Machackova, L, Hanisova, A, and Krekule, J, 1989, Levels of ethylene, ACC. MACC, ABA and proline as indicators of cold hardening and fro.st resistance in winter wheat. Plant, 76;[603][604][605][606][607] Changes in ethylene production and in the contents of 1-aminoeyelopropane-l-carbt>xylic acid (ACC), l-(malonylamino)-cyclopropane-l-carboxylic aeid (MACC), abscisic aeid (ABA) and L-proline were detennined after 40 days of cold hardening at 4°C in three wheat cultivars differing in frost resistance, Proline and especially ABA accumulated with hardening in all varieties in parallel with the degree of frost resistance, e,g, proline and ABA increases in the non-resistant cv, Slavia were 2x and 5x, whilst in the resistant cv, Mironovska 808 increases were 4x and 20x, Ethylene production and MACC level showed no significant changes with hardening in any of the cultivars after 40 d, but ACC levels did increase with hardening. The production of ethylene, ACC and MACC was studied during hardening, Ethylene production deereased sharply at low temperature and rose rapidly (within 1 day) on return to normal temperature, while ACC production reacted in the opposite direetion, MACC levels rose rapidly during the first 4 days of cold, then more slowly for about 2 weeks, thereafter decreasing again steadily. The only varietal differences occurring at maximum levels were correlated with the degree of frost resistance.
