Organ-Specific Invertase Deficiency in the Primary Root of an Inbred Maize Line

Duke, Edwin R.; McCarty, Donald R.; Koch, Karen E.

doi:10.1104/pp.97.2.523

Cited by 23 publications

(19 citation statements)

References 24 publications

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“…Koch et al (1992) found that, in intact maize roots, Suc synthase genes are strongly expressed in virtually a11 root tip cells except for columella cells of the cap, implying that substantial Suc metabolism occurs in the meristematic region. In addition, cell-wallbound invertase activity, which would be required for this transport mechanism, is highest in the apical 2 mm of the maize primary root, and has vanished by 8 mm from the tip (Duke et al, 1991).…”

Section: Alternative Mechanisms Of Transport: Symplasmic Possibilitiesmentioning

confidence: 99%

Nonvascular, Symplasmic Diffusion of Sucrose Cannot Satisfy the Carbon Demands of Growth in the Primary Root Tip of Zea mays L

1994

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Nonvascular, symplasmic transport of sucrose (Suc) was investigated theoretically in the primary root tip of maize (Zea mays 1.cv WF9 x Mo 17) seedlings. Symplasmic diffusion has been assumed to be the mechanism of transport of Suc to cells in the root apical meristem (R.T. Ciaquinta, W. Lin, N.L. Sadler, V.R. Franceschi [1983] Plant Physiol 72: 362-367), which grow apical to the end of the phloem and must build all biomass with carbon supplied from the shoot or kernel. We derived an expression for the growthsustaining Suc flux, which is the minimum longitudinal flux that would be required to meet the carbon demands of growth in the root apical meristem. We calculated this flux from data on root growth velocity, area, and biomass density, taking into account construction and maintenance respiration and the production of mucilage by the root cap. We then calculated the conductivity of the symplasmic pathway for diffusion, from anatomical data on cellular dimensions and the frequency and dimensions of plasmodesmata, and from two estimates of the diffusive conductance of a plasmodesma, derived from independent data. Then, the concentration gradients required to drive a growth-sustaining Suc flux by diffusion alone were calculated but were found not to be physiologically reasonable. We also calculated the hydraulic conductivity of the plasmodesmatal pathway and found that mass flow of Suc solution through plasmodesmata would also be insufficient, by itself, to satisfy the carbon demands of growth. However, much of the demand for water to cause cell expansion could be met by the water unloaded from the phloem while unloading Suc to satisfy the carbon demands of growth, and the hydraulic conductivity of plasmodesmata is high enough that much of that water could move symplasmically. Either our current understanding of plasmodesmatal ultrastructure and function is flawed, or alternative transport mechanisms must exist for Suc transport to the meristem.Understanding the control of plant growth and development must include an understanding of the transport of photoassimilates from sources into developing sinks. Transport of solutes through the differentiated phloem is explained well by quantitative treatments of Miinch's (1930) pressure flow hypothesis (Christy and Femer, 1973;Tyree et al., 1974a;Ross and Tyree, 1980), and experimental data are in reasonably good agreement with their predictions (cf. Zimmermann and Brown, 1971; Pickard et al.,

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Section: Alternative Mechanisms Of Transport: Symplasmic Possibilitiesmentioning

confidence: 99%

Nonvascular, Symplasmic Diffusion of Sucrose Cannot Satisfy the Carbon Demands of Growth in the Primary Root Tip of Zea mays L

1994

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“…A vacuolar invertase path for Suc hydrolysis would be especially useful in a symplastically continuous system of phloem-unloading and post-phloem transport where internal Suc cleavage could sustain Suc gradients across plasmodesmata (Duke et al, 1991;Sturm et al, 1995;Fisher and Cash-Clark, 2000b;Kim et al, 2000). The abundant activity and mRNA localization in parenchyma surrounding terminal regions of vascular bundles in maize ovaries (Figs.…”

