Functions of Hormones at the Cellular Level of Organization

Evans, Michael L.

doi:10.1007/978-3-642-67731-1_3

Cited by 72 publications

(48 citation statements)

References 382 publications

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“…Cytokinin production is believed to be associated with the division of root cells. Initiation of lateral roots might be responsible for the increase in the ability of roots to supply the shoot with cytokinins (Evans, 1984). Cytokinin is vey helpful to control shoot growth (Beck, 1996).…”

Section: Discussionmentioning

confidence: 99%

Effects of root pruning on the growth and rhizosphere soil characteristics of short-rotation closed-canopy poplar

Xing

et al. 2012

For. syst.

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When poplar trees planted at a high density are canopy-closed in plantation after 4-5 years of growth, the roots of adjacent trees will inevitably intermingle together, which possibly restricts the nutrient uptake by root system. Root pruning might stimulate the emergence of fine roots and benefit the tree growth of short-rotation poplar at the stage of canopy closing. The aim of this study is to evaluate the effects of root pruning on DBH (diameter at breast height, 1.3 m), tree height, nutrients (N, P and K) and hormones (indoleacetic acid and cytokinin) in poplar leaves, gas exchange variables (photosynthetic rate and stomatal conductance), and rhizosphere soil characteristics. Field experiment was carried out with four-yearold poplar (Populus × euramericana cv. 'Neva') planted in a fluvo-aquic loam soil in Shandong province, China in early April, 2008. Three root pruning treatments (severe, moderate and light degree) were conducted at the distances of 6, 8 and 10 times DBH on both inter-row sides of the trees to the depth of 30 cm, respectively. The results showed that the growth performance was obtained in the following order of treatments: moderate > light = control > severe. In the rhizophere soil, moderate and light pruning increased the microbial populations, enzymatic activities, and the concentrations of available N, P, K and organic matter. Generally, root pruning to improve tree growth and rhizosphere soil fertility can be recommended in canopy-closed poplar plantation. The appropriate selection of root pruning intensity is a pivotal factor for the effectiveness of this technique.Key words: root pruning method; poplar plantation; growth performance; rhizosphere soil fertility. ResumenEfectos de la poda de raíces sobre el crecimiento y las características de la rizosfera del suelo de los álamos de corta rotación en la etapa del dosel cerradoCuando los chopos plantados a alta densidad cierran el dosel de copas después de 4-5 años, las raíces de árboles adyacentes inevitablemente se mezclan, lo que posiblemente limita la absorción de nutrientes por el sistema radicular. La poda de raíces podría estimular la aparición de raíces finas y beneficiar al crecimiento de los álamos de corta rotación en la etapa del dosel cerrado. El objetivo de este estudio es evaluar los efectos de la poda de raíces en el DAP (diámetro a la altura del pecho, 1,3 m), altura de los árboles, los nutrientes (N, P y K) y las hormonas (ácido indolacético y citoquininas) en las hojas, variables de intercambio gaseoso (tasa de fotosíntesis y conductancia estomática) y característi-cas de la rizosfera del suelo. El experimento de campo se llevó a cabo con chopos (Populus × euramericana cv. 'Neva') de cuatro años de edad plantadas en un suelo franco fluvo-ácuico en la provincia de Shandong, China, a principios de abril de 2008. Se efectuaron tres tratamientos de poda de raíces (severa, moderada y el grado de luz) a distancias de 6, 8 y 10 veces DAP en ambos lados entre las filas de los árboles a la profundidad de 30 cm. Los res...

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Section: Discussionmentioning

confidence: 99%

Effects of root pruning on the growth and rhizosphere soil characteristics of short-rotation closed-canopy poplar

Xing

et al. 2012

For. syst.

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“…Plant growth in response to environmental factors is modulated by plant hormones acting alone or in concert (Evans, 1984), and growth depends on regulated cellular events, such as division, elongation, and differentiation. In addition to the classic hormones, such as auxin and gibberellic acid (GA), brassinosteroids (BRs) have been discovered to be important in growth promotion (reviewed in Clouse, 1996).…”

Section: Introductionmentioning

confidence: 99%

The DWF4 Gene of Arabidopsis Encodes a Cytochrome P450 That Mediates Multiple 22α-Hydroxylation Steps in Brassinosteroid Biosynthesis

