Abstract
This study aimed to examine the effects of different soil moisture conditions (waterlogging, moderate, drought) on acropetal lignification in protective tissues (hypodermis, cortical sclerenchyma, endodermis) in the 1st nodal roots of Job's tears (waterlogging tolerant, drought susceptible), Japanese barnyard millet (walerlogging and drought tolerant), and pearl millet (drought tolerant, waterlogging susceptible). They were grown in root boxes for 41 days. For Job's tears, lignification in the hypodermis and the cortical sclerenchyma tended to be promoted as the soil moisture conditions became drier, and the reduction in shoot dry weight by drought was not very serious. For Japanese barnyard millet, lignification in the hypodermis tended to be promoted by wetter conditions, while in the cortical sclerenchyma, drought also tended to promote lignification. The shoot dry weight was only slightly reduced under both coditions. Conversely, in pearl millet, the waterlogging drastically inhibited not only the lignification in the hypodermis but even the differentiation of the cortical sclerenchyma itself. Accordingly, shoot as well as root system growth was severely restricted under the same conditions. In contrast, for pearl millet grown under drought, the lignification was promoted in all the three protective tissues, and the shoot growth reduction was relatively slight. These results strongly suggest that the acropetal lignification in these tissues, especially that of the cortical sclerenchyma, may be closely related to waterlogging and drought tolerances of the crops.