Section: Role Of Vacuolar Invertase In Young Ovariesmentioning

confidence: 99%

Soluble Invertase Expression Is an Early Target of Drought Stress during the Critical, Abortion-Sensitive Phase of Young Ovary Development in Maize

et al. 2002

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To distinguish their roles in early kernel development and stress, expression of soluble (Ivr2) and insoluble (Incw2) acid invertases was analyzed in young ovaries of maize (Zea mays) from 6 d before (Ϫ6 d) to 7 d after pollination (ϩ7 d) and in response to perturbation by drought stress treatments. The Ivr2 soluble invertase mRNA was more abundant than the Incw2 mRNA throughout pre-and early post-pollination development (peaking at ϩ3 d). In contrast, Incw2 mRNAs increased only after pollination. Drought repression of the Ivr2 soluble invertase also preceded changes in Incw2, with soluble activity responding before pollination (Ϫ4 d). Distinct profiles of Ivr2 and Incw2 mRNAs correlated with respective enzyme activities and indicated separate roles for these invertases during ovary development and stress. In addition, the drought-induced decrease and developmental changes of ovary hexose to sucrose ratio correlated with activity of soluble but not insoluble invertase. Ovary abscisic acid levels were increased by severe drought only at Ϫ6 d and did not appear to directly affect Ivr2 expression. In situ analysis showed localized activity and Ivr2 mRNA for soluble invertase at sites of phloem-unloading and expanding maternal tissues (greatest in terminal vascular zones and nearby cells of pericarp, pedicel, and basal nucellus). This early pattern of maternal invertase localization is clearly distinct from the well-characterized association of insoluble invertase with the basal endosperm later in development. This localization, the shifts in endogenous hexose to sucrose environment, and the distinct timing of soluble and insoluble invertase expression during development and stress collectively indicate a key role and critical sensitivity of the Ivr2 soluble invertase gene during the early, abortion-susceptible phase of development.

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“…In organs that import sugar, Suc is converted to Glc by locally expressed Suc synthase or invertase (Koch, 2004). In root, for example, Suc invertase and synthase are expressed preferentially in the meristem and early elongation zone (Duke et al, 1991;Barratt et al, 2009). Consequently, sugar concentration is high in cells that are involved in uploading and downloading.…”

mentioning

confidence: 99%

SCARECROW Has a SHORT-ROOT-Independent Role in Modulating the Sugar Response

2012

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Sugar is essential for all cellular activities, but at high levels it inhibits growth and development. How plants balance the tradeoffs between the need for sugars and their growth inhibitory effects is poorly understood. SHORT-ROOT (SHR) and SCARECROW (SCR) are key regulators of stem cell renewal and radial patterning in the root of Arabidopsis (Arabidopsis thaliana). Recently, we identified direct targets of SHR at the genome scale. Intriguingly, among the top-ranked list, we found a number of genes that are involved in stress responses. By chromatin immunoprecipitation-polymerase chain reaction (PCR), we showed that SHR and SCR regulate a similar but not identical set of stress response genes. Consistent with this, scr and shr were found to be hypersensitive to abscisic acid (ABA). We further showed that both mutants were hypersensitive to high levels of glucose (Glc) but responded normally to high salinity and osmoticum. The endogenous levels of sucrose, Glc, and fructose were also elevated in shr and scr. Intriguingly, although shr had sugar content and developmental defects similar to those of scr, it was much less sensitive to Glc. Chromatin immunoprecipitation-PCR and reverse transcription-PCR assays as well as transgenic studies with an ABA-INSENSITIVE2 (ABI4)-b-glucuronidase reporter construct revealed that in root, SCR, but not SHR, repressed ABI4 and ABI5 directly and specifically in the apical meristem. When combined with abi4, scr became much more tolerant of high Glc. Finally, transgenic plants expressing ABI4 under the control of the SCR promoter manifested a shortroot phenotype. These results together suggest that SCR has a SHR-independent role in mitigating the sugar response and that this role of SCR is important for root growth.

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Organ-Specific Invertase Deficiency in the Primary Root of an Inbred Maize Line

Cited by 23 publications

References 24 publications

Nonvascular, Symplasmic Diffusion of Sucrose Cannot Satisfy the Carbon Demands of Growth in the Primary Root Tip of Zea mays L

Nonvascular, Symplasmic Diffusion of Sucrose Cannot Satisfy the Carbon Demands of Growth in the Primary Root Tip of Zea mays L

Soluble Invertase Expression Is an Early Target of Drought Stress during the Critical, Abortion-Sensitive Phase of Young Ovary Development in Maize

SCARECROW Has a SHORT-ROOT-Independent Role in Modulating the Sugar Response

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