POLYAMINE PATTERN AND BIOSYNTHESIS IN ZYGOTIC AND SOMATIC EMBRYO STAGES OF VITIS-VINIFERA

A comparative study of free polyamine levels, arginine decarboxylase (ADC, EC 4.1.1.19) and ornithine decarboxylase (ODC, EC 4.1.1.17) activities was carried out in the different stages of somatic embryos of Vitis vinifera cv. Grenache noir, and in zygotic embryos of the same cultivar, before and after germination. Somatic embryos showed a high level of free polyamines and a high putrescine/spermidine ratio. On a per unit basis, an accumulation of putrescine (Put) and spermidine (Spd) occurred in the late torpedo stage, which coincided with the beginning of abnormal growth and disorganized cell proliferation. In globular, heart-shaped and torpedo somatic embryos, ADC activity was higher than ODC activity. Later, in giant somatic embryos, a very high ADC and an even higher ODC activity occurred, except when expressed on a dry weight basis. By contrast, zygotic embryos showed a low level of free polyamines and a Put/Spd ratio approximately equal to one. These data suggest that the abnormal behaviour of grape somatic embryos and their low rate of development into plantlets (< 5%) could be due to the high free polyamine content and/or to an inadequate Put/Spd ratio.