Glyceollins Trigger Anti-Proliferative Effects in Hormone-Dependent Aromatase-Inhibitor-Resistant Breast Cancer Cells through the Induction of Apoptosis

Aromatase inhibitors (AIs) are standard treatment for estrogen-dependent postmenopausal breast tumors; however, resistance develops leading to tumor relapse and metastasis. We previously demonstrated that glyceollin inhibits proliferation, survival, and migration of hormone-independent letrozole-resistant breast cancer. Since many AI-resistant tumors remain hormone-dependent, identifying distinctions between estrogen-receptor-positive (ER+) and ER-negative (ER-) AI-resistant tumor response to therapy is critical. We hypothesize that treating ER+ letrozole-resistant T47D breast cancer cells (T47DaromLR) with a combination of 10 μM glyceollin and 0.5 μM lapatinib (a dual EGFR/HER2 inhibitor) will decrease cell proliferation through induction of apoptosis. The T47DaromLR cells were found to overexpress HER2 and MAPK while maintaining aromatase and ER levels compared to their letrozole-sensitive (T47Darom) counterparts. In the absence of estrogen stimulation, glyceollin ± lapatinib had no effect on the proliferation of the T47Darom cells, while glyceollin treatment caused 46% reduction in the proliferation of T47DaromLR cells, which was further diminished when combined with lapatinib. While neither agent influenced cell migration, glyceollin and lapatinib reduced S and G2/M phase cell entry and exclusively induced apoptosis by 1.29-fold in the T47DaromLR cells. Taken together, these results suggest that glyceollins and lapatinib may have potential as a novel combination therapeutic approach for hormone-dependent, letrozole-resistant tumors.

Mammospheres of letrozole-resistant breast cancer cells enhance breast cancer aggressiveness

Aromatase inhibitors (AIs), such as letrozole, are considered as first-line treatment for estrogen receptor-positive breast cancer in postmenopausal women. Despite the successful use of letrozole, resistance to therapy, tumor relapse and metastasis remain principal causes of patient mortality. Although there is no therapy currently available for AI-resistant breast cancer, previous reports have demonstrated that AI resistance is associated with hormone independence, increased growth factor signaling, enhanced cellular motility and epithelial to mesenchymal transition (EMT). This suggests a convergence of EMT and cancer stem cells (CSCs) in endocrine resistance. The present study evaluated the contribution of mammospheres in letrozole-resistant breast cancer by characterizing mammospheres and their potential impact on cellular motility. Ovariectomized immunocompromised female mice were inoculated in the mammary fat pad with either letrozole-resistant MCF-7 cells (LTLT-Ca) or letrozole-sensitive MCF-7 cells (AC-1). Subsequently, intratumoral CSC marker expression was assessed by immunohistochemistry. The results indicated that LTLT-Ca tumors were CD44+/CD24+, while AC-1 tumors presented low CD44/CD24 expression. Since mammosphere formation depends on CSCs, both cell lines were cultured either adherently (2D) or as mammospheres (3D) to assess the CD44/CD24 protein expression profile. When 3D culturing both cell lines, higher expression levels of CD44 and CD24 were observed when compared with their adherent counterparts, with the most robust change observed in the LTLT-Ca cell line. To quantitate the breast cancer stem cell activity, mammosphere formation assays were performed, and the LTLT-Ca cells formed mammospheres at a 3.4-fold higher index compared with AC-1 cells. Additionally, targeted gene expression arrays were conducted to compare the LTLT-Ca 3D and 2D cells, revealing that LTLT-Ca 3D cells displayed decreased expression levels of genes involved in cell adhesion and tumor suppression (e. g., E-cadherin, caveolin 1 and β-catenin). To validate this finding, wound healing assays were performed, and LTLT-Ca mammospheres exhibited a 70% wound closure, whereas AC-1 mammospheres exhibited a 39% wound closure. Collectively, the present findings demonstrated a strong association between AI-resistant mammospheres and an increased propensity for migration, which may be indicative of a poor prognosis.

