MECANISMOS DE TOLERÂNCIA AO DÉFICIT HÍDRICO E A ALTA TEMPERATURA EM PLANTAS DE GIRASSOL TRATADAS COM COMPOSTOS MITIGADORES

Abstract

Water and heat stress are two of the most important abiotic factors that affect crop productivity, including sunflower. In agriculture, the use of stress-mitigating compounds has been a promising strategy to reduce the negative effects of these stresses on plants. This study evaluated the effect of spraying zinc sulfate (SZn), potassium phosphate (KPhi), and hydrogen sulfide (NaHS) on sunflower plants under drought and heat stress. In Chapter 1, it was observed that the application of SZn, KPhi, and NaHS induced drought stress defense responses related to antioxidant metabolism and water maintenance in leaf tissues. These compounds were able to increase water potential (ΨW) and reduce malondialdehyde (MDA) levels in treated plant leaves, through increased antioxidant defenses. In Chapter 2, the effect of spraying SZn and KPhi on dwarf sunflower plants subjected to heat and drought stresses was studied. It was found that the spraying of these compounds helped the plants to tolerate the negative effects of these stresses, even when combined. Plants treated with SZn showed higher antioxidant enzyme activity, effective quantum yield, and proline production compared to untreated plants. KPhi was also effective in increasing the activity of ascorbate peroxidase and peroxidase enzymes, as well as effective quantum yield of FSII and carotenoid content under combined drought and high temperature conditions. In summary, the results support the hypothesis that spraying SZn and KPhi can be effective in reducing the detrimental effects of drought and heat stress in sunflower plants under controlled conditions. These compounds act through different mechanisms, including water maintenance in leaf tissues and increased antioxidant defenses.