Annual Review of Plant Biology

Henderson, James HM

doi: 10.1146/annurev.arplant.52.1.1pmid: 11337390

▪ Abstract This chapter is a chronological and biographical sketch of the professional life of a botanist-plant physiologist. He just happens to be of African-American descent. He cites his early education and through college and graduate school, as well as his war years at the University of Chicago. His postdoc appointment at Caltech with James Bonner was really his professional beginning and highlight. Most of his teaching and research years were spent at Tuskegee University and the George Washington Carver Research Foundation. He spent several tours of research activity, in both the United States and foreign countries. His contact with plant physiologists was quite broad, both in the United States and overseas. Finally, in his senior years, he has turned to mentoring young students into careers in the biological and allied sciences. This activity, he states, has “kept me young beyond my chronological age.”

Facchini, Peter J

doi: 10.1146/annurev.arplant.52.1.29pmid: 11337391

▪ Abstract Recent advances in the cell, developmental, and molecular biology of alkaloid biosynthesis have heightened our appreciation for the complexity and importance of plant secondary pathways. Several biosynthetic genes involved in the formation of tropane, benzylisoquinoline, and terpenoid indole alkaloids have now been isolated. The early events of signal perception, the pathways of signal transduction, and the function of gene promoters have been studied in relation to the regulation of alkaloid metabolism. Enzymes involved in alkaloid biosynthesis are associated with diverse subcellular compartments including the cytosol, vacuole, tonoplast membrane, endoplasmic reticulum, chloroplast stroma, thylakoid membranes, and perhaps unique “biosynthetic” or transport vesicles. Localization studies have shown that sequential alkaloid biosynthetic enzymes can also occur in distinct cell types, suggesting the intercellular transport of pathway intermediates. Isolated genes have also been used to genetically alter the accumulation of specific alkaloids and other plant secondary metabolites. Metabolic modifications include increased indole alkaloid levels, altered tropane alkaloid accumulation, elevated serotonin synthesis, reduced indole glucosinolate production, redirected shikimate metabolism, and increased cell wall–bound tyramine formation. This review discusses the biochemistry, cell biology, molecular regulation, and metabolic engineering of alkaloid biosynthesis in plants.

Richards, Donald E; King, Kathryn E; Ait-ali, Tahar; Harberd, Nicholas P

doi: 10.1146/annurev.arplant.52.1.67pmid: 11337392

▪ Abstract Gibberellins are hormones that control growth and a wide variety of other plant developmental processes. In recent years, significant progress has been made on the biochemistry of gibberellin biosynthesis and on the mechanisms by which gibberellin levels are regulated in plants. There have also been major advances in the understanding of gibberellin signaling, with several key genes being cloned. This review discusses our current understanding of gibberellin signaling, as seen from the perspective of molecular genetic analysis, and relates these observations to previous biochemical studies. In particular, we highlight an important conclusion of recent years: that GAI/RGA and orthologs play major roles in gibberellin signaling in diverse plant species, and that gibberellin probably stimulates growth by derepression of GAI/RGA.

Mok, David WS; Mok, Machteld C

doi: 10.1146/annurev.arplant.52.1.89pmid: 11337393

▪ Abstract Cytokinins are structurally diverse and biologically versatile. The chemistry and physiology of cytokinin have been studied extensively, but the regulation of cytokinin biosynthesis, metabolism, and signal transduction is still largely undefined. Recent advances in cloning metabolic genes and identifying putative receptors portend more rapid progress based on molecular techniques. This review centers on cytokinin metabolism with connecting discussions on biosynthesis and signal transduction. Important findings are summarized with emphasis on metabolic enzymes and genes. Based on the information generated to date, implications and future research directions are presented.

Hanson, Andrew D; Roje, Sanja

doi: 10.1146/annurev.arplant.52.1.119pmid: 11337394

▪ Abstract The metabolism of one-carbon (C 1 ) units is essential to plants, and plant C 1 metabolism has novel features not found in other organisms—plus some enigmas. Despite its centrality, uniqueness, and mystery, plant C 1 biochemistry has historically been quite poorly explored, in part because its enzymes and intermediates tend to be labile and low in abundance. Fortunately, the integration of molecular and genetic approaches with biochemical ones is now driving rapid advances in knowledge of plant C 1 enzymes and genes. An overview of these advances is presented. There has also been progress in measuring C 1 metabolite fluxes and pool sizes, although this remains challenging and there are relatively few data. In the future, combining reverse genetics with flux and pool size determinations should lead to quantitative understanding of how plant C 1 pathways function. This is a prerequisite for their rational engineering.

