Progressive inhibition by water deficit of cell wall extensibility and growth along the elongation zone of maize roots is related to increased lignin metabolism and progressive stelar accumulation of wall phenolics.
Water deficit caused by addition of polyethylene glycol 6000 at -0.5 MPa water potential to well-aerated nutrient solution for 48 h inhibited the elongation of maize (Zea mays) seedling primary roots. Segmental growth rates in the root elongation zone were maintained 0 to 3 mm behind the tip, but in comparison with well-watered control roots, progressive growth inhibition was initiated by water deficit as expanding cells crossed the region 3 to 9 mm behind the tip. The mechanical extensibility of the cell walls was also progressively inhibited. We investigated the possible involvement in root growth inhibition by water deficit of alterations in metabolism and accumulation of wall-linked phenolic substances. Water deficit increased expression in the root elongation zone of transcripts of two genes involved in lignin biosynthesis, cinnamoyl-CoA reductase 1 and 2, after only 1 h, i.e. before decreases in wall extensibility. Further increases in transcript expression and increased lignin staining were detected after 48 h. Progressive stress-induced increases in wall-linked phenolics at 3 to 6 and 6 to 9 mm behind the root tip were detected by comparing Fourier transform infrared spectra and UV-fluorescence images of isolated cell walls from water deficit and control roots. Increased UV fluorescence and lignin staining colocated to vascular tissues in the stele. Longitudinal bisection of the elongation zone resulted in inward curvature, suggesting that inner, stelar tissues were also rate limiting for root growth. We suggest that spatially localized changes in wall-phenolic metabolism are involved in the progressive inhibition of wall extensibility and root growth and may facilitate root acclimation to drying environments.
Fan
Ling
L
Plant Physiology Laboratory, Department of Environmental, Water, and Agricultural Engineering, Faculty of Civil and Environmental Engineering , Technion-Israel Institute of Technology, Haifa 32000, Israel.
Linker
Raphael
R
Gepstein
Shimon
S
Tanimoto
Eiichi
E
Yamamoto
Ryoichi
R
Neumann
Peter M
PM
D015152:Blotting, Northern; D002473:Cell Wall / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D008031:Lignin / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D010636:Phenols / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D018517:Plant Roots / Q000166:cytology / Q000187:drug effects / Q000254:growth & development; D011092:Polyethylene Glycols / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water / Q000378:metabolism*; D003313:Zea mays / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism
D010636:Phenols; D010940:Plant Proteins; D014867:Water; D011092:Polyethylene Glycols; D008031:Lignin