Abstract
More than 4 billion inhabitants in Asia depend on rice for 35–60% of the calories consumed in their diets, but new rice cultivars frequently do not reach expected yields because of poor rice grain filling. Here, we quantified the activities of enzymes involved in starch metabolization in rice to investigate the mechanisms regulating the accumulation and translocation of stem non-structural carbohydrates (NSC) under different levels of nitrogen fertilizer application. A pot experiment was conducted using two rice cultivars, Liangyoupeijiu (LYPJ) and Shanyou63 (SY63), under high and low nitrogen applications. Compared with high nitrogen application (HN), low nitrogen application (LN) increased stem NSC concentration before the heading stage and NSC translocation during the grain filling stage; concomitantly, LN significantly shortened the active grain filling period and increased the grain filling rate in superior spikelets. Compared with the LYPJ cultivar, SY63 exhibited a higher grain weight, higher grain filling percentage, and higher stem NSC concentration before heading and greater NSC translocation after heading. During the period between panicle initiation and heading, the activities of adenosine diphosphate-glucose pyrophosphorylase (AGP), starch synthase (StS), and starch branching enzyme (SBE), all enzymes involved in starch synthesis, increased under the LN treatment and positively correlated with increases in stem NSC. During grain filling, the activities of enzymes involved in starch-to-sucrose conversion [α-amylase, β-amylase, and sucrose phosphate synthase (SPS)] increased under the LN treatment and positively correlated with stem NSC remobilization. Overall, the investigated enzymes exhibited higher activities in SY63 than in LYPJ. Our results suggest that low nitrogen increases the activities of AGP, StS, SBE, α-amylase, β-amylase, and SPS, leading to increased accumulation and remobilization of stem starch and NSC in SY63. We conclude that calculated reductions in nitrogen application and the choice of an appropriate cultivar may improve rice grain yields via enhanced stem NSC accumulation and translocation, thereby reducing the costs and increasing the sustainability of rice production.
Highlights
Rice (Oryza sativa L.) provides 35–60% of the calories consumed by the more than 4 billion inhabitants of Asia (Fageria, 2007; Yorobe et al, 2016)
The low nitrogen application (LN) treatment significantly increased the grain filling rate and shortened the active grain filling period of superior spikelets compared with the high nitrogen application (HN) treatment (Figures 1C,E)
The photosynthetic rate of LYPJ is higher than that of SY63 (Lv et al, 2017); LYPJ had low stem non-structural carbohydrates (NSC) and starch accumulation under both N application rates (Figures 3A,B). These results suggest that higher activities of adenosine diphosphate-glucose pyrophosphorylase (AGP), StS, and starch branching enzyme (SBE) may contribute to higher stem starch and NSC concentrations in SY63 than LYPJ and that SBE may contribute more strongly to pre-anthesis starch and NSC accumulation in the stems of SY63 than LYPJ
Summary
Rice (Oryza sativa L.) provides 35–60% of the calories consumed by the more than 4 billion inhabitants of Asia (Fageria, 2007; Yorobe et al, 2016). High-yield varieties include those developed by the International Rice Research Institute, such as hybrid rice and “super” rice (Cheng et al, 2007; Peng et al, 2008). These cultivars, frequently do not reach expected yields because of poor rice grain filling. Improvements in the accumulation of NSC in stems and their translocation to rice grains increases sink capacity, grain filling rates, and grain yields (Yang and Zhang, 2006; Fu et al, 2011). It is important to elucidate the mechanisms of stem NSC accumulation and translocation to maximize rice yield potentials and increase future rice yields
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