Browsing by Subject "Fruktane"

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Studies on water-soluble carbohydrates in wheat (Triticum aestivum L.): regulating traits, model analysis, early chilling effects, and future perspectives
(2009) Valluru, Ravi; Claupein, Wilhelm
Wheat is one of the major staple food crops of the world. Although a wealth of research has been made a significant progress in wheat productivity through genetic interventions in the last two decades, there remains an untapped potential for further yield gain. Water-soluble carbohydrates (WSCs) are excess carbohydrates stored in vegetative organs such as stem, sheaths, and tiller base during vegetative period. They are highly heritable agronomic trait that regulates plant growth and development as well as grain yields. In addition, WSCs also contribute to plant adaptation to abiotic stresses. Improving current understanding of the multi-faceted roles of WSCs is therefore essential for future crop improvement. The present thesis provides information on WSCs, its associated traits and future perspectives that derived from several experiments conducted under field and glasshouse conditions. Typically, the thesis has four objectives dealing with a specific set of questions. The first objective explains the traits regulating WSCs under three N levels (0, 100 and 200 kg ha-1). N concentration in the plant is negatively correlated with WSCs storage. The traits associated with total WSCs storage are also influenced by N levels. Three vegetative traits, viz., total biomass, flag-leaf width, root: shoot ratio and two physiological traits, viz., radiation use efficiency, and leaf N concentration were considered. Under high N level, lower biomass, flag-leaf width and root: shoot ratio is beneficial to increase total WSC storage. In contrast, increasing biomass and flag-leaf width is advantageous under lower N level. However, a specific set of traits, rather than a single trait, appeared to evolve under N-specific selection maximizing total WSC storage. The second objective describes the simulation model for WSC accumulation under three N levels. A simple phenological model for carbon accumulation, in the form of WSCs, during vegetative period in four wheat genotypes was developed. This model was integrated and evaluated under crop management factors such as low (0 kg ha-1), medium (100 kg ha-1), and high (200 kg ha-1) nitrogen supply. The proposed model predicted higher rate of WSC accumulation in the early stages of crop growth and lower rates in the later stages. Overall, the model predicted the rate of WSC accumulation with a RMSE of 6.58, suggesting that the proposed model simulated well. Nevertheless, the predicted rate of WSC accumulation was close to the observed data only in low and high N level. The model predicted total WSCs well with the observed data; however, it overestimated total WSCs at early stages and underestimated total WSCs at later stages, largely due to the respective rate of WSC accumulation. Overall, evaluation of the model with the predicted dataset indicated that the prediction errors for the rate of WSC accumulation were more with RMSE between 20-30% in all N levels. For total WSC accumulation, the prediction errors were less, and the RMSE, in most cases, was less than 20% in all N levels. The third objective reveals the plasticity of the phenotypic expression of two primitive wheat species (Triticum monococcum L. and T. dicoccum S.) in response to early chilling stress (4 oC). Early chilling stress resulted in lower total WSCs, in addition to lower flag leaf size, total biomass, specific leaf area and early flowering. While lower specific leaf area may reduce the early chilling stress effects at an individual leaf level, a higher leaf mass ratio and utilization of reserve carbohydrates indicated that the compensatory growth of chilled plants during the recovery period relied on the concerted action of altered resource allocations and reserve carbohydrate consumption. However, the lack of direct selection on sucrose indicates that sucrose has indirect effects on total WSCs. Thus, the total effects of reserve sucrose on relative fitness seem to be buffered via rapid growth rate in chilled plants. Nevertheless, a significant cost of plasticity was evident only for fructans. Further, a regression of daily cumulative plant biomass derived from a crop growth simulation model (CERES-Wheat) on crop growing period revealed a divergent developmental pathway for early chilled plants. These results showed that not only are the characteristic architectures in two Triticum species plastic, but the regulating mechanism of intrinsic developmental (ontogenetic) pathway is also sensitive to early chilling stress. Fourth objective provides future perspectives for WSCs, in particular fructans. Fructans can be involved in freezing tolerance by protecting cellular membranes. This opinion postulates that fructans can be transported from vacuole (site of synthesis) to apoplast (site of action) through vesicles derived from the vacuole. These results can improve the current understanding of WSCs in plant growth and development as well as grain yields. Traits can be used as WSCs markers to prescreen a large number of wheat germplasm for high total WSCs contents. However, a further understanding of different dimensions of WSCs in grain yield improvement and plant growth and development deserves more attention.