The objective is to study whether the accumulation and utilization of plant N are controlled by Mo status in winter wheat cultivars. Mo-efficient cultivar 97003 (eff) and Mo-inefficient cultivar 97014 (ineff) were grown in severely Mo-deficient acidic soil (Tamm-reagent-extractable Mo 0.112 mg kg-1) with (+Mo) and without (-Mo) the application of 0.13 mg kg-1 Mo. The accumulation and use efficiency of plant total N were significantly higher in +Mo than that in -Mo and in eff than that in ineff under Mo deficiency. N use efficiency was remarkably higher in maturity but it was forwarded to jointing stage after Mo supply, thus indicating that Mo supply promoted the N use efficiency besides N uptake and eff was efficient in N uptake and utilization. The overall activity of nitrate reductase (NR, EC 1.6.6.1) was significantly higher in +Mo than in -Mo and ratio of +Mo/-Mo was even to 14.8 at tillering stage for ineff. Activity of glutamine synthetase (GS, EC 6.3.1.2) was significantly lower in +Mo than in -Mo. Concentration of nitrate and glutamate were also significantly lower in +Mo than in -Mo, thus provided evidences for enhancing N use efficiency by Mo supply. Activities of NR and GS were significantly higher and concentrations of nitrate and glutamate were significantly lower in eff than ineff under Mo deficiency, thus indicated eff was more efficient in N reduction and utilization. It is therefore concluded that Mo could promote N accumulation and utilization in winter wheat which was directly related to NR and feedback regulated by GS. Higher Mo status also results in higher accumulation and utilization of plant N in eff.
The objective was to probe the site where the biosynthesis of chlorophyll was blocked under Mo deficiency at low temperature, which led to the decrease of chlorophyll in winter wheat cultivars. The intermediates of chlorophyll biosyn- thesis were analyzed in winter wheat cultivars in soil culture, miniblock culture, and solution culture to study the effects of Mo on chlorophyll biosynthesis without Mo addition (CK, soil available Mo 0.112 mg kg-1) and Mo addition (+ Mo, 0.13 mg kg-1 Mo was added). Laevulinic acid (LA), the competitive analog of δ-aminolaevulinic acid (ALA) was also introduced in the experiment. The ratio of Chl a/Chl b was constant between CK and + Mo treatment, whereas it increased at low temperature, which indicated that Mo deficiency did not inhibit the transformation of Chl a to Chl b at low temperature. Under Mo deficiency, the contents of protochlorophyll (Pchl), Mg-protoporphyrin Ⅸ (Mg-Proto Ⅸ), protoporphyrin Ⅸ (proto Ⅸ), and uroporphyrinogen Ⅲ (Uro Ⅲ) decreased [Uro Ⅲ decreased significantly (P < 0.01)], whereas ALA and glutamate increased significantly (P < 0.01) compared with that of Mo addition, which suggested that the transformation from ALA to Uro Ⅲ might be inhibited. The content of ALA reversed after addition of LA, it was significantly higher (P < 0.01) in Mo addition than in CK. The results indicated that the transformation from ALA to Uro Ⅲ was blocked under Mo deficiency, which resulted in the inhibition of the biosynthesis of chlorophyll and led to the decrease of chlorophyll in winter wheat cultivars.
