Metabolic and morphological changes in grass and legume tropical forages related to sulfur supply

Author(s)

Fábiana Schmidt

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2012-12-12

Examining board members

Francisco Antonio Monteiro; Patricia Bulbovas; Helio Grassi Filho; Julio Cesar Lima Neves; Ciro Antonio Rosalem

• Advisor: Francisco Antonio Monteiro

Abstract

Sulfur is an essential element required by plants and the nutritional requirements in this nutrient vary according to species and plant growth rate. This research had the main objective of evaluating the effect of sulfur nutrition on growth and metabolism of Guinea grass (Panicum maximum cv. Tanzânia) and stylo (Stylosanthes guianensis cv. Mineirão) and was developed with the specific objectives to determine the effects on i) morphological, productive and nutritional changes in plant shoots and roots, ii) nitrogen metabolism and the changes in the composition and concentrations of amino acids, iii) concentrations of total sulfur, sulfur-sulfate and glutathione and the activity of the enzymes glutathione reductase and glutathione sulfo-transferase in recently expanded leaves and roots, iv) growth, glutathione metabolism and activity of enzymes involved in ascorbate-glutathione cycle and v) sulfate uptake and expression of sulfur transporters genes. The experiments were carried out in greenhouse and growth chamber, by using nutrient solutions. Sulfur supply were adjusted to low, intermediate and high S nutrition for each species. Sulfur supply influences the emission of leaves, tillering, leaf area, root length and surface of Guinea grass and stylo increasing production of dry mass of aboveground and roots. Sulfur limitation alters the distribution of photosynthates between aboveground and roots of Guinea grass and stylo providing reduction in dry matter production of roots. The plants of Guinea grass increase root surface as a mechanism for adaptation to limited S in the culture medium. The relative chlorophyll index (RCI) in the recently expanded leaves relates to the production of dry mass of aboveground and can be used to assess S nutritional status in Guinea grass and stylo. The application of S proves necessary to increase production of dry mass in Guinea grass and stylo. Low S availability caused nutritional imbalance with N in Guinea grass and stylo plants, as shown by a high N:S ratio and high concentrations of N-nitrate and free amino acids in plant tissues. Among amino acids, asparagine predominated in S-limited guineagrass and arginine in Slimited stylo. Increased S supply regulates N:S ratio at values close to 20:1, which provides N and S concentrations that are more suitable for protein synthesis and forage production in plants of both species. Adding S increased concentrations of total S, S-sulfate, and glutathione in diagnostic leaves and roots of both species collected at the two harvests. Plants grown under S limitation showed high levels of GR activity, related to the regeneration of GSH, which acts to protect cells against oxidative damage caused by the stress of nutritional deficiency. S supply increased GST activity, and consequently plants\' capacity to withstand environmental stresses. Low S availability increased activity of the antioxidant enzymes that act in the regeneration of GSH and AsA. Plants grown with low S availability showed higher concentration of glutathione and greater allocation of glutathione to roots. For Guinea grass, high glutathione concentrations in roots decrease the 34S uptake. For stylo not cause reduction of 34S uptake. (AU)