The protein product of the gene that when mutated is responsible for Lowe syndrome, or oculocerebrorenal syndrome (OCRL), is an inositol polyphosphate 5-phosphatase. It has a marked preference for phosphatidylinositol 4,5-bisphosphate although it hydrolyzes all four of the known inositol polyphosphate 5-phosphatase substrates: inositol 1,4,5-trisphosphate, inositol 1,3,4,5-tetrakisphosphate, phosphatidylinositol 4,5-bisphosphate, and phosphatidylinositol 3,4,5-trisphosphate. The enzyme activity of this protein is determined by a region of 672 out of a total of 970 amino acids that is homologous to inositol polyphosphate 5-phosphatase II. Cell lines from kidney proximal tubules of a patient with Lowe syndrome and a normal individual were used to study the function of OCRL. The cells from the Lowe syndrome patient lack OCRL protein. OCRL is the major phosphatidylinositol 4,5-bisphosphate 5-phosphatase in these cells. As a result, these cells accumulate phosphatidylinositol 4,5-bisphosphate even though at least four other inositol polyphosphate 5-phosphatase isozymes are present in these cells. OCRL is associated with lysosomal membranes in control proximal tubule cell lines suggesting that OCRL may function in lysosomal membrane trafficking by regulating the specific pool of phosphatidylinositol 4,5-bisphosphate that is associated with lysosomes.Lowe syndrome, or oculocerebrorenal syndrome, is a rare X chromosome-linked disorder that is characterized by severe mental retardation, congenital cataracts, and renal Fanconi syndrome (1). The renal Fanconi syndrome develops in the neonatal period with impaired renal proximal tubular function including acidosis, amino aciduria, phosphaturia, and proteinuria (1, 2). The gene responsible for Lowe syndrome was identified by positional cloning of X chromosome breakpoints in two affected females (3). The predicted protein, designated OCRL, 1 is comprised of 970 amino acids and is 51% identical to inositol polyphosphate 5-phosphatase type II (5-phosphatase II) over a span of 672 amino acids. The amino-terminal one-third has no homology to 5-phosphatase II or any other sequences in GenBank (3). The striking homology between OCRL and 5-phosphatase II suggested that OCRL belongs to the 5-phosphatase gene family and that Lowe syndrome represents an inborn error of inositol phosphate metabolism.Inositol polyphosphate 5-phosphatases (5-phosphatases) are a group of enzymes containing 5-phosphatase homology domains, and two conserved signature motifs within these domains define proteins that have 5-phosphatase activity (for review, see Refs. 4 -6). The substrates of 5-phosphatases include two soluble inositol polyphosphates inositol 1,4,5-trisphosphate (Ins 1,4,5-P 3 ) and inositol 1,3,4,5-tetrakisphosphate (Ins 1,3,4,5-P 4 ), and two inositol lipids phosphatidylinositol 4,5-bisphosphate (PtdIns 4,5-P 2 ) and phosphatidylinositol 3,4,5-trisphosphate (PtdIns 3,4,5-P 3 ). The 5-phosphatase isozymes have varying substrate specificities. Seven mammalian 5-phosphatases have been cloned and...

In the present study, two accessions of Centella asiatica (CA03 and CA23) were subjected to gamma radiation to examine the response of these accessions in terms of survival rate, flavonoid contents, leaf gas exchange and leaf mass. Radiation Sensitivity Tests revealed that based on the survival rate, the LD50 (gamma doses that killed 50% of the plantlets) of the plantlets were achieved at 60 Gy for CA03 and 40 Gy for CA23. The nodal segments were irradiated with gamma rays at does of 30 and 40 Gy for Centella asiatica accession ‘CA03’ and 20 and 30 Gy for accession ‘CA23. The nodal segment response to the radiation was evaluated by recording the flavonoid content, leaf gas exchange and leaf biomass. The experiment was designed as RCBD with five replications. Results demonstrated that the irradiated plantlets exhibited greater total flavonoid contents (in eight weeks) significantly than the control where the control also exhibited the highest total flavonoid contents in the sixth week of growth; 2.64 ± 0.02 mg/g DW in CA03 and 8.94 ± 0.04 mg/g DW in CA23. The total flavonoid content was found to be highest after eight weeks of growth, and this, accordingly, stands as the best time for leaf harvest. Biochemical differentiation based on total flavonoid content revealed that irradiated plantlets in CA23 at 20 and 30 Gy after eight weeks contained the highest total flavonoid concentrations (16.827 ± 0.02; 16.837 ± 0.008 mg/g DW, respectively) whereas in CA03 exposed to 30 and 40 Gy was found to have the lowest total flavonid content (5.83 ± 0.11; 5.75 ± 0.03 mg/g DW). Based on the results gathered in this study, significant differences were found between irradiated accessions and control ones in relation to the leaf gas. The highest PN and gs were detected in CA23 as control followed by CA23 irradiated to 20Gy (CA23G20) and CA23G30 and the lowest PN and gs were observed in CA03 irradiated to 40Gy (CA03G40). Moreover, there were no significant differences in terms of PN and gs among the irradiated plants in each accession. The WUE of both irradiated accessions of Centella asiatica were reduced as compared with the control plants (p < 0.01) while Ci and E were enhanced. There were no significant differences in the gas exchange parameters among radiated plants in each accession. Moreover, malondialdehyde (MDA) of accessions after gamma treatments were significantly higher than the control, however, flavonoids which were higher concentration in irradiated plants can scavenge surplus free radicals. Therefore, the findings of this study have proven an efficient method of in vitro mutagenesis through gamma radiation based on the pharmaceutical demand to create economically superior mutants of C. asiatica. In other words, the results of this study suggest that gamma irradiation on C. asiatica can produce mutants of agricultural and economical importance.

