Apoptosis in Wheat Seedlings Grown under Normal Daylight

N. I. Aleksandrushkina¹, V. A. Zamyatnina¹, L. E. Bakeeva¹, A. V. Seredina^1,2, E. G. Smirnova², L. S. Yaguzhinsky¹, and B. F. Vanyushin^1,2*

¹Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119899, Russia; fax: (7-095) 939-3181; E-mail: vanyush@belozersky.msu.ru

²Institute of Agricultural Biotechnology, Russian Academy of Agricultural Sciences, Timiryazevskaya ul. 42, Moscow 27550, Russia

^* To whom correspondence should be addressed.

Received February 12, 2003; Revision received July 2, 2003

---

Apoptosis was observed in the coleoptile and initial leaf in 5-8-day-old wheat seedlings grown under normal daylight. Apoptosis is an obligatory event in early wheat plant ontogenesis, and it is characterized by cytoplasmic structural reorganization and fragmentation, in particular, with the appearance in vacuoles of specific vesicles containing intact organelles, chromatin condensation and margination in the nucleus, and internucleosomal fragmentation of nuclear DNA. The earliest signs of programmed cell death (PCD) were observed in the cytoplasm, but the elements of apoptotic degradation in the nucleus appeared later. Nuclear DNA fragmentation was detected after chromatin condensation and the appearance in vacuoles of specific vesicles containing mitochondria. Two PCD varieties were observed in the initial leaf of 5-day-old seedlings grown under normal daylight: a proper apoptosis and vacuolar collapse. On the contrary, PCD in coleoptiles under various growing (light) conditions and in the initial leaf of etiolated seedlings is only a classical plant apoptosis. Therefore, various tissue-specific and light-dependent PCD forms do exist in plants. Amounts of O₂^-· and H₂O₂ evolved by seedlings grown under normal daylight are less than that evolved by etiolated seedlings. The amount of H₂O₂ formed in the presence of sodium salicylate or azide by seedlings grown under normal daylight was increased. Contrary to etiolated seedlings, the antioxidant BHT (ionol) did not inhibit O₂^-· formation and apoptosis and it had no influence on ontogenesis in the seedlings grown under normal daylight. Thus, in plants grown under the normal light regime the powerful system controlling the balance between formation and inactivation of reactive oxygen species (ROS) does exist and it effectively functions. This system is responsible for maintenance of cell homeostasis, and it regulates the crucial ROS level controlling plant growth and development. In etiolated plants, this system seems to be absent, or it is much less effective.

---

KEY WORDS: antioxidant, apoptosis, cytoplasm fragmentation, coleoptile, hydrogen peroxide, ontogenesis, plants, wheat

---