Efeito do estresse do retículo endoplasmático induzido por Ditiotreitol e tunicamicina em plantulas de sorgo: aspectos morofofisiológicos e metabólicos

Abstract

Adverse environmental conditions can disturb endoplasmic reticulum (ER) homeostasis, from abiotic stresses such as salinity, drought, high temperatures, as well as biotic stresses, such as pathogens and herbivory. This disturbance can lead to an accumulation of misfolded proteins in the lumen, causing an ER stress condition, and thereby activating a cytoprotective pathway, called Unfolded Protein Response (UPR). ER stress and UPR are also induced, in the laboratory, by several chemicals, such as dithiothreitol (DTT) and tunicamycin (TM). Thus, the aim of this work was the induction of ER stress by DTT and TM, evaluating their morphophysiological and metabolic variations in sorghum shoots and roots. For this, seedlings were germinated three days in distilled water, then transferred to half-strength Clark's solution and subjected to ER stress by adding 10 mM DTT and 2.5 μg / ml TM, individually, for four days and evaluated every 24 hours. The shoots dry mass (SDM) had slight differences only at 24 and 48h, while the shoot length (SL) decreased from 24 h in the treatment with TM and 48 h in the treatment with DTT. On the other hand, roots under DTT and TM showed a considerable decrease in both dry mass and length from 24h. Under DTT, roots showed longer length and less root dry mass than under TM, which had a wider abundance of secondary roots and a longer root hair length than DTT. Amino acids, organic acids, carbohydrates, and other groups of metabolites were significantly increased or reduced by ER stress. The shoots had a modulation of 23 and 13 metabolites by DTT and TM, respectively. In turn, the roots had a modulation 37 and 17 metabolites by DTT and TM, respectively. Carbohydrates were the group that showed the highest statistical differences in both shoot and roots. Maltose was the metabolite with the highest accumulation in the initial stages, while Kestose exhibited the highest accumulation in the final stages. Conversely, it was contributed to the separation of roots metabolic profiles of 48 and 72h under DTT, and 72h under TM. Whereas glycolic acid and pyruvic acid showed a significant contribution to the roots under DTT in the early stages. Some amino acids were accumulated in the first hours but others were decreased in the last hours. In general, the roots of seedlings under both ER stressors showed more significant differences than shoots. Besides, in shoots, the cycle of tricarboxylic acids mobilizes amino acid accumulation in the early stages, while in the later stages there was an accumulation of sugars. In roots, inhibition of both glycolysis, the cycle of tricarboxylic acids, and metabolism of amino acids are observed, being more evident in seedlings under DTT. This may be related to the fact that this organ is the first to have contact with the stressor and thus try to mitigate the effects on the shoots.