Ion concentrations in the roots of two barley (Hordeum vulgare) varieties that differed in NaCl tolerance were compared after exposure to NaCl. Triple-barreled H ϩ -, K ϩ -, and Na ϩ -selective microelectrodes were used to measure cytosolic activities of the three ions after 5 and 8 d of NaCl stress. In both varieties of barley, it was only possible to record successfully from root cortical cells because the epidermal cells appeared to be damaged. The data show that from the 1st d of full NaCl stress, there were differences in the way in which the two varieties responded. At 5 d, the tolerant variety maintained a 10-fold lower cytosolic Na ϩ than the more sensitive variety, although by 8 d the two varieties were not significantly different. At this time, the more tolerant variety was better at maintaining root cytosolic K ϩ in the high-NaCl background than was the more sensitive variety. In contrast to earlier work on K ϩ -starved barley (Walker et al., 1996), there was no acidification of the cytosol associated with the decreased cytosolic K ϩ activity during NaCl stress. These single-cell measurements of cytosolic and vacuolar ion activities allow calculation of thermodynamic gradients that can be used to reveal (or predict) the type of active transporters at both the plasma membrane and tonoplast.In plant cells, maintaining cytosolic K ϩ in an environment with a high Na ϩ concentration is a key factor in determining the ability to tolerate salinity (Maathuis and Amtmann, 1999). In the cytosol, K ϩ is an essential activator for some enzymes and Na ϩ rarely substitutes for this biochemical function (Wyn Jones and Pollard, 1983; Flowers and Dalmond, 1992). Na ϩ can compete directly for K ϩ -binding sites on enzymes, suggesting that the cytosolic K ϩ to Na ϩ ratio, rather than the absolute Na ϩ concentration, is critical for tolerance. Although the relationship between the cytosolic concentrations of Na ϩ and K ϩ is of fundamental importance in understanding the response of a plant to salinity, it is difficult to obtain direct measurements of the cytosolic concentrations of these two ions in plant cells.Most crop plants are NaCl sensitive, although cereals show a range of tolerance, with barley (Hordeum vulgare) considered more tolerant than wheat (Triticum aestivum) or rice (Oryza sativa; Downton, 1984). Some barley varieties can complete their life cycle growing in 125 mm NaCl, even sustaining a 50% loss in biomass (Greenway, 1962). In a recent survey of NaCl sensitivity among barley genotypes, two varieties were identified that are representative examples from either end of the tolerance range of the species: the sensitive Triumph and the tolerant Gerbel (Flowers and Hajibagheri, 2001). The more sensitive variety accumulated more Na ϩ in the shoot than the tolerant variety and the authors suggested that this might reflect a more sensitive cultivar, having a higher concentration of Na ϩ in its cytoplasm than a more resistant variety. However, for roots growing for 15 d in 200 mm NaCl, the mean cytoplasmic Na ...
We show how the processes of visual detection and of temporal and spatial summation may be analyzed in terms of parallel luminance (achromatic) and opponent-color systems; a test flash is detected if it exceeds the threshold of either system. The spectral sensitivity of the luminance system may be determined by a flicker method, and has a single broad peak near 555 nm; the spectral sensitivity of the opponent-color system corresponds to the color recognition threshold, and has three peaks at about 440, 530, and 600 nm (on a white background). The temporal and spatial integration of the opponent-color system are generally greater than for the luminance system; further, a white background selectively depresses the sensitivity of the luminance system relative to the opponent-color system. Thus relatively large (1 degree) and long (200 msec) spectral test flashes on a white background are detected by the opponent-color system except near 570 nm; the contribution of the luminance system becomes more prominent if the size or duration of the test flash is reduced, or if the white background is extinguished. The present analysis is discussed in relation to Stiles' model of independent eta mechanisms.
A rapid portable technique for estimating macular pigment optical density (MPOD) in large populations is described. The new instrument utilises a novel method for setting flicker thresholds which is undemanding for naïve and elderly observers and easily operated by a non-technical person. The method has good repeatability (r = 0.97) and the data are comparable with an optical method based on retinal reflectometry (r = 0.78). MPOD spatial profiles are presented for seven normal observers and these are well described (r = 0.99) by a decaying exponential function consistent with previous reports. MPOD values are presented from 5581 (2435 females and 3146 males) individuals measured in 48 optometric practices. The mean MPOD of this population was 0.33 (S.D. +/- 0.187) which is similar to previous large scale studies of MP.
PURPOSE.We investigated the effect of daily supplementation with lutein (L) capsules on macular pigment optical density (MPOD) and visual acuity (VA) in patients with early age-related macular degeneration (AMD). METHODS.A randomized, double-blind, placebo-controlled, twocenter investigation of the effects of L supplementation in early AMD was conducted. The duration of the trial was 12 months. The centers were Manchester, United Kingdom and Maastricht, the Netherlands. L capsules (10 mg Ester) or a placebo (P) were taken daily. There were 72 patients (mean age 70.5 6 8.7) assigned randomly to either L (n ¼ 36) or P (n ¼ 36) groups. MPOD using a flicker-based technique (MPS9000) and best corrected VA (LogMAR) were measured at the beginning and at 4-month intervals over the duration of the 12-month supplementation period. Blood serum samples were collected to monitor compliance. RESULTS.At the end of the trial, an overall increase in the mean MPOD level was found for the L group from 0.38 6 0.19 to 0.53 6 0.22 optical density (OD) units. According to a mixed design ANOVA, this was statistically significant (P < 0.001). No change in MPOD was found for the P group. There was no significant change in VA in the L group (n ¼ 36). The P group (n ¼ 36) showed a statistically significant deterioration from 0.05 6 0.13 to 0.09 6 0.13 (P < 0.05). When comparing the change in VA over the supplementation period, there was a significant difference between the two groups (P < 0.05). To avoid ceiling effects, 2 subgroups of patients with VA worse than 0.06 at baseline were reanalyzed. In the L subgroup (n ¼ 19) a mean improvement in VA from 0.23 6 0.12 at baseline to 0.16 6 0.10 at visit 4 was observed (P < 0.05). In the P subgroup (n ¼ 14), there was a small deterioration from 0.18 6 0.13 to 0.19 6 0.12 (P ¼ 0.70). The improvement in VA in the L subgroup was compared to the deterioration in VA in the P group and this effect reached statistical significance (P < 0.05).CONCLUSIONS. L supplementation increases MPOD levels in early stage AMD patients. According to the VA measurements, the progress of the disease might be slowed in some patients with augmented levels of MP. (ClinicalTrials.gov number NCT01042860.) (Invest Ophthalmol Vis Sci.
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