Claudia Regina Baptista Haddad

The effect of 24-epibrassinolide and clotrimazole on the adaptation of Cajanus cajan (L.) Millsp. to salinity

The objective of this study was to evaluate the effects of one of brassinosteroids (24-epibrassinolide) and clotrimazole, (an inhibitor of brassinosteroid synthesis) on plant growth parameters, parameters related to leaf gas exchange (photosynthetic and transpiration rates; stomatal conductance; water use efficiency), photosynthetic pigment content and osmolyte (sugars and proline) content in Cajanus cajan exposed to salinity. Salt stress—caused by NaCl treatment—affected values of all parameters analyzed. The effects were ameliorated by 24-epibrassinolide and intensified by clotrimazole. The hormone increased fresh mass of the plant, shoot dry mass, leaf area, water content of leaves and roots, photosynthetic pigments, sugar concentration, photosynthetic rate, and water use efficiency. The effects of hormone were less evident in the absence of salt. However, under this condition the application of clotrimazole affected the values of parameters studied, indicating the importance of brassinosteroid synthesis for the normal development of the plant.

24-epibrassinolide restores nitrogen metabolism of pigeon pea under saline stress

BackgroundSeveral studies have shown that brassinosteroids attenuate the effects of salt stress. However, nothing is known about their effects on amino acid transport, nor the effects of these hormones on nitrate uptake under saline conditions. This study set out to determine the effects of 24-epibrassinolide, at concentrations of 10-7 M and 0.5 × 10-9 M, and clotrimazole (inhibitor of brassinosteroid synthesis), at 10-4 M, on nitrate uptake and metabolism in plants of C. cajan (L.) Millsp, cultivar C11, growing under salinity. The following aspects were analyzed: levels of proteins, amino acids, nitrate, nitrate reductase of roots and the composition of xylem sap amino acids.ResultsSalinity reduced the proportion of N-transport amino acids ASN (the major component), GLU, ASP and GLN. The effect of the hormone in reducing the adverse effects of salt was related to the reestablishment (totally or partially) of the proportions of GLU, ASN and GLN, transported in the xylem and to the small but significant increase in uptake of nitrate. Increased nitrate uptake, induced by 24- epibrassinolide, was associated with a higher activity of nitrate reductase together with greater levels of free amino acids and soluble proteins in roots of plants cultivated under saline conditions.ConclusionThe decline in several components of nitrogen metabolism, induced by salt, was attenuated by 24-epibrassinolide application and accentuated by clotrimazole, indicating the importance of brassinosteroid synthesis for plants growing under salinity.

Effect of salt on the growth and metabolism of Glycine max

Soybean plants cultivated with 50, 100 and 200 mM of NaCl, revealed that root growth was less affected by salinity than shoots. Salinity led to a reduction in leaf area and an increase in water content of the roots. These factors could contribute to the adaptation of the plant, improving its hydration. Although nitrate and free amino acid levels were reduced by salt treatment in roots, protein content of leaves was not altered. Salinity led to alterations in xylem amino acid composition, with increases in Ser, Ala, Gaba and Pro and a decrease in Asn. Similar changes were seen for Asn and Ser in roots together with a much stronger increase in Gaba. It is suggested that the decline in Asn reflects its conversion to Ala and Gaba (via Glu) in the roots while the increase in Pro and Gaba could be related to the adaptation of the plant to salinity.

Leaf life span and nitrogen content in semideciduous forest tree species (Croton priscus and Hymenaea courbaril)

In comparison to deciduous species, evergreen plants have lower leaf nutrient contents and higher leaf life span, important mechanisms for nutrient economy, allowing the colonization of low fertility soils. Strategies to conserve nitrogen in two semideciduous tropical forest tree species, with different leaf life spans were analyzed. The hypothesis was the fact that the two species would present different nitrogen conservation mechanisms in relation to chemical (total nitrogen, protein, chlorophyll, and proteolytic activity), functional (leaf life span, N-use efficiency, and N-resorption efficiency), morphological (specific leaf mass) leaf characteristics, and total nitrogen in the soil. Hymenaea courbaril L. presented lower nitrogen compounds in leaves, longer leaf life span, higher N-use efficiency, and higher specific leaf mass, while absorbing proportionally less nitrogen from the soil than Croton priscus Croizat. These characteristics can contribute for a better nitrogen economy strategy of H. courbaril. No relationship was found between leaf life span and N resorption efficiency, nor between leaf life span, protease activity and nitrogen mobilization. The electrophoretic profiles of proteolytic enzymes in young leaves of the two species presented more bands with enzymatic activity than other kinds of leaves.