Quantitative Proteomic Profiling Identifies a Potential Novel Chaperone Marker in Resistant Breast Cancer

Development of aromatase inhibitor resistant breast cancer among postmenopausal women continues to be a major clinical obstacle. Previously, our group demonstrated that as breast cancer cells transition from hormone-dependent to hormone-independent, they are associated with increased growth factor signaling, enhanced cellular motility, and the epithelial to mesenchymal transition (EMT). Given the complexity of cancer stem cells (CSC) and their implications on endocrine resistance and EMT, we sought to understand their contribution towards the development of aromatase inhibitor resistant breast cancer. Cells cultured three dimensionally as mammospheres are enriched for CSCs and more accurately recapitulates tumors in vivo. Therefore, a global proteomic analysis was conducted using letrozole resistant breast cancer cells (LTLT-Ca) mammospheres and compared to their adherent counterparts. Results demonstrated over 1000 proteins with quantitative abundance ratios were identified. Among the quantified proteins, 359 were significantly altered (p < 0.05), where 173 were upregulated and 186 downregulated (p < 0.05, fold change >1.20). Notably, midasin, a chaperone protein required for maturation and nuclear export of the pre-60S ribosome was increased 35-fold. Protein expression analyses confirmed midasin is ubiquitously expressed in normal tissue but is overexpressed in lobular and ductal breast carcinoma tissue as well as ER+ and ER- breast cancer cell lines. Functional enrichment analyses indicated that 19 gene ontology terms and one KEGG pathway were over-represented by the down-regulated proteins and both were associated with protein synthesis. Increased midasin was strongly correlated with decreased relapse free survival in hormone independent breast cancer. For the first time, we characterized the global proteomic signature of CSC-enriched letrozole-resistant cells associated with protein synthesis, which may implicate a role for midasin in endocrine resistance.

Acquisition of Letrozole Resistance Through Activation of the p38/MAPK Signaling Cascade

BACKGROUND/AIM

Previous reports identified a global proteomic signature of estrogen-independent letrozole resistant breast cancer cells, however, it remains unclear how letrozole-resistance is impacted when cells remain estrogen receptor positive (ER+).

MATERIALS AND METHODS

To capture the protein expression profile associated with ER+ Aromatase inhibitor (AI) resistance, a global proteomic analysis was conducted using the letrozole-sensitive (T47Darom cells) and letrozole-resistant cells (T47DaromLR cells). To examine the molecular features associated with this phenotype Kaplan- Meier analysis, phospho-antibody arrays, proliferation and apoptosis assays were conducted.

RESULTS

MAP3K6 was up-regulated in the T47DaromLR cells by 3.2-fold (p<0.01) which was associated with a decrease in relapse-free survival among breast cancer patients (p=0.0019). Members of the MAPK/p38 pathway (i.e., phospho-MKK6, phospho-p38, phospho-RSK1, phospho-RSK2, and p70S6K MAPK) were also increased in the T47DaromLR cells, while inhibiting p38 led to decreased proliferation and induction of apoptosis.

CONCLUSION

Activation of the p38/MAPK pathway leads to ER+ AI-resistance.

Abstract 3794: Mammary cancer stem cells promote an aggressive phenotype in letrozole resistant breast cancer

Aromatase inhibitors (AI), like letrozole, are the first-line treatment for ER+ breast cancer in post-menopausal women. Despite widespread successful usage of letrozole, resistance to therapy, tumor relapse, and metastasis remain the principal causes of death for breast cancer patients. While there are no cures for AI-resistant breast cancer, previous reports demonstrate AI resistance is associated with hormone independence, increased growth factor signaling, enhanced cellular motility and the epithelial to mesenchymal transition (EMT). Given recent evidence suggesting a convergence of EMT and cancer stem cells (CSC) and their combined implications in endocrine resistance, we hypothesized that breast cancer stem cells contribute to letrozole resistant breast cancer cells by increasing cellular motility. To test this hypothesis, ovariectomized immunocompromised female mice were inoculated in the mammary fat pad with either MCF-7 cells stably transfected with the human aromatase gene that were long term letrozole-treated (LTLT-Ca) or letrozole sensitive, MCF-7 cells stably transfected with the human aromatase gene (AC-1). Afterwards, intratumoral putative CSC marker expression was assessed by immunohistochemistry. Results indicate LTLT-Ca tumors were CD44+/CD24+ while AC-1 tumors were CD44low/CD24low. Both cell lines were cultured either adherently (2D) or as mammospheres (3D) and CD44/CD24 protein expression was assessed by immunoblots. When both cell lines were cultured three dimensionally, they expressed higher levels of CD44 and CD24 compared to their adherent counterparts, with the most robust change occurring within the LTLT-Ca cells. In order to quantitate the breast cancer stem cell activity mammosphere formation assay was performed and LTLT-Ca cells formed mammospheres at a 3.4-fold higher index compared to AC-1 cells. Additionally, we performed targeted gene expression arrays and our results demonstrated decreased expression of genes involved in cell adhesion and tumor suppression (ie., E-cadherin, caveolin 1 and β catenin). Taken together our study demonstrated a strong correlation between AI resistance, increased cancer stem cell expression, an invasive phenotype that may be associated with a poor prognosis. This work was supported by an NIH grant awarded to SL Tilghman (1SC1GM125617).

