The blue light receptor CRY1 interacts with GID1 and DELLA proteins to repress gibberellin signaling and plant growth.

Improvements in plant architecture, such as reduced plant height under high-density planting, are important for agricultural production. Light and gibberellin (GA) are essential external and internal cues that affect plant architecture. In this study, we characterize the direct interaction of distinct receptors that link light and GA signaling in Arabidopsis (Arabidopsis thaliana) and wheat (Triticum aestivum L.). We show that the light receptor CRY1 represses GA signaling through interaction with all five DELLA proteins and promotion of RGA protein accumulation in Arabidopsis. Genetic analysis shows that CRY1-mediated growth repression is achieved by means of the DELLA proteins. Interestingly, we find that CRY1 also directly interacts with the GA receptor GID1 to competitively inhibit the GID1-GAI interaction. We also show that overexpression of TaCRY1a reduces plant height and coleoptile growth in wheat and that TaCRY1a interacts with both TaGID1 and Rht1 to competitively attenuate the TaGID1-Rht1 interaction. Based on these findings, we propose that the photoreceptor CRY1 competitively inhibits the GID1-DELLA interaction, thereby stabilizing DELLA proteins and enhancing their repression of plant growth.

Gamma rays induced acquisition of structural modification in chitosan boosts photosynthetic machinery, enzymatic activities and essential oil production in citronella grass (Cymbopogon winterianus Jowitt).

Oligomers derived through irradiation of marine polysaccharides have generated a lot of interest of plant biologists as the application of these molecules has yielded positive results regarding various plant processes. To comprehend the previously established growth-promoting activity of irradiated chitosan (ICH) and to gain insight of the structure-property relationship, gamma rays induced structural changes were analyzed using techniques such as Fourier Transform Infrared (FT-IR) spectroscopy, Ultraviolet-visible (UV-Vis) spectroscopy, 13C-Nuclear Magnetic Resonance (NMR) spectroscopy and Scanning Electron Microscopy (SEM). Moreover, to study the bioactivity of ICH samples a pot experiment was conducted on citronella grass (Cymbopogon winterianus) to access its response to foliar application of various levels (40, 60, 80 and 100 mg L-1) of ICH in terms of growth, physiological attributes and essential oil (EO) production. The application of ICH at 80 mg L-1(ICH-80) resulted in the maximum values of most of the attributes studied. Due to this treatment, the maximum improvement in the content (29.58%) and yield (90.81%) of EO in Cymbopogon winterianus were achieved. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that ICH-80 also increased the content of citronellal (14.81%) and geraniol (18.15%) of the EO as compared to the control.

Pre-harvest UV-C irradiation triggers VOCs accumulation with alteration of antioxidant enzymes and phytohormones in strawberry leaves.

Recent studies have highlighted the biological and physiological effects of pre-harvest ultraviolet (UV)-C treatment on growing plants. However, little is known about the involvement of volatile organic compounds (VOCs) and their response to this treatment. In this study, strawberry plants were exposed to three different doses of UV-C radiation for seven weeks (a low dose: 9.6kJm-2; a medium dose: 15kJm-2; and a high-dose: 29.4kJm-2). Changes in VOC profiles were investigated and an attempt was made to identify factors that may be involved in the regulation of these alterations. Principle compounds analysis revealed that VOC profiles of UV-C treated samples were significantly altered with 26 VOCs being the major contributors to segregation. Among them, 18 fatty acid-derived VOCs accumulated in plants that received high and medium dose of UV-C treatments with higher lipoxygenase and alcohol dehydrogenase activities. In treated samples, the activity of the antioxidant enzymes catalase and peroxidase was inhibited, resulting in a reduced antioxidant capacity and higher lipid peroxidation. Simultaneously, jasmonic acid level was 74% higher in the high-dose group while abscisic acid content was more than 12% lower in both the medium and high-dose UV-C treated samples. These results indicated that pre-harvest UV-C treatment stimulated the biosynthesis of fatty acid-derived VOCs in strawberry leaf tissue by upregulating the activity of enzymes of the LOX biosynthetic pathway and downregulating antioxidant enzyme activities. It is further suggested that the mechanisms underlying fatty acid-derived VOCs biosynthesis in UV-C treated strawberry leaves are associated with UV-C-induced changes in phytohormone profiles.

