Influence of thiourea application on some physiological and molecular criteria of sunflower (Helianthus annuus L.) plants under conditions of heat stress.

High temperature is a major factor limiting the growth of plant species during summer. Understanding the mechanisms of plant tolerance to high temperature would help in developing effective management practices and heat-tolerant cultivars through breeding or biotechnology. The present investigation was carried out to study the role of thiourea in enhancing the tolerance of sunflower plants to heat stress. Sunflower plants were subjected to temperature stress by exposing plants to 35 or 45 °C for 12 h. Two levels of thiourea (10 and 20 mM) were applied before sowing (seed treatment). The results indicated that the plants exposed to temperature stress exhibited a significant decline in growth parameters, chlorophylls, relative leaf water content, oil content, leaf nutrient status, and nitrate reductase activity. Treatment with thiourea, especially when applied at 10 mM, improved the above parameters and induced non-enzymatic and enzymatic antioxidants responsible for antioxidation. SDS-PAGE of protein revealed that high-temperature treatments alone or in combination with thiourea were associated with the disappearance of some bands or the appearance of unique ones. The result of RAPD analysis using five primers showed variable qualitative and quantitative changes. These findings confirm the effectiveness of applying thiourea on alleviating heat injuries in sunflower plants.