Citation Format: Karen Melissa Gallegos, Jankiben Patel, Rashidra R. Walker, A Michael Davidson, Ian R. Davenport, Syreeta L. Tilghman. Mammary cancer stem cells promote an aggressive phenotype in letrozole resistant breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3794.

Abstract 4116: A novel phytoalexin, glyceollins, trigger anti-proliferative and apoptotic effects in aromatase inhibitor resistant breast cancer cells

Aromatase inhibitors (AIs) are the standard endocrine treatment for postmenopausal women with estrogen-dependent metastatic breast cancer. While effective, some patients develop resistance leading to tumor relapse, metastasis, and more aggressive phenotypes. Previous research suggested that AI resistance arises as a result of increased growth factor pathways (i.e., HER2 and EGFR) and is associated with increased cellular motility. Our lab previously demonstrated that a novel phytoalexin, glyceollins, inhibits proliferation, survival, and migration of hormone independent letrozole-resistant breast cancer cells. However, many postmenopausal women with AI-resistant tumors remain hormone dependent. Therefore, there is a need to understand distinctions between estrogen receptor positive (ER+) and ER negative (ER-) AI resistant tumors and their response to therapy. We hypothesize that treating ER+ letrozole-resistant breast cancer with a combination of glyceollin and lapatinib (a dual EGFR/HER2 inhibitor) will reduce growth factor signaling, inhibit proliferation, and induce apoptosis. T47Darom cells (T47D cells which stably express the aromatase gene) and T47DaromLR cells (letrozole-resistant T47Darom cells) were characterized by measuring protein expression. As cells transition from letrozole-sensitive to letrozole-resistance ERα and aromatase expression were slightly decreased while HER2 was increased. A receptor tyrosine kinase phospho-antibody array was performed to evaluate changes in protein expression between the two cell lines. While many proteins were altered, two cell cycle regulators (p38 and p53) were significantly downregulated by in the T47DaromLR cells suggesting that T47DaromLR cells have acquired the ability to progress uncontrollably through the cell cycle, thereby causing enhanced proliferation and cell survival. To interrogate the hypothesis, both cell lines were treated with lapatinib, glyceollin, or the combination and cell viability was measured. Results demonstrated that drug treatment had no effect on the proliferation of T47Darom cells, however, glyceollin alone and glyceollin + lapatinib inhibited T47DaromLR cell viability by 46% and 59%, respectively. Glyceollin alone or the combination caused a 33% and 60% reduction in T47Darom colony formation, respectively. Interestingly, glyceollin alone or the combination of glyceollin + lapatinib significantly inhibited T47DaromLR colony formation by greater than 90%. Apoptosis studies were conducted to measure caspase 3/7 activity in both cell lines. Lapatinib alone had no effect on apoptosis, however glyceollin and the combination significantly induced apoptosis in both cell lines; the most dramatic effect was observed in T47Darom cells, suggesting that additional mechanisms may contribute to the anti-cancer effect observed in T47DaromLR cells. Taken together, these results suggest that dual inhibition using glyceollins and lapatinib may have potential as a novel combination therapy approach for postmenopausal patients with hormone-dependent, letrozole-resistant breast cancer. This work was funded by an NIH grant awarded to SL Tilghman (1SC1GM125617).

Citation Format: Rashidra R. Walker, Jankiben Patel, A. Michael Davidson, Syreeta L. Tilghman. A novel phytoalexin, glyceollins, trigger anti-proliferative and apoptotic effects in aromatase inhibitor resistant breast cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4116.

