanisms in plants [5]. Nitrate (NO3− ) is the main N source for the crop in the soil. Once taken up by plants, the NO3− is reduced to nitrite (NO2− ) by nitrate reductase (NR; EC 1.7.1.1) to ammonium (NH4+ ) by nitrite reductase (NiR; EC 1.7.2.2). Amino transferases like glutamic oxalacetic transaminase (GOT; EC 2.6.1.1) and glutamate pyruvate transaminase (GPT; EC 2.6.1.2)
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