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1.  Release of extracellular purines from plant roots and effect on ion fluxes 
Plant Signaling & Behavior  2011;6(11):1855-1857.
Extracellular purine nucleotides appear capable of regulating plant development, defence and stress responses by acting in part as agonists of plasma membrane calcium channels. Factors stimulating ATP release include wounding, osmotic stress and elicitors. Here we show that exogenous abscisic acid and L-glutamate can also cause ATP accumulation around Arabidopsis thaliana roots. Release of ADP from root epidermis would trigger ionotropic receptor-like activity in the plasma membrane, resulting in transient elevation of cytosolic free calcium. Root epidermal protoplasts (expressing aequorin as a cytosolic free calcium reporter) can support an extracellular ADP-induced cytosolic calcium elevation in the presence of an extracellular reductant. This confirms that ADP could elicit calcium-based responses distinct to those of ATP, which have been shown previously to involve production of extracellular reactive oxygen species.
doi:10.4161/psb.6.11.17014
PMCID: PMC3329368  PMID: 22057319
abscisic acid; ADP; ATP; calcium; channel; glutamate; root
2.  Heme-independent soluble and membrane-associated peroxidase activity of a Zea mays annexin preparation 
Plant Signaling & Behavior  2009;4(5):428-430.
Annexins are cytosolic proteins capable of reversible, Ca2+-dependent membrane binding or insertion. Animal annexins form and regulate Ca2+-permeable ion channels and may therefore participate in signaling. Zea mays (maize) annexins (ZmANN33 and ZmANN35) have recently been shown to form a Ca2+-permeable conductance in planar lipid bilayers and also exhibit in vitro peroxidase activity. Peroxidases form a superfamily of intra- or extracellular heme-containing enzymes that use H2O2 as the electron acceptor in a number of oxidative reactions. Maize annexin peroxidase activity appears independent of heme and persists after membrane association, the latter suggesting a role in reactive oxygen species signaling.
PMCID: PMC2676756  PMID: 19816107
annexin; calcium; C2; lipoxygenase; maize; peroxidase
3.  Identifying the transporters of different flavonoids in plants 
Plant Signaling & Behavior  2010;5(7):860-863.
We recently identified a new component of flavonoid transport pathways in Arabidopsis. The MATE protein FFT (Flower Flavonoid Transporter) is primarily found in guard cells and seedling roots, and mutation of the transporter results in floral and growth phenotypes. The nature of FFT's substrate requires further exploration but our data suggest that it is a kaempferol diglucoside. Here we discuss potential partner H+-ATPases and possible redundancy among the close homologs within the large Arabidopsis MATE family.
doi:10.4161/psb.5.7.11894
PMCID: PMC3115035  PMID: 20505354
auxin; flavonoid; guard cell; pollen; transporter
4.  Extracellular ATP activates an Arabidopsis plasma membrane Ca2+-permeable conductance 
Plant Signaling & Behavior  2009;4(10):989-991.
Extracellular ATP has been found to elevate cytosolic free Ca2+ in Arabidopsis thaliana and trigger gene transcription, suggesting that it acts as a plant cell regulator. Recent findings place extracellular ATP upstream of Arabidopsis thaliana NADPH oxidase activity and plasma membrane Ca2+-permeable channels in the root epidermis. Here we show that increasing extracellular ATP concentration evokes a larger but more irregular Ca2+ influx conductance in root epidermal protoplasts. This may help modulate changes in cytosolic free Ca2+ as a second messenger and help explain the dose-dependent effects of extracellular ATP on cell function. The receptors for ATP and the downstream plasma membrane Ca2+ channels remain unknown at the protein or gene level. No equivalents of animal ATP receptors have been identified in higher plant genomes. We propose here that annexins could perceive extracellular ATP and participate in Ca2+ influx.
PMCID: PMC2801370  PMID: 19826233
ADP; annexin; ATP; calcium; channel
5.  An Arabidopsis flavonoid transporter is required for anther dehiscence and pollen development 
Journal of Experimental Botany  2009;61(2):439-451.
FLOWER FLAVONOID TRANSPORTER (FFT) encodes a multidrug and toxin efflux family transporter in Arabidopsis thaliana. FFT (AtDTX35) is highly transcribed in floral tissues, the transcript being localized to epidermal guard cells, including those of the anthers, stigma, siliques and nectaries. Mutant analysis demonstrates that the absence of FFT transcript affects flavonoid levels in the plant and that the altered flavonoid metabolism has wide-ranging consequences. Root growth, seed development and germination, and pollen development, release and viability are all affected. Spectrometry of mutant versus wild-type flowers shows altered levels of a glycosylated flavonol whereas anthocyanin seems unlikely to be the substrate as previously speculated. Thus, as well as adding FFT to the incompletely described flavonoid transport network, it is found that correct reproductive development in Arabidopsis is perturbed when this particular transporter is missing.
doi:10.1093/jxb/erp312
PMCID: PMC2803208  PMID: 19995827
Anther; fertility; flavonoid; MATE transporter; nectary; pollen
6.  Voltage, reactive oxygen species and the influx of calcium 
Plant Signaling & Behavior  2008;3(9):698-699.
The apical plasma membrane of young Arabidopsis root hairs has recently been found to contain a depolarisation-activated Ca2+ channel, in addition to one activated by hyperpolarisation. The depolarisation-activated Ca2+ channel may function in signalling but the possibility that the root hair apical plasma membrane voltage may oscillate between a hyperpolarized and depolarized state suggests a role in growth control. Plant NADPH oxidase activity has yet to be considered in models of oscillatory voltage or ionic flux despite its predicted electrogenicity and voltage dependence. Activity of root NADPH oxidase was found to be stimulated by restricting Ca2+ influx, suggesting that these enzymes are involved in sensing Ca2+ entry into cells.
PMCID: PMC2634563  PMID: 19704832
calcium; channel; NADPH oxidase; oscillation; root hair
7.  Laser Microsurgery Permits Fungal Plasma Membrane Single-Ion-Channel Resolution at the Hyphal Tip 
A method for formation of high-electrical-resistance seals on the Neurospora crassa plasma membrane, allowing resolution of single-ion-channel activity by patch clamp electrophysiology, is reported. Laser microsurgery permits access to the hyphal apex without enzymatic cell wall digestion and loss of morphological polarity. Cell wall reformation is delayed by brefeldin. This method can allow full characterization of apical plasma membrane channels, which are implicated in tip growth.
PMCID: PMC106192  PMID: 16349556

Results 1-7 (7)