[1] Methyl chloride (CH 3 Cl) fluxes were investigated at leaf and forest-canopy scales in tropical forests in Malaysia. Screening of CH 3 Cl-emitting species showed that 21% of 117 tree species were CH 3 Cl emitters; the percentage was markedly higher for dipterocarps (66%) than nondipterocarps (6%). The dipterocarp-derived CH 3 Cl was characterized by high emissions (median: 0.03 mg g À1 h À1 ) and low stable carbon isotope ratios (mean: À88.9 ± 11.0%). Measurements of CH 3 Cl above the canopy showed a slight decrease in the mixing ratios with increasing height. These values were used to estimate the canopy-scale flux of about 14 mg m À2 h À1 , comparable to that extrapolated from the leaf-scale emissions. Using the canopy-scale flux, global CH 3 Cl emission by tropical forests was estimated to be 1.3 Tg yr À1 , representing approximately 30% of the global emissions. Above-canopy measurements were also made for isoprene, with a mean flux of 1.2 mg m À2 h À1 .

Vertical variation in leaf gas exchange characteristics of trees grown in a lowland dipterocarp forest in Peninsular Malaysia was investigated. Maximum net photosynthetic rate, stomatal conductance, and electron transport rate of leaves at the upper canopy, lower canopy, and forest floor were studied in situ with saturated condition photosynthetic photon flux density. The dark respiration rate of leaves at the various heights was also studied. Relationships among gas exchange characteristics, and also with nitrogen content per unit leaf area and leaf dry matter per area were clearly detected, forming general equations representing the vertical profile of several important parameters related to gas exchange. Numerical analysis revealed that the vertical distribution of gas exchange parameters was well determined showing both larger carbon gain for the whole canopy and at the same time positive carbon gain for the leaves of the lowest layer. For correct estimation of gas exchange at both leaf and canopy scales using multi-layer models, it is essential to consider the vertical distribution of gas exchange parameters with proper scaling coefficients.

We investigated effects of heterogeneous stomatal behavior on diurnal patterns of leaf gas exchange in 10 tree species. Observations were made in middle and upper canopy layers of potted tropical rainforest trees in a nursery at the Forest Research Institute Malaysia. Measurements were taken from 29 January to 3 February 2010. We measured in situ diurnal changes in net photosynthetic rate and stomatal conductance in three leaves of each species under natural light. In both top-canopy and sub-canopy species, midday depression of net assimilation rate occurred in late morning. Numerical analysis showed that patchy bimodal stomatal behavior occurred only during midday depression, suggesting that the distribution pattern of stomatal apertures (either uniform or non-uniform stomatal behavior) varies flexibly within single days. Direct observation of stomatal aperture using Suzuki's Universal Micro-Printing (SUMP) method demonstrated midday patchy stomatal closure that fits a bimodal pattern in Shorea leprosula Miq., Shorea macrantha Brandis. and Dipterocarpus tempehes V.Sl. Inhibition of net assimilation rate and stomatal conductance appears to be a response to changes in vapor pressure deficit (VPD). Variable stomatal closure with increasing VPD is a mechanism used by a range of species to prevent excess water loss from leaves through evapotranspiration (viz., inhibition of midday leaf gas exchange). Bimodal stomatal closure may occur among adjacent stomata within a single patch, rather than among patches on a single leaf. Our results suggest the occurrence of patches at several scales within single leaves. Further analysis should consider variable spatial scales in heterogeneous stomatal behavior between and within patches and within single leaves.