The Viviparous12 Maize Mutant Is Deficient In Abscisic Acid, Carotenoids, And Chlorophyll Synthesis

The carotenoid/viviparous maize (Zea mays L.) mutant vp12 is a single locus mutation that results in lemon-coloured endosperms, viviparous embryos and albino seedlings. This work presents the first molecular and biochemical analysis of vp12. Levels of ABA were measured during embryo development and also in isolated organs under water deficit stress. ABA levels were lower in developing embryos of mutants than in non-mutant siblings at all stages analysed. In addition, under water deficit, mutant organs accumulated less ABA than corresponding non-mutant sibling organs. Furthermore, immature mutant embryos accumulated transcripts for several ABA or water deficit-responsive genes, Em, glb1, glb2, rab17, and vp1. These results indicated that vp12 is deficient in ABA accumulation, but not in the ABA signal transduction pathway. Analysis of carotenoid extracts showed that mutant endosperms accumulated lower amounts of coloured precursors than non-mutant endosperms. The expression of key enzymes in the carotenoid biosynthesis pathway was also analysed in vp12 endosperms. Western analysis indicated that phytoene synthase (PSY) was present at equal levels in normal and mutant endosperms. In addition, phytoene desaturase (PDS) transcript levels were similar in non-mutant and mutant tissues. Transcripts for geranylgeranyl, pyrophosphate synthase (GGPPS), on the other hand, accumulated at lower levels in mutant endosperms than in non-mutant ones. However, Southern analysis of genomic DNA from normal and mutant tissues indicated that the gene encoding GGPPS is unlikely to be directly affected in vp12. 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Crescimento de espécies do gênero Brachiaria sob alagamento em casa de vegetação Effect of flooding on the growth of Brachiaria species in greenhouse

Objetivou-se avaliar a tolerância ao alagameto de quatro espécies de Brachiaria (B. decumbens,B. brizantha, B. humidicola e B. mutica), a partir de suas características morfogênicas, fisiológicas e produtivas. Os tratamentos foram arranjados segundo esquema fatorial 4 x 3 quatro espécies de Brachiaria e três níveis de disponibilidade de água no solo (capacidade de campo, lâmina d'água de 1 e 10 cm acima do solo). O delineamento experimental foi de blocos completos ao acaso, com três repetições. O experimento foi instalado em casa de vegetação, utilizando-se colunas de PVC com 60 cm de altura x 30 cm de diâmetro. Os níveis de alagamento foram impostos a partir do 22º dia de rebrota após corte de uniformização. O acréscimo de água aos vasos, necessário para satisfazer a lâmina d'água a 1 e 10 cm do nível do solo nos respectivos vasos, foi controlado com o auxílio de furos presentes nas paredes dos vasos a 1 e 10 cm acima do nível do solo, respectivamente. O alagamento comprometeu a taxa de alongamento e acentuou a taxa de senescência das lâminas foliares, independentemente da espécie. Observou-se controle estomático das trocas gasosas em folhas de todas as espécies. O alagamento reduziu a fotossíntese líquida das espécies de Brachiaria, exceto de B. mutica, que superou as demais espécies sob a lâmina d'água de 10 cm acima do solo. Também diminuiu significativamente a área e o peso das lâminas foliares verdes, exceto em B. mutica, que apresentou apenas ligeira tendência de queda. A B. muticaapresentou numerosas raízes adventícias, que, possivelmente, lhe conferiram superior tolerância ao alagamento.<br>This study aimed to evaluate the tolerance of four Brachiaria species (B. decumbens,B. brizantha, B. humidicola and B. mutica) to flooding with regard to their morphogenetical, physiological and production characteristics. The experimental treatments resulted from a 4 x 3 factorial arrangement of four Brachiaria species and three flooding conditions (water field capacity, 1 and 10 cm water lamina above the soil surface) distributed in a completely randomized block design, with three replications. The experiment was carried out in greenhouse, in PVC column pot 60 cm high and 30 cm in diameter. The flooding was imposed during 18 days from the 22nd days of regrowth, after uniformization clipping. Small holes made 1 and 10 cm above soil level allowed to control the desired water lamina level in the pots. Flooding hindered leaf blade elongation rate and increased leaf blade senescence rate, regardless of species. Stomatal control of gas exchanges was observed in all species. Flooding reduced the photosynthesis rate in all species, except B. mutica, which out-yielded the others species under the 10 cm water level. Flooding significantly reduced the area and weight of green leaf blade, except in B. mutica which showed only a slight decrease tendency. The numerous adventitious roots of B. mutica would have played an important role in its tolerance to flooding