A novel and cost-effective ex vivo orthotopic model for the study of human breast cancer in mouse mammary gland organ culture

Mouse mammary organ culture (MMOC) is used to evaluate the efficacy of chemopreventive agents against the development of carcinogen-induced preneoplastic lesions and is highly correlative to in vivo carcinogenesis models. Here, we developed a new ex vivo MMOC model, by introducing human breast cancer cells into the mouse mammary gland. This novel model, termed human breast cancer in MMOC (BCa-MMOC), mimics in vivo orthotopic breast cancer mouse models. To develop this model, estradiol- and progesterone-sensitized female mice were injected with letrozole-sensitive and -resistant T47D breast cancer cells in the mammary glands and then euthanized. The glands were cultured in vitro with hormone-supplemented media. On day 25, the glands were fixed and processed by histopathology and immunohistochemistry to evaluate for the presence of T47D cells, growth pattern, cancer markers and estradiol responsiveness. Histopathological analyses demonstrated an identical pattern of growth between the breast cancer cells injected ex vivo and in vivo Interestingly, clusters of cancer cells in the mammary gland stroma appeared similar to those observed in human breast tumors. The injected T47D cells survived and proliferated for 15 days maintaining expression of estrogen receptor alpha (ER), progesterone receptor (PR), epidermal growth factor receptor (EGFR), and aromatase. The aromatase-overexpressing T47D grown in the BCa-MMOC sufficiently metabolized estrogen, resulting in enhanced cell proliferation, induction of estrogen target genes (i.e. ER and PR-B), and showed typical changes to estrogenic milieu. In summary, here we show a novel, inexpensive ex vivo model, to potentially study the effects of therapeutic agents on cancer cells grown in an orthotopic micromilieu.This article has an associated First Person interview with the first author of the paper.

Abstract P3-11-15: A novel phytoalexin, glyceollins, trigger anti-proliferative effects in aromatase inhibitor resistant breast cancer cells

Aromatase inhibitors (AIs) are currently the standard treatment for postmenopausal women with estrogen-dependent metastatic breast cancer. While effective, patients develop resistance leading to tumor relapse, metastasis, and more aggressive phenotypes. Previous research suggested that AI resistance is due to upregulation of growth factor pathways (i.e., HER2 and EGFR) and increased cellular motility. Our lab previously demonstrated that a novel phytoalexin, glyceollins, inhibits proliferation, survival, and migration of hormone independent letrozole-resistant breast cancer cells (LTLT-Ca). However, many postmenopausal women with AI-resistance tumors remain hormone dependent. Therefore, there is a need to understand distinctions between estrogen receptor (ER+) positive and ER negative (ER-) AI resistant tumors and their response to therapy. We hypothesize that treating ER+ letrozole-resistant breast cancer using a combination approach of glyceollin and lapatinib (a dual EGFR/HER2 inhibitor) will reduce growth factor signaling, inhibit proliferation and motility. To test this hypothesis, T47Darom cells (T47D cells which stably overexpress aromatase) and T47DaromLR cells (T47Darom cells that are letrozole resistant) were treated with lapatinib, glyceollin, or the combination. To evaluate viability, resazurin assays were performed and results demonstrated that glyceollin and/or lapatinib had no effect on proliferation in the T47Darom cells. However, glyceollin alone and glyceollin + lapatinib inhibited proliferation of T47DaromLR cells by 46% and 59%, respectively. Cell survival was assessed by colony formation assays and glyceollin caused a 33% reduction in cell survival and glyceollin + lapatinib caused a 60% reduction in the colony formation of T47Darom cells. Interestingly, in T47DaromLR cells glyceollin and the combination significantly inhibited cell survival by 94% alone and 96%. To further evaluate changes that occur as AI sensitive cells transition to AI resistance, a quantitative proteomic analysis of the whole cell lysates of T47DaromLR (AI-resistant) versus T47Darom cells (AI-sensitive) was performed to identify significant protein expression changes. Results demonstrated a 3.195-fold-increase (p&lt;0.01) in protein disulfide isomerase (P4HB) and a 0.484-fold decrease (p&lt;0.01) in peptidyl-prolyl cis-trans isomerase (FKBP4) which was validated by immunoblotting. While the molecular mechanism by which P4HB contributes to tumorigenesis and metastasis is unknown, it has been demonstrated to be involved in the proliferation, survival, and metastasis of several types of cancer cells. FKBP4 is also of interest as it has been shown to be involved in mitotic arrest and apoptotic signaling. To interrogate the effect of combination therapy on HER effector signaling cascades, western blot analyses were performed to establish the endogenous expression of various proteins. Results demonstrated ERα expression was increased while HER2 was decreased in T47Darom cells compared to T47DaromLR cells. The protein expression findings from the T47D variant cell lines followed a similar trend as those previously reported in LTLT-Ca cells and their AI-sensitive counterparts. Taken together, these results suggest that dual inhibition using glyceollins and lapatinib may have potential as a novel combination therapy approach for postmenopausal patients with hormone-dependent, letrozole-resistant breast tumors. This work was also supported by NIH grant 1SC1GM126617 awarded to SL Tilghman.

