Morpho-physiological, nutritional, and yield responses of tomato ethylene-insensitive mutant Never Ripe to manganese absence

Abstract

Manganese (Mn) is a micronutrient for plants, fundamental for several metabolic process and its deficiency can drastically reduce crop productivity. Ethylene is a phytohormone that can act in responses to nutritional stress that limits growth and development. However, little is known about the role of the ethylene perception and its impact in physiological responses to Mn absence. The tomato ethylene-insensitive mutant Never ripe (Nr) is more tolerant to some nutritional stress. Therefore, the aim of this work was to evaluate the connections of the ethylene perception with Mn absence on the level of plant growth and metabolism. The experiment was conducted in a completely randomized design, comparing two genotypes, the wild-type (WT) and the ethylene-insensitive mutant Nr, in two nutritional levels (control and Mn absence), totaling four treatments. Tomato plants were sown in trays with sand and irrigated daily until cotyledon protrusion. Afterward, the seedlings were transferred to 1L pots containing sand. Control plants received Hoagland's nutrient solution, initially at half strength and then at full strength after one week, while other plants received the Mn-absence treatment. At the end of the vegetative stage, analyses of chlorophyll fluorescence, gas exchange, and sampling of leaves for biochemical analysis were performed. Photosynthetic pigments, carbohydrates, nitrogen compounds, stress-related metabolites and enzymatic activity were quantified. At the end of the experiment, growth and production analyses were performed. For biomass quantification, the plant material was dried and weighed to quantify the dry biomass, which was also used for the determination of nutrient content in the root, stem and leaves. The total nutrient content, accumulation, and manganese use efficiency were determined. In total, 94 parameters of plants subjected to Mn absence were analyzed. Our results show that WT plants presented more stress-related responses than Nr during the Mn absence with several changes in its physiology, here observed for instance by the increase in root size and partition and affected chlorophyll fluorescence. Overall, Nr plans performed better than WT in the Mn absence. We can infer that this was due to the low sensitivity to ethylene, which allowed these plants to maintain their balanced metabolism even under stress due to the Mn absence, observed here by the nutrient use efficiency and gas exchange parameters.