McClung, C Robertson

doi: 10.1146/annurev.arplant.52.1.139pmid: 11337395

▪ Abstract Circadian rhythms, endogenous rhythms with periods of approximately 24 h, are widespread in nature. Although plants have provided many examples of rhythmic outputs and our understanding of photoreceptors of circadian input pathways is well advanced, studies with plants have lagged in the identification of components of the central circadian oscillator. Nonetheless, genetic and molecular biological studies, primarily in Arabidopsis, have begun to identify the components of plant circadian systems at an accelerating pace. There also is accumulating evidence that plants and other organisms house multiple circadian clocks both in different tissues and, quite probably, within individual cells, providing unanticipated complexity in circadian systems.

Grossman, Arthur

doi: 10.1146/annurev.arplant.52.1.163pmid: 11337396

▪ Abstract Organisms acclimate to a continually fluctuating nutrient environment. Acclimation involves responses specific for the limiting nutrient as well as responses that are more general and occur when an organism experiences different stress conditions. Specific responses enable organisms to efficiently scavenge the limiting nutrient and may involve the induction of high-affinity transport systems and the synthesis of hydrolytic enzymes that facilitate the release of the nutrient from extracellular organic molecules or from internal reserves. General responses include changes in cell division rates and global alterations in metabolic activities. In photosynthetic organisms there must be precise regulation of photosynthetic activity since when severe nutrient limitation prevents continued cell growth, excitation of photosynthetic pigments could result in the formation of reactive oxygen species, which can severely damage structural and functional features of the cell. This review focuses on ways that photosynthetic eukaryotes assimilate the macronutrients nitrogen, sulfur, and phosphorus, and the mechanisms that govern assimilatory activities. Also discussed are molecular responses to macronutrient limitation and the elicitation of those responses through integration of environmental and cellular cues.

Wang, Xuemin

doi: 10.1146/annurev.arplant.52.1.211pmid: 11337397

▪ Abstract Phospholipases are a diverse series of enzymes that hydrolyze phospholipids. Multiple forms of phospholipases D, C, and A have been characterized in plants. These enzymes are involved in a broad range of functions in cellular regulation, lipid metabolism, and membrane remodeling. In recent years, increasing attention has been paid to the many roles of phospholipases in signal transduction. This review highlights recent developments in the understanding of biochemical, molecular biological, and functional aspects of various phospholipases in plants.

Olsen, Odd-Arne

doi: 10.1146/annurev.arplant.52.1.233pmid: 11337398

▪ Abstract The endosperm develops from the central cell of the megagametophyte after introduction of the second male gamete into the diploid central cell. Of the three forms of endosperm in angiosperms, the nuclear type is prevalent in economically important species, including the cereals. Landmarks in nuclear endosperm development are the coenocytic, cellularization, differentiation, and maturation stages. The differentiated endosperm contains four major cell types: starchy endosperm, aleurone, transfer cells, and the cells of the embryo surrounding region. Recent research has demonstrated that the first two phases of endosperm occur via mechanisms that are conserved among all groups of angiosperms, involving directed nuclear migration during the coenocytic stage and anticlinal cell wall deposition by cytoplasmic phragmoplasts formed in interzones between radial microtubular systems emanating from nuclear membranes. Complete cellularization of the endosperm coenocyte is achieved through centripetal growth of cell files, extending to the center of the endosperm cavity. Key points in cell cycle control and control of the MT (microtubular) cytoskeletal apparatus central to endosperm development are discussed. Specification of cell fates in the cereal endosperm appears to occur via positional signaling; cells in peripheral positions, except over the main vascular tissues, assume aleurone cell fate. Cells over the main vascular tissue become transfer cells and all interior cells become starchy endosperm cells. Studies in maize have implicated Crinkly4, a protein receptor kinase-like molecule, in aleurone cell fate specification.

Christiansen, Jason; Dean, Dennis R

doi: 10.1146/annurev.arplant.52.1.269pmid: 11337399

▪ Abstract Nitrogenase is the complex metalloenzyme responsible for biological dinitrogen reduction. This reaction represents the single largest contributor to the reductive portion of the global nitrogen cycle. Recent developments in understanding the mechanism of the Mo-based nitrogenase are reviewed. Topics include how nucleotide binding and hydrolysis are coupled to electron transfer and substrate reduction, how electrons are accumulated and transferred within the MoFe-protein, and how substrates bind and are reduced at the active site metal cluster.