RESUMO: Resultados de pesquisa envolvendo aspectos fisiológicos da pupunheira (Bactris gasipaes Kunth), fruteira nativa da América Tropical, são escassos. Procurando completar essa lacuna, um experimento sob deficiência hídrica foi conduzido em casa de vegetação, durante um período de 13 dias, utilizando plantas de 12 meses de idade. O objetivo principal foi avaliar as respostas da pupunheira à deficiência hídrica. As variáveis observadas foram: taxa de assimilação de CO 2 , transpiração, condutância estomática e potencial de água das folhas. As coletas dos dados foram realizadas diariamente em laboratório e sob fluxo de 1200 µm -2 s -1 . Os resultados foram submetidos à análise de variância e de regressão. Verificou-se decréscimo no potencial de água da folha e nas trocas gasosas quando a irrigação foi interrompida por mais de seis dias. Valores mínimos foram obtidos no décimo dia, com redução de 92% da fotossíntese líquida, 87% da condutância estomática e 70% da transpiração. O menor potencial de água nas folhas (-1,9 MPa) foi também observado nesse período. Houve recuperação total de todas as variáveis dois dias após reirrigação, com exceção da condutância estomática. A diminuição da condutância estomática e a queda mais rápida da taxa de transpiração que a queda na fotossíntese, indicam a existência de mecanismos de aclimatação em pupunheira, no sentido de diminuir as perdas de água, quando sob condição de estresse hídrico moderado. Palavras-chave: Bactris gasipaes, deficiência hídrica, fotossíntese PHOTOSYNTHESIS, STOMATAL CONDUCTANCE AND TRANSPIRATION IN PEACH PALM UNDER WATER STRESSABSTRACT: Research results on physiological aspects of peach palm (Bactris gasipaes Kunth), a native fruit tree from tropical America, are scarce. Trying to fill this gap, a water deficit experiment was performed under nursery conditions during 13 days, utilizing 12 months old plants. The main objective was to evaluate peach palm responses to water deficit. The measured variables were: CO 2 assimilation rate, transpiration rate, stomatal conductance and leaf water potential. Data were collected daily in a laboratory, under a photosynthetic photon flux (PPF) of 1200 µm -2 s -1 , and studied by variance and regression analysis. Significant decreases of leaf water potential values and gas exchange rates were verified when water was withhold for more than six days.The smallest values were found at the tenth day without water replacement, with a reduction of 92% of the net photosynthetic rate, 87% of the stomatal conductance and 70% of the transpiration. By that time, the smallest measured leaf water potential was -1.9 MPa. Recovering from water stress was accomplished two days after rewatering, except for stomatal conductance. The partial closing of the stomata (decrease in stomatal conductance) and the reduction of photosynthesis, suggest the existence of an acclimation mechanism of the peach palm, diminishing water loss under moderate stress.
Brassinosteroid and substrates in acclimatization of 'Imperial' pineapple. This work aimed to evaluate the effects of different concentrations of a brassinoesteroid analogue (BIOBRAS-16) and two substrates on the growth of micropropagated seedlings of 'Imperial' pineapple. A randomized block design was used in a 2 x 5 x 4 factorial scheme, evaluating five concentrations of BIOBRAS-16 (0; 0.1; 0.3; 0.5 and 1 mg L-1), two types of substrates and four sampling periods (60, 90, 120 and 150 days after planting). The substrates used were Plantmax ® and another obtained from a mix of composting sugar-cane bagasse and filter cake (CC). The seedlings were transplanted to small conic tubes and allocated in a greenhouse equipped with an intermittent mist. The plants cultivated in CC substrate and sprayed with 0.1 mg L-1 of BIOBRAS-16 showed higher growth of shoots with greater numbers of leaves, rosette diameter, leaf width, fresh and dry matter production at 150 days after planting. The plants that were cultivated on CC substrate and sprayed with BIOBRAS-16 at a 0.1 mg L-1 produced 2.8 times more dry matter than the control cultivated in Plantmax ® substrate. The fresh and dry matter of roots were superior in Plantmax ® when compared to CC at late sampling periods.
The molecule vitamin C, in the chemical form of ascorbic acid (AsA), is known to be essential for the metabolism of humans and animals. Humans do not produce AsA, so they depend on plants as a source of vitamin C for their food. The AsA synthesis pathway occurs partially in the cytosol, but the last oxidation step is physically linked to the respiratory chain of plant mitochondria. This oxidation step is catalyzed by l-galactono-1,4-lactone dehydrogenase (l-GalLDH). This enzyme is not considered a limiting step for AsA production; however, it presents a distinguishing characteristic: the l-GalLDH can introduce electrons directly into the respiratory chain through cytochrome c (Cytc) and therefore can be considered an extramitochondrial electron source that bypasses the phosphorylating Complex III. The use of Cytc as electron acceptor has been debated in terms of its need for AsA synthesis, but little has been said in relation to its impact on the functioning of the respiratory chain. This work seeks to offer a new view about the possible changes that result of the link between AsA synthesis and the mitochondrial respiration. We hypothesized that some physiological alterations related to low AsA may be not only explained by the deficiency of this molecule but also by the changes in the respiratory function. We discussed some findings showing that respiratory mutants contained changes in AsA synthesis. Besides, recent works that also indicate that the excessive electron transport vial-GalLDH enzyme may affect other respiratory pathways. We proposed that Cytc reduction by l-GalLDH may be part of an alternative respiratory pathway that is active during AsA synthesis. Also, it is proposed that possible links of this pathway with other pathways of alternative electron transport in plant mitochondria may exist. The review suggests potential implications of this relationship, particularly for situations of stress. We hypothesized that this pathway of alternative electron input would serve as a strategy for adaptation of plant respiration to changing conditions.
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