Pedro A.O. Mangabeira

Leaf gas exchange, chlorophyll fluorescence and growth responses of Genipa americana seedlings to soil flooding

Abstract Effects of soil flooding on photosynthesis and growth of Genipa americana L. seedlings, a neotropical fruit-tree species used in gallery forest restoration programs, were studied under glasshouse conditions. Despite the high survival rate and wide distribution in flood-prone habitats of the neotropics, previous studies demonstrated that growth of G. americana is reduced under soil flooding. Using leaf gas exchange and chlorophyll fluorescence measurements, we tested the hypothesis that stomatal limitation of photosynthesis is the main factor that reduces carbon uptake and growth rates of G. americana seedlings. Throughout a 63-day flooding period, the survival rates were 100%. The maximum values of the net photosynthetic rate ( A ) and stomatal conductance to water vapor ( g s ) of control seedlings were 9.86 μmol CO 2 m −2 s −1 and 0.525 mol H 2 O m −2 s −1 , respectively. The earliest effects of flooding were significant decreases in g s and A , development of hypertrophied lenticels and decrease in the dry weight of roots. A strong effect of the leaf-to-air vapor pressure deficit (LAVPD) on g s and A were observed that was enhanced under flooded conditions. Between 14 and 63 days after flooding, significant reductions in g s (31.7% of control) and A (52.9% of control) were observed followed by significant increments in non-photochemical quenching ( q N ) (187.5% of control). During the same period, there were no differences among treatments for the ratio between variable to initial fluorescence ( F v / F 0 ), the maximum quantum efficiency of the photosystem II ( F v / F m ) and photochemical quenching ( q P ), indicating that there was no damage to the photosynthetic apparatus. Based on the results, we conclude that decreases in stomatal opening and stomatal limitation of photosynthesis, followed by decrease in individual leaf area are the main causes of reductions in carbon uptake and whole plant biomass of flooded seedlings.

Some photosynthetic and growth responses of Annona glabra L. seedlings to soil flooding

Um experimento foi conduzido com o objetivo de analisar os efeitos do alagamento e da posicao das folhas na produtividade primaria liquida e no balanco de carbono em plântulas de Annona glabra L. (Annonaceae), uma especie altamente tolerante ao alagamento e nativa na America tropical. Todas as plântulas sobreviveram ao periodo de alagamento de 56 dias sem apresentarem sintomas de estresse. O alagamento induziu incrementos significativos (P <0,01) na biomassa de raizes, caules e planta inteira, e na razao raizes/parte aerea. Medicoes das trocas gasosas foliares foram conduzidas aos quatro, 11, 18 e 56 dias apos o alagamento, na primeira (L1), quarta (L4) e setima (L7) folha completamente expandida a partir do apice em cada plântula. Os valores medios da condutância estomatica ao vapor de agua (gs) e da taxa fotossintetica liquida (A) nas plântulas controle foram 0,26 mol m-2s-1 e 8,8 µmol m-2s-1, respectivamente. Reducoes significativas (P <0,05) em A foram observadas entre L1 e L7 nas plântulas controle em todos os tres dias de medicoes. As reducoes em A com o aumento da idade foliar tambem ocorreram nas plantas alagadas, apenas nos dias 4 e 18. O alagamento induziu alteracoes significativas em gs (P <0,05), alcancando 65% em relacao ao controle no dia 4 e 152% em relacao ao controle no dia 56. Com base nos resultados obtidos foi possivel concluir que as elevadas taxas de sobrevivencia e de crescimento de plântulas de A. glabra estao diretamente relacionadas com a capacidade de manter elevados valores de condutância estomatica e de taxa fotossintetica liquida em condicoes de alagamento do solo.

Photosynthetic, antioxidative, molecular and ultrastructural responses of young cacao plants to Cd toxicity in the soil

Cadmium (Cd) is a highly toxic metal for plants, even at low concentrations in the soil. The annual production of world cocoa beans is approximately 4 million tons. Most of these fermented and dried beans are used in the manufacture of chocolate. Recent work has shown that the concentration of Cd in these beans has exceeded the critical level (0.6mgkg-1 DM). The objective of this study was to evaluate the toxicity of Cd in young plants of CCN 51 cacao genotype grown in soil with different concentrations of Cd (0, 0.05 and 0.1gkg-1 soil) through photosynthetic, antioxidative, molecular and ultrastructural changes. The increase of Cd concentration in the soil altered mineral nutrient absorption by competition or synergism, changed photosynthetic activity caused by reduction in chloroplastidic pigment content and damage to the photosynthetic machinery evidenced by the Fv/Fm ratio and expression of the psbA gene and increased GPX activity in the root and SOD in leaves. Additionally, ultrastructural alterations in roots and leaves were also evidenced with the increase of the concentration of Cd in the soil, whose toxicity caused rupture of biomembranes in root and leaf cells, reduction of the number of starch grains in foliar cells, increase of plastoglobules in chloroplasts and presence of multivesiculated bodies in root cells. It was concluded, therefore, that soil Cd toxicity caused damage to the photosynthetic machinery, antioxidative metabolism, gene expression and irreversible damage to root cells ultrastructure of CCN 51 cocoa plants, whose damage intensity depended on the exposure time to the metal.

