Kosala Ranathunge - Academia.edu (original) (raw)

Papers by Kosala Ranathunge

New Phytologist

Summary Endemism and rarity have long intrigued scientists. We focused on a rare endemic and crit... more Summary Endemism and rarity have long intrigued scientists. We focused on a rare endemic and critically‐endangered species in a global biodiversity hotspot, Grevillea thelemanniana (Proteaceae). We carried out plant and soil analyses of four Proteaceae, including G. thelemanniana, and combined these with glasshouse studies. The analyses related to hydrology and plant water relations as well as soil nutrient concentrations and plant nutrition, with an emphasis on sodium (Na) and calcium (Ca). The local hydrology and matching plant traits related to water relations partially accounted for the distribution of the four Proteaceae. What determined the rarity of G. thelemanniana, however, was its accumulation of Ca. Despite much higher total Ca concentrations in the leaves of the rare G. thelemanniana than in the common Proteaceae, very few Ca crystals were detected in epidermal or mesophyll cells. Instead of crystals, G. thelemanniana epidermal cell vacuoles contained exceptionally high ...

Plant and Soil

Aims South-western Australia has some of the most phosphorus (P)-impoverished soils in the world.... more Aims South-western Australia has some of the most phosphorus (P)-impoverished soils in the world. Hakea prostrata (Proteaceae) has nitrate (NO3−)-uptake restraint, associated with its high P-use efficiency. This research explores how common this trait is in other Proteaceae and in co-occurring plant species in south-western Australia. Methods Banksia attenuata (Proteaceae), B. telmatiaea (Proteaceae), Melaleuca seriata (Myrtaceae) and M. rhaphiophylla (Myrtaceae) were grown with no NO3−, Medium (500 µM) NO3− or High (2500 µM) NO3− treatments with no other source of nitrogen (N). Plants were harvested after treatments. Leaf nitrate and phosphate concentrations were determined, as well as biomass, total N and total P concentrations of leaves, stems and roots separately. Results Banksia attenuata, B. telmatiaea and M. seriata had similar total N content when supplied with High NO3− as they did when supplied with Medium NO3−. All four species had the same low leaf NO3−-N concentration i...

Text file of alignment of ABCG proteins studied in the work

Plant and Soil, 2021

Aim Organic substances in leaves of several southwest Australian native species interfere with se... more Aim Organic substances in leaves of several southwest Australian native species interfere with sensitive colorimetric assays and prevent quantification of inorganic phosphate concentration ([Pi]). We aimed to develop a reproducible routine procedure for treating leaf extracts with activated charcoal (AC) to remove interfering substances, allowing the determination of [Pi] by the malachite green spectrophotometric assay. Methods Leaf extracts of native plants from southwest Australia in 1% (v/v) acetic acid were treated with 10 mg mL−1 acid-washed AC for removal of interfering substances. Standard solutions (0 to 18 μM Pi) with and without AC treatment were compared to quantify Pi loss. A spiking and recovery test was performed to validate the AC treatment. Results Leaf extracts treated with AC exhibited distinguishable absorbance peaks for the malachite green-orthophosphate complex between 630 and 650 nm, as opposed to untreated samples. The Pi-adsorption by AC represented a relativ...

Functional Plant Biology, 2021

Hakea prostrata R.Br. (Proteaceae) shows a ‘delayed greening’ strategy of leaf development charac... more Hakea prostrata R.Br. (Proteaceae) shows a ‘delayed greening’ strategy of leaf development characterised by reddish young leaves that become green as they mature. This trait may contribute to efficient use of phosphorus (P) during leaf development by first investing P in the development of leaf structure followed by maturation of the photosynthetic machinery. In this study, we investigated the properties of delayed greening in a highly P-efficient species to enhance our understanding of the ecological significance of this trait as a nutrient-saving and photoprotective strategy. In glasshouse-grown plants, we assessed foliar pigments, fatty acids and nutrient composition across five leaf developmental stages. Young leaves had higher concentrations of anthocyanin, P, nitrogen (N), copper (Cu), xanthophyll-cycle pigments and saturated fatty acids than mature leaves. As leaves developed, the concentration of anthocyanins decreased, whereas that of chlorophyll and the double bond index o...

