Low red/far-red ratios delay spike and stem growth in wheat

The responses to low red light/far-red light (R/FR) ratios simulating dense stands were evaluated in wheat (Triticum aestivum L) cultivars released at different times in the 20th century and consequently resulting from an increasingly prolonged breeding and selection history. While tillering responses to the R/FR ratio were unaffected by the cultivars, low R/FR ratios reduced grain yield per plant (primarily grain number and secondarily grain weight per plant) particularly in modern cultivars. Low R/FR ratios delayed spike growth and development, reduced the expression of spike marker genes, accelerated the development of florets already initiated, and reduced the number of fertile florets at anthesis. It is noteworthy that low R/FR ratios did not promote stem or leaf sheath growth and therefore the observed reduction of yield cannot be accounted for as a consequence of divergence of resources towards increased plant stature. It is proposed that the regulation of yield components by the R/FR ratio could help plants to adjust to the limited availability of resources under crop conditions

Use of Confocal Laser as Light Source Reveals Stomata-Autonomous Function

In most terrestrial plants, stomata open during the day to maximize the update of CO(2) for photosynthesis, but they close at night to minimize water loss. Blue light, among several environmental factors, controls this process. Stomata response to diverse stimuli seems to be dictated by the behaviour of neighbour stomata creating leaf areas of coordinated response. Here individual stomata of Arabidopsis leaves were illuminated with a short blue-light pulse by focusing a confocal argon laser. Beautifully, the illuminated stomata open their pores, whereas their dark-adapted neighbours unexpectedly experience no change. This induction of individual stomata opening by low fluence rates of blue light was disrupted in the phototropin1 phototropin2 (phot1 phot2) double mutant, which exhibits insensitivity of stomatal movements in blue-illuminated epidermal strips. The irradiation of all epidermal cells making direct contact with a given stoma in both wild type and phot1 phot2 plants does not trigger its movement. These results unravel the stoma autonomous function in the blue light response and illuminate the implication of PHOT1 and/or PHOT2 in such response. The micro spatial heterogeneity that solar blue light suffers in partially shaded leaves under natural conditions highlights the physiological significance of the autonomous stomatal behaviour

Colour assessment outcomes – a new approach to grading the severity of color vision loss

INTRODUCTION: Recent studies have shown that a significant percentage of subjects with anomalous, congenital trichromacy can perform the suprathreshold, colour-related tasks encountered in many occupations with the same accuracy as normal trichromats. In the absence of detailed, occupation-specific studies, an alternative approach is to make use of new findings and the statistical outcomes of past practices that have been considered safe to produce graded, justifiable categories of colour vision that can be enforced. METHODS: We analyzed traditional color assessment outcomes and measured severity of colour vision loss using the CAD test in 1363 subjects (336 normals, 705 deutan, 319 protan and 3 tritan). The severity of colour vision loss was measured in each subject and statistical, pass / fail outcomes established for each of the most commonly used, conventional colour assessment tests and protocols. RESULTS: The correlation between the number of Ishihara (IH) test plates subjects fail and the severity of RG colour vision loss was very poor. The 38 plates IH test has high sensitivity when no errors are allowed (i.e., only 0.71% deutans and 0.63% protans pass). Protocols based on zero errors are uncommon since 18.15% of normal trichromats fail. The most common protocols employ either the 24 or the 14 plates editions with two or less errors. These protocols pass almost all normal trichromats, but the deutans and some protans that also pass (when two or less errors are allowed) can be severely deficient. This is simply because the most challenging plates have not been included in the 24 and 14 plates editions. As a result, normals no longer fail, but the deutans and protans that pass have more severe loss of colour vision since they fail less challenging plates. The severity of colour vision loss was measured in each subject and statistical, pass / fail outcomes established for each of the most commonly used, conventional colour assessment tests and protocols. DISCUSSION: Historical evidence and new findings that relate severity of loss to the effective use of colour signals in a number of tasks provide the basis for a new colour grading system based on six categories. A single colour assessment test is needed to establish the applicant’s Colour Vision category which can range from ‘supernormal’ (CV0), for the most stringent, colour-demanding tasks, to ‘severe colour deficiency’, when red / green colour vision is either absent or extremely weak (CV5)

