Microscopic and Protein Expression Analysis of Grain Weight Variation within the Spike of Triticum aestivum

The kernels possess significant grain weight variation in one wheat (Triticum aestivum L) plant because of their different positions within the spike. In order to understand the molecular basis of weight, a proteomic approach, employing twodimensional electrophoresis and matrix-assisted laser desorptionfionization time of flight mass spectrometry (MALDI-TOF MS), was used to identify proteins between two kinds of kernels, the high weight kernel (large kernel) and the low weight kernel (small kernels) with different positions within spikes of one wheat cultivar, Shannong. Microscopic observation showed that the endosperm cells in large kernels enlarged their volume and accumulated storage materials at grain filling stage (17 days after anthesis, DAP), whilst those in small kernels were mainly in cell division with larger vacuoles during this period. Proteins were extracted from the kernels at this time, and resolved using 24-cm immobilized pH gradient strips with a pH 3–10 linear gradient in the first dimension and a 12.0% sodium dodecyl sulphate-polyacrylamide gel electrophoresis in the second dimension. About 750 protein spots in each gel were resolved after electrophoresis and 45 proteins were expressed significantly differently between the two kernels. MALDI-TOF MS characterization of the resolved spots in the two samples enabled us to identify 28 proteins whose levels were altered; 19 and 9 proteins were up-regulated in high and low weight kernels, respectively. In particular, proteins beneficial to materials synthesis and transmission increased distinctly in high weight kernels, while in low weight kernels, proteins involved in cell division were increased. The kernels with different position in spike might be at different physiological status, and this might be one of the causes resulting in grain weight differences within one spike.