Citation Format: Rashidra R Walker, Jankiben Patel, A. Michael Davidson, Karen Gallegos, Syreeta L Tilghman. A novel phytoalexin, glyceollins, trigger anti-proliferative effects in aromatase inhibitor resistant breast cancer cells [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-11-15.

Abstract 3183: Proteomic characterization of aromatase inhibitor resistant mammospheres reveal the presence of a novel nuclear chaperone

Postmenopausal women with early-stage metastatic estrogen-dependent breast cancer are generally treated with aromatase inhibitors (AIs) (e.g., letrozole). However, acquired resistance remains a major clinical obstacle. Previously, our group revealed a global proteomic signature of a letrozole-resistant cell line (LTLT-Ca) associated with hormone independence, enhanced cell motility and epithelial to mesenchymal (EMT). Given recent evidence suggesting a convergence of EMT and cancer stem cells (CSC), we chose to utilize a two-dimensional (2D) vs three-dimensional (3D) culture system to compare the proteome of LTLT-Ca cells, as 3D culture not only enriches for CSC, but more accurately recapitulates the tumor microenvironment, morphology, function and response to therapy compared to conventional 2D culture. We hypothesize utilizing a novel systems biology approach may reveal previously unconsidered molecular changes that could aid in understanding complex signaling networks and be exploited as therapeutic targets. To address this hypothesis ovariectomized immunocompromised female mice were inoculated in the mammary fat pad with LTLT-Ca or letrozole sensitive cells (AC-1) and intratumoral putative CSC marker expression was assessed by immunohistochemistry. Results indicate LTLT-Ca tumors were CD44high/CD24low while AC-1 tumors were CD44-/CD24low. Mammosphere formation assays were conducted and LTLT-Ca cells formed mammospheres at a 3.4-fold higher index than AC-1 cells. A quantitative proteomic analysis of whole cell lysates from LTLT-Ca (2D adherent cells) versus LTLT-Ca (3D mammospheres) was conducted. Results identified significant protein expression changes within a panel of 1010 proteins; 173 were upregulated and 186 downregulated (p&lt;0.05, fold change &gt;1.20). Additionally, functional enrichment analyses were performed and 19 gene ontology (GO) terms and one KEGG pathway (hsa03010:Ribosome) were over-represented (BH adjusted p-value &lt; 0.01) by the cognate genes. Notably, there was a 35.04-fold increase in midasin (MDN1), a nuclear chaperone protein required for maturation and nuclear export of pre-60S ribosome subunit. Increased MDN1 expression was strongly correlated with highly tumorigenic breast cancer spheres. Additionally, Kaplan-Meier survival plots demonstrate that increased MDN1 levels were positively correlated with decreased relapse free survival in estrogen receptor negative breast cancer, and is constitutively expressed as breast tumors progress from atypical ductal hyperplasia to ductal carcinoma in situ to invasive, metastatic breast cancer. The TGCA database was interrogated and MDN1 was frequently amplified or mutated in breast tumors. Taken together our study for the first time implicates a role for ribosomal assembly in AI resistant cells enriched for CSCs and underscores a potential for MDN1 in the progression and responsiveness to therapy.

