F. J. Pereira

Leaf ontogeny of Schinus molle L. plants under cadmium contamination: the meristematic origin of leaf structural changes

Previous works show the development of thicker leaves on tolerant plants growing under cadmium (Cd2+) contamination. The aim of this study was to evaluate the Cd2+ effects on the leaf meristems of the tolerant species Schinus molle. Plants were grown in nutrient solution containing 0, 10, and 50xa0μM of Cd2+. Anatomical analysis was performed on leaf primordia sampled at regular time intervals. Under the lowest Cd2+ level (10xa0μM), increased ground meristem thickness, diameter of the cells, cell elongation rate, and leaf dry mass were found. However, 50xa0μM of Cd2+ reduced all these variables. In addition, the ground meristem cells became larger when exposed to any Cd2+ level. The epidermis, palisade parenchyma, and vascular tissues developed earlier in Cd2+-exposed leaves. The modifications found on the ground meristem may be related to the development of thicker leaves on S. molle plants exposed to low Cd2+ levels. Furthermore, older leaves showed higher Cd2+ content when compared to the younger ones, preventing the Cd2+ toxicity to these leaves. Thus, low Cd2+ concentrations change the ground meristem structure and function reflecting on the development of thicker and enhanced leaves.

Anatomic and physiological responses of Panicum aquaticum related to cadmium tolerance

This study evaluated anatomic and physiological modifications in Panicum aquaticum plants related to cadmium (Cd) tolerance. The plants were cultivated in a nutritive solution, with addition of increasing concentration of Cd. The following parameters were analyzed: absorption, translocation, concentration and Cd accumulation, growth, gas exchanges, activity of the antioxidant system, and anatomy of roots and leaves. Absorption and Cd concentration increased throughout the treatments, while accumulation and Cd translocation did not vary, due to maintenance of the biomass. Gas exchanges were not affected by Cd. Specific foliar area increased in the presence of the metal, and might be related to the reduction in leaf blade thickness and chlorophyllic parenchyma. Modifications in stomatal characteristics did not negatively affect gas exchanges. An increase in the exodermis and endodermis thickness restricted Cd translocation to the aerial part, avoiding damages to the photosynthetic system. Activity of the ascorbate peroxidase and catalase in the root contributed to a reduction in the metal toxicity. P. aquaticum presented an efficient capacity for Cd absorption, but restricted translocation. Cd accumulation was higher in the roots. Anatomic and physiological responses show a tolerance of the species to Cd in the evaluated concentrations.

Aerenchyma development in different root zones of maize genotypes under water limitation and different phosphorus nutrition

Root cortical aerenchyma (RCA) is suggested to reduce metabolic cost for root growth, but it might lower water uptake by plants. The objective of this work was to evaluate the effects of drought and phosphorus on the RCA development along the root axis and to elucidate its role in water stress tolerance of two maize genotypes. Plants of drought-tolerant DKB390 and drought-sensitive BRS1010 genotypes were grown in Vermiculite at field capacity of 100, 75, 50, and 25 % and supplied with 0.1, 0.4, and 0.8 mM phosphorus. Growth parameters, RCA, and plant P content were evaluated for all plants. Higher RCA development was observed in DKB390 than in BRS1010. Drought reduced the percentage of RCA in the root-hair zone of both genotypes but increased its development in the root maturation zone. Phosphorus limitation enhanced RCA development only in the DKB390. Under drought stress, DKB390 showed resilient growth whereas growth was inhibited in BRS1010. Higher root P content was related to its higher supply. Therefore, RCA formation was induced either by drought or by phosphorus limitation, while no interaction was evident. The RCA development varied along the root axis in order to balance water and phosphorus uptake and the drought response was genotype dependent.

Cadmium tolerance of Typha domingensis Pers. (Typhaceae) as related to growth and leaf morphophysiology

Typha domingensis (cattail) is a native macrophyte known by its capacity to tolerate several heavy metals effects and the potential use for phytoremediation. However, in despite that cadmium (Cd) is one of the most toxic pollutants; its effects in T. domingensis biology remain uninvestigated. Thus, the objective of this study was to study the tolerance of T. domingensis to cadmium contamination by evaluating its growth, Cd uptake, leaf anatomy and gas exchange. The experiment was designed using three cadmium concentrations (0, 10 and 50 µM) and ten replicates for 90 days. The cadmium uptake, growth, gas exchange, chlorophyll content and leaf anatomy were evaluated. Data was submitted to ANOVA and Scott-Knott test for P<0.05. Typha domingensis accumulates Cd proportionally to its concentration on the solution and the content of this metal was higher in roots as compared to shoots. Plants showed no significant modifications on growth parameters such as the biomass production, number of leaves, number of clones and the biomass allocation to organs. The photosynthesis, transpiration and chlorophyll content were not modified by Cd. Most anatomical traits evaluated were not modified by the metal but the stomatal density and the proportion of vascular tissues were reduced under 50 µM of Cd. In despite, the leaf anatomy showed no toxicity evidences for any Cd level. The absence of growth reduction and the stability of anatomical and physiological traits give insight about the Cd tolerance of this species. Therefore, T. domingensis is able to overcome Cd toxicity and shows potential for phytoremediation.

Effects of paclobutrazol on leaf anatomy and gas exchange of Toona ciliata clones

ABSTRACT Interest in Australian cedar (Toona ciliata M. Roemer var. australis) has increased due to its economic potential as an alternative to the use of native hardwood, and because of its resistance to the Hypsipyla grandella moth, which affects native cedars. The use of growth regulators such as paclobutrazol (PBZ) in the planting of T. ciliata is aimed mostly at obtaining seedlings with greater resistance to H. grandella and a desirable height for handling. However, this growth regulator tends to induce modifications to both leaf anatomy and photosynthetic potential. The present study aimed to evaluate the effect of increasing concentrations of PBZ on the leaf anatomy and gas exchange pattern in different T. ciliata clones. Seedlings from four T. ciliata clones (BV1110, BV1321, BV1120 and BV1151) were propagated by rooting cuttings and exposed to four concentrations of PBZ (0 μM, 0.5 μM, 1.0 μM and 2.0 μM), then the anatomy of the leaf blade and midrib vascular bundles and parameters related to gas exchange were analysed. Clones were significantly different for most of the characteristics studied. PBZ showed an effect only on the thickness of the palisade and spongy parenchyma. There was no effect of PBZ on gas exchange, but higher concentrations of PBZ induced thicker leaflets with scleromorphic characteristics.