My journey from horticulture to plant biology.

The author describes the circumstances and opportunities that led him to higher education and to pursue a research career in plant biology. He acknowledges the important roles a few individuals played in guiding him in his career. His early work on flowering was followed by studies on the physiological roles and the metabolism of gibberellins and abscisic acid.

A novel class of gibberellin 2-oxidases control semidwarfism, tillering, and root development in rice.

Gibberellin 2-oxidases (GA2oxs) regulate plant growth by inactivating endogenous bioactive gibberellins (GAs). Two classes of GA2oxs inactivate GAs through 2beta-hydroxylation: a larger class of C(19) GA2oxs and a smaller class of C(20) GA2oxs. In this study, we show that members of the rice (Oryza sativa) GA2ox family are differentially regulated and act in concert or individually to control GA levels during flowering, tillering, and seed germination.

Leaf-produced floral signals.

Florigen is the hypothetical leaf-produced signal that induces floral initiation at the shoot apex. The nature of florigen has remained elusive for more than 70 years. But recent progress toward understanding the regulatory network for flowering in Arabidopsis has led to the suggestion that FLOWERING LOCUS T (FT) or its product is the mobile flower-inducing signal that moves from an induced leaf through the phloem to the shoot apex.

Evidence for abscisic acid biosynthesis in Cuscuta reflexa, a parasitic plant lacking neoxanthin.

Abscisic acid (ABA) is a plant hormone found in all higher plants; it plays an important role in seed dormancy, embryo development, and adaptation to environmental stresses, most notably drought. The regulatory step in ABA synthesis is the cleavage reaction of a 9-cis-epoxy-carotenoid catalyzed by the 9-cis-epoxy-carotenoid dioxygenases (NCEDs). The parasitic angiosperm Cuscuta reflexa lacks neoxanthin, one of the common precursors of ABA in all higher plants.

Regulation of gibberellin 20-oxidase1 expression in spinach by photoperiod.

The multifunctional gibberellin (GA) 20-oxidase [GA(53), 2-oxoglutarate:oxygen oxidoreductase (20-oxidizing), EC 1.14.11] has been extensively investigated in various species at the genetic and molecular levels, but not at the protein level.

Expression of ABA 8'-hydroxylases in relation to leaf water relations and seed development in bean.

In plants, the level of abscisic acid (ABA) is determined by synthesis and catabolism. Hydroxylation of ABA at the 8' position is the key step in ABA catabolism. This reaction is catalyzed by ABA 8'-hydroxylase, a cytochrome P450 (CYP).

Molecular cloning of GA 2-oxidase3 from spinach and its ectopic expression in Nicotiana sylvestris.

Previous work has shown that 13-hydroxylated gibberellins (GAs) are predominant in the long-day (LD) plant spinach (Spinacia oleracea; GA53, GA44, GA19, GA20, GA1, GA8, and GA29). Also present in spinach are 2-hydroxylated C20-GAs: GA97, GA98, GA99, and GA110. Levels of the most abundant GA, GA97, decreased when plants were transferred from short photoperiods (SD) to LD.

Overexpression of a novel class of gibberellin 2-oxidases decreases gibberellin levels and creates dwarf plants.

Degradation of active C(19)-gibberellins (GAs) by dioxygenases through 2beta-hydroxylation yields inactive GA products. We identified two genes in Arabidopsis (AtGA2ox7 and AtGA2ox8), using an activation-tagging mutant screen, that encode 2beta-hydroxylases. GA levels in both activation-tagged lines were reduced significantly, and the lines displayed dwarf phenotypes typical of mutants with a GA deficiency.

Substrate specificity and kinetics for VP14, a carotenoid cleavage dioxygenase in the ABA biosynthetic pathway.

The plant growth regulator, abscisic acid (ABA), is synthesized via the oxidative cleavage of an epoxy-carotenoid. Specifically, a double bond is cleaved by molecular oxygen and an aldehyde is formed at the site of cleavage in both products. The Vp14 gene from maize encodes an oxidative cleavage enzyme for ABA biosynthesis and the recombinant VP14 protein catalyzes the cleavage reaction in vitro.

Differential regulation of RNA levels of gibberellin dioxygenases by photoperiod in spinach.

Previous work with spinach (Spinacia oleracea) has shown that the level of gibberellin (GA) 20-oxidase is strongly up-regulated by long days (LD). In the present work, the effect of photoperiod on expression of other GA dioxygenases was investigated and compared with that of GA 20-oxidase. Two GA 2-oxidases and one GA 3-oxidase were isolated from spinach by reverse transcription-polymerase chain reaction with degenerate primers and by 5'- and 3'-rapid amplification of cDNA ends.

Comparison of peptides in the phloem sap of flowering and non-flowering Perilla and lupine plants using microbore HPLC followed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Physiological evidence indicates that flower formation is hormonally controlled. The floral stimulus, or florigen, is formed in the leaves as a response to an inductive photoperiod and translocated through the phloem to the apical meristem. However, because of difficulties in obtaining and analyzing phloem sap and the lack of a bioassay, the chemical nature of this stimulus is one of the major unsolved problems in plant biology.

The 120-yr period for Dr. Beal's seed viability experiment.

After 120 yr of burial in moist, well-aerated sand, 23 seeds of Verbascum blattaria and two seeds of a Verbascum sp. germinated and produced normal plants (50% germination for Verbascum). After a 6-wk cold treatment, a single seed of Malva rotundifolia germinated also, producing a normal plant (2% germination).

Characterization of mutants with reduced seed dormancy at two novel rdo loci and a further characterization of rdo1 and rdo2 in Arabidopsis.

Seed dormancy and germination are complex traits that are controlled by many genes. Four mutants in Arabidopsis thaliana exhibiting a reduced dormancy phenotype, designated rdo1, rdo2, rdo3, and rdo4, have been characterized, both genetically and physiologically. Two of these mutants, rdo1 and rdo2, have been described before, the other two represent novel loci.

Overexpression of a 9-cis-epoxycarotenoid dioxygenase gene in Nicotiana plumbaginifolia increases abscisic acid and phaseic acid levels and enhances drought tolerance.

The plant hormone abscisic acid (ABA) plays important roles in seed maturation and dormancy and in adaptation to a variety of environmental stresses. An effort to engineer plants with elevated ABA levels and subsequent stress tolerance is focused on the genetic manipulation of the cleavage reaction. It has been shown in bean (Phaseolus vulgaris) that the gene encoding the cleavage enzyme (PvNCED1) is up-regulated by water stress, preceding accumulation of ABA.