Robustness of central carbohydrate metabolism in developing maize kernels

Area of Science:

• Plant biochemistry
• Metabolic flux analysis
• Maize (Zea mays L.) genetics

Background:

• Central carbohydrate metabolism supplies precursors for seed storage product synthesis.
• Organization and flexibility of these metabolic fluxes under varying demands remain poorly understood.
• Developing maize kernels serve as a model for starch and sugar metabolism studies.

Purpose of the Study:

• To investigate the organization and flexibility of carbohydrate metabolic fluxes in developing maize kernels.
• To determine how biosynthetic demands and genetic perturbations influence these fluxes.
• To understand the stability of carbohydrate flux distribution in response to genetic mutations.

Main Methods:

• Utilized (13)C-labeling experiments with maize inbred lines, hybrids, and starch-deficient mutants.
• Conducted 46 labeling experiments using [U-(13)C(6)]glucose or [U-(13)C(12)]sucrose across three kernel development stages.
• Estimated carbohydrate flux distributions via quantitative (13)C-NMR and GC-MS analysis of glucose isotopologues in starch hydrolysates.

Main Results:

• Observed similar labeling patterns across all samples, indicating robust and stable carbohydrate fluxes in maize endosperm.
• Fluxes remained stable despite variations in glucose/sucrose feeding and during kernel development.
• Mutations in ADP-glucose pyrophosphorylase (bt2, sh2) significantly increased hexose cycling, unlike other mutations with similar kernel phenotypes.

Conclusions:

• Carbohydrate flux distribution in maize kernels is stable and not primarily determined by sink strength.
• Specific genetic defects, particularly in starch synthesis, can perturb metabolic flux distribution.
• The findings highlight the robustness of central carbohydrate metabolism in maize seeds.