RESUMO A seca é o fator ambiental que mais prejudica a produtividade das culturas. Alguns produtos químicos têm sido utilizados na agricultura para mitigar os danos causados por esse estresse nas plantas. Portanto, examinamos se a pulverização dos compostos sulfato de zinco (ZS), fosfito de potássio (FP) e doador de sulfeto de hidrogênio (H2S) - hidrossulfeto de sódio (NaHS) - mitigam os efeitos deletérios do déficit hídrico em plantas de girassol, analisando características fisiológicas e biométricas. O experimento foi conduzido em casa de vegetação sob delineamento de blocos ao acaso com cinco repetições. Os tratamentos foram arranjados em esquema fatorial 4 x 2: [Fator A (aliviadores)] - pulverização de FP (0.5 L ha-1), ZS (3.2 kg ha-1), NaHS (1.2 g ha-1), e água; [Fator B (umidade do substrato, US)] - 100% (bem irrigado) e 30% (déficit hídrico, DH) da capacidade de campo. Nas condições de DH, os aliviadores levaram à manutenção de maiores valores de potencial hídrico (ΨW), menor teor de malonaldeído foliar (MDA) e aumento da atividade da enzima antioxidante peroxidase (POX), exceto para ZS. Entretanto, o potencial osmótico foliar, a concentração de prolina, as variáveis relacionadas às trocas gasosas, fluorescência da clorofila a e as características biométricas diferiram apenas em função do fator US. Os resultados de ΨW e MDA em plantas de girassol sob DH são indicativos da capacidade mitigadora do ZS, FP e H2S. Assim, a pulverização desses compostos em plantas de girassol mitiga os efeitos do DH, atuando especificamente em processos fisiológicos relacionados a respostas antioxidantes e na manutenção de água nos tecidos foliares.

ABSTRACT Drought is the most harmful environmental factor crop productivity. Some chemicals are used in agriculture to mitigate the damage from this stress on plants. Therefore, we examined whether the spraying of zinc sulfate (ZS), potassium phosphite (KPhi) and the hydrogen sulfide (H2S) donor sodium hydrosulfide (NaHS) would mitigate the deleterious effects of water deficit on sunflower plants by analyzing physiological and biometric characteristics. The experiment was carried out in a greenhouse using a randomized block design with five replications. The treatments were arranged in a 4 x 2 factorial scheme: [Factor A (Alleviators)] - spraying of KPhi (0.5 L ha-1), ZS (3.2 kg ha-1), NaHS (1.2 g ha-1), and water; [Factor B (substrate humidity, SH)] - 100% (well irrigated) and 30% (water deficit, WD) of field capacity. Under WD conditions, alleviators led to the maintenance of higher values of water potential (ΨW), a lower content of leaf malonaldehyde (MDA), and increased activity of the antioxidant enzyme peroxidase (POX), except for ZS. However, leaf osmotic potential, proline concentration, variables related to gas exchange and chlorophyll a fluorescence, and biometric characteristics differed only according to the SH factor. The results of ΨW and MDA for sunflower plants under WD are indicative of the mitigating capacity of ZS, KPhi, and H2S. Thus, the spraying of these compounds on sunflower plants mitigates the effects of WD, acting specifically in physiological processes related to antioxidant responses and in the maintenance of water in leaf tissues.

ABSTRACT The maturing of drift used in the culture of sugar cane can have harmful effects on other crops grown in the vicinity of sugar cane plantations. Among these, sunflower grown in the off-season can have its growth and productivity affected by drift. The objective of this research was to evaluate whether the drift of trinexapac-ethyl and glyphosate promotes changes in the photosynthetic metabolism of sunflower plants. Two trials were carried out to evaluate the effects of these products on gas exchange, chlorophyll fluorescence, chloroplastid pigments, membrane permeability, sugar content, as well as shikimic acid and malondialdehyde concentration in the treated plants. In the first experiment, we tested glyphosate in doses of 0 (control); 3.6; 7.2; 14.4; 28.8; and 86.4 g a.e.∙ha−1 and in the second, trinexapac-ethyl at doses of 0 (control) 3.12; 6.25; 12.50; 25, and 75 g a.i.∙ha−1. The growth regulator trinexapac-ethyl did not change the photosynthetic metabolism of plants. However, glyphosate caused damage to the photosynthetic apparatus and a reduction in the carbohydrate concentration and chloroplastid pigments, with casual damage to cell membranes; these effect were more intense at increased doses. The effects of glyphosate were evidenced by the increased concentration of shikimic acid, derived from its mechanism of action. Concludes that, the photosynthetic metabolism of sunflower plants is not affected by the growth regulator trinexapac-ethyl, unlike to the evident effects after application of glyphosate.