Phloem Proteins

Cronshaw, James; Sabnis, D. D.

doi:10.1007/978-3-642-74445-7_13

Cited by 61 publications

(59 citation statements)

References 91 publications

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“…Such barriers aggregate from parietal P-proteins and the contents of phloem-specific SE-plastids, which in the functional state are located near the longitudinal walls of the SEs (Ehlers et al, 2000). Thus, at least some of the confusingly multifarious structures previously described (Cronshaw and Sabnis, 1990;Sabnis and Sabnis, 1995) actually represent the same material at different states of a cellular wound response.…”

Section: Introductionmentioning

confidence: 93%

“…However, on the basis of descriptive studies alone, the structural state of these protein bodies in transporting SEs could not be established unequivocally (reviewed in Cronshaw and Sabnis, 1990;Sabnis and Sabnis 1995). In our plant material, we were able not only to reproduce all major ultrastructural features described previously, including crystalloid, fibrillar, and intermediate states ( Figure 1), but also to observe directly the transformation of crystalloids into filamentous plugs in intact SEs (Figure 2).…”

Section: Structural Dynamics Of P-protein Crystalloidsmentioning

confidence: 99%

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Reversible Calcium-Regulated Stopcocks in Legume Sieve Tubes [W]

et al. 2001

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Sieve tubes of legumes (Fabaceae) contain characteristic P-protein crystalloids with controversial function. We studied their behavior by conventional light, electron, and confocal laser scanning microscopy. In situ, crystalloids are able to undergo rapid ( Ͻ 1 sec) and reversible conversions from the condensed resting state into a dispersed state, in which they occlude the sieve tubes. Crystalloid dispersal is triggered by plasma membrane leakage induced by mechanical injury or permeabilizing substances. Similarly, abrupt turgor changes imposed by osmotic shock cause crystalloid dispersal. Because chelators generally prevent the response, divalent cations appear to be the decisive factor in crystalloid expansion. Cycling between dispersal and condensation can be induced in opened cells by repetitive exchange of bathing media containing either Ca 2 ؉ or chelators. Sr 2 ؉ and Ba 2 ؉ , but not Mg 2 ؉ , are equally active. In conclusion, the fabacean P-protein crystalloids represent a novel class of mechanically active proteinaceous structures, which provide an efficient mechanism with which to control sieve tube conductivity.

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Section: Introductionmentioning

confidence: 93%

Section: Structural Dynamics Of P-protein Crystalloidsmentioning

confidence: 99%

Reversible Calcium-Regulated Stopcocks in Legume Sieve Tubes [W]

et al. 2001

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“…It was learned that the cytoplasm of mature SEs of dicotyledons has an endoplasmic reticulum (ER), P plastids, mitochondria, and with few exceptions (Esau and Gill, 1972; Walsh and Popovich, 1977), proteins in several forms (e.g., Cronshaw and Sabnis, 1990). The presumptive occlusion of the sieve pores by fine P protein threads conflicted with the mass flow hypothesis and gave rise to the conception of the electroosmotic theory (Fensom, 1957;Spanner, 1958Spanner, , 1970.…”

Section: Introductionmentioning

confidence: 99%

“…There are conflicting opinions as to whether crystalline proteins disperse into other morphological forms during SE differentiation (Wergin and Newcomb, 1970;Palevitz and Newcomb, 1971;Fisher, 1975;Lawton, 1978a). To make the terminology more confusing, filamentous P proteins were reported to occur in P plastids (Cronshaw and Sabnis, 1990). We could discriminate between proteinaceous materials only on the basis of their locations.…”