Modulation of light sensitivity in plants. Molecular mechanisms and agro-biotechnological applications

Incrementos en la densidad de cultivo producen aumentos en el rendimiento por área hasta alcanzar un óptimo. A partir de allí, densidades mayores pueden repercutir negativamente. Esto se debería a una mayor competencia por recursos y a señales lumínicas asociadas a altas densidades. Estas señales son percibidas por fotorreceptores de luz roja y rojo lejana conocidos como fitocromos. Dilucidar los mecanismos mediante los cuales las plantas modulan la sensibilidad a la luz es fundamental para diseñar estrategias que aplaquen el impacto negativo de altas densidades de cultivo sobre el rendimiento. En la primera etapa de esta tesis se estudiaron los papeles que cumplen ciertos actores de la señalización lumínica (PKS1, PKS2 y COP1) bajo condiciones controladas en la planta modelo, Arabidopsis thaliana. PKS1 y PKS2 promovieron una rama discreta de la señalización del fitocromo A (VLFR), e interactúaron negativamente entre sí. Un balance entre PKS1 y PKS2 sería necesario para respuestas VLFR normales. COP1, cuya función como represor de la fotomorfogénesis en oscuridad es bien conocida, mostró una inesperada correlación positiva entre los niveles de COP1 y la respuesta de plántulas de Arabidopsis a luz roja percibida por el fitocromo B. Al igual que PKS1 y PKS2, COP1 también demostró ser una proteína bifuncional (con actividad represora/activadora). Distintas variantes genéticas con niveles alterados de PKS1, PKS2, COP1 y PHYB (fitocromo B) fueron evaluadas a distintas densidades bajo radiación natural. La sobreexpresión de PHYB fue la estrategia más efectiva para producir insensibilidad a la densidad en Arabidopsis. La aplicación de esta estrategia en plantas de interés comercial (Solanum tuberosum) mostró que la sobreexpresión de PHYB es capaz de provocar mayores rendimientos en altas densidades de cultivo.At low plant densities, increasing the number of plants per unit area results in proportional increments in crop yield, above certain plant densities the marginal increment of yield with increased population decreases and may become negative. This could be due to higher competition by resources and by light signals associated to dense canopies characteristics of high densities. These light signals are perceived by photoreceptors of red and far red light known as phytochromes. Uncovering of the mechanisms through which the plants modulate light sensitivity is crucial to design strategies to abolish deleterious effects of high densities on crop yield. The first step in this theses was to study the role that play certain actors of the light signalling (PKSl ,PKS2 y COP1) under controlled environments in the model plant, Arabidopsis thaliana. PKSl and PKS2 promoted a discrete branch of phytochrome A signalling (VLFR), and they negatively interact between them. A balance between PKS 1 and PKS2 would be necessary for normal VLFR responses. COP1, a known repressor of photomorphogenesis in darkness, showed an unsuspected positive correlation between COPl levels and the responses of seedlings of Arabidopsis to the red light perceived by phytochrome B. Surprisingly, PKSl, PKS2 and COPl behaved as bifunctional proteins (with activity of repressor/activator in the same molecule). Different genotypes with altered levels of PKS 1, PKS2, COPl and PHYB (phytochrome B) were evaluated at distinct plant densities under natural radiation. PHYB overexpression was the more effective strategy to diminish responses to stand density in Arabidopsis. The application of this strategy in crops (Solanum tuberosum) showed that PHYB overexpression increased potential tuber yield of potato crops planted at high densities.Fil: Boccalandro, Hernán Esteban. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

PHYTOCHROME KINASE SUBSTRATE4 Modulates Phytochrome-Mediated Control of Hypocotyl Growth Orientation1[W][OA]

