Enhancement of Developmental Defects in the Boron-Deficient Maize Mutant tassel-less1 by Reduced Auxin Levels

Background Plant responses to deficiencies of the micronutrient boron are diverse and go beyond the well-characterized function of boron in cell wall crosslinking. To explain these phenotypic discrepancies, hypotheses about interactions of boron with various phytohormones have been proposed, particularly auxin. While these hypotheses are intensely tested in the root meristem of the model species, Arabidopsis thaliana, studies in crop species and the shoot are limited. Aims To address potential boron–auxin interactions during the vegetative and reproductive development of the crop maize (Zea mays), we utilized the boron-deficient tassel-less1 (tls1) mutant and the auxin-deficient vanishing tassel2 (vt2) mutant. We investigated interactions of boron and auxin on the levels of auxin biosynthesis and auxin transport in leaves and shoot meristems. Methods and Results By using genetic interaction analysis, hormone quantification, and confocal microscopy, we show that boron-deficient leaf phenotypes in tls1 are enhanced in double mutants with vt2 in both greenhouse and field conditions. However, auxin levels are not altered in developing leaves in tls1. Rather, the localization of ZmPIN1a:YFP, a marker for auxin transport, is altered in young tassel meristems and is absent from organ initiation sites during vegetative development. Conclusions Our data suggest a link between polar auxin transport and phenotypic consequences in boron-deficient conditions and further show that boron deficiency-induced developmental defects are sensitive to low auxin levels. Our study, therefore, offers new insight into nutrient–hormone interactions to regulate crop development

Mutations in the Arabidopsis RPK1 gene uncouple cotyledon anlagen and primordia by modulating epidermal cell shape and polarity

Summary Plant seedlings have either one or two cotyledons. The mechanisms that regulate this organ number are poorly understood. Mutations in the RECEPTOR-LIKE PROTEIN KINASE1 (RPK1) gene of the dicot Arabidopsis have only one cotyledon, with low penetrance due to complex genetic redundancy. An analysis of patterning genes required for cotyledon initiation showed that these have normal expression patterns, defining the cotyledon anlagen, in rpk1. This was also true for key genes, which organize the shoot apical meristem (SAM). By contrast, epidermal cell shape and polarity were compromised in rpk1 embryos, as evidenced by disturbed polarity of the auxin efflux carrier PIN1. PIN1 is required for the establishment of auxin maxima, which induce and maintain organ primordia. The effects in rpk1 mutants manifest in a spatially and timely stochastic fashion probably due to redundancy of RPK1-like functions. Consistently, auxin maxima showed a stochastic distribution in rpk1 embryos, being at times entirely absent and at other times supernumerary. This variability may explain how monocotyledonous seedlings and cotyledon shape variants can developmentally arise in Arabidopsis and possibly in other plants

Carbon-11 Radiotracing Reveals Physiological and Metabolic Responses of Maize Grown under Different Regimes of Boron Treatment

In agriculture, boron is known to play a critical role in healthy plant growth. To dissect the role of boron in maize metabolism, radioactive carbon-11 (t½ 20.4 min) was used to examine the physiological and metabolic responses of 3-week-old B73 maize plants to different levels of boron spanning 0 mM, 0.05 mM, and 0.5 mM boric acid (BA) treatments. Growth behavior, of both shoots and roots, was recorded and correlated to plant physiological responses. 11CO2 fixation, leaf export of [11C]-photosynthates, and their rate of transport increased systematically with increasing BA concentrations, while the fraction of [11C]-photosynthates delivered to the roots under 0 mM and 0.5 mM BA treatments was lower than under 0.05 mM BA treatment, likely due to changes in root growth. Additionally, solid-phase extraction coupled with gamma counting, radio-fluorescence thin layer chromatography, and radio-fluorescence high-performance liquid chromatography techniques applied to tissue extracts provided insight into the effects of BA treatment on ‘new’ carbon (as 11C) metabolism. Most notable was the strong influence reducing boron levels had on raising 11C partitioning into glutamine, aspartic acid, and asparagine. Altogether, the growth of maize under different regimes of boron affected 11CO2 fixation, its metabolism and allocation belowground, and altered root growth. Finally, inductively coupled plasma mass spectrometry provided insight into the effects of BA treatment on plant uptake of other essential nutrients. Here, levels of boron and zinc systematically increased in foliar tissues with increasing BA concentration. However, levels of magnesium, potassium, calcium, manganese, and iron remained unaffected by treatment. The rise in foliar zinc levels with increased BA concentration may contribute to improved 11CO2 fixation under these conditions

Stratospheric ozone and surface ultraviolet

As a result of the Montreal Protocol, ozone is expected to recover from the effect of ozone-depleting substances (ODSs) as their abundances decline in the coming decades. The 2006 Assessment showed that globally averaged column ozone ceased to decline around 1996, meeting the criterion for the first stage of recovery. Ozone is expected to increase as a result of continued decrease in ODSs (second stage of recovery). This chapter discusses recent observations of ozone and ultraviolet radiation in the context of their historical records. Natural variability, observational uncertainty, and stratospheric cooling necessitate a long record in order to attribute an ozone increase to decreases in ODSs. Table S2-1 summarizes ozone changes since 1980. The primary tools used in this Assessment for prediction of ozone are chemistry-climate models (CCMs). These CCMs are designed to represent the processes determining the amount of stratospheric ozone and its response to changes in ODSs and greenhouse gases. Eighteen CCMs have been recently evaluated using a variety of process-based comparisons to measurements. The CCMs are further evaluated here by comparison of trends calculated from measurements with trends calculated from simulations designed to reproduce ozone behavior during an observing period.Fil: Douglass, Anne R.. No especifíca;Fil: Fioletov, Vitali E.. No especifíca;Fil: Godin Beekmann, Sophie. No especifíca;Fil: Müller, Rolf. No especifíca;Fil: Stolarski, Richard S.. No especifíca;Fil: Webb, Ann R.. No especifíca;Fil: Arola, Antti. No especifíca;Fil: Burkholder, James B.. No especifíca;Fil: Burrows, John P.. No especifíca;Fil: Chipperfield, Martyn P.. No especifíca;Fil: Cordero, Raul. No especifíca;Fil: David, Christine. No especifíca;Fil: den Outer, Peter N.. No especifíca;Fil: Diaz, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Flynn, Lawrence E.. No especifíca;Fil: Hegglin,Michaela I.. No especifíca;Fil: Herman, Jay R. No especifíca;Fil: Huck, Petra. No especifíca;Fil: Janjai, Serm. No especifíca;Fil: Jánosi, Imre M. No especifíca;Fil: Krzyścin, Janusz W. No especifíca;Fil: Liu, Yi. No especifíca;Fil: Logan, Jennifer. No especifíca;Fil: Matthes, Katja. No especifíca;Fil: McKenzie, Richard L.. No especifíca;Fil: Muthama, Nzioka John. No especifíca;Fil: Petropavlovskikh, Irina. No especifíca;Fil: Pitts, Michael. No especifíca;Fil: Ramachandran, S.. No especifíca;Fil: Rex, Markus. No especifíca;Fil: Salawitch, Ross J.. No especifíca;Fil: Sinnhuber, Björn Martin. No especifíca;Fil: Staehelin, Johannes. No especifíca;Fil: Strahan, Susan. No especifíca;Fil: Tourpali, Kleareti. No especifíca;Fil: Valverde Canossa, Jéssica. No especifíca;Fil: Vigouroux, Corinne. No especifíca