Angular sensitivity of blowfly photoreceptors: intracellular measurements and wave-optical predictions

The angular sensitivity of blowfly photoreceptors was measured in detail at wavelengths λ = 355, 494 and 588 nm. The measured curves often showed numerous sidebands, indicating the importance of diffraction by the facet lens. The shape of the angular sensitivity profile is dependent on wavelength. The main peak of the angular sensitivities at the shorter wavelengths was flattened. This phenomenon as well as the overall shape of the main peak can be quantitatively described by a wave-optical theory using realistic values for the optical parameters of the lens-photoreceptor system. At a constant response level of 6 mV (almost dark adapted), the visual acuity of the peripheral cells R1-6 is at longer wavelengths mainly diffraction limited, while at shorter wavelengths the visual acuity is limited by the waveguide properties of the rhabdomere. Closure of the pupil narrows the angular sensitivity profile at the shorter wavelengths. This effect can be fully described by assuming that the intracellular pupil progressively absorbs light from the higher order modes. In light-adapted cells R1-6 the visual acuity is mainly diffraction limited at all wavelengths.

Metarhodopsin control by arrestin, light-filtering screening pigments, and visual pigment turnover in invertebrate microvillar photoreceptors

The visual pigments of most invertebrate photoreceptors have two thermostable photo-interconvertible states, the ground state rhodopsin and photo-activated metarhodopsin, which triggers the phototransduction cascade until it binds arrestin. The ratio of the two states in photoequilibrium is determined by their absorbance spectra and the effective spectral distribution of illumination. Calculations indicate that metarhodopsin levels in fly photoreceptors are maintained below ~35% in normal diurnal environments, due to the combination of a blue-green rhodopsin, an orange-absorbing metarhodopsin and red transparent screening pigments. Slow metarhodopsin degradation and rhodopsin regeneration processes further subserve visual pigment maintenance. In most insect eyes, where the majority of photoreceptors have green-absorbing rhodopsins and blue-absorbing metarhodopsins, natural illuminants are predicted to create metarhodopsin levels greater than 60% at high intensities. However, fast metarhodopsin decay and rhodopsin regeneration also play an important role in controlling metarhodopsin in green receptors, resulting in a high rhodopsin content at low light intensities and a reduced overall visual pigment content in bright light. A simple model for the visual pigment–arrestin cycle is used to illustrate the dependence of the visual pigment population states on light intensity, arrestin levels and pigment turnover

Evaluation of Morpho-physiological Responses of Iranian Rice Landraces and Improved Genotypes to Iron Deficiency in Nutrient Solution

Excessive application of P fertilizers, use of the bicarbonated water sources for irrigation concomitant to a  low level of organic matter have resulted in widespread iron deficiencies in crop plants in Iran. One of the strategies to overcome this problem is to select tolerant genotypes to iron deficiency (i.e. iron-use-efficient genotypes) or bred genotypes with high-micronutrient-uptake ability. Therefore, this experiment was conducted to study the behavior of twelve Iranian rice landraces and improved genotypes to iron deficiency (Tarom Mahalli, Amol 2, Musa-Tarom, Gharib, Shiroudi, Bejar, Neda, Nogouran, Jozdan, Sazandegi, Zayande Roud, and Kouhrang) as exposed to two levels of chelated iron fertilizers, including 5mM (iron deficiency) and 50mM (no iron deficiency) in Yushida nutrient solution culture.  A factorial experiment based on a completely randomized design with four replicates was carried out in Soilless Culture Center at Isfahan University of Technology, Isfahan, Iran in 2013. The results showed that the iron content, shoot and root dry weights, total dry weight, leaf area, root length and volume and the number of tillers were significantly affected by genotypes, iron fertilizer, and their interaction. The mean dry weights were 0.215, 0.138, and 0.255 g per plant in northern landraces, northern improved, and central Iranian genotypes under no iron deficiency condition, but they were decreased by 25.7, 35.2, and 23.0% under iron deficiency condition, respectively. Based on the magnitude of decrease of total biomass under iron deficiency condition, genotypes such as Musa-Tarom, Bejar, and Zayande Roud seemed to be more tolerant in comparison to Jozdan, Amol 2, and Shiroudi

An Assessment of the Effect of Nitrogen Application and Planting Methods on Yield and Yield Components ofLinseed and Berseem Clover Intercropping System

In order to assess the effect of nitrogen application and planting methods on linseed and berseem clover yield and yield components in an intercropping system an experiment was conducted as a split plot based on randomized complete block design with three replications at the Research Farm of College of Agriculture, Isfahan University of Technology, Isfahan, Iran in 2013. Experimental factors included three levels of nitrogen (zero, 30 and 60 kg ha-1) as main plots and linseed and berseem clover planting methods in 4 levels (pure culture of linseed, berseem clover monoculture, mixed cropping) (50%:50%), intercropping row) 50%:50%)) as sub-plots. Results showed that different levels of nitrogen had no effect on the main stem, seed weight and harvest index of both plants, but the number of lateral branches, number of capsules per plant (linseed), inflorescences number per plant (berseem clover), number of seeds per capsules (linseed), biological yield and grain yield were affected by nitrogen fertilizer. Among the methods of planting, pure cultures of linseed and berseem clover with 1604 and 830 kg ha-1 had the highest yield, respectively. Significant difference between treatments was found in the land equivalent ratio, but the highest land equivalent ratio, was archived at 30 kg nitrogen fertilizer application (1.35) and row intercropping treatment (1.32), respectively. According to the results of this research, the use of berseem clover as a nitrogen-fixing plant, intercropped with linseed under 30 kg of nitrogen application per hectare could, probably, be useful for achieving an appropriate grain yield