Stem Non-structural Carbohydrates Research Articles

Relationship between Nonstructural Carbohydrate Concentration and Snow Tolerance of Broad Bean (Vicia faba L.).

The relationship between nonstructural carbohydrate (NSC) concentration and snow tolerance of the broad bean was investigated. The growth and NSC of plants in early winter were changed by several sowing times and the use of three varieties (hardy, intermediate, susceptible) to clarify the relation with snow tolerance; furthermore, changes in NSC and injury caused by snow were examined. Although intermediate and susceptible varieties sown in early autumn almost died after 54 days under snow, a hardy variety sown in early autum showed high wintering ability. Plants sown in late autum, which gave a younger morphological state in early winter immediately after germination, showed high wintering ability and a high concentration of over 15% NSC in cotyledon. NSC in cotyledon of the hardy variety was not higher than that in the other two varieties, whereas NSC in foliage except cotyledon and the root of the hardy variety sown earlier was higher than those of two other varieties. From these results, it is suggested that the hardy variety accumulated high NSC in the plants, and that the intermediate and susceptible varieties showed high wintering ability when NSC in cotyledon was utilized for winter. Under the snow, NSC in leaf and stem decreased rapidly. The snow injury of intermediate and susceptible varieties increased rapidly after 36 days under snow, accompanying the decrease of NSC below 1% NSC in leaf and 2% NSC in stem. In contrast, the hardy variety showed no serious injury because of high NSC. The indication was introduced that more than a definite value of NSC in plants was important to maintain a tolerance of snow injury.

Nitrogen and Carbon Accumulation and Remobilization during Grain Filling in Maize under Different Source/Sink Ratios

The relative flow and remobilization of carbon (C) and nitrogen (N) to the grain during the grain filling period depends on the particular source/sink ratio of the crop. The objective of this work was to analyze the C and N accumulation and remobilization patterns of maize (Zea mays L.) under a wide range of source/sink ratios. The experiment was conducted at Balcarce, Argentina, during 2 yr with both a shortand long‐season hybrid. The treatments consisted of two levels of source reduction (45 and 55% shading during the grain filling period), two levels of reproductive sink reduction (45 and 55% shading during a 30‐d period bracketing silking), and an unshaded control. The shading treatments had a variable duration (30=38 d) to ensure constant incident radiation. The source limitation produced increases in remobilization rates of leaf + stem reduced N (Nred) and stem nonstructural carbohydrates (CH) compared with the control. The sink limitation generated greater stem CI‐I accumulation and less Nred remobilization from the leaf and stem. Sink‐limited treatments had greater postanthesis N absorption and grain N concentration than the sourcelimited treatments. As the source/sink ratio decreased, N flow to the grain per unit of C flow decreased suggesting that N becomes more limiting for grain yield with increasing source limitation. Linear quantitative relationships between source/sink ratio and CH remobilization, N remobilization, relative C‐N fluxes to the kernel, and kernel N concentrations have been established.

Defoliation and Plant Density Effects on Maize Selected for Reduced Plant Height

AbstractSelection for reduced plant height in maize (Zea mays L.) has been accompanied by a reduction in stem volume and in stem nonstructural carbohydrate (SNSC) reserves, which may result in increased instability of grain yield when plants are exposed to stress during grain filling. This possibility was examined when cycles 0, 6, 12, and 18 of a tropical maize population selected recurrently for reduced height were grown in four environments at 3.5 and 6.7 plants m−2 and defoliated by removing all but five, all but three, or no leaves 7 d after 50% silking. Per‐cycle changes were observed in undefoliated plots for stem biomass (−0.116 Mg ha−1), grain yield (0.052 Mg ha−1), optimum plant density for grain yield (0.14 plants m−2), and harvest index (0.009). Lodging declined from 39 to 10% with 18 cycles (C18) of selection. The reduction in SNSC in C18, compared with C0, was 0.66 Mg ha−1. Defoliation increased the per‐cycle reduction in final stem biomass to −0.146 Mg ha−1, but reduced grain yield and harvest index equally in all cycles of selection. At 7 d after silking, SNSC was correlated with final plant height (r = −0.66**, 16 df) and with final kernel number per plant (r = 0.48*, 16 df). Reduction in plant height increased stability of grain yield by reducing lodging and by increasing tolerance to stresses occurring near flowering.

