Cortical Sclerenchyma Development in Axile Roots of Cereal Crops

A cereal root system consists of different axile roots that develop sequentially, i.e. (a) seminal root(s) (SR), mesocotylar roots (MR), nodal roots which originate from coleoptilar node (coleoptilar nodal root (CNR)), those from the 1st node (1 NR) and so on. The main objective of this study was to examine the histological features of basal parts of these roots with special reference to the occurrence of heterorhizy in cortical sclerenchyma development. Job's tears, Japanese barnyard millet, and pearl millet were planted in root boxes and grown in a growth chamber, with air temperature maintained at 25°C. The root systems were sampled at the 7th leaf expansion stage. In SRs and MRs, cortical sclerenchyma development was not observed among the three species. Some of the MRs in Japanese barnyard millet and pearl millet lacked the central metaxylem vessel. In all the species examined, it was CNR that first developed cortical sclerenchyma in the process of root system formation. In half of the CNRs observed for pearl millet, however, cortical sclerenchyma development was absent, suggesting that its development is quite plastic. Subsequently, its development was also recognized in 1 NRs and 2 NRs. Histological characteristics of this tissue were less distinct in the CNRs, while they were most distinct in the 2 NR. This result suggests that cortical sclerenchyma development in the axile roots of the species proceeded with the progress of ontogeny.