Citation Format: Syreeta L. Tilghman, Jamal Pratt, Shawn D. Llopis, A. Michael Davidson, Rashidra R. Walker, Patrick Carriere, Ian R. Davenport, Wensheng Zhang, Karen Zhang. Proteomic characterization of aromatase inhibitor resistant mammospheres reveal the presence of a novel nuclear chaperone [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3183. doi:10.1158/1538-7445.AM2017-3183

Unilateral mandible fracture with bilateral TMJ dislocation

Temporomandibular joint (TMJ) dislocation occurs when the condylar head slips forward causing the posterior articulating surface of the condyle to advance ahead of the articular eminence, possibly becoming entrapped. Following dislocation, the ligaments around the joint often stretch, causing severe muscle spasms and joint pain. There is no standard evaluation and treatment method for acute TMJ dislocation, but the most effective course is immediate reduction. This paper presents a 42-year-old woman who sustained a unilateral mandible fracture with bilateral TMJ dislocation in an automobile crash. Although the fracture was apparent on plane film and panorex, the dislocation was not found until six weeks later, when the jaw was unwired. At that time, the dislocation was suspected because of decreased range of motion, but was not verified until an MRI was performed. The result was long-term therapy, eventual bilateral TMJ surgery, and chronic TMJ pain for the patient.

Choice of soft pulse shapes for signal excitation in chemical shift selective imaging

The choice of soft pulse shapes for chemical shift selective excitation in chemical shift imaging is discussed. In the presence of inhomogeneities in the static magnetic field resulting from susceptibility anomalies, it is important to optimise pulse bandshape and frequency offset as well as bandwidth, in order to minimize artefacts arising from excitation of unwanted resonances. A comparison of the use of Gaussian and sinc shaped excitation pulses in the chemical shift micro-imaging of grapes serves to illustrate some of the effects that may be observed.

Artifacts in chemical shift selective imaging

The role of susceptibility effects in the production of artifacts in chemical shift images generated by the selective excitation technique is discussed. The effects are demonstrated in images of phantom samples of agarose gels containing small air bubbles. The artifacts can lead to erroneous interpretations, in which the resonances to be resolved exhibit a relatively small chemical shift separation, such as that between water and soluble carbohydrates (sugars).

The Multidimensional Scale of Perceived Social Support: a confirmation study

This study examined the psychometric properties of the Multidimensional Scale of Perceived Social Support (MSPSS; Zimet, Dahlem, Zimet, & Farley, 1988) with a diverse group of 154 students at an urban college. The following areas were investigated: internal reliability, factorial validity, social desirability bias, and the moderating effect of social support between stressful life events and depression (i.e., the buffering hypothesis). The MSPSS had good internal reliability, and the factor analysis confirmed the subscale structure of the measure: family, friends, and significant other. There was no indication that social desirability bias influenced subjects' responses. Finally, social support was related to depression only for those subjects who were experiencing high levels of life stress, which lends support for the buffering hypothesis.

Uptake and distribution of chloride, sodium and potassium ions and growth of salt-treated pistachio plants

Plant growth rates and rates of uptake and root to shoot transport of chloride and sodium were compared between seedlings of the rootstock Pistacia atlantica Desf. and a scion cultivar P. Vera L. cv. Kerman treated with 30 mM NaCl for 63 days. Uptake and distribution of chloride, sodium and potassium ions were then investigated in P. atlantica and in another rootstock P. terebinthus L. subjected to periods of increasing salinity, commencing with 30 mM chloride and 18 mM sodium, and then increasing sequentially by these amounts every 3 weeks to reach a maximum of 150 mM chloride and 90 mM sodium. Shoot growth rates of P. Vera and P. atlantica were not affected by treatment with 30 mM NaCl. Rates of uptake and root to shoot transport of chloride were similar between the two species. However, the rates of uptake and root to shoot transport of sodium by P. atlantica were approximately 2-fold and 4-fold higher, respectively, than in P. vera. The chloride and sodium accumulated in the shoots of both species was diluted by growth, with the result that there was no marked increase in leaf and stem chloride and sodium concentrations in either species with time. After 63 days of salt-treatment, mean leaf chloride concentrations were less in P. atlantica, which had a higher relative growth rate and a higher shoot to root ratio than P. vera. Mean leaf sodium concentrations were higher in P. atlantica, reflecting the greater rate of root to shoot transport of sodium by this species. Sequentially increasing salinities up to a maximum of 150 mM chloride and 90 mM sodium had no significant effect on the dry matter production of P. atlantica and P. terebinthus. Laminae chloride concentrations of both species increased as the level of salinity was increased. Sodium concentrations in laminae of P. terebinthus showed a small but significant increase during treatment with the two highest salinity levels. Chloride concentrations on a tissue water basis were highest in laminae and petioles of salt-treated plants, whereas sodium concentrations were highest in roots, especially the proximal root, indicating retention of sodium in the lower part of the plant.