Effect of fire on flowering of Lantana montevidensis Briq.

Summary Lantana montevidensis Briq. is an endemic species of the brazilian «cerrado» (savannah) that usually flowers abundantly after burning of the vegetation. Several possible effects of fire on the induction of flowering in this species were tested with no significant result. It seems that the removal of the aerial part of the plant caused by the fire is the necessary stimulus for flowering induction. Pruning the plants caused similar results.

The effect of ants on the seed dispersal cycle of the typical myrmecochorous Ricinus communis

The directed dispersal hypothesis has two components: (1) non-random seed deposition by a predicted vector, which removes greater amounts of seeds to specific sites, and (2) higher seed survival and seedling establishment in these specific sites. Several studies suggest that ants perform both tasks. This study was designed to cover the processes from post-dispersed seeds to established juvenile plants of a typical ant-dispersed species. Our main objective was to determine whether Ricinuscommunis benefits from directed dispersal by ants to maintain its populations in previously colonized habitats. We examined whether there were differences between ant nest pile mounds and their vicinities in the: (1) densities of seeds with and without elaiosome, seedlings and juveniles; (2) performance of post-dispersed seeds (without elaiosome), which may be affected by seed density, a key feature attracting seed predators; (3) nutrient quantities; (4) number of germinated seeds and juvenile biomass measurements; and (5) ant protection of seedlings from herbivores. There were more seeds without elaiosome, seedlings and juveniles in pile mounds, and seeds with elaiosome were equally distributed. There was no difference in the number of non-removed seeds in pile mounds and in their vicinities, and there was no tendency for this difference to increase or decrease with time or with initial seed density. Apparently, there was no difference in nutrient contents in soils of pile mounds and their vicinities. Likewise, there was no difference in the number of seeds germinated and in the biomass measurements of juveniles in both soils. Ants did not provide differential protection for seedlings in pile mounds against potential herbivores. The dispersal of Ricinus seeds by ants had a marked effect on the distribution pattern of the seeds, seedlings and juveniles of this species. However, there were no additional advantages for the seeds, seedlings and juveniles in pile mounds and, therefore, Ricinus does not benefit from directed dispersal by ants to maintain its populations in the study sites.

Seed germination of Ricinus communis in predicted settings after autochorous and myrmecochorous dispersal.

Abstract Seeds of Ricinus communis are primarily dispersed by autochory and secondarily dispersed by ants, which are attracted to their lipid-rich elaiosome. The aim of this study was to determine how the conditions to which Ricinus seeds are submitted after these two types of dispersal affect their germination. We examined the germination responses of freshly harvested and one-year-old seeds to combinations of light (present or absent), temperature (alternating or constant), and elaiosome (present or absent). We also checked the soil for persistent seed banks. The seeds presented different germination responses but germinated in all conditions to which they were submitted. More specifically, germination of fresh seeds was higher in the environmental conditions to which they are submitted after being dispersed by ants, although seeds with elaiosome germinated in greater number. Germination of old seeds was not enhanced in alternating temperatures and/or presence of light, as would be expected for seeds that make up persistent soil seed banks. This, and the fact that we found only a few viable seeds in the soil, indicates that Ricinus does not form seed banks. Nevertheless, we observed massive seedling emergence after soil disturbance and, therefore, the existence or not of seed banks is not yet clear and deserves further investigation. This study shows that the generalist germination behavior of Ricinus seeds guarantees that they germinate under various environmental conditions.