Effects of cadmium on the anatomy and photosynthesis of two aquatic macrophytes.

As macrofitas aquaticas vem sendo usadas no monitoramento de aguas poluidas por metais pesados, dessa forma, avaliou-se a capacidade fitorremediadora de Alternanthera philoxeroides (Mart.) Griseb. (Amaranthaceae) e de Polygonum ferrugineum Wedd. (Polygonaceae). As duas especies foram submetidas as concentracoes 0, 25 e 50 mg L-1 de cadmio em solucao nutritiva. Aos sete dias apos a aplicacao dos tratamentos, foram efetuadas medicoes de trocas gasosas foliares e de emissao de fluorescencia da clorofila em folhas expandidas e maduras. Amostras de raiz, caule e folha foram fixadas em FAA 70, incluidas em historresina, seccionadas em microtomo rotativo e submetidas a coloracao com azul de toluidina a 1%. Determinou-se o teor de Cd nas amostras vegetais utilizando ICP-MS. Na nervura central da folha e na raiz de P. ferrugineum, a 50 mg L-1 Cd observou-se alteracoes nas lacunas do aerenquima. Alem disso, a 50 mg L-1 Cd, verificou-se acrescimo de tricomas glandulares nas folhas e compactacao do mesofilo. No caule de A. philoxeroides, a 50 mg L-1 Cd, os nucleos das celulas do cortex apresentaram formato eliptico e a 25 e 50 mg L-1 Cd, ocorreu diminuicao de drusas em celulas da nervura central da folha. Os teores de Cd para A. philoxeroides foram maiores na raiz, seguido do caule e da folha. A taxa de fotossintese liquida de P. ferrugineum foi mais afetada pelo Cd em comparacao a A. philoxeroides. Nao houve variacao da atividade do fotossistema II (Fv/Fm) entre as duas especies e os tratamentos com Cd. A. philoxeroides foi mais tolerante ao Cd do que P. ferrugineum, o que indica sua potencialidade para uso em programas de fitorremediacao.

Molecular, Biochemical and Ultrastructural Changes Induced by Pb Toxicity in Seedlings of Theobroma cacao L.

Pb is a metal which is highly toxic to plants and animals, including humans. High concentrations of Pb have been observed in beans of T. cacao, as well as in its products. In this work, we evaluated the molecular, biochemical, and ultrastructural alterations in mature leaves and primary roots of seedlings of two progenies of T. cacao, obtained from seed germination in different concentrations of Pb (0, 0.05, 0.1, 0.2, 0.4, 0.8 g L-1), in the form of Pb(NO3)2. The progenies resulted from self-fertilization of Catongo and a cross of CCN-10 x SCA-6. The Pb, supplied via seminal, caused alterations in the ultrastructures of the mesophyll cells and in the amount of starch grains in the chloroplasts. The dosage of substances reactive to thiobarbituric acid showed that Pb induced lipid peroxidation. The activity of guaiacol peroxidases and the expression of genes associated to synthetase of phytochelatin, SODcyt and PER increased in response to Pb. In addition, there was alteration in the expression of stress-related proteins. The progeny of CCN-10 x SCA-6 was more tolerant to Pb stress when compared to Catongo, since: (i) it accumulated more Pb in the roots, preventing its translocation to the shoot; (ii) it presented higher activity of peroxidases in the roots, which are enzymes involved in the elimination of excess of reactive oxygen species; and (iii) increased expression of the gene in the phytochelatin biosynthesis route. The results of the proteomic analysis were of paramount importance to differentiate the defense mechanisms used by both progenies of T. cacao.

