Limitation of Unloading in the Developing Grains Is a Possible Cause Responsible for Low Stem Non-structural Carbohydrate Translocation and Poor Grain Yield Formation in Rice through Verification of Recombinant Inbred Lines

Abstract

Remobilisation of non-structural carbohydrates (NSC) from leaves and stems and unloading into developing grains are essential for yield formation of rice. In present study, three recombinant inbred lines of rice, R91, R156 and R201 have been tested for source-flow-sink related attributes determining the nature of NSC accumulation and translocation at two nitrogen levels in the field. Compared to R91 and R156, R201 had lower grain filling percentage, harvest index, and grain yield. Meanwhile, R201 had significantly lower stem NSC translocation during grain filling stage. Grain filling percentage, harvest index, and grain yield showed the consistent trend with stem NSC translocation among the three lines. In comparison with R91 and R156, R201 had similarity in leaf area index, specific leaf weight, stem NSC concentration at heading, biomass, panicles m^-2, spikelets per panicle, remobilization capability of assimilation in stems, sink capacity, sink activity, number and cross sectional area of small vascular bundles, greater number and cross sectional area of large vascular bundles, and higher SPAD, suggesting that source, flow, and sink were not the limiting factors for low stem NSC translocation and grain filling percentage of R201. However, R201 had significant higher stem and rachis NSC concentrations at maturity, which implied that unloading in the developing grains might result in low NSC translocation in R201. The results indicate that stem NSC translocation could be beneficial for enhancement of grain yield potential, and poor unloading into caryopsis may be the possible cause of low stem NSC translocation, poor grain filling and yield formation in R201.

Keywords: grain yield formation; non-structural carbohydrates; rice (Oryza sativa L.); source-flow-sink attributes; translocation; unloading of assimilates.

FIGURE 1

The non-structural carbohydrates (NSC) concentration in stems (A,B) and rachis (C) and the ratio of stem NSC to rachis NSC (D) of rice R91, R156 and R201 under low (LN) and high nitrogen (HN) conditions at heading and maturity. Different letters placed on top of histograms denote significant difference at p < 0.05 under the same nitrogen condition. ^∗Indicates significant difference for the same line between LN and HN at p < 0.05. Data are shown as mean ± standard error.

FIGURE 2

The apparent transferred mass (A) and apparent ratio (B) of stem NSC, and apparent contribution of stem NSC to grain yield (C) of rice R91, R156 and R201 under low (LN) and high nitrogen (HN) conditions during grain filling period. Different letters placed on top of histograms denote significant difference at p < 0.05 under the same nitrogen condition. ^∗Indicates significant difference for the same line between LN and HN at p < 0.05. Data are shown as mean ± standard error.

FIGURE 3

The leaf area index (A), specific leaf weight (B) at heading stage and dynamic of SPAD values (C,D) during grain filling of rice R91, R156 and R201 under low (LN) and high nitrogen (HN) conditions. Different letters placed on top of histograms denote significant difference at p < 0.05 under the same nitrogen condition. ^∗Indicates significant difference for the same line between LN and HN at p < 0.05. Vertical bars indicate LSD_0.05 for comparing the means among the three lines at an identical stage or date. PI, panicle initiation; HD, heading date; DAH, day after heading. Data are shown as mean ± standard error.

FIGURE 4

Activities of α-amylase (A), β-amylase (B), sucrose phosphate synthase (C), and sucrose synthase in the synthetic direction (D) in stems of rice R91, R156 and R201 under low (LN) and high nitrogen (HN) conditions. Different letters placed on top of histograms denote significant difference among the three lines at p < 0.05 under the same nitrogen condition. ^∗Indicates significant difference for the same line between LN and HN at p < 0.05. Data are shown as mean ± standard error.

FIGURE 5

Number (A,B), average cross sectional area (C,D), total cross sectional area (E,F) of large and small vascular bundle of rice R91, R156 and R201 under low (LN) and high nitrogen (HN) conditions. Different letters placed on top of histograms denote significant difference at p < 0.05 under the same nitrogen condition. ^∗Indicates significant difference for the same line between LN and HN at p < 0.05. Data are shown as mean ± standard error.

FIGURE 6

The ratio of number (A,C) and cross sectional area of vascular bundle (B,D,E), and non-structural carbohydrates (NSC) content to spikelet (F) of rice R91, R156 and R201 under low (LN) and high nitrogen (HN) conditions. Different letters placed on top of histograms denote significant difference at p < 0.05 under the same nitrogen condition. ^∗Indicates significant difference for the same line between LN and HN at p < 0.05. Data are shown as mean ± standard error.

FIGURE 7

Activities of acid invertase (A), neutral invertase (B), sucrose synthase in the cleavage direction (C), and AGPase (D) in developing grains of rice R91, R156 and R201 under low (LN) and high nitrogen (HN) conditions. Different letters placed on top of histograms denote significant difference among the three lines at p < 0.05 under the same nitrogen condition. Data are shown as mean ± standard error.