Changes in gene expression in slash pine in response to disease and water stress

Abstract

Evidence is presented here for stress-induced changes in gene expression and the specificity of plant metabolic responses to applied stress. Analysis of changes in the rate and pattern of protein synthesis in slash pine (Pinus elliottii Engelm) due to disease and water stress was investigated. Electrophoretic analyses of extracts of slash pine seedlings infected with the pitch canker fungus (Fusarium moniliforme var. subglutinans) revealed induction of a 55 kD stress protein in hypocotyl and root sections after a lag phase of 16 h. The stress protein is best extracted from stressed tissues with slightly alkaline Tris-HCl (pH 8.65) buffer and is not detected in healthy tissues. Further, the possibility of induction of stress proteins under different pathological conditions was investigated with abiotic elicitors as challenge inoculum. Gel electrophoretic separations of protein ex tracts revealed no detectable changes in seedlings challenged with heat killed and autoclaved spore suspensions. In contrast, seedlings challenged with cell-free culture extracts responded with induction of a 57 kD protein. The relationship between low water potentials and protein synthesis was also investigated in slash pine hypocotyls and callus cultures. Protein synthesis was assessed at varying water potentials (-0.8, -1.3, -1.8 and -2.5 M Pa) by labeling cells with [35]S-methionine at different incubation times. Water stress was induced by incubating seedling and callus cultures in growth media containing different levels of mannitol (0 to 15%). As the water potential decreased, the relative rates of the label uptake as well as its incorporation into proteins also decreased. The responses elicited by water stress in hypocotyls and callus cultures arc apparently distinct and tissue specific. Hypocotyl sections exposed to -1.8 M Pa for 24 h show induction of a 46 kD protein; at -2.5 M Pa at least five new proteins of 82 kD, 71 kD, 70 kD, 64 kD and 58 kD were induced. When stressed hypocotyl sections were returned to treatment medium without mannitol, normal protein synthesis appeared to resume. The pattern of protein synthesis in slash pine callus cultures subjected to -1.8 M Pa for 16 h showed induction of three proteins of 21 kD, 57 kD 80 kD and enhanced synthesis of five other proteins...