The root cambium ultrastructure during drought stress in Corylus avellana

Abstract

The activity of the vascular cambium, which plays an important role in plant growth and development, is well known to respond to environmental changes such as drought. Although plant death is suggested to be tightly associated with the death of cambium and other meristematic tissues, direct observations of the cambium ultrastructure during drought-induced mortality remain poorly documented. Here, seedlings of Corylus avellana were drought stressed over various days in autumn to reach xylem water potentials (Ψx, -MPa) between -1 and -5.2 MPa. Light and transmission electron microscopy was applied to visualize the ultrastructure of the root cambial cells, while stem vulnerability curves were obtained to quantify embolism resistance. Seedlings that were moderately water stressed with Ψx less negative than P50 (-2.0 MPa, i.e., the xylem water potential at 50% loss of hydraulic conductivity) showed intact cambium cells. In contrast, the cell membrane of fusiform cambial cells became detached, the tonoplast was shrunken or damaged and cell organelles started to disintegrate in severely water stressed plants with Ψx more negative than P50. Ray cambial cells, however, remained intact and alive for a longer period than fusiform cells. Death of the cambial fusiform cells corresponded more or less to the lethal water potential of this species (Ψlethal = -4.83 MPa). These observations suggest that drought-induced mortality of C. avellana is closely associated with cambial death.