Compostos nitrogenados e carboidratos em sorgo submetido à salinidade e combinações de nitrato e amônio

Abstract

Compostos nitrogenados e carboidratos em sorgo submetido à salinidade e combinações de nitrato e amônio 1 Nitrogenous compounds and carbohydrates in sorghum subjected to salinity and combinations of nitrate and ammonium ), na presença e ausência de salinidade. A salinidade reduziu a concentração de nitrato nas folhas e colmo, nos tratamentos 100:0 e 75:25. O amônio acumulou-se mais nas plantas com NaCl, nas folhas e colmo. Os teores de aminoácidos livres totais nas folhas não se alteraram, mas, no colmo, aumentaram na presença de sal e aumento do amônio. A concentração de prolina livre nas folhas e colmo elevou-se nas plantas sob salinidade. O conteúdo de nitrogênio total foi maior nas folhas, entretanto não houve grandes alterações com a presença do sal. A concentração de carboidratos solúveis totais foi maior nas plantas tratadas com sal, exceto no colmo 0:100. Nas folhas, o teor de sacarose foi reduzido na presença do NaCl e aumento de amônio, enquanto, no colmo, foi maior no tratamento 75:25 com NaCl. O teor de amido não sofreu alterações com as diferentes combinações nas formas de N e salinidade. Conclui-se que combinações de NO -3 e NH 4 + no meio afetam a acumulação de compostos nitrogenados e carboidratos em folhas e colmo, com presença ou ausência de salinidade, em plantas de sorgo forrageiro. Palavras-chave -Sorghum bicolor. Nitrogênio. Estresse salino.Abstract -The objective of this study was to evaluate the effects of combinations of nitrate and ammonium in the medium, on the accumulation of nitrogen compounds and carbohydrates, in the presence and absence of salinity in sorghum plants. CSF 20 genotype sorghum seeds, were grown in the greenhouse and supplied with a nutritive solution at three different concentrations of nitrate and ammonium (100% NO 3 -: 0% NH 4 + , 75% NO 3 -: 25% NH 4 + e 0% NO 3 -: 100% NH 4 + ) both in the presence and absence of NaCl. Salinity reduced the nitrate concentration in both leaves and stalks in treatments at 100:0 and 75:25. The accumulation of ammonium was higher in those plants, in both leaves and stalk, in the presence of NaCl. The levels of free amino acids in the leaves showed no change, whereas those in the stalk increased in the presence of salt and with the increase of ammonium. The concentration of free proline in both leaves and stalk was higher in plants under salinity. The total nitrogen content was higher in the leaves without, however, showing much change in the presence of salt. The concentration of total soluble carbohydrates was higher in those plants treated with salt, except in the stalk 0:100. Sucrose levels in the leaves were lower in the presence of NaCl and the increase in ammonium, while they were higher in the stalk at 75:25 NaCl. The starch content did not alter much with the different levels of nitrogen and salinity. It is concluded that NO -3 and NH 4 + combinations in the medium affect the accumulation of nitrogen compounds and carbohydrates in the leaves and stalks of sorghum plants, both in the presence and absence of salinity.

Photosynthetic pigments, cell extrusion and relative leaf water content of the castor bean under silicon and salinity

“…The decrease in the contents of chlorophyll 'b' was less in plants subjected to the highest Si levels. This can be a consequence of the beneficial effect of Si on plant metabolism, especially through the amorphous Si layer formed in epidermal cells (Lima et al, 2011), which can promote greater relief of the water deficit stress (Ávila et al, 2010) caused by the reduction of soil water potential and the accumulation of toxic ions of Na + and Cl - (Rodrigues et al, 2013).…”

“…These values represented increments in cell extrusion of 61.3, 59.5, 59.4 and 66.9%, compared with the estimates in the control (0 dS m -1 ), despite the decrease in electrolyte leakage as a function of the increment in Si levels. This may have occurred due to the increase in cell wall thickness and the strengthening of the membrane, promoted by the action of Si in the plant tissue (Lima et al, 2011).…”

“…The depletion in RWC in the leaves must have occurred due to the osmotic effect of the salts in the substrate (Sousa et al, 2011), especially because of the reduction in soil water potential, which compromises water absorption by plants (Lobo et al, 2011). Thus, the lower reduction in RWC with higher Si levels must be related to its beneficial effect, which is due to the decrease in transpiration rate and consequent better use of water, resulted from the improvement in plant morphophysiological structure associated with the reduction of the osmotic effect of salts in the substrate, facilitating the absorption by the roots (Lima et al, 2011).…”

“…Thus, the lower reduction in RWC with higher Si levels must be related to its beneficial effect, which is due to the decrease in transpiration rate and consequent better use of water, resulted from the improvement in plant morphophysiological structure associated with the reduction of the osmotic effect of salts in the substrate, facilitating the absorption by the roots (Lima et al, 2011).…”

“…The use of silicon (Si) through foliar application can be a viable alternative to mitigate the harmful effects of salts in plants (Lima et al, 2011). This occurs because, although Si is not considered an essential element (Giongo & Bohnen, 2011), it can optimize some desirable physiological processes, by increasing significantly the yield of cultivated species, notably by the accumulation and polymerization of silicates in epidermal cells.…”