Root cortical senescence enhances drought tolerance in cotton

The root cortex is an important anatomical phenes, and root cortical senescence (RCS) is closely associated with root absorptive function. However, characteristics and responses of RCS to drought stress in cotton have received little attention. This study subjected the drought-tolerant cotton variety “Guoxin 02” and the drought-sensitive variety “Ji 228” to drought stress (8% PEF6000) and no-stress (0% PEG6000) treatments to determine the characteristics and responses of cotton RCS to drought stress. The results showed that the RCS of the two varieties was significantly promoted under drought stress. The greater the distance from the root tip, the more severe the RCS occurrence under drought stress compared with non-stress treatment. The occurrence of RCS in “Guoxin 02” highered by 14.03%-20.18% compared to “Ji 228” under drought stress. Moreover, the RCS was significantly negatively correlated with root respiration but significantly positively correlated with total root length and leaf water potential ( p < 0.05). Indole-3-acetic acid (IAA) content increased, while abscisic acid (ABA) content decreased as the RCS increased. In summary, endogenous hormones regulated the occurrence of RCS, which reduced the root metabolic costs and seemingly achieved more resource redistribution to new roots, thereby expanding the water absorption capacity of roots to fully utilize deep water resources. Thus, the study demonstrates the potential of RCS in improving the drought stress tolerance of cotton.