Chloroplast membrane organization in chilling-tolerant and chilling-sensitive maize seedlings

Resistance of maize (Zea mays L.) seedlings to chilling-induced damage and its potential bearing on chloroplast membrane organization have been invest igated using a chilling-sensitive inbred CO 316 and a chilling-tolerant inb red CO 328. Paclobutrazol treatment of the chilling-sensitive CO 316 (CO 31 6P) induced chilling tolerance, also causing several morphological and phys iological changes, and served as another means of exploring the relation be tween chloroplast membrane changes and chilling tolerance. Chilling treatme nt [6 degrees C/2 degrees C (day/night)] resulted in a reduction of Fv/Fm r atio, photosynthetic pigment levels and an increase in leakage of electroly tes. Within 24 h of exposure of CO 316 to chilling, the granal and stromal membrane showed extensive vesiculation and disruption of the granal array. By contrast, the granal and stromal organization of chilling-tolerant CO 32 8 and P-treated CO 316 remained nearly intact. Our studies suggest that pac lobutrazol treatment can alter the membrane deterioration and disassembly p rocesses of the thylakoid membranes of chilling-sensitive CO 316 to make th em functionally similar to the chloroplast membrane of genetically chilling -tolerant CO 328.