Gravity and light are major factors shaping plant growth. Light perceived by phytochromes leads to seedling deetiolation, which includes the deviation from vertical hypocotyl growth and promotes hypocotyl phototropism. These light responses enhance survival of young seedlings during their emergence from the soil. The PHYTOCHROME KINASE SUBSTRATE (PKS) family is composed of four members in Arabidopsis (Arabidopsis thaliana): PKS1 to PKS4. Here we show that PKS4 is a negative regulator of both phytochrome A- and B-mediated inhibition of hypocotyl growth and promotion of cotyledon unfolding. Most prominently, pks4 mutants show abnormal phytochrome-modulated hypocotyl growth orientation. In dark-grown seedlings hypocotyls change from the original orientation defined by seed position to the upright orientation defined by gravity and light reduces the magnitude of this shift. In older seedlings with the hypocotyls already oriented by gravity, light promotes the deviation from vertical orientation. Based on the characterization of pks4 mutants we propose that PKS4 inhibits changes in growth orientation under red or far-red light. Our data suggest that in these light conditions PKS4 acts as an inhibitor of asymmetric growth. This hypothesis is supported by the phenotype of PKS4 overexpressers. Together with previous findings, these results indicate that the PKS family plays important functions during light-regulated tropic growth responses

Dissociation of PHOT1 from the plasma membrane in blue-light irradiated cells

<div><p>(A) Stomata blue-light irradiation.</p> <p>Confocal section of the epidermis of a dark-adapted <i>PHOT1-GFP</i> seedling showing all GFP signal attached to the cell surface (left).</p> <p>Section of the same field 3 min after the initial scan (right).</p> <p>The intensity of the GFP signal decreased in the irradiated stoma.</p> <p>No changes were detected in its neighbour epidermal cells.</p> <p>(B) Stomatal neighbour cell irradiation.</p> <p>Epidermal sections before (left) and after (right) the blue-light illumination.</p> <p>The argon laser provided the blue-light source.</p> <p>Scale bar: 3 µm; all images are the same magnification.</p></div

Blue light-induced stomatal movement signals are not transmitted from non-stomatal epidermal cells to their adjacent stomata

<div><p>A short pulse of blue light from the argon laser was applied to all epidermal cells adjacent to randomly selected stomata in both wild type and <i>phot1-5 phot2-1</i> double mutant.</p> <p>Such irradiation caused no effect in the stomatal movements.</p> <p>(A) Confocal sections show the stomatal apertures before (left) and two hours later (right) the non-stomatal epidermal cells illumination.</p> <p>(B) Differences between the stomatal aperture before and after the blue light treatment.</p> <p>Note that illuminated stomata increased opening in the wild type, and remained unaltered in the <i>phot1-5 phot2-1</i> double mutant.</p> <p>Bars show the mean of at least 15 measurements with standard deviations.</p> <p>Images show staining with calcofluor resulting in strong fluorescence in cell walls.</p> <p>Scale bar: 3 µm; all images are the same magnification.</p></div

Nearby parts of an Arabidopsis leaf can experience steep differences in irradiance

<div><p>Solar blue light decreases sharply between the unshaded (0 µm) and shaded portions of the abaxial side of an Arabidopsis leaf.</p> <p>The average distance among stomata in Arabidopsis varies between 50 and 100 µm, indicating that neighbour stomata may be exposed to widely different light conditions.</p> <p>Data are means and standard errors of three replicates.</p> <p>Inset, Image of overlapping leaves illustrating the sharp transition between illuminated and shaded areas.</p></div

Stoma autonomy in its blue light-induced opening

<div><p>Individual stomata were irradiated with a short pulse of blue light by focusing an argon laser attached to a confocal microscope.</p> <p>(A) Irradiated stomata.</p> <p>(B) Nearest neighbour of the irradiated stoma.</p> <p>Confocal sections showing the stomatal opening in both wild type and <i>phot1-5 phot2-1</i> double mutant, before (left) and two hours later (right) the blue-light treatment.</p> <p>(C) Differences between the stomatal opening before and two hours after the blue light treatment in both irradiated stomata and their nearest neighbours dark-adapted stomata.</p> <p>Wild-type irradiated stomata increased pore opening.</p> <p>In contrast, the irradiated stomata of the <i>phot1-5 phot2-1</i> double mutant experienced no change.</p> <p>The nearest neighbours to the irradiated stomata remained unaltered in their movements.</p> <p>Bars indicate the mean of at least 15 measurements with standard deviations.</p> <p>Calcofluor staining (0.1%) produced a blue fluorescence in all cell walls when excited with a 405-nm laser line of a diode laser.</p> <p>White line shows the initial opening; red one represents the final aperture.</p> <p>Scale bar: 3 µm; all images are the same magnification.</p></div