Alterações fisiológicas e bioquímicas em plantas de Macroptilium lathyroides (L.) Urb submetidas ao déficit hídrico e diferentes fontes de nitrogênio

Abstract

Several works in the literature address the plant biochemical changes in response to drought such as the accumulation of osmoprotectants and antioxidants. It should be highlighted that the understanding of the effect of N sources such as nitrate and ammonium in the response of leguminous forages, mainly native species, such as “feijão dos arrozais” (Macroptilium lathyroides (L.) Urb) is extremely important because it allows to know the adaptative responses of this species, especially in the current scenario of climate change in relation to water deficit tolerance. The objectives of this study was to characterize the biochemical and morphophysiological alterations in M. lathyroides plants subjected to different periods and intensities of water deficit and recovery and, evaluate the effects of nitrogen sources, nitrate or ammonium in relation to biochemical responses to water deficit tolerance and stress recovery. Thus, two experiments were conducted with plants grown from seeds collected in the field and grown in greenhouse conditions. After 42 days of sowing, the plants were transferred to hydroponics in plastic pots, with capacity of 3 L containing half strength Hoagland´s nutrient solution. In the first experiment, four plants per pot were grown in hydroponic system and after 25 days, when plants reached the reproductive stage, they were subjected to water deficit treatments by the application of PEG 6000 with water potentials: -0; -0.0125, -0.025, -0.05 and - 0.1MPa. The treatments consisted of control (without application of water deficit) and application of water deficit (24h-DH and 72h-DH), followed by recovery, when roots were washed with distilled water and kept in hydroponics for 24 hours and 72 hours (24h-REC and 72h-REC) in the absence of PEG, for further evaluation. In the second experiment, the plants were transferred to hydroponics in 3 L plastic pots, containing the nitrogen sources NO3- (15mM) or NH4+ (15mM). After 26 days of grown in the hydroponic system, when the plants were at the reproductive stage, the water stress induction was established with PEG-6000 for the hydric potentials of zero and -0.025MPa. The periods of water deficit and recovery where the same of first experiment. The water potentials of -0.05 and -0.1 MPa in the first experiment were the ones that induced physiological responses, with the most severe effect of water deficit, interfering significantly in growth characteristics of shoots and roots. The enzymatic antioxidant defense system was activated avoiding ou minimizing oxidative damages by the EROs formation in the water potential -0.0125, -0.025 MPa and -0.05 MPa in leaves and -0.0125 and -0.025 MPa in roots. Osmotic adjustment occured concomitantly with proline, amino acids and total soluble sugars accumulation in leaves and roots, favoring the uptake of water by the plants and promoting recovery of oxidative stress. In the second experiment, plants under water deficiency responded efficiently to nitrogen sources, presenting increase of proline, amino acids and total soluble sugars, wich allow tolerance to stress under both sources. Accumulation of these osmolytes were differentiated in leaves and roots, besides higher activities of enzyme nitrate reductase and glutamine synthetase. Nitrate source reduced 12 oxidative stress in leaves and roots of plants subjected to water stress. Results indicate that M. lathyroides presents high adaptative capacity to water deficit and source of available nitrogen.