Stem Carbohydrate and Lignin Concentrations in Sorghum Hybrids at Seven Growth Stages

Grain yield and quality of vegetative material from sorghum [Sorghum bicolor (L.) Moench] are affected by carbohydrate and lignin partitioning within the plant and translocation of nonstructural carbohydrates (NSC) to the kernels. This field study was conducted during two growing seasons to determine concentrations of NSC, hemicellulose (HC), cellulose~ and lignin in four sorghum hybrids at seven growth stages from panicle differentiation through 45 days post anthesis (DPA) of plants. Stem NSC increased to 148 g kg−1 in ATx378 × RTx7000, 208 in ATx378 × RTx430, and 268 in ATx623 × SC599‐ 11E from PD to ≈15 DPA, decreased to 47, 85, and 183 between 23 and 32 DPA (kernel blacklayer) and then increased to 280, 340, and 380 at 45 DPA. Stem NSC increased at most stages in ATx623 × Hegari from panicle differentiation to a maximum of 450 g kg−1 at 32 DPA. Hemicellulose decreased and cellulose increased from panicle differentiation to preboot, but concentrations remained relatively stable from anthesis to 45 DPA, with ranges of 425 to 475 g HC kg−1 neutral detergent fiber (NDF) and 440 to 490 g cellulose kg−1NDF. Lignin increased from panicle differentiation to 15 DPA and then stabilized, with concentrations ranging from 75 to 105 g kg−1 NDF. The concentration patterns indicate plant breeders can increase stem NSC in hybrids during kernel filling with careful selection of R.lines and that quality of vegetative material intended for forage or CH4 production can be influenced by harvest at selected growth stages.

Contribution of Stem Dry Matter to Grain Yield in Wheat Cultivars

Field experiments were conducted in the eastern wheat belt of Western Australia in a dry year with and without irrigation (1987) and in a wet year (1988), comparing three cultivars of wheat differing in height and yield potential. The aim of the study was to determine the contribution of remobilisable stem dry matter to grain dry matter under different water regimes in old and modern wheats. Stem non-structural carbohydrate was labelled with 14C 1 day after anthesis and the activity and weight of this pool and the grain was measured at 2, 18 and 58 days after anthesis. Gutha and Kulin, modern tall and semi-dwarf cultivars respectively, yielded higher than Gamenya, a tall older cultivar in all conditions, but the percentage reduction in yield under water stress was greater for the modern cultivars (41, 34 and 23%). In the grain of Gamenya, the increase in 14C activity after the initial labelling was highest under water stress. Generally, loss of 14C activity from the non-structural stem dry matter was less than the increase in grain activity under water stress but similar to or greater than grain activity increase under well watered conditions. Averaged over environments and cultivars, non-structural dry matter stored in the stem contributed at least 20% of the grain dry matter.

Assimilation, Partitioning, and Nonstructural Carbohydrates in Sweet Compared with Grain Sorghum

Nonstructural carbohydrate concentrations in stems are greater for sweet than grain sorghums [Sorghum bicolor (L.) Moench). Knowledge of plant characteristics associated with high nonstructural carbohydrates in sweet sorghum will aid efforts to increase nonstructural carbohydrates in grain sorghum stems. This study tested the hypothesis that variation of CO2 assimilation rate, leaf area, branching at upper nodes, and partitioning of 14C‐labeled assimilate to main stems are associated with variation of stem nonstructural carbohydrates. A sweet (Atlas ✕ Rio) and a grain (ATx623 ✕ RTx5388) hybrid, stages near and after physiological maturity, and defoliation and gibberellic acid (GA3) treatments provided sources of variation for study. Concentrations of nonstructural carbohydrates in lower and upper stems of the sweet hybrid were 1.4 and 2.7 times higher, respectively, than for the grain hybrid, after physiological maturity. Variation in branching, including 14C‐assimilate partitioning to branches, was not consistently associated with hybrid differences in stem nonstructural carbohydrates. Increased recovery (twofold) of 14C‐assimilate in roots and labeled leaves corresponded with lower percentages of 14C‐assimilate and lower concentrations of nonstructural carbohydrates in stems of the grain hybrid. Leaf areas and leaf CO2 exchange rate were twice as great for the sweet hybrid. Although defoliation of the sweet hybrid minimized leaf area differences between hybrids, the sweet hybrid accumulated twice as much nonstructural carbohydrates in branches after physiological maturity. Greater potentials for CO2 assimilation and for 14C‐assimilate accumulation in mature stem tissue were associated with higher levels of stem nonstructural carbohydrates in the sweet compared with the grain hybrid.