Abstract
The existence of pronounced cytoplasmic pH gradients within the apices of tip-growing cells, and the role of cytoplasmic pH in regulating tip growth, were investigated in three different cell types: vegetative hyphae of Neurospora crassa; pollen tubes of Agapanthus umbellatus; and rhizoids of Dryopteris affinis gametophytes. Examination of cytoplasmic pH in growing cells was performed by simultaneous, dual emission confocal ratio imaging of the pH-sensitive probe carboxy SNARF-1. Considerable attention was paid to the fine tuning of dye loading and imaging parameters to minimise cellular perturbation and assess the extent of dye partitioning into organelles. With optimal conditions, cytoplasmic pH was measured routinely with a precision of between +/-0.03 and +/-0.06 of a pH unit and a spatial resolution of 2.3 microm2. Based on in vitro calibration, estimated values of mean cytoplasmic pH for cells loaded with dye-ester were between 7.15 and 7.25 for the three cell types. After pressure injecting Neurospora hyphae with dextran-conjugated dye, however, the mean cytoplasmic pH was estimated to be 7.57. Dextran dyes are believed to give a better estimate of cytoplasmic pH because of their superior localisation and retention within the cytosol. No significant cytoplasmic pH gradient (delta pH of >0.1 unit) was observed within the apical 50 microm in growing cells of any of the three cell types. Acidification or alkalinisation of the cytoplasm in Neurospora hyphae, using a cell permeant weak acid (propionic acid at pH 7.0) or weak base (trimethylamine at pH 8.0), slowed down but did not abolish growth. However, similar manipulation of the cytoplasmic pH of Agapanthus pollen tubes and Dryopteris rhizoids completely inhibited growth. Modification of external pH affected the growth pattern of all cell types. In hyphae and pollen tubes, changes in external pH were found to have a small transient effect on cytoplasmic pH but the cells rapidly readjusted towards their original pH. Our results suggest that pronounced longitudinal gradients in cytoplasmic pH are not essential for the regulation of tip growth.
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Claims 8
Claim · model-written summary
No significant cytoplasmic pH gradient was observed within the apical 50 microm of growing cells in any of the three tip-growing cell types.
- Organ / stage
- apical 50 microme0
- Outcome
- cytoplasmic pH gradiente0
- Qualifier
- any of the three cell typese0
Not reportedTaxonDirection
Verbatim
e0“No significant cytoplasmic pH gradient (delta pH of >0.1 unit) was observed within the apical 50 microm in growing cells of any of the three cell types”
Claim · model-written summary
Mean cytoplasmic pH of dye-ester-loaded cells was estimated at 7.15 to 7.25 for the three cell types.
Not reportedTaxon
Verbatim
e0“estimated values of mean cytoplasmic pH for cells loaded with dye-ester were between 7.15 and 7.25 for the three cell types”
Claim · model-written summary
After injection of dextran-conjugated dye, mean cytoplasmic pH of Neurospora hyphae was estimated at 7.57.
- Taxon
- Neurospora
Neurosporae0 - Organ / stage
- hyphaee0
- Outcome
- mean cytoplasmic pHe0
- Value
- 7.57e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“After pressure injecting Neurospora hyphae with dextran-conjugated dye, however, the mean cytoplasmic pH was estimated to be 7.57”
Claim · model-written summary
Acidifying or alkalinising the cytoplasm of Neurospora hyphae slowed growth but did not abolish it.
- Taxon
- NeurosporaNeurosporae0
- Organ / stage
- hyphaee0
- Treatment
- Acidification or alkalinisation of the cytoplasme0
- Outcome
- growthe0
- Direction
- slowed downe0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Acidification or alkalinisation of the cytoplasm in Neurospora hyphae, using a cell permeant weak acid (propionic acid at pH 7.0) or weak base (trimethylamine at pH 8.0), slowed down but did not abolish growth”
Claim · model-written summary
Manipulating cytoplasmic pH of Agapanthus pollen tubes completely inhibited growth.
- Taxon
- Agapanthus
Agapanthuse0 - Organ / stage
- pollen tubese0
- Treatment
- manipulation of the cytoplasmic pHe0
- Outcome
- growthe0
- Direction
- completely inhibitede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“similar manipulation of the cytoplasmic pH of Agapanthus pollen tubes and Dryopteris rhizoids completely inhibited growth”
Claim · model-written summary
Manipulating cytoplasmic pH of Dryopteris rhizoids completely inhibited growth.
- Taxon
- Dryopteris
Dryopterise0 - Organ / stage
- rhizoidse0
- Treatment
- manipulation of the cytoplasmic pHe0
- Outcome
- growthe0
- Direction
- completely inhibitede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“similar manipulation of the cytoplasmic pH of Agapanthus pollen tubes and Dryopteris rhizoids completely inhibited growth”
Claim · model-written summary
Modifying external pH affected the growth pattern of all cell types.
Not reportedTaxonComparatorDirection
Verbatim
e0“Modification of external pH affected the growth pattern of all cell types”
Claim · model-written summary
In hyphae and pollen tubes, changes in external pH had a small transient effect on cytoplasmic pH and the cells rapidly readjusted to their original pH.
- Organ / stage
- hyphae and pollen tubese0
- Treatment
- changes in external pHe0
- Outcome
- cytoplasmic pHe0
- Qualifier
- small transient effecte0
Not reportedTaxonComparatorDirection
Verbatim
e0“In hyphae and pollen tubes, changes in external pH were found to have a small transient effect on cytoplasmic pH but the cells rapidly readjusted towards their original pH”