Frontiers in Plant Science, 2018

The present review examines recent experimental findings in root transport phenomena in terms of ... more The present review examines recent experimental findings in root transport phenomena in terms of the composite transport model (CTM). It has been a well-accepted conceptual model to explain the complex water and solute flows across the root that has been related to the composite anatomical structure. There are three parallel pathways involved in the transport of water and solutes in roots-apoplast, symplast, and transcellular paths. The role of aquaporins (AQPs), which facilitate water flows through the transcellular path, and root apoplast is examined in terms of the CTM. The contribution of the plasma membrane bound AQPs for the overall water transport in the whole plant level was varying depending on the plant species, age of roots with varying developmental stages of apoplastic barriers, and driving forces (hydrostatic vs. osmotic). Many studies have demonstrated that the apoplastic barriers, such as Casparian bands in the primary anticlinal walls and suberin lamellae in the secondary cell walls, in the endo-and exodermis are not perfect barriers and unable to completely block the transport of water and some solute transport into the stele. Recent research on water and solute transport of roots with and without exodermis triggered the importance of the extension of conventional CTM adding resistances that arrange in series (epidermis, exodermis, mid-cortex, endodermis, and pericycle). The extension of the model may answer current questions about the applicability of CTM for composite water and solute transport of roots that contain complex anatomical structures with heterogeneous cell layers.

Journal of Plant Physiology, 2018

Water is the most important prerequisite for life and plays a major role during uptake and transp... more Water is the most important prerequisite for life and plays a major role during uptake and transport of nutrients. Roots are the plant organs that take up the major part of water, from the surrounding soil. Water uptake is related to the root system architecture, root growth, age and species dependent complex developmental changes in the anatomical structures. The latter is mainly attributed to the deposition of suberized barriers in certain layers of cell walls, such as endo-and exodermis. With respect to water permeability, changes in the suberization of roots are most relevant. Water transport or hydraulic conductivity of roots (Lp r) can be described by the composite transport model and is known to be very variable between plant species and growth conditions and root developmental states. In this review, we summarize how anatomical structures and apoplastic barriers of roots can diversely affect water transport, comparing the model plant Arabidopsis with crop plants, such as barley and rice. Results comparing the suberin amounts and water transport properties indicate that the common assumption that suberin amount negatively correlates with water and solute transport through roots may not always be true. The composition, microstructure and localization of suberin may also have a great impact on the formation of efficient barriers to water and solutes.

Annals of Botany, 2017

Background and Aims Roots have complex anatomical structures, and certain localized cell layers d... more Background and Aims Roots have complex anatomical structures, and certain localized cell layers develop suberized apoplastic barriers. The size and tightness of these barriers depend on the growth conditions and on the age of the root. Such complex anatomical structures result in a composite water and solute transport in roots. Methods Development of apoplastic barriers along barley seminal roots was detected using various staining methods, and the suberin amounts in the apical and basal zones were analysed using gas chromatography-mass spectometry (GC-MS). The hydraulic conductivity of roots (Lp r) and of cortical cells (Lp c) was measured using root and cell pressure probes. Key Results When grown in hydroponics, barley roots did not form an exodermis, even at their basal zones. However, they developed an endodermis. Endodermal Casparian bands first appeared as 'dots' as early as at 20 mm from the apex, whereas a patchy suberin lamellae appeared at 60 mm. The endodermal suberin accounted for the total suberin of the roots. The absolute amount in the basal zone was significantly higher than in the apical zone, which was inversely proportional to the Lp r. Comparison of Lp r and Lp c suggested that cell to cell pathways dominate for water transport in roots. However, the calculation of Lp r from Lp c showed that at least 26 % of water transport occurs through the apoplast. Roots had different solute permeabilities (P sr) and reflection coefficients (r sr) for the solutes used. The r sr was below unity for the solutes, which have virtually zero permeability for semipermeable membranes. Conclusions Suberized endodermis significantly reduces Lp r of seminal roots. The water and solute transport across barley roots is composite in nature and they do not behave like ideal osmometers. The composite transport model should be extended by adding components arranged in series (cortex, endodermis) in addition to the currently included components arranged in parallel (apoplastic, cell to cell pathways).

Frontiers in Plant Science, 2015

Glutaredoxins (GRXs) are small glutathione dependent oxidoreductases that belong to the Thioredox... more Glutaredoxins (GRXs) are small glutathione dependent oxidoreductases that belong to the Thioredoxin (TRX) superfamily and catalyze the reduction of disulfide bonds of their substrate proteins. Plant GRXs include three different groups based on the motif sequence, namely CPYC, CGFS, and CC-type proteins. The rice CC-type proteins, OsGRX6 was identified during the screening for genes whose expression changes depending on the level of available nitrate. Overexpression of OsGRX6 in rice displayed a semi-dwarf phenotype. The OsGRX6 overexpressors contain a higher nitrogen content than the wild type, indicating that OsGRX6 plays a role in homeostatic regulation of nitrogen use. Consistent with this, OsGRX6 overexpressors displayed delayed chlorophyll degradation and senescence compared to the wild type plants. To examine if the growth defect of these transgenic lines attribute to disturbed plant hormone actions, plant hormone levels were measured. The levels of two cytokinins (CKs), 2-isopentenyladenine and trans-zeatin, and gibberellin A1 (GA1) were increased in these lines. We also found that these transgenic lines were less sensitive to exogenously applied GA, suggesting that the increase in GA1 is a result of the feedback regulation. These data suggest that OsGRX6 affects hormone signaling and nitrogen status in rice plants.