Photo-catalytic activities of plant hormones on semiconductor nanoparticles by laser-activated electron tunneling and emitting.

Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO2), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi2O3)0.07(CoO)0.03(ZnO)0.9 semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated.

Light is a positive regulator of strigolactone levels in tomato roots.

Strigolactones (SLs) or closely related molecules were recently identified as phytohormones, acting as long-distance branching factors that suppress growth of pre-formed axillary buds in the shoot. The SL signaling pathways and light appear to be connected, as SLs were shown to induce light-regulated pathways and to mimic light-adapted plant growth. However, it is not yet clear how light affects SL levels. Here, we examined the effect of different light intensities on SL levels in tomato roots. The results show that light intensity, above a certain threshold, is a positive regulator of SL levels and of Sl-CCD7 transcription; Sl-CCD7 is involved in SLs biosynthesis in tomato. Moreover, SL accumulation in plant roots is shown to be a time-dependent process. At least some of the similar effects of light and SLs on plant responses might result from a positive effect of light on SL levels.

Interactions between circadian and hormonal signalling in plants.

Growth and development of plants is controlled by external and internal signals. Key internal signals are those generated by hormones and the circadian clock. We highlight interactions between the circadian clock and hormonal signalling networks in regulating the physiology and growth of plants. Microarray analysis has shown that a significant proportion of transcripts involved in hormonal metabolism, catabolism, perception and signalling are also regulated by the circadian clock. In particular, there are interactions between the clock and abscisic acid, auxin, cytokinin and ethylene signalling. We discuss the role of circadian modulation ('gating') of hormonal signals in preventing temporally inappropriate responses. A consideration of the daily changes in physiology provides evidence that circadian gating of hormonal signalling couples the rhythmic regulation of carbon and water utilisation to rhythmic patterns of growth.

Molecular interactions between light and hormone signaling to control plant growth.

As sessile organisms, plants modulate their growth rate and development according to the continuous variation in the conditions of their surrounding environment, an ability referred to as plasticity. This ability relies on a web of interactions between signaling pathways triggered by endogenous and environmental cues. How changes in environmental factors are interpreted by the plant in terms of developmental or growth cues or, in other words, how they contribute to plant plasticity is a current, major question in plant biology. Light stands out among the environmental factors that shape plant development. Plants have evolved systems that allow them to monitor both quantitative and qualitative differences in the light that they perceive, that render important changes in their growth habit. In this review we focus on recent findings about how information from this environmental cue is integrated during de-etiolation and in the shade-avoidance syndrome, and modulated by several hormone pathways-the endogenous cues. In some cases the interaction between a hormone and the light signaling pathways is reciprocal, as is the case of the gibberellin pathway, whereas in other cases hormone pathways act downstream of the environmental cue to regulate growth. Moreover, the circadian clock adds an additional layer of regulation, which has been proposed to integrate the information provided by light with that provided by hormone pathways, to regulate daily growth.

Low irradiances affect abscisic acid, indole-3-acidic acid, and cytokinin levels of wheat (Triticum aestivum L.) tissues.

Wheat (Triticum aestivum L.) plants were grown under four irradiance levels: 1,400, 400, 200, and 100 micromol m-2 s-1. Leaves and roots were sampled before, during, and after the boot stage, and levels of abscisic acid (ABA), indole-3-acetic acid (IAA), zeatin, zeatin riboside, dihydrozeatin, dihydrozeatin riboside, isopentenyl adenine, and isopentenyl adenosine were quantified using noncompetitive indirect ELISA systems. Levels of IAA in leaves and roots of plants exposed to 100 micromol m-2 s-1 of irradiance were 0.7 and 2.9 micromol kg-1 dry mass (DM), respectively. These levels were 0.2 and 1.0 micromol kg-1 DM, respectively, when plants were exposed to 1,400 micromol m-2 s-1. Levels of ABA in leaves and roots of plants exposed to 100 micromol m-2 s-1 were 0.65 and 0.55 micromol kg-1 DM, respectively. They were 0.24 micromol kg-1 DM (both leaves and roots) when plants were exposed to 1,400 micromol m-2 s-1. Levels of isopentenyl adenosine in leaves (24.3 nmol kg-1 DM) and roots (29.9 nmol kg-1 DM) were not affected by differences in the irradiance regime. Similar values were obtained in a second experiment. Other cytokinins could not be detected (<10 nmol kg 1 DM) in either experiment with the sample sizes used (150-600 mg DM for roots and shoots, respectively).