N availability and mechanisms of N conservation in deciduous and semideciduous tropical forest legume trees

Prior to abscission, nutrients are redeployed from leaves and redistributed to other parts of the plant. Data comparing nutrient resorption to soil fertility and leaf life span remains controversial in the literature. We compared nitrogen (N) conservation mechanisms among four legume trees with different leaf life spans (Hymenaea courbaril L. var. stilbocarpa (Hayne) Lee et Lang., Lonchocarpus guilleminianus (Tul.) Malme, Enterolobium contortisiliquum (Vell.) Morong and Peltophorum dubium (Spreng.) Taub.), from a semideciduous tropical forest, remnant of the Atlantic Forest. We hypothesized that these mechanisms differ among the four species and are affected by their leaf life span and by the availability of N, both as a mineral in the soil and, in the case of L. guilleminianus and E. contortisiliquum, from symbiotic nitrogen fixation (SNF), as these species form associations with rhizobia. The plants were grown in a greenhouse using pots filled with forest soil, enriched (50 or 100 mg of NH4NO3 plant-1week-1) or not with nitrogen. H. courbaril, a semideciduous tree, without SNF, and with the highest leaf life span, presented the greatest N-resorption efficiency (NRE), N-resorption proficiency (NRP) and N-use efficiency (NUE). Increase in soil N and the presence of symbiotic N fixation led to a decrease in NRE, NRP and NUE.

Nitrogenous compounds, phenolic compounds and morphological aspects of leaves: comparison of deciduous and semideciduous arboreal legumes

Em geral as especies perenifolias possuem maior concentracao de alguns compostos secundarios, como por exemplo fenois, menor concentracao de compostos nitrogenados e maior massa foliar especifica (MFE), quando comparadas a especies deciduas. O objetivo deste trabalho foi verificar se as observacoes encontradas na literatura, comparando especies perenifolias e deciduas aplicam-se tambem a quatro especies de uma mata semidecidua, remanescente da Mata Atlântica. Das quatro especies usadas neste estudo, que aparentemente apresentavam longevidades foliares diferentes, duas eram semideciduas (Hymenaea courbaril L. var. stilbocarpa (Hayne) Lee et Lang. e Lonchocarpus guilleminianus (Tul.) Malme) e duas deciduas (Enterolobium contortisiliquum (Vell.) Morong. e Peltophorum dubium (Spreng.) Taub.). As plantas foram cultivadas em vasos plasticos, contendo solo da mata. O cultivo foi feito em casa de vegetacao. Folhas maduras foram coletadas para analise de fenois totais, taninos condensados, nitrato, proteinas totais, aminoacidos livres totais, clorofila total, nitrogenio total e MFE. Os resultados obtidos corroboram os da literatura, ja que as especies com folhas mais longevas apresentaram concentracoes maiores de fenois totais, menores de taninos condensados, nitrato, proteinas soluveis totais, aminoacidos livres totais, clorofilas totais, nitrogenio total e maior MFE.

Nitrogen availability, leaf life span and nitrogen conservation mechanisms in leaves of tropical trees

Evergreen species of temperate regions are dominant in low-nutrient soils. This feature is attributed to more efficient mechanisms of nutrient economy. Nevertheless, the cashew (Anacardium occidentale- Anacardiaceae), a deciduous species, is native to regions in Brazil with sandy soil, whilst the annatto (Bixa orellana- Bixaceae), classified as an evergreen species native to tropical America, grows spontaneously in regions with more humid soils. Evergreens contain robust leaves that can resist adverse conditions for longer. The physical aspects of the leaves and mechanisms of nutrient economy between the two species were compared, in order to verify whether the deciduous species had more efficient mechanisms that might explain its occurrence in regions of low soil fertility. The mechanisms of nitrogen economy were also compared for the two species at available concentrations of this nutrient. The following were analysed: (i) leaf life span, (ii) physical leaf characteristics (leaf mass per area, and rupture strain), (iii) nitrogenous compounds (nitrogen, chlorophyll, and protein), (iv) nitrogen conservation mechanisms (nitrogen resorption efficiency, resorption proficiency, and use efficiency), and (v) nitrogen conservation mechanisms under different availability of this mineral. The higher values of leaf mass per area and leaf rupture strain found in A. occidentale were related to its longer leaf life span. A. occidentale showed lower concentrations of nitrogen and protein in the leaves than B. orellana. Under lower nitrogen availability, A. occidentale had higher nitrogen resorption proficiency, nitrogen use efficiency and leaf life span than B. orellana. These characteristics may contribute to the adaptation of this species to sandy soils with low nitrogen content.