Planta, 2003

A new pressure-perfusion technique was used to measure hydraulic and osmotic properties of the ou... more A new pressure-perfusion technique was used to measure hydraulic and osmotic properties of the outer part of roots (OPR) of 30-day-old rice plants (lowland cultivar: IR64, and upland cultivar: Azucena). The OPR comprised rhizodermis, exodermis, sclerenchyma and one cortical cell layer. The technique involved perfusion of aerenchyma of segments from two different root zones (20-50 mm and 50-100 mm from the tip) at precise rates using aerated nutrient solution. The hydraulic conductivity of the OPR (Lp(OPR)=1.2x10(-6) m s(-1) MPa(-1)) was larger by a factor of 30 than the overall hydraulic conductivity (Lp(r)=4x10(-8) m s(-1) MPa(-1)) as measured by pressure chamber and root pressure probe. Low reflection coefficients were obtained for mannitol and NaCl for the OPR (sigma(sOPR)=0.14 and 0.09, respectively). The diffusional water permeability ( P(dOPR)) estimated from isobaric flow of heavy water was smaller by three orders of magnitude than the hydraulic conductivity (Lp(OPR)/ P(fOPR)...

The Plant Cell, 2014

Effective regulation of water balance in plants requires localized extracellular barriers that co... more Effective regulation of water balance in plants requires localized extracellular barriers that control water and solute movement. We describe a clade of five Arabidopsis thaliana ABCG half-transporters that are required for synthesis of an effective suberin barrier in roots and seed coats (ABCG2, ABCG6, and ABCG20) and for synthesis of an intact pollen wall (ABCG1 and ABCG16). Seed coats of abcg2 abcg6 abcg20 triple mutant plants had increased permeability to tetrazolium red and decreased suberin content. The root system of triple mutant plants was more permeable to water and salts in a zone complementary to that affected by the Casparian strip. Suberin of mutant roots and seed coats had distorted lamellar structure and reduced proportions of aliphatic components. Root wax from the mutant was deficient in alkylhydroxycinnamate esters. These mutant plants also had few lateral roots and precocious secondary growth in primary roots. abcg1 abcg16 double mutants defective in the other tw...

Phytopathology®, 2008

Phytophthora sojae is the causal agent of root and stem rot of soybean (Glycine max). Various cul... more Phytophthora sojae is the causal agent of root and stem rot of soybean (Glycine max). Various cultivars with partial resistance to the pathogen have been developed to mitigate this damage. Herein, two contrasting genotypes, the cultivar Conrad (with strong partial resistance) and the line OX760-6 (with weak partial resistance), were compared regarding their amounts of preformed and induced suberin components, and to early events during the P. sojae infection process. To colonize the root, hyphae grew through the suberized middle lamellae between epidermal cells. This took 2 to 3 h longer in Conrad than in OX760-6, giving Conrad plants more time to establish their chemical defenses. Subsequent growth of hyphae through the endodermis was also delayed in Conrad. This cultivar had more preformed aliphatic suberin than the line OX760-6 and was induced to form more aliphatic suberin several days prior to that of OX760-6. However, the induced suberin was formed subsequent to the initial in...

The Plant Cell, 2011

Aliphatic alcohols naturally exist in many organisms as important cellular components; however, t... more Aliphatic alcohols naturally exist in many organisms as important cellular components; however, their roles in extracellular polymer biosynthesis are poorly defined. We report here the isolation and characterization of a rice (Oryza sativa) male-sterile mutant, defective pollen wall (dpw), which displays defective anther development and degenerated pollen grains with an irregular exine. Chemical analysis revealed that dpw anthers had a dramatic reduction in cutin monomers and an altered composition of cuticular wax, as well as soluble fatty acids and alcohols. Using map-based cloning, we identified the DPW gene, which is expressed in both tapetal cells and microspores during anther development. Biochemical analysis of the recombinant DPW enzyme shows that it is a novel fatty acid reductase that produces 1-hexadecanol and exhibits >270-fold higher specificity for palmiltoyl-acyl carrier protein than for C16:0 CoA substrates. DPW was predominantly targeted to plastids mediated by i...