et al. 1998

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dwarf4 ( dwf4 ) mutants of Arabidopsis display a dwarfed phenotype due to a lack of cell elongation. Dwarfism could be rescued by the application of brassinolide, suggesting that DWF4 plays a role in brassinosteroid (BR) biosynthesis. The DWF4 locus is defined by four mutant alleles. One of these is the result of a T-DNA insertion. Plant DNA flanking the insertion site was cloned and used as a probe to isolate the entire DWF4 gene. Sequence analysis revealed that DWF4 encodes a cytochrome P450 monooxygenase with 43% identity to the putative Arabidopsis steroid hydroxylating enzyme CONSTITUTIVE PHOTOMORPHOGENESIS AND DWARFISM. Sequence analysis of two other mutant alleles revealed deletions or a premature stop codon, confirming that DWF4 had been cloned. This sequence similarity suggests that DWF4 functions in specific hydroxylation steps during BR biosynthesis. In fact, feeding studies utilizing BR intermediates showed that only 22 ␣ -hydroxylated BRs rescued the dwf4 phenotype, confirming that DWF4 acts as a 22 ␣ -hydroxylase. INTRODUCTIONThe sessile nature of plants requires that they make fine but responsive adjustments in growth to survive harsh environmental conditions and to optimize their use of limited resources ( Trewavas, 1986). Plant growth in response to environmental factors is modulated by plant hormones acting alone or in concert (Evans, 1984), and growth depends on regulated cellular events, such as division, elongation, and differentiation. In addition to the classic hormones, such as auxin and gibberellic acid (GA), brassinosteroids (BRs) have been discovered to be important in growth promotion (reviewed in Clouse, 1996). This conclusion is based on the results of experiments in which a BR was applied to a series of Arabidopsis dwarf ( dwf ) mutants. Several types of dwarf or dwarflike mutants have been described in Arabidopsis. Among these are the dwarfs that are rescued by GA (Koornneef and Van der Veen, 1980) as well as a collection of dwf mutants that are rescued by BRs (Kauschmann et al., 1996;Li et al., 1996;Szekeres et al., 1996;Azpiroz et al., 1998). There are additional dwarfs that are insensitive to one of these hormones, such as bri ( brassinosteroid insensitive ; Clouse et al., 1996;, gai ( gibberellic acid insensitive ; Koornneef et al., 1985), and axr2 ( auxin resistant2 ; Timpte et al., 1994). We are characterizing a large collection of BR-rescued dwf mutants as an approach to understanding the mechanisms involved in the biosynthesis of these compounds.The term BRs collectively refers to the growth-promoting steroids found in plants (Grove et al., 1979). They are structurally very similar to the molting hormones of insects, ecdysteroids (Richter and Koolman, 1991), but active BRs have unique structural features. As shown in Figure 1, a 6-oxolactone or 7-oxalactone in the B ring, 5 ␣ hydrogen, and multiple hydroxylations at four different positions with specific stereochemistry have been proposed as an essential configuration for BRs (reviewed in Marquardt and Adam, 1991). Amon...

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“…In contrast, the role of 'classical' plant hormones such as auxins (Davies, 1988;Evans, 1984), gibberellins (Hooley, 1994), cytokinins (Brzobohaty' etal., 1994;Kaminek, 1992), ethylene (Abeles et al, 1992;Zarembinski and Theologis, 1994), or abscisic acid in plant development has been well proven through studies of mutants with biosynthetic or perception/signal transduction deficiencies (Hobbie and Estelle, 1994;Hobbie et aL, 1994). Further evidence has been obtained through the modification of endogenous hormone levels by expression of bacterial genes in transgenic plants (Klee and Estelle, 1991) and the exogenous application of these substances or their antagonists in addition to the determination of the endogenous hormone levels.…”

Section: Introductionmentioning

confidence: 99%

Genetic evidence for an essential role of brassinosteroids in plant development

et al. 1996

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SummaryBrassinosteroids which show high structural similarity to animal steroid hormones elicit a variety of growth responses when exogeneously applied to plant tissues. Thus far however, the function of endogeneous brassinosteroids in higher plants has been unclear. This paper describes three extremely dwarfed Arabidopsis thaliana mutants, cbbl (dwfl-6), cbb2and cbb3, which are impared in cell elongation controlled by brassinosteroids. While cbbl (dwfl-6) and cbb3 can be phenotypically normalized to wild-type by feeding with brassinosteroids indicating deficiencies of brassinosteroid biosynthesis, cbb2 is brassinosteroid-insensitive and defines a function required for further metabolic conversion necessary for biological activity or for perception/signal transduction of these growth-regulating plant steroid hormones. Expression of the meri5 and TCH4 genes is low in all three cbb mutants and can be restored to wild-type levels by brassinosteroid treatment in the cbbl (dwfl-6) and cbb3 mutants but are unaffected in the cbb2 mutant. These data indicate that brassinosteroids are essential for proper plant development and play an important role in the control of cell elongation.

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Functions of Hormones at the Cellular Level of Organization

Cited by 72 publications

References 382 publications

Effects of root pruning on the growth and rhizosphere soil characteristics of short-rotation closed-canopy poplar

Effects of root pruning on the growth and rhizosphere soil characteristics of short-rotation closed-canopy poplar

The DWF4 Gene of Arabidopsis Encodes a Cytochrome P450 That Mediates Multiple 22α-Hydroxylation Steps in Brassinosteroid Biosynthesis

Genetic evidence for an essential role of brassinosteroids in plant development

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