Different salt concentrations induce alterations both in photosynthetic parameters and salt gland activity in leaves of the mangrove Avicennia schaueriana

Mangrove sites are constantly under tidal regimes, where there is variation of dissolved oxygen and saline content in water. This study evaluated the effects of varying salinity in Avicennia schaueriana, an abundant species in the sea-mangrove-river interface. Seedlings of A. schaueriana were harvested at the riverbank and placed in different saline and nutrient solutions in a greenhouse in order to simulate a saline flow. After 7 acclimatization days, plants were exposed to the following saline concentrations: 0, 50, 170 and 250mM NaCl, for a period of 30 days. After this, leaf gas exchange, chlorophyll a fluorescence, Falker chlorophyll index, leaf ultrastructure and micromorphology were evaluated. The highest saline concentration affected mainly the CO2 assimilation, internal CO2 concentration and the intrinsic efficiency of water use. The chlorophyll a fluorescence and Falker index were not significantly affected by any of the saline conditions, however chloroplast was damaged. Concomitantly, leaf salt glands clearly evidenced a higher salt secretion, when plants were submitted to the greatest saline concentration. The results indicated that A. schaueriana tolerates different salt concentration in the mangrove and excretes salt excess by salt gland, and this can attenuate the saline stress. However, when exposed to longer periods of higher salt fluxes the plant growth can be affected.

Morphophysiological, ultrastructural, and nutritional changes induced by Cu toxicity in young Erythrina fusca plants

ABSTRACT Erythrina fusca is an important legume used for shade cover in cacao plantations in Brazil. Cacao plantations receive large quantities of copper (Cu)-containing agrochemicals, mainly for control of diseases. Therefore, Cu toxicity was investigated in seedlings grown in hydroponics with increasing concentrations of Cu (0.005–32 mg L−1) in a greenhouse. Ultrastructural analyses showed cell plasmolysis in the root cortical area and changes in thylakoid membranes at 8 mg Cu L−1 and higher. There were changes in epicuticular wax deposition on the leaf surface at the 16 and 32 mg Cu L−1 treatments. Leaf gas exchanges were highly affected 24 hours after application of treatments beginning at 8 mg Cu L−1 and higher Cu concentrations. Chemical analyses showed that Cu content in E. fusca roots increased as Cu concentration in the nutrient solution increased, whereas the shoot did not show significant changes. It is also observed that excess Cu interfered with Zn, Fe, Mn, Mg, K, P, and Ca content in the different E. fusca organs. Investigation of Cu toxicity symptoms focusing on morphophysiological, ultrastructural, gas exchange, and nutritional changes would be useful to alleviate Cu toxicity in E. fusca under field conditions, an important agroforestry species in cacao plantation.

Short-term cadmium exposure induces gas exchanges, morphological and ultrastructural disturbances in mangrove Avicennia schaueriana young plants

Mangroves have been subject to more metal contamination, including cadmium (Cd). This study evaluated if a relatively short Cd exposure may induce metabolic, morphological and ultrastructural cell disturbance in Avicennia schaueriana. Cd induced evident constraints to seedlings since there was reduction in leaf gas exchanges and the plants did not survive for more than 10 days at a higher Cd exposure in controlled conditions. The highest Cd accumulation was observed in roots and gradually less in stem and leaves. Cadmium induced lignin deposition was observed in xylem cells of all vegetative organs. Intense sclerification in xylem cells, endoderm and change in the hypoderm organization were also detected. Cadmium clearly induced chloroplast deformities with ruptures of its membranes, thylakoids and core and provoked cytoplasm disorganization. These metal constraints under natural conditions for long term can lead to the accumulation of cellular and metabolic damages and jeopardize seedlings establishment and local biodiversity.

Physiological, ultrastructural, biochemical and molecular responses of young cocoa plants to the toxicity of Cr (III) in soil

The objective of this study was to evaluate Cr toxicity in young plants of the CCN 51 Theobroma cacao genotype at different concentrations of Cr3+ in the soil (0, 100, 200, 400 and 600 mg kg-1) through physiological, ultrastructural, antioxidant and molecular changes. Doses of 400 and 600 mg Cr3+ kg-1 soil severely affected foliar gas exchange, promoted by damages in photosynthetic machinery evidenced by the decrease in CO2 fixation. Decreased expression of psbA and psbO genes, changes in enzymatic activity and lipid peroxidation also affected leaf gas exchange. A hormesis effect was observed at 100 mg Cr3+ kg-1 soil for the photosynthetic activity. As a metal exclusion response, the roots of the cocoa plants immobilized, on average, 75% of the total Cr absorbed. Ultrastructural changes in leaf mesophyll and roots, with destruction of mitochondria, plasmolysis and formation of vesicles, were related to the oxidative stress promoted by excess ROS. The activity of the antioxidant enzymes SOD, APX, GPX and CAT and the amino acid proline coincided with the greater expression of the sod cyt gene demonstrating synchronicity in the elimination of ROS. It was concluded, therefore, that the tolerance of the cocoa plants to the toxicity of Cr3+ depends on the concentration and time of exposure to the metal. Higher doses of Cr3+ in the soil promoted irreversible damage to the photosynthetic machinery and the cellular ultrastructure, interfering in the enzymatic and non-enzymatic systems related to oxidative stress and gene expression. However, the low mobility of the metal to the leaf is presented as a strategy of tolerance to Cr3+.