Water uptake, anatomical, and biochemical changes of sorghum genotypes subjected to polyethylene glycol-induced drought stress

Abstract

Absract To investigate the water uptake, anatomical and biochemical changes of sorghum, three genotypes including grain sorghum [Sorghum bicolor (L.) Moench subsp. bicolor], Sudan grass [Sorghum bicolor (L.) Moench subsp. drummondii (Steud.) de Wet ex Davidse] and Johnson grass [Sorghum halepense (L.) Pers.] were subjected to polyethylene glycol (PEG 60000)-induced drought stress (PEG 60000) at 0, −0.15, and −0.3 MPa levels, hydroponically. In all genotypes, stele diameter decreased as osmotic potential of the medium decreased and the largest stele diameter (247 µm) was observed in Johnson grass at control and declined to 196 µm under −0.3 MPa PEG. Drought affected the diameter of peripheral metaxylem (PMX) and central metaxylem (CMX), negatively. The number of PMX and CMX in Johnson grass was 36 and 200% more than in grain sorghum under −0.3 MPa PEG, respectively. In all genotypes, chlorophyll a and b declined under drought, but in Johnson grass, it only decreased 25 and 29%, respectively. Johnson grass had the highest total chlorophyll content, while carotenoid content was stable under drought stress in this genotype. Drought stress increased catalase and peroxidase activities but decreased relative water content (RWC) and hydraulic conductivity (hc). Under drought, the higher seedling dry weight and root to shoot ratio in Johnson grass might be related to higher hc, total chlorophyll content, and RWC. Moreover, Johnson grass showed less water loss and more efficiency in water uptake under induced drought stress; and it could be attributed to the larger stele diameter, number, and diameter of PMX, substantiating their roles in drought adaptation.