Planta, 2010

Whether a seed coat of a soybean (Glycine max L. Mer.) seed is permeable or non-permeable is gove... more Whether a seed coat of a soybean (Glycine max L. Mer.) seed is permeable or non-permeable is governed by a number of quantitative trait loci further influenced by environmental factors. In soybean seeds, water loss is controlled by a thin, inconspicuous outer cuticle. When intact, the outer cuticle constitutes a barrier to water passage; however, the presence of minute cracks in the cuticle results in the ready passage of water. We explored the timing of cuticular development in soybean seeds by measuring the deposition of the cutin in relation to seed growth and cell viability. Cutin deposition occurred early in the development and ceased just prior to the final stage of rapid seed expansion. Cracks in the cuticle appeared after cutin synthesis ceased while the seed continued to grow. In permeable seeds (regardless of genotype) the resistance of the cuticle to water passage increased steadily during development until seed expansion was maximal and cracks appeared in the cuticle. Once cracks formed, they became the primary site of water passage and the cuticle lost its ability to control the process. In non-permeable seeds, no cracks appeared at this critical point and the cuticle continued to restrict water passage. Microarray analysis of gene expression during seed coat development revealed a complex transcriptome with many genes uniquely expressed in the seed coat. However, the expression patterns were remarkably similar between permeable and non-permeable types, in keeping with the complexity of the underlying genetics of seed coat permeability.

Planta, 2009

Increasing soil salinity reduces crop yields worldwide, with rice being particularly aVected. We ... more Increasing soil salinity reduces crop yields worldwide, with rice being particularly aVected. We have examined the correlation between apoplastic barrier formation in roots, Na + uptake into shoots and plant survival for three rice (Oryza sativa L.) cultivars of varying salt sensitivity: the salt-tolerant Pokkali, moderately tolerant Jaya and sensitive IR20. Rice plants grown hydroponically or in soil for 1 month were subjected to both severe and moderate salinity stress. Apoplastic barriers in roots were visualized using Xuorescence microscopy and their chemical composition determined by gas chromatography and mass spectrometry. Na + content was estimated by Xame photometry. Suberization of apoplastic barriers in roots of Pokkali was the most extensive of the three cultivars, while Na + accumulation in the shoots was the least. Saline stress induced the strengthening of these barriers in both sensitive and tolerant cultivars, with increase in mRNAs encoding suberin biosynthetic enzymes being detectable within 30 min of stress. Enhanced barriers were detected after several days of moderate stress. Overall, more extensive apoplastic barriers in roots correlated with reduced Na + uptake and enhanced survival when challenged with high salinity.

Plant, Cell & Environment, 2005

ABSTRACTUsing an insoluble inorganic salt precipitation technique, the permeability of cell walls... more ABSTRACTUsing an insoluble inorganic salt precipitation technique, the permeability of cell walls and especially of endodermal Casparian bands (CBs) for ions was tested in young roots of corn (Zea mays) and rice (Oryza sativa). The test was based on suction of either 100 µm CuSO4 or 200 µm K4[Fe(CN)6] into the root from its medium using a pump (excised roots) or transpirational stream (intact seedlings), and subsequent perfusion of xylem of those root segments with the opposite salt component, which resulted in precipitation of insoluble brown crystals of copper ferrocyanide. Under suction, Cu2+ could cross the endodermis apoplastically in both plant species (although at low rates) developing brown salt precipitates in cell walls of early metaxylem and in the region between CBs and functioning metaxylem vessels. Hence, at least Cu2+ did cross the endodermis dragged along with the water. The results suggested that CBs were not perfect barriers to apoplastic ion fluxes. In contrast, f...

Plant, Cell & Environment, 2011

It has been shown that rice roots grown in a stagnant medium develop a tight barrier to radial ox... more It has been shown that rice roots grown in a stagnant medium develop a tight barrier to radial oxygen loss (ROL), whereas aerated roots do not. This study investigated whether the induction of a barrier to ROL affects water and solute permeabilities. Growth in stagnant medium markedly reduced the root growth rate relative to aerated conditions. Histochemical studies revealed an early deposition of Casparian bands (CBs) and suberin lamellae (SL) in both the endodermis (EN) and exodermis, and accelerated lignification of stagnant roots. The absolute amounts of suberin, lignin and esterified aromatics (coumaric and ferulic acid) in these barriers were significantly higher in stagnant roots. However, correlative permeability studies revealed that early deposition of barriers in stagnant roots failed to reduce hydraulic conductivity (Lpr) below those of aerated roots. In contrast to Lpr, the NaCl permeability (Psr) of stagnant roots was markedly lower than that of aerated roots, as indicated by an increased reflection coefficient (ssr). In stagnant roots, Psr decreased by 60%, while ssr increased by 55%. The stagnant medium differentially affected the Lpr and Psr of roots, which can be explained in terms of the physical properties of the molecules used and the size of the pores in the apoplast.