Effect of salinity level on uptake and distribution of chloride, sodium and potassium ions in citrus plants

Seedlings of the Citrus rootstocks Rangpur lime (Citrus reticulata var. austera hybrid?), Kharna khatta (C. karna Raf.) and Etrog citron (C. medica L.), were grown in a porous medium under glasshouse conditions and irrigated with 0, 25, 50 or 100 mM NaCl for 6 weeks. Chloride concentrations in roots of all three rootstocks were increased by salt treatment. Increasing the level of salinity from 25 to 100 mM NaCl did not increase further the chloride concentrations in roots of any rootstock, implying an upper limit to the extent of chloride loading in roots. The upper limit appeared to be similar for all rootstocks. Differences between the rootstocks were found in chloride concentrations in leaves and to a lesser extent in stems, emphasizing pronounced rootstock differences in root to shoot transport of chloride, i.e. in their ability for chloride exclusion. This ability increased in the order: Etrog citron, Kharna khatta, and Rangpur lime. Root, stem and leaf sodium concentrations increased with salt treatment, but a concurrent reduction in potassium concentrations with salt treatment occurred only in roots and stems. Shoot growth of Etrog citron and Kharna khatta plants was reduced significantly by 50 mM NaCl, but growth of Rangpur lime plants showed a marked reduction only at 100 mM NaCl. Shoot-growth and salt-induced changes in the concentrations of chloride, sodium and potassium in leaves and roots of each rootstock were unaffected by sodium to calcium ratios in the range 6.25 : 1 to 25 : 1 for plants treated with 50 mM NaCl, and in the range 12.5 : 1 to 50 : 1 for plants treated with 100 mM NaCl. Shoot growth and ion uptake patterns

Uptake and distribution of chloride, sodium and potassium ions in salt-treated citrus plants

Seedlings of a range of citrus rootstocks were grown under glasshouse conditions and supplied with dilute nutrient solution containing either 0 or 50 mM NaCl. The partitioning of accumulated chloride and sodium into and within the major organs was compared between plants of Rangpur lime (Citrus reticulata var. austera hybrid?), Trifoliata (Poncirus trifoliata) and sweet orange (C. sinensis). Rootstocks differed in their leaf and stem chloride and sodium concentrations, but there was little or no difference between the rootstocks in root chloride and sodium concentrations. The lowest leaf chloride and sodium concentrations were found in the top region of shoots of all rootstocks. The different patterns of accumulation of chloride and sodium found in the three rootstocks were consistent with the existence of apparently separate mechanisms which operate to limit the transport of these two ions from the roots into the young leaves of citrus plants. The chloride excluding ability of 10 rootstocks and two hybrids was also compared and assessed in relation to rootstock vigour. Sampling from the middle leaves on salt-treated plants enabled a distinction to be made between rootstocks in their chloride accumulation properties. Cleopatra mandarin (C. reticulata), Rangpur lime, Macrophylla (C. macrophylla) and Appleby smooth Seville (C. paradisi x C. sinensis) accumulated significantly less chloride than did Trifoliata and rough lemon (C. jambhiri). Differences in chloride accumulation properties between rootstocks were unrelated to rootstock vigour.

Characterisation of a salt-stimulated ATPase activity associated with vacuoles isolated from storage roots of red beet (Beta vulgaris L.)

Ion stimulation and some other properties of an ATPase activity associated with vacuoles isolated from storage roots of red beet (Beta vulgaris L.) have been determined. The ATPase had a specific requirement for Mg(2+) and in the presence of Mg(2+) it was stimulated by salts of monovalent cations. The degree of stimulation by monovalent salts was influenced mainly by the anion and the order of effectiveness of the anions tested was Cl(-)>HCO 3 (-) >Br(-)>malate>acetate>SO 4 (2-) . For any given series of anions the magnitude of the stimulation obtained was influenced by the accompanying cation (NH 4 (+) ≫ Na(+)>K(+)). This cation effect was abolished by 0.01% (v/v) Triton X-100 and it is suggested that it is the result of different permeabilities of membrane vesicles to the cations. There was no evidence of synergistic stimulation of the ATPase by mixtures of Na(+) and K(+). KCl- and NaCl-stimulation was maximal with salt concentrations in the range 60-150 mM. The true substrate of the enzyme was shown to be MgATP. It was shown that KCl stimulation was the result of an increase in Vmax rather than a change in the affinity of the enzyme for MgATP. The ATPase was inhibited by N,N'-dicyclohexylcarbodiimide, diethylstilbestrol, mersalyl and KNO3 but other inhibitors tested (azide, oligomycin, orthovanadate, K3[Cr(oxalate)6] and ethyl-3-[3-dimethylaminopropyl]carbodiimide) were without effect or caused only partial inhibition at the highest concentration tested. The ATPase activity was equally distributed between pellet and supernatant fractions obtained after the subfractionation of vacuoles but the properties of the ATPase in each fraction were the same. It is suggested that beet vacuoles possess only one ATPase. The properties of the ATPase are compared with those of ATPases associated with other plant membranes and organelles and its possible role in transport at the tonoplast is discussed.

