Abstract:

Solution culture experiments were carried to explore the relationships between nitrate contents, parameters
relevant to photosynthesis and key enzymes involved in nitrogen metabolism in ten bok choy varieties (Brassica chinensis L.)
by setting NO3-/NH4+ ratio as 50:50, 75:25 and 100:0. The results showed that six out of ten bok choy varieties investigated
indicated an increase in total dry weight respectively by 12.66%-76.88% and 17.98%-95.07% at NO3-/NH4+ ratio of 75:25
and 100:0 compared with that at NO3-/NH4+ ratio of 50:50, though total dry weight of the Tianjin and Datouqingjiang
varieties decreased firstly and then increased whereas the Xianggang Chunxiu Tianbaicai 236 and Zhengwangda 88 varieties
exhibited an initial increase followed by a decrease with increasing NO3-/NH4+ ratio. Nitrate contents of leaves and roots
of bok choy rose, while those of petiole increased initially and then decreased. Moreover, the decreasing order of nitrate
contents was petiole (3 882.62–5 448.81 mg/kg) > leaf (2 004.86–4 146.50 mg/kg) > root (505.39–2 188.68 mg/kg).
Increasing NO3-/NH4+ ratio could result in an increase in nitrate contents of leaves and roots of most bok choy varieties and
an initial increase and then decrease in petiole. Significantly negative correlation was observed between nitrate reductase (NR)
and nitrate content in leaves of bok choy, while there was significantly positive correlation between nitrite reductase (NiR)
and glutamine synthetase (GS). Nitrate content of bok choy leaves decreased with an increase in net photosynthetic rate (Pn)
and intercellular CO2 concentration (Ci), while enhancing along with an increase in transpiration (Tr).

Key words: bok choy varieties, nitrate, NO3-/NH4+ ratio, key enzymes involved in nitrogen metabolism, correlation