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Studies of cambial dynamics have been employed to investigate the growth behavior of trees. In these investigations, however, spatial variation in cambial rhythm within the stem is usually not taken into account. This study aims to evaluate the contribution of multiple sampling scales on the cambial dynamics of Cedrela odorata L. (Meliaceae) in different seasons. The effects of slope orientation were also tested. Samples were processed and analyzed with standard plant histology techniques. Data from multiple sampling scales were analyzed with nested ANOVA for each season, and the total variance was partitioned according to the fraction related to each scale. The main sources of variability were associated with the scale of tree and scales smaller than 1 cm. Radial growth was not significantly related to acclivity orientation. Thus, to obtain samples that represent total variability in cambial dynamics, it is preferable to increase the number of sampled trees; to take multiple samples from a few millimetres apart from each other, or to assess multiple histological sections. Samples on scales greater than a few centimetres apart should not be given priority. [ABSTRACT FROM AUTHOR]

The auxin-ethylene interaction in regulating root elongation and radial expansion was analysed through the application of the ethylene precursor 1-aminocyclopropane-1- carboxylic acid (ACC) and the synthetic auxin 1-naphthaleneacetic acid (NAA). NAA and ACC, in the concentration range of 0.01-0.1 μmol/L and 1-5 μmol/L, respectively, inhibited root elongation and increased root diameter in a concentration-dependent manner. The inhibitory effect of auxin on root elongation was increased by ethylene applied at low as well as high concentrations. Auxin-induced radial expansion was also enhanced by ethylene, although this effect depended on the level of auxin applied. In the presence of very low exogenous auxin (0.01 μmol/L NAA), ethylene stimulated radial growth at both low and high levels (1-5 μmol/L ACC), whereas the effect of higher auxin concentrations (>0.025 μmol/L NAA) was only enhanced by high ethylene production (5 μmol/L ACC). Interaction was analysed by two-way ANOVA; the results showed that both the effect of each hormone and the interactions responsible for controlling elongation and radial expansion were concentration-dependent. The relative effects of auxin and ethylene on the two growth parameters were also analysed; they showed different types of behaviour. In summary, the results obtained suggest that auxin is the main hormone involved in regulating root growth but that ethylene may modulate its effects. Our research also suggests that root elongation and radial expansion may be independently regulated despite being closely related. [ABSTRACT FROM AUTHOR]