Rates of ethylene release, photosynthesis and transpiration of rice measured in closed-type chamber.

To obtain the basic data of gas exchange of rice (Oryza sativa L. cv. Nipponbare), rates of ethylene release, photosynthesis and transpiration of the rice plant were measured by using a closed-type chamber. Each rate increased until the heading stage and thereafter decreased. Ethylene release rate (E) gradually increased with day after seeding and rates of photosynthesis (P) and transpiration (T) did exponentially. At the heading stage, E, P and T were maximum and had values of about 2.0 mmol plant-1 h-1, 3.0 mmol plant-1 h-1 and 0.60 mol plant-1 h-1, respectively. E in the light period was 1.5-3 times as much as that in the dark period, whereas T in the light period was 5-6 times as much as that in the dark period. E of rice per plant was lower than those of lettuce and Brassica genera which were reported previously. Especially, the rate of rice was about one-tenth that of lettuce. However, when ethylene release rates were estimated on a growth area basis, the rate of rice was about half that of lettuce, and was more than those of Brassica genera.

[The reversibility of the action of solar UV radiation on the growth of and on the level of growth regulators in barley plants]. / Ob obratimosti deistviia solnechnoi UF-radiatsii na rost i uroven' reguliatorov rosta v rasteniiakh iachmenia.

Effects of UV radiation on a growth regulators activity of barley plants were studied in the West Pamir at 2.320 m above sea level. Inhibition of plant growth in a highlands environment was discussed. Inhibition appears as either a change of stimulating for inhibitory activity or an increased activity of the growth inhibitors. The plant growth inhibition during a bush phase which is a more sensitive period of growth in barley plants is reversible.

[The effect of natural UV-radiation on the growth and activity of endogenous growth regulators in barley leaves]. / Deistvie estestvennoi UF-radiatsii na rost i aktivnost' éndogennykh reguliatorov rosta v list'iakh iachmenia.

The effect of natural UV-radiation on the growth of two barley varieties in the Pamir highlands was investigated. It was found that UV-radiation, whose portion in the light structure of that region was high, inhibited the growth of barley stems. The growth processes were inhibited via involvement of growth stimulants and inhibitors. UV-radiation suppressed endogenous stimulants of indole nature. Growth inhibitors proved resistant to UV-radiation.

A volatile factor inducing transmissible lysis in Gaeumannomyces graminis (Sacc.) Arx and Olivier var. tritici Walker.

Filtered water extract of Gabalong soil with a recent history of take-all in wheat caused lytic plaques to form in agar cultures of a virulent strain of Gaeumannomyces graminis var. tritici. The plaques resembled those produced by Bdellovibrio on plate seeded with bacteria. However, there was no evidence of the presence of bacteria, viruses, or mycoplasmas. The lytic factor was transmissible in culture filtrates to fresh subcultures of the fungus. Exposure of young healthy colonies to sublethal doses of ultraviolet light also induced transmissible lysis. The lytic factor was heat-stable, passed through a 25-nm filter, and was not affected by nuclease (enzymes) or severe irradiation with UV light. It also induced bysis in several other strains of G. graminis. Lysis was always preceded by a growth-stimulatory effect on the fungus. The lytic factor was active as a volatile chemical which induced transmissible lysis and continued to be formed, apparently as a self-perpetuating agent, in lysing cultures of the fungus.