Effect of Melatonin and Dehydration on Lipid Peroxidation Level and Respiration of Pea Embryos, Growth of Seedlings, and Oxidative Activity of Mitochondria in Epicotyls.

Effect of pretreatment with 0.1 µM melatonin and brief dehydration of swelling seeds on water deficit, LP level, respiration of embryos, subsequent growth of epicotyls, and oxidative activity of mitochondria isolated from them were investigated in the seedlings of pea (Pisum sativum L.). Two groups of embryos of the same age but differing by weight and the stage of development were examined separately: swollen embryos that so far did not break the seed coat (group one) and embryos that have broken through the seed coat (group two). Without water supply, water deficit in the embryos from groups one and two increased by 8.7 and 6.9%, respectively, which was tangible for respiratory activity of the embryos. It was shown that the embryos from group two, which broke through the seed coat and contacted air oxygen, experienced a sharp rise in respiratory activity associated with elevation of LP intensity registered by accumulation of the products reacting with thiobarbituric acid. A brief dehydration suppressed respiration of the embryos in this group related to activity of the cytochrome pathway but did not cause oxidative stress; on the contrary, it reduced LP intensity. In swollen embryos that have not yet broken through the seed coat (group one), oxidative stress upon dehydration did not arise either. Pretreatment with melatonin considerably elevated the activity of the cytochrome pathway of respiration in both groups of embryos (in control seeds and upon their dehydration). In mitochondria isolated from the epicotyls of 5-day-old seedlings grown from the seeds pretreated with melatonin and exposed to dehydration, oxidation of NAD-dependent substrate (malate) was activated both under normal and stress conditions. It was also shown that melatonin pretreatment stimulated growth of epicotyls in the seedlings of group two in all the types of treatment, whereas it was observed in the seedlings of group one only after exposure to dehydration. It was concluded that pretreatment of the seeds with melatonin stimulated embryonic respiration owing to activation of the cytochrome pathway, boosted oxidation of malate by mitochondria from epicotyls of the seedlings, and stimulated growth of epicotyls after dehydration. It was shown for the first time that a brief dehydration of embryonic tissues is not necessarily accompanied by oxidative stress. [ABSTRACT FROM AUTHOR]