Turkish Journal of Botany

Effect of High-Temperature and Salt (NaCl) Stresses on Polyphenoloxidase Activity During Seed Germination




The ability of the polyphenoloxidase (PPO) enzyme in the embryos and food tissues of the seeds of bean (Phaseolus vulgaris L. cv. Magnum) and corn (Zea mays L. cv. Merit) to oxidize the substrates of dopa and catechol was studied in order to record how it is affected by temperature and salt (NaCl) factors during a 5-day period of germination of these seeds. The higher salt concentration, the lower activity of PPO which oxidizes dopa in the embryo and cotyledon of bean. Salinity and temperature, particularly 30¼ and 35¼C, probably had a synergistic effect on the inhibition of enzyme activity in the embryo of this seed. Catechol - oxidizing PPO in the embryo and cotyledon was generally insensitive to the factors of salt and temperature. The increasing concentrations of salt did not generally inhibit dopa oxidation in corn embryos. This substrate oxidation generally rose with an increase in the salt level at all the temperatures, particularly at 20¼C, in the endosperm. Catechol oxidation markedly increased with a rise in the level of salt, especially at 20¼C, in both parts of the seed. On the other hand, dopa oxidation was higher in the embryos of both types of seed than in their food tissues. In addition, dopa oxidation in the embryos of these seeds was found to be higher than that of catechol. The oxidation of both substrates occurred to a greater extent in corn than in bean.


Germination, high temperature stress, salt stress, polyphenoloxidase.

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