Optimized nitrogen fertilizer application strategies under supplementary irrigation improved winter wheat (Triticum aestivum L.) yield and grain protein yield

Background Exploring suitable split nitrogen management is essential for winter wheat production in the Huang-Huai-Hai Plain of China (HPC) under water-saving irrigation conditions, which can increase grain and protein yields by improving nitrogen translocation, metabolic enzyme activity and grain nitrogen accumulation. Methods Therefore, a 2-year field experiment was conducted to investigate these effects in HPC. Nitrogen fertilizer was applied at a constant total rate (240 kg/ha), split between the sowing and at winter wheat jointing growth stage in varying ratios, N1 (0% basal and 100% dressing fertilizer), N2 (30% basal and 70% dressing fertilizer), N3 (50% basal and 50% dressing fertilizer), N4 (70% basal and 30% dressing fertilizer), and N5 (100% basal and 0% dressing fertilizer). Results We found that the N3 treatment significantly increased nitrogen accumulation post-anthesis and nitrogen translocation to grains. In addition, this treatment significantly increased flag leaf free amino acid levels, and nitrate reductase and glutamine synthetase activities, as well as the accumulation rate, active accumulation period, and accumulation of 1000-grain nitrogen. These factors all contributed to high grain nitrogen accumulation. Finally, grain yield increase due to N3 ranging from 5.3% to 15.4% and protein yield from 13.7% to 31.6%. The grain and protein yields were significantly and positively correlated with nitrogen transport parameters, nitrogen metabolic enzyme activity levels, grain nitrogen filling parameters. Conclusions Therefore, the use of split nitrogen fertilizer application at a ratio of 50%:50% basal-topdressing is recommended for supporting high grain protein levels and strong nitrogen translocation, in pursuit of high-quality grain yield.

ppGpp is a bacterial cell size regulator

SummaryGrowth and division are central to cell size. Bacteria achieve size homeostasis by dividing when growth has added a constant size since birth, termed the “adder” principle, by unknown mechanisms [1–4]. Growth is well known to be regulated by ppGpp, which controls anything from ribosome production to metabolic enzyme activity and replication initiation, and whose absence or excess can induce the stress response, filamentation, and yield growth-arrested miniature cells [5–8]. These observations raise unresolved questions about the relation between ppGpp and size homeostasis mechanisms during normal exponential growth. Here, to untangle effects of ppGpp and nutrients, we gained control of cellular ppGpp by inducing the synthesis and hydrolysis enzymes RelA and Mesh1. We found that ppGpp not only exerts control over the growth rate, but also over cell division and hence the steady state cell size. The added size responds rapidly to changes in the ppGpp level, aided by transiently accelerated or delayed divisions, and establishes its new constant value while the growth rate still adjusts. Moreover, the magnitude of the added size and resulting steady-state birth size correlate consistently with the ppGpp level, rather than with the growth rate, which results in cells of different size that grow equally fast. Our findings suggest that ppGpp serves as a critical regulator that coordinates cell size and growth control.

Compositional, organoleptic, metabolic enzyme activity and fibre characteristics of muscle from bulls with different growth paths to a common carcass weight

The proximate composition, organoleptic quality, metabolic enzyme activity and fibre characteristics of longissimus thoracis muscle from suckler bulls assigned to three target indoor winter (from 9 to 13 months of age approximately) growth rates (average daily gain of 0.6, 1.0 and 1.5 kg; n = 14/group) were investigated. The feeding regimes to achieve the target average daily gains were 2, 4 and 6 kg of concentrate respectively, plus grass silage ad libitum. The duration of the winter feeding period was 123 days, after which bulls were turned out to pasture and grazed for 99 days before re-housing and finishing on concentrates ad libitum plus grass silage until they reached a liveweight to yield a target carcass weight of 380 kg. The average daily gain during the grazing period was higher (P < 0.001) for the 0.6 than for the 1.0 and 1.5 average daily-gain groups, which did not differ. Proximate composition, collagen content, metabolic enzyme activity and fibre-type distribution of the longissimus thoracis muscle were similar (P > 0.05) between the 0.6, 1.0 and 1.5 average daily-gain groups. Apart from tenderness, which was rated higher (P < 0.05) for the 0.6 group than for the 1.0 average daily-gain group, the sensory characteristics of the beef were not influenced by the different winter growth rates applied. Overall, restricting the growth rate during winter had little effect on subsequent beef appearance or eating quality.