The scaling of respiratory metabolism with body mass is one of the most pervasive phenomena in biology. Using a single allometric equation to characterize empirical scaling relationships and to evaluate alternative hypotheses about mechanisms has been controversial. We developed a method to directly measure respiration of 271 whole plants, spanning nine orders of magnitude in body mass, from small seedlings to large trees, and from tropical to boreal ecosystems. Our measurements include the roots, which have often been ignored. Rather than a single power-law relationship, our data are fit by a biphasic, mixed-power function. The allometric exponent varies continuously from 1 in the smallest plants to 3/4 in larger saplings and trees. The transition from linear to 3/4-power scaling may indicate fundamental physical and physiological constraints on the allocation of plant biomass between photosynthetic and nonphotosynthetic organs over the course of ontogenetic plant growth.allometry | metabolic scaling | mixed-power function | whole-plant respiration | simple-power function F rom the smallest seedlings to giant trees, the masses of vascular plants span 12 orders of magnitude in mass (1). The growth rates of most plants, which are generally presented in terms of net assimilation rates of CO 2 , are believed to be controlled by respiration (2, 3). Furthermore, many of the CO 2 -budget models of plant growth and carbon dynamics in terrestrial ecosystems are based on whole-plant respiration rates in relation to plant size (2, 4-7). Thus far, however, there have been few studies of wholeplant respiration over the entire range of plant size from tiny seedlings to large trees. The purpose of the present study was to quantify the allometric scaling of metabolism by directly measuring whole-plant respiration over a representative range of sizes.For the past century, the scaling of metabolic rate with body size has usually been described using an allometric equation, or simple power function, for the form (8-17)where Y is the respiratory metabolic rate (μmol s −1 ), F is a constant (μmol s −1 kg -f ), M is the body mass (kg), and f is the scaling exponent. The exponent f has been controversial, and various values have been reported based on studies of both animals and plants (15). Recently, it was suggested that f = 1 for relatively small plants, based on data for a 10 6 -fold range of body mass (16), including measurements using a whole-plant chamber (18,19). If f = 1, this means that whole-plant respiration scales isometrically with body mass, which may be reasonable in the case of herbaceous plants and small trees because nearly all of their cells, even those in the stems, should be active in respiration. However, it was suggested that f = 3/4 based originally on empirical studies of animal metabolism (8). This idea is consistent with the mechanistic models of resource distribution in vascular systems (10, 11), including the pipe model (20, 21) and models based on space-filling, hierarchical, fractal-like networks of br...

Ralstonia solanacearum is a Gram-negative bacterium and the causative agent of bacterial wilt in many important crops. We treated R. solanacearum with three lytic phages: RSA1, RSB1, and RSL1. Infection with RSA1 and RSB1, either alone or in combination with the other phages, resulted in a rapid decrease in the host bacterial cell density. Cells that were resistant to infection by these phages became evident approximately 30 h after phage addition to the culture. On the other hand, cells infected solely with RSL1 in a batch culture were maintained at a lower cell density (1/3 of control) over a long period. Pretreatment of tomato seedlings with RSL1 drastically limited penetration, growth, and movement of root-inoculated bacterial cells. All RSL1-treated tomato plants showed no symptoms of wilting during the experimental period, whereas all untreated plants had wilted by 18 days postinfection. RSL1 was shown to be relatively stable in soil, especially at higher temperatures (37 to 50°C). Active RSL1 particles were recovered from the roots of treated plants and from soil 4 months postinfection. Based on these observations, we propose an alternative biocontrol method using a unique phage, such as RSL1, instead of a phage cocktail with highly virulent phages. Using this method, RSL1 killed some but not all bacterial cells. The coexistence of bacterial cells and the phage resulted in effective prevention of wilting.

Four kinds of bacteriophage (wRSL, wRSA, wRSM and wRSS) were isolated from Ralstonia solanacearum, a soil-borne Gram-negative bacterium that is the causative agent of bacterial wilt in many important crops. The Myovirus-type phages wRSL1 and wRSA1 contained dsDNA genomes of 240 kbp and 39 kbp, respectively. These phages have relatively wide host ranges and gave large clear plaques with various host strains; especially wRSA1 was able to infect all 15 R. solanacearum strains of different races or different biovars tested in this study. Three host strains contained wRSA1-related sequences in their genomic DNAs, suggesting a lysogenic cycle of wRSA1. Two phages, wRSM1 and wRSS1, were characterized as Ff-type phages (Inovirus) based on their particle morphology, genomic ssDNA and infection cycle. However, despite their similar fibrous morphology, their genome size (9.0 kb for wRSM1 and 6.6 kb for wRSS1) and genome sequence were different. Strains of R. solanacearum that were sensitive to wRSM1 were resistant to wRSS1 and vice versa. Several R. solanacearum strains contained wRSM1-related sequences and at least one strain produced wRSM1 particles, indicating the lysogenic state of this phage. These phages may be useful as a tool not only for molecular biological studies of R. solanacearum pathogenicity but also for specific and efficient detection (wRSM1 and wRSS1) and control of harmful pathogens (wRSL and wRSA) in cropping ecosystems as well as growing crops.

φRSM1 and φRSM3 (φRSM phages) are filamentous phages (inoviruses) that infect Ralstonia solanacearum, the causative agent of bacterial wilt. Infection by φRSM phages causes several cultural and physiological changes to host cells, especially loss of virulence. In this study, we characterized changes related to the virulence in φRSM3-infected cells, including (i) reduced twitching motility and reduced amounts of type IV pili (Tfp), (ii) lower levels of β-1,4-endoglucanase (Egl) activity and extracellular polysaccharides (EPS) production, and (iii) reduced expression of certain genes (egl, pehC, phcA, phcB, pilT, and hrpB). The significantly lower levels of phcA and phcB expression in φRSM3-infected cells suggested that functional PhcA was insufficient to activate many virulence genes. Tomato plants injected with φRSM3-infected cells of different R. solanacearum strains did not show wilting symptoms. The virulence and virulence factors were restored when φRSM3-encoded orf15, the gene for a putative repressor-like protein, was disrupted. Expression levels of phcA as well as other virulence-related genes in φRSM3-ΔORF15-infected cells were comparable with those in wild-type cells, suggesting that orf15 of φRSM3 may repress phcA and, consequently, result in loss of virulence.

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