Respostas fisiológicas e bioquímicas na germinação e desenvolvimento inicial de dois genótipos de Jatropha curcas l. sob deficiência hídrica

Abstract

Jatropha curcas L., commonly known as jatropha, is a species of great economic importance, because the oil contained in its seeds has great potential for the production of biodiesel, besides being used in the manufacture of soap, in the pharmaceutical and cosmetic industries. Physic nut is not yet ready to be cultivated on a large scale, since there is a lack of further studies on the physiology and genetic improvement of the species, among others. On the other hand, water deficiency is one of the climatic factors that characterizes semiarid of the Northeast of Brazil and that most affects the development of the plant, from the germination to the end of its life cycle, and the species that inhabit there, are endowed with an adaptation to survive in these conditions of climate and soil. Thus, this research aimed to evaluate the tolerance to water stress induced by polyethylene glycol (PEG) 6000 in two jatropha genotypes. For that, two experiments were developed and the genotypes used (CNPAE 263 and CNPAE 256) were from Embrapa Agroenergia, Brasília-DF. The first experiment evaluated the percentage of germination (%G), the germination speed index (GSI) and the mean germination time (MGT) of the seeds, in treatments 0,0 (control); -0.2; (Total soluble amino acids, soluble proteins, total carbohydrates and free proline) and the activity of antioxidant enzymes (ascorbate peroxidase - APX, catalase - CAT and guaiacol peroxidase - GPX), in the seedlings of the control treatments and -0.2 MPa. The %G of CNPAE 263 was more affected than the control, from -0.4 MPa, whereas CNPAE 256, significantly reduced the %G in the treatment -0.2 MPa, in 64%, in relation to the control. The GSI of both genotypes was reduced from -0.2 MPa, but in the CNPAE 256 this reduction was more significant (95%). The MGT of the seeds under stress was higher than in the control condition, and these results were more expressive in the CNPAE 256. The seedlings of the genotype CNPAE 263 reduced the protein and carbohydrates contents and did not present changes in the levels of amino acids and proline. Seedlings of the genotype CNPAE 256 reduced the levels of amino acids, proteins and proline, and did not alter those of carbohydrates. With respect to the anti-oxidative enzymes, the genotypes present the same pattern of behavior, with differences in the magnitude of the values. The second experiment evaluated some mechanisms of response of the two Genotypes of jatropha used in the first experiment (CNPAE 263 and CNPAE 256), submitted to the water stress of -0.2 MPa induced by PEG 6000, in hydroponic culture medium. After 30 days of acclimation, the PEG was applied and the treatments were: control (without addition of PEG), after 2, 24 and 48 h of stress imposition. The water relations (leaf water potential - relative water content - RWC), gas exchanges (liquid photosynthesis - A, transpiration - E, stomatal conductance - gs and water use efficiency - WUE) were evaluated. (Total soluble carbohydrates, soluble proteins, total free amino acids and free proline), as well as the activity of antioxidant enzymes (catalase - CAT and ascorbate peroxidase - APX), photosynthetic pigments (chlorophyll a, b, total and carotenoids) In leaves and roots of plants. The experimental design was completely randomized, in a 2x2 factorial arrangement, corresponding to two genotypes (CNPAE 263 and 256) and two water treatments (control and stress - 0.2 MPa of PEG 6000). The water relations of both genotypes were little affected by stress, and there was no change of YL in CNPAE 263, in relation to the control. The RWC of both genotypes were recovered, being more evident in the CNPAE 263. The gas exchanges of both genotypes were affected by the water deficit, being more evident after 48 h, with emphasis on the USA, that after 2 and 24 h of stress were not reduced by this variable. The photosynthetic pigment contents were slightly altered by water stress in both genotypes, with increase of chlorophyll b to CNPAE 263 after 2 h. The organic solutes contents were higher in the leaves than in the roots. At CNPAE 263, water stress increased the carbohydrate, amino acid and proline levels in the leaves, and of carbohydrates and proteins in the roots, while in the CNPAE 256, promoted increase of proline in the leaves and of proteins and proline in the roots. The activity of the antioxidative enzymes was increased in leaves and roots due to stress, in both genotypes, with emphasis on the roots, when CAT and APX activity was significantly higher after 2 h of stress imposition. It can be concluded that both genotypes show differences in the degree of stress tolerance, where the CNPAE 263 showed a higher degree of germination in a stress condition of -0.2 MPa, besides not altering the water relations and accumulating more solutes With the aim of adjusting osmotically, both in the seedlings and in the jatropha plants.