A survey of woody tropical species for boron retranslocation

The mobility in phloem of boron (B) has been reported to vary among plant species. Boron is phloem immobile in many species and completely mobile in others. Recent reports regarding phloem B mobility or immobility only considered temperate plants, and there is no information on tropical species. Information of phloem B mobility is useful for improving the diagnosis of B deficiency and management of B status in crop production. This study aimed to survey tropical species for their B mobility. Leaf samples of 17 species, including cashew (Anacardium occidentale L.), mango (Mangifera indica L.), custard apple (Annona squamosa L.), papaya (Canca papaya L.), cassava (Manihot esculenta Crantz.), Indian walnut (Samanea samen (Jacq.) Marrill.), cork wood tree (Sesbania grandiflora (L.) Pers.), tamarind (Tamarindus indica L.), jackfruit (Artocarpus heterophyllus Lamk.), guava (Psidium guajava L.), star fruit (Averrhoa carambola L.), passion fruit (Passiflora edulis Sims.), coffee (Coffea arabica L.), lime (Citrus aurantifolia Swingle.), longan (Euphoria longana Lam.), lychee (Lychi chinensis Sonn.) and teak (Tectona grandis L.) were collected in the position of the youngest fully expanded leaf (YFEL), the middle leaf age of a branch (ML) and the oldest leaf (OL). Based on a premise that the nutrient concentration gradient between young and old leaves will be steeper in those species in which B is immobile, B concentration in the different leaf positions was examined in comparison with calcium (Ca is phloem immobile) and potassium (K is phloem mobile). Concentrations of K in all leaf types were not significantly different or decreased with leaf age, while Ca concentrations were always higher in the older leaves. Three species; tamarind, guava and teak, showed concentration gradients of B that were similar to K. The results suggested that B may be retranslocated from older to younger leaves of these species, hence indicating that B may be phloem mobile in these species. However, this hypothesis needs confirmation through studies examining retranslocation of B using 10B isotope or identification of B-complexing molecules in the phloem, e.g. sugar alcohols

Boron mobility in peanut (Arachis hypogaea L.)

In most plant families, boron (B) is phloem immobile. For plants such as peanut which bury their fruit, the mechanism for B delivery and the B source for fruit and seed growth remains enigmatic. Therefore, this study aimed to establish evidence of B retranslocation in peanut and to identify its importance in plant development. In a sand culture experiment, the increase in B contents in new organs after B withdrawal and the corresponding decline in B contents in older organs was evidence of B redistribution. In a foliar 10B experiment, the 10B abundance of treated-leaves decreased and 10B was detected in leaves and flowers formed after the application of foliar B. Application of 10B to the roots for a period also provided evidence for the retranslocation of 10B accumulated during the first growth period. The 10B abundance in older plant parts declined and 10B appeared in new organs (flowers, pegs, leaves) that had developed after the 10B supply had been replaced by 11B. In the fourth experiment, foliar application of B reduced hollow heart, a symptom of B deficiency in seeds, in cv. TAG 24 from 39 to 8% and in Tainan 9 from 63 to 18%. These experiments all provide evidence for B retranslocation in peanut, but further work on the relative importance of the xylem and phloem pathways for B loading into the fruit is needed

Genotypic variation in response to low boron in eucalypt clones

Eucalypts are increasingly important in the tropics for meeting growing demand for timber, wood chips, paper pulp and biofuel. Many new plantations are planted on low boron (B) soils, with adverse effects on plant growth and productivity. Two experiments in sand culture with different levels of added B, from 0 to 10 μM B, examined the effect of B deficiency on growth, wood yield and morphology of fibres of three commercially available eucalypt clones: K7 (Eucalyptus camaldulensis × E. deglupta), K51 (E. brassiana × E. grandis) and K57 (E. camaldulensis). In plant height, dry weight and wood production, K7 was more tolerant of B deficiency, but K57 and K51 were more responsive to increasing B. At the level of B that depressed growth by up to 54% and wood yield by up to 65%, no significant effect of B deficiency was observed on fibre morphology. However, as the wood:shoot ratio in K51 and K57 increased with increasing B, there is a possibility that B has a direct effect on wood production in some genotypes, in addition to an indirect effect via better growth. These results indicate that attention to B nutrition in eucalypt plantations would be beneficial to plant growth and productivity before effects of B on individual wood fibres becomes detectable. Selection for B-efficient genotypes could be useful for plantations on low B soils, and the full potential of sites where B is not limiting could be better realised with B-responsive genotypes

