To understand the physiological and ecological aspects of plant growth, it is necessary to study the physiology of plant development, as well as the effects of certain environmental factors on plant growth depending upon the developmental stages when these factors act. The effect of a long-term (24 h) high-temperature (42 °C) shock on wheat seedlings (Triticum aestivum L.) was analyzed taking into consideration changes in the growth of wheat seedlings (maximum length of root and length of first leaf and coleoptile) and some changes on the molecular level, such as superoxide anion (O₂^–) production and malodialdehyde (MDA) content. The effect of high temperature was analyzed at the early (4-day-old) and late stages (7-day-old) of seedling development. The long-term high-temperature exposure strongly inhibited the development of roots and first leaves, but did not affect the growth of the coleoptile at the early stages of development. However, high-temperature exposure at the late stages of seedling development affected only the growth of the root system. This effect remained also two days after the high-temperature exposure. The increase of O₂^– production, which was observed in the first leaf of wheat seedlings at all stages of development, led to an increase of MDA concentration. Material changes in the level of O₂^– production were observed in the roots of wheat seedlings grown under high temperature exposure for 24 h at all stages of development, but MDA concentration in the roots of experimental and control seedlings almost did not differ at the early and late stages of development. The level of O₂^– production in the coleoptile cells increased after a high-temperature exposure at the late stages of seedling development. A significant increase of MDA content in the coleoptile was observed immediately after the experiment at both early and late stages of seedling development and then decreased slightly within two days after treatment, though it was higher than MDA content in control seedlings.

Keywords: heat shock, lipid peroxidation, malondialdehyde, oxidative stress, superoxide production, wheat seedlings