The aim of this study was to evaluate the sugarcane responses to varying ammonium:nitrate (NH 4 ? :NO 3-) ratio and to reveal how much NH 4 ?

Acetylcholine (Ach) is a common neurotransmitter in animals, also synthesized in plants, which can have an influence on plant response to stress, also acting as a signaling molecule between root and shoot. The objective of this study was to analyze the possible mitigating effects of exogenous application of Ach on soybean germination under different levels of osmotic potential. The experiments were conducted with soybean [Glycine max (L.) Merrill] genotype Intacta. The seeds were first treated with Ach solutions with the following concentrations: 0.0 (control); 0.5; 1. 0 and 2.0 mM. Then, the seeds were subjected to two water potentials,-0.5 and-1.0 MPa, reached by using mannitol solutions, for the induction of osmotic stress, and a control condition with distilled water. Thus, 12 treatments were established in a double factorial 4 9 3, with 4 levels of Ach and 3 osmotic potential treatments (0.0,-0.5 and-1.0 MPa) with four replicates per treatment. The results showed that the concentration of 1.0 mM Ach, without osmotic stress, presented higher values for total dry mass of the seedlings compared to the control treatment (without Ach supply). In the treatments conducted to test the effectiveness of Ach on the mitigation of severe osmotic stress effects (-1.0 MPa), results showed that the concentration of 0.5 mM Ach showed positive results for the following parameters; dry weight of shoot, root dry weight, total dry mass, which were significantly higher than treatment under 1.0 MPa.

No abstract

Nitric oxide (NO) is an important signaling molecule associated with many biochemical and physiological processes in plants under stressful conditions. Nitrate reductase (NR) not only mediates the reduction of NO 3 − to NO 2 − but also reduces NO 2 − to NO, a relevant pathway for NO production in higher plants. Herein, we hypothesized that sugarcane plants supplied with more NO 3 − as a source of N would produce more NO under water deficit. Such NO would reduce oxidative damage and favor photosynthetic metabolism and growth under water limiting conditions. Sugarcane plants were grown in nutrient solution and received the same amount of nitrogen, with varying nitrate:ammonium ratios (100:0 and 70:30). Plants were then grown under well-watered or water deficit conditions. Under water deficit, plants exhibited higher root [NO 3 − ] and [NO 2 − ] when supplied with 100% NO 3 −. Accordingly, the same plants also showed higher root NR activity and root NO production. We also found higher photosynthetic rates and stomatal conductance in plants supplied with more NO 3 − , which was associated with increased root growth. ROS accumulation was reduced due to increases in the activity of catalase in leaves and superoxide dismutase and ascorbate peroxidase in roots of plants supplied with 100% NO 3 − and facing water deficit. Such positive responses to water deficit were offset when a NO scavenger was supplied to the plants, thus confirming that increases in leaf gas exchange and plant growth were induced by NO. Concluding, NO 3 − supply is an interesting strategy for alleviating the negative effects of water deficit on sugarcane plants, increasing drought tolerance through enhanced NO production. Our data also provide insights on how plant nutrition could improve crop tolerance against abiotic stresses, such as drought.

The root system is essential for sugarcane regrowth and the vigor of ratoon cycles as it represents the unique source of carbon skeletons and energy for the initial plant development. However, root system dynamics after shoot harvesting and its role in sugarcane regrowth remains poorly known. Here, it was hypothesized that sugarcane plants with small volume of root system will accumulate less biomass after shoot harvesting than plants with larger volume and that such regrowth is dependent on root reserves. In sugarcane plants grown in nutrient solution, shoots were cut, and two root treatments were established: reference plants with the entire root system (100%); and plants with half of the root system (50%), randomly removing half of root system. After 37 days of shoot harvesting, plants with the entire root system showed higher shoot, root and total dry mass, root length, root diameter, root area and root volume, when compared with those with 50% of the root system. Sugarcane plants with the entire root system had higher root content of starch, soluble sugar and nonstructural carbohydrates as compared to plants with 50% of the root system. A significant positive correlation was found between the variation of shoot dry mass and the variation of root nonstructural carbohydrates. Interestingly, this data revealed a disproportionate effect of root system size on sugarcane regrowth, with plants with the entire root system accumulating almost three times more biomass than plants with half of the root system during regrowth.