Variation in responses to boron in rice

Background and aims: Boron (B) deficiency depresses grain set and grain yield of wheat and maize while having little effect on their vegetative growth. This paper describes effects of B deficiency in rice and how these vary with planting season and variety. Methods: Three rice varieties (KDML105, CNT1, SPR1) were grown in sand culture without (B0) and with 10 μM (B10) B added to the nutrient solution, in the cool season of 2007/08 and 2008/09 and the hot season of 2011 in Chiang Mai, Thailand (18°47′N, 98°59′E). Boron responses were measured in growth and yield parameters, pollen viability and B concentration of the flag leaf and anthers at anthesis. Results: Grain weight was strongly depressed by B deficiency ranging from 28 % in SPR1 to 79 % in CNT1, and the yield was much lower in the cool season than in the hot season plantings. The variation in grain weight was closely associated with grain set and number of spikelets but not with shoot dry weight or tillering. Grain set was closely related to pollen viability, and both were increased with increasing anther B concentration at >20 mg B kg-1. In addition to its adverse effect on grain set, B deficiency also depressed grain filling and weight of individual grains in rice. Conclusions: Boron deficiency depressed rice grain yield through adverse effects on reproductive growth, panicle and spikelet formation and grain filling, in addition to grain set as in wheat and maize

Phloem mobility of Boron in two eucalypt clones Mobilidade floemática de Boro em dois clones de eucalipto

Boron deficiency causes large productivity losses in eucalypt stands in extensive areas of the Brazilian Cerrado region, thus understanding B mobility is a key step in selecting genetic materials that will better withstand B limitation. Thus, in this study B mobility was evaluated in two eucalypt clones (68 and 129), under B sufficiency or B deficiency, after foliar application of the 10B isotope tracer to a single mature leaf. Samples of young tissue, mature leaves and roots were collected 0, 1, 5, 12 and 17 days after 10B application. The 10B:11B isotope ratio was determined by HR-ICP-MS. Samples of leaves and xylem sap were collected for the determination of soluble sugars and polyalcohols by ion chromatography. Boron was translocated within eucalypt. Translocation of foliar-applied 10B to the young tissues, mature leaves and roots was higher in clone 129 than in 68. Seventeen days after 10B application to a single mature leaf, between 14 and 18 % of B in the young tissue was originated from foliar B application. In plants with adequate B supply the element was not translocated out of the labeled leaf.<br>A deficiência de boro tem causado perdas expressivas de produtividade em extensas áreas de eucalipto no Brasil, principalmente na região do Cerrado. A mobilidade de B é um fator chave na seleção de materiais genéticos mais tolerantes à deficiência deste nutriente. Neste trabalho, a mobilidade de B foi avaliada em dois clones de eucalipto (68 e 129), com e sem deficiência de B, após a aplicação foliar do traçador isotópico 10B em uma única folha madura. Amostras de tecidos jovens, folhas maduras e raízes foram coletadas nos tempos de 0, 1, 5, 12 e 17 dias após a aplicação. A determinação da razão isotópica 10B:11B foi feita por meio de HR-ICP-MS. Foram coletadas amostras de folhas e do exsudato xilemático para determinação de açúcares solúveis e poliálcoois, por meio de cromatografia iônica. Houve translocação de B no eucalipto. O clone 129 apresentou maior translocação de B da folha aplicada para tecidos jovens, folhas maduras e raízes, quando comparado ao clone 68. Aos dezessete dias após a aplicação do 10B em uma única folha madura, entre 14 e 18 % do B do tecido jovem era proveniente do B aplicado. As plantas com suprimento adequado de B não apresentaram translocação do elemento