Structural development of the nutrient transfer tissues in different waxy wheat grain

Abstract

In the developing wheat grain, nutrients from the spikelet axis are delivered to the endosperm via the nutrient transfer tissues (NTTs). Knowledge of the NTTs development is paramount to understanding the accumulation of starch and protein in wheat grain. In this study, two near-isogenic lines including ‘Shimai19-P’ and ‘Shimai19-N’ and a wheat cultivar ‘Shimai19’ were used to analyze the anatomical structure of the large vascular bundle, chalaza, nucellar projection, and the small vascular bundle in wheat grains at 0–20 days after pollination (DAP) using paraffin sectioning and semi-thin sectioning techniques. The phloem sieve tubes reached the maximal number at 4 DAP in ‘Shimai19-P’ and ‘Shimai19’; however, phloem sieve tubes of ‘Shimai19-N’ reached the maximum number at 6 DAP. The transverse section areas of the small vascular bundles of ‘Shimai19-N’ and ‘Shimai19-P’ reached the highest value at 8 DAP, while the sieve tubes and parenchyma cells in the small vascular vessels decreased significantly. At 12 DAP, nuclei of the chalazal cells in the three wheat varieties began gradually disappearing, with the most apparent changes reported in ‘Shimai19-N’. In conclusion, there was significant variation in the formation of sieve tubes and vessels in large vascular bundles, the disappearance of chalazal cell nuclei, and the transverse section area of small vascular bundles in different waxy wheat grains, which is considered as the important morphological and anatomical basis for the difference of wheat starch and nutrients accumulation.