Mg(2+)-Dependent, cation-stimulated inorganic pyrophosphatase associated with vacuoles isolated from storage roots of red beet (Beta vulgaris L.)

Vacuoles isolated from storage roots of red beet (Beta vulgaris L.) posess a Mg(2+)-dependent, alkaline pyrophosphatase (PPase) activity which is further stimulated by salts of monovalent cations. The requirement for Mg(2+) is specific. Mn(2+) and Zn(2+) permitted only 20% and 12%, respectively, of the PPase activity obtained in the presence of Mg(2+) while Ca(2+), Co(2+) and Cu(2+) were ineffective. Stimulation of Mg(2+)-PPase activity by salts of certain monovalent cations was due to the cation and the order of effectiveness of the cations tested was K(+)=Rb(+)=NH 4 (+) >Cs(+). Salts of Li(+) and Na(+) inhibited Mg(2+)-PPase activity by 44% and 24%, respectively. KCl-stimulation of Mg(2+)-PPase activity was maximal with 60-100 mM KCl. There was a sigmoidal relationship between PPase activity and Mg(2+) concentrations which resulted in markedly non-linear Lineweaver-Burk plots. At pH 8.0, the optimal [Mg(2+)]:[PPi] ratio for both Mg(2+)-PPase and (Mg(2+)+KCl)-PPase activities was approximately 1:1, which probably indicates MgP2O7 (2-) is the true substrate.

ATPase and acid phosphatase activities associated with vacuoles isolated from storage roots of red beet (Beta vulgaris L.)

Phosphatase activities were measured in preparations of vacuoles isolated from storage roots of red beet (Beta vulgaris L.). The vacuoles possessed both acid phosphatase and ATPase activities which could be distinguished by their susceptibility to inhibition by low concentrations of ammonium molybdate [(NH4)6Mo7O24·4H2O]. The acid phosphatase was completely inhibited by 100 μM ammonium molybdate but the ATPase was unaffected. The acid phosphatase was a soluble enzyme which hydrolysed a large number of phosphate esters and had a pH optimum of 5.5. In contrast, the ATPase was partially membrane-bound, had a pH optimum of 8.0 and hydrolysed ATP preferentially, although it was also active agianst PPi, GTP and GDP. At pH 8.0 both the ATPase and PPase activities were Mg(2+)-dependent and were further stimulated by KCl. The ATPase and PPase activities at pH 8.0 may be different enzymes. The recovery and purification of the ATPase during vacuole isolation were determined. The results indicate that the Mg(2+)-dependent, KCl-stimulated ATPase activity is not exclusively associated with vacuoles.

Growth, leaf physiology and fruit development in salt-stressed guavas

Two cultivars of guava (Psidium guajava L.) were grown in a porous medium irrigated with dilute nutrient solution containing 0, 25, 50 and 75 mM sodium chloride. The distribution of sodium and chloride between leaves, stems, roots and fruit of the two cultivars is described. Total biomass (and especially fruit fresh weight) was reduced by all salt treatments; however, fruit maturation was accelerated. Symptoms associated with high chloride concentrations developed only on leaves of plants treated with 25 mM sodium chloride. Different symptoms, associated with high sodium concentrations, developed on leaves of plants from the 50 and 75 mM treatments. Transpiration and photosynthesis were reduced in leaves of plants from the 50 and 75 mM treatments. Increased stomatal resistance and a reduction in apparent photochemical efficiency were largely responsible for the reduction in photosynthesis.