Although boron (B) is an element that has long been assumed to be an essential plant micronutrient, this assumption has been recently questioned. Cumulative evidence has demonstrated that the players associated with B uptake and translocation by plant roots include a sophisticated set of proteins used to cope with B levels in the soil solution. Here, we summarize compelling evidence supporting the essential role of B in mediating plant developmental programs. Overall, most plant species studied to date have exhibited specific B transporters with tight genetic coordination in response to B levels in the soil. These transporters can uptake B from the soil, which is a highly uncommon occurrence for toxic elements. Moreover, the current tools available to determine B levels cannot precisely determine B translocation dynamics. We posit that B plays a key role in plant metabolic activities. Its importance in the regulation of development of the root and shoot meristem is associated with plant developmental phase transitions, which are crucial processes in the completion of their life cycle. We provide further evidence that plants need to acquire sufficient amounts of B while protecting themselves from its toxic effects. Thus, the development of in vitro and in vivo approaches is required to accurately determine B levels, and subsequently, to define unambiguously the function of B in terrestrial plants.

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Changes in amino acid composition are frequently observed in plants under various conditions of stress, such as nutrient deficiencies. Hence, amino acids have been proposed as more sensitive indicators of N status than total N concentration. The goal of this study was to evaluate alterations in amino acid composition of young eucalyptus clones as a result of variable N supply. An experiment was carried out in a greenhouse with two Eucalyptus clones (VM-01 and I-144) and six N application rates (0, 0.74, 2.93, 4.39, 5.85, and 8 mmol L-1 of NH 4 NO 3) grown in a nutrient solution in a randomized block design. Amino acid concentrations varied greatly as a function of N supply and depended on the organ (root or leaf) and the genotype evaluated. Roots showed greater number of amino acids than leaves (17 and 14, respectively), probably because of a higher amino acids synthesis or translocation to the roots. For both clones, N deficiency induced a significant decrease in proline, arginine, and methionine concentration in roots and a decrease in tyrosine, alanine, threonine, and methionine in leaves. These decreases were also associated with lower total N concentration and total dry matter of the eucalyptus clones. In conclusion, N supply affects amino acid composition, and the amino acids listed above are likely to be more sensitive indicators of N status than total N in eucalyptus clones.

Eucalyptus requires large amounts of nitrogen (n); however, it responds in diverse manners to the application of this nutrient. the aim of this study was to evaluate the differential performance in growth, mineral nutrition, and gas exchanges of n-fertilized Eucalyptus clones. the treatments consisted of two Eucalyptus clones (vM-01 and i-144) and six n application rates (0, 0.74, 2.93, 4.39, 5.85, and 8 mmol l -1 nh 4 no 3 ) arranged in a randomized complete block design with five replications. VM-01 had greater plant height and greater height/collar diameter ratio, as well as higher leaf concentrations of all macronutrients and of cu, fe, Mo, and Zn. in terms of total and root dry matter production, root/shoot ratio, and collar diameter, as well as stomatal conductance and transpiration, i-144 performed better. the performance of the clones was clearly differentiated, and the growth of i-144, despite lower leaf n concentration, was in general better than vM-01.