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confidence: 99%

Sieve Tubes in Action

1998

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A method was designed for in vivo observation of sieve element/companion complexes by using confocal laser scanning microscopy. A leaf attached to an intact fava bean plant was mounted upside down on the stage of a confocal microscope. Two shallow paradermal cortical cuts were made in the major vein. The basal cortical window allowed us to observe the phloem intact. The apical window at 3 cm from the site of observation was used to apply phloem-mobile fluorochromes, which identified living sieve elements at the observation site. In intact sieve tubes, the sieve plates did not present a barrier to mass flow, because the translocation of fluorochromes appeared to be unhindered. Two major occlusion mechanisms were distinguished. In response to intense laser light, the parietal proteins detached from the plasma membrane and formed a network of minute strands and clustered material that aggregated and pressed against the sieve plate. In response to mechanical damage, the evenly distributed P plastids exploded, giving rise to the formation of a massive plug against the sieve plate. In case of mechanical damage, the parietal proteins transformed into elastic threads (strands) that extended throughout the sieve element lumen. Our observations cover the phenomena encountered in previous microscopic and electron microscopic studies and provide a temporal disentanglement of the events giving rise to the confusing mass of structures observed thus far. INTRODUCTIONSince the discovery of sieve elements (SEs) by Theodor Hartig (1837), countless attempts have been made to elucidate their structure and mode of action. It was understood that SEs are involved in long-distance transport of photoassimilates (Hartig, 1860), but the mechanism of translocation had not yet been determined. Diffusion and protoplasmic streaming were discarded as potential mechanisms as soon as the transport velocities proved to be typically 50 to 100 cm hr Ϫ 1 (Canny, 1975). Currently, the most widely favored mechanism for long-distance transport through SEs is the pressure flow hypothesis (Münch, 1930).One of the stumbling blocks to full acceptance of pressure flow as the mechanism of phloem translocation is the typical components of the SEs. In particular, those directly behind the sieve plates may obstruct mass flow. These bodies, originally designated as Schleim (slime) by Hartig (1854), were later rebaptized as P proteins due to their proteinaceous character. Another hindrance may be presented by transcellular strands observed by light microscopy ( Thaine, 1961). Initially, the strands were considered to be membranous structures ( Thaine, 1962) but later respected as P protein filaments enclosing "endoplasmic tubules" (Thaine, 1969). Their rhythmic contraction produced peristaltic waves to facilitate long-distance transport (Thaine, 1969).In electron microscopic images, a parietal filamentous network that fully or partly plugged the sieve pores was observed (Robidoux et al., 1973;Johnson et al., 1976). These filaments sometimes transformed into lon...

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“…The phloem specific proteins (P-proteins) based occlusion occurs in some seconds in the Fabaceae family plants. The insoluble form of the P-proteins in sieve element present in the form like amorphous, granular, fibrillar, filamentous, tubular, and crystalline [19], but the type of form is dependent on plant species [20]. It was well reported in V. faba that utilizes the "forisome dispersion" mechanisms (P-protein based occlusion) to avoid the phloem sap immediately.…”

Section: Introductionmentioning

confidence: 99%

Differential Aphid Colony Establishment in <i>Dolichos lablab</i> Varieties Correlated with Some Plant Specific Factors That Impact on Aphid Fecundity

Mondal¹,

Roy²,

Hijam³

et al. 2017

AJPS

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Aphid establishes colony in the selective plant parts like vine, leaf petiole, leaflet, inflorescence, and tender fruit in Dolichos lablab Linn but not the entire plant. In this study, the aphid colony establishment in vine is focused to understand the differential resistance response between two varieties. At the early stage of aphid infestation, the aphid colony establishment was significantly different between two genotypes (p value = 0.00) and abbreviated as "resistant" variety that supported lower aphid proliferation (mean value = 48.2 ± 2.2) and "susceptible" variety that supported comparatively higher aphid proliferation (mean value = 215.5 ± 16.9). The total aphid number was significantly different between the two varieties, realized at the early infestation stage when both "antixenosis" and "antibiosis" defense mechanisms were working on. Some plant specific factors like vine diameter, wet/ dry weight ratio of vine, phloem sap pressure, the compactness of the vine, wet/dry weight ratio of leaflet, length of leaf petiole, diameter of leaflet vein were identified as modulating factors. The impact of resistant variety on aphid was also investigated for better understanding of aphid defense mechanism.

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Phloem Proteins

Cited by 61 publications

References 91 publications

Reversible Calcium-Regulated Stopcocks in Legume Sieve Tubes [W]

Reversible Calcium-Regulated Stopcocks in Legume Sieve Tubes [W]

Sieve Tubes in Action

Differential Aphid Colony Establishment in <i>Dolichos lablab</i> Varieties Correlated with Some Plant Specific Factors That Impact on Aphid Fecundity

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Phloem Proteins

Cited by 61 publications

References 91 publications

Reversible Calcium-Regulated Stopcocks in Legume Sieve Tubes [W]

Reversible Calcium-Regulated Stopcocks in Legume Sieve Tubes [W]

Sieve Tubes in Action

Differential Aphid Colony Establishment in &lt;i&gt;Dolichos lablab&lt;/i&gt; Varieties Correlated with Some Plant Specific Factors That Impact on Aphid Fecundity

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Differential Aphid Colony Establishment in <i>Dolichos lablab</i> Varieties Correlated with Some Plant Specific Factors That Impact on Aphid Fecundity