Physiological and metabolic changes in response to Boron levels are mediated by ethylene affecting tomato fruit yield.

Boron (B) is an essential nutrient for the plant, and its stress (both deficiency and toxicity) are major problems that affect crop production. Ethylene metabolism (both signaling and production) is important to plants' differently responding to nutrient availability. To better understand the connections between B and ethylene, here we investigate the function of ethylene in the responses of tomato (Solanum lycopersicum) plants to B stress (deficiency, 0 µM and toxicity, 640 µM), using ethylene related mutants, namely nonripening (nor), ripening-inhibitor (rin), never ripe (Nr), and epinastic (Epi). Our results show that B stress does not necessarily inhibit plant growth, but both B stress and ethylene signaling severely affected physiological parameters, such as photosynthesis, stomatal conductance, and chlorophyll a fluorescence. Under B toxicity, visible symptoms of toxicity appeared in the roots and margins of the older leaves through necrosis, caused by the accumulation of B which stimulated ethylene biosynthesis in the shoots. Both nor and rin (ethylene signaling) mutants presented similar responses, being these genotypes more sensitive and displaying several morphophysiological alterations, including fruit productivity reductions, in response to the B toxicity conditions. Therefore, our results suggest that physiological and metabolic changes in response to B fluctuations are likely mediated by ethylene signaling.

Spatio-temporal characterization of the fruit metabolism in contrasting accessions of Macauba (Acrocomia aculeata).

Although Macauba (Acrocomia aculeata) has been highlighted by its high-quality oil to fit edible and nonedible purposes, data addressing carbon and nitrogen metabolism underlying development and ripening of fruits remain scarce. In addition, accessions of Macauba exibit varied oil yield in fruits, including during the fruit development stages. Here, we monitored contents of carbohydrates, proteins, amino acids and lipids in the mesocarp and endosperm of Macauba fruits until ripening. We selected three accessions from different Brazilian regions (southeast, MG; northeast, PE; and central-west, MS) that differ in the mesocarp lipid content of ripe fruits. Despite the anatomical differences, mesocarp and endosperm exhibited similar trends of metabolite accumulation for most of the analyzed compounds. In the mesocarp, total soluble protein, free amino acids, sucrose, starch and total lipids accumulate towards ripening, while glucose and fructose declined in all accessions. Endosperm differed from mesocarp solely in the amino acid content, which decreased in ripe fruits. In the endosperm, accessions accumulated carbohydrates differently. Accession PE showed comparable fructose and starch contents in the endosperm between the beginning of fruit development and ripening, while in accessions MG and MS, both compounds decreased and increased, respectively, towards ripening. Accession MG was highlighted by its highest lipid content in the two tissues indicating its potential for energy and cosmetic industries. Our results provide novel insights into metabolic changes underlying development and ripening of Macauba fruits and variability in oil content among accessions, indicating new targets for breeding programs.

Boron: More Than an Essential Element for Land Plants?

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.