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The effect of nitrogen fertilization and water stress on the spectral signature of winter wheat Triticum aestivum cv. Astral were measured with a field radiometer over two years. Spectral reflectance of the canopy has been related to the most indicative physiological parameters (nitrogen and photosynthetic pigment content, biomass, leaf area and LAI), but only a few of these parameters can be estimated independently of plant treatment.The normalized difference vegetation index seems the most powerful spectral combination with which to estimate the total area of plant leaves and LAI. The nitrogen content of plants can also be related to a linear combination of green and red canopy refleetances independently of plant treatment. Relations between canopy reflectance and other physiological parameters are not independent of plant treatment.

pulvini received R and the other FR in all experiments comparing these two light treatments. Light sources for phytochrome photoconversion (R = 3-or 5-min exposure at 2.2 J m-2, 600 to 690 nm, and FR = 1.5-min exposure at 9 J m-2, 710 to 750 nm) and the dim green light used during the measurements and experimental manipulations are described in reference 15. The beginning of the dark period, DD = 0, coincides with the regular lights off signal. RESULTSExcised pulvini incubated in H20 during DD oscillate for only one cycle before the rhythm damps in the open position (18). R or FR administered at regular intervals (Fig. 1) permit the rhythm to persist for two to three cycles, although the amplitude of the oscillations and R-FR differences tend to decrease with time, and oscillations cease after 72 hr darkness. Since sucrose is required for sustained rhythmicity in DD (18), all pulvini were supplied with 50 mm sucrose in the remaining experiments. As will become apparent (see Figs. 5 and 6), R and FR have very different effects on the phase, period, and amplitude of the movement, when sucrose is available.Two types of experiments were performed. To investigate phase response, one R or FR light pulse was presented at different times of the rhythm. To test for rhythmic entrainment, pulses of R or FR light were presented every 24 hr. In all cases, the effects of light treatments were compared to free running dark controls.Phase Shifting with One Red Light Flash. The effects of R presented at 25 different times during a long dark cycle were analyzed; Figure 2 indicates the results of eight such treatments, while Figure 3 compares the effects of all 25 treatments. One R pulse presented during the second two-thirds of pulvinal opening or the first half of closure reduces the duration of the next cycle, thereby producing a phase advance, while one pulse presented during the second half of pulvinal closure, or the first third of the opening movement increases the duration of the next cycle, thereby causing a phase delay. R presented at the middle of closure has no effect on the phase; we have designated this as the ZPST.Phase and Amplitude Response Curves. The amount-of phase shift was determined by comparing the time of the first maximum after the R light treatment with that of the same maximum in the dark control. R produces a maximum phase shift of about 12 hr when presented during pulvinal opening, 12 hr from ZPST. The amount of phase shift depends primarily upon the interval between the light pulse and ZPST and is remarkably independent of the cycle in which the R treatment is presented, except for the first 8 hr of DD. R at this time is much less effective than if presented at an equivalent part of a later cycle, as also reported in other plants (5,22

Acclimation to high salt concentrations involves concerted changes in gene expression. For the majority of salt-regulated genes, the mechanism underlying the induction process is not known. The gene ggpS (sll1566), which encodes the glucosylglycerol-phosphate synthase responsible for the synthesis of the compatible solute glucosylglycerol (GG), is specifically induced by salt in the cyanobacterial model strain Synechocystis sp. strain PCC 6803. To identify mechanisms mediating this salt-specific gene regulation, the ggpS promoter was analyzed in more detail. 5 rapid amplification of cDNA ends (5-RACE) experiments revealed that the adjacent open reading frame (ORF), which is annotated as unknown protein Ssl3076, overlaps with the transcriptional start site of the ggpS gene. Reporter gene expression analyses indicated an essential role for the intact ssl3076 gene in the salt-regulated transcription of a gfp reporter gene. Promoter fragments containing a mutated ssl3076 lost the salt regulation; similarly, a frameshift mutation in ssl3076 resulted in a high level of ggpS expression under low-salt conditions, thereby establishing this small ORF, named ggpR, as a negative regulator of ggpS. Interestingly, small ORFs were also found adjacent to ggpS genes in the genomes of other GG-accumulating cyanobacteria. These results suggest that the GgpR protein represses ggpS expression under low-salt conditions, whereas in salt-shocked and salt-acclimated cells a stress-proportional ggpS expression occurs, leading to GG accumulation.Cyanobacteria represent an evolutionarily old phylum of the domain Bacteria. These organisms are currently attracting much interest due to their global importance as primary producers and as possible sources of renewable bioenergy (1, 6). Cyanobacteria are found in nearly all aquatic systems, including freshwater, marine water, and hypersaline environments. In saline habitats, microorganisms have to cope with two major problems: (i) a permanent ion influx due to a high concentration gradient and (ii) a low external osmotic potential, which causes an efflux of water and loss of turgor pressure (5). Cyanobacteria use the "salt-out" strategy to acclimate to high salt concentrations. Toxic inorganic ions (mainly Na ϩ and Cl Ϫ ) are continuously pumped out from the cytoplasmic space; at the same time, the cells accumulate compatible solutes, which adjust the cellular osmotic potential to levels that allow water uptake (e.g., see references 17 and 40).The freshwater strain Synechocystis sp. strain PCC 6803 (here referred to as PCC 6803) has been established as a model organism for investigating the salt acclimation strategies of cyanobacteria. The main compatible solute accumulated by PCC 6803 is the heteroside glucosylglycerol (GG) (39), which has been found to be characteristic of moderately halotolerant cyanobacteria. GG is obtained either by de novo synthesis or by active uptake from the medium (36). The biosynthesis of GG occurs by a two-step reaction, in which the enzymatic condensation of ADP-glu...

Abstract— The effect of external calcium level, calcium ionophore A23187 and red light on the circadian rhythm of Robinia pseudoacacia leaflet movements has been studied. Fifteen minute red light pulses shifted the phase of leaflet rhythmic movement with a phase‐response curve type 0. Maximum advances and delays (about 10 h and 8 h, respectively) were obtained between circadian time (CT) 10 and CT 12 at the end of a subjective day. An almost null effect was obtained at the end of a subjective night. Phytochrome is the photoreceptor involved in phase shifting since this effect of red light is reversed by 5 min of far red light. Two hour pulses of external calcium, applied as CaCl2 (10 mM), and 2 h pulses of calcium ionophore A23187 (10–50 μM) also shifted the phase of leaflet circadian movement and caused the same type of phase‐response curve, with maximum advances and delays at the same time as those produced by red light. Two hour pulses of an external calcium chelator, EGTA (5 mM), and a calcium channel blocker, LaCl3 (10–50 mM), damped the circadian rhythm or did not change the phase when they were applied at lower concentration. These results indicate that phytochrome could control the circadian oscillator, which drives Robinia leaflet movements by increasing the intracellular calcium concentration.

Seasonal changes in water relations, production and mineral composition were studied in a sward of Cynodon dac~lon (L). Pers. subjected to water deficits during a dry summer, and at recovery in autumn. The experiment was carried out under Mediterranean field conditions. Water deficits during summer reduced total dry matter production by 60%, but in autumn there were no differences between treatments. Compared to well-watered sward, the sward grown under drought showed an increase in potassium, calcium and nitrogen of 55, 10 and 10% respectively. These differences decreased with the arrival of autumn rains. Leaf osmotic potential (~P~) fell during the dry summer to -2.8 MPa in well-watered plants and to -4.2 MPa in stressed plants. In autumn there were no differences between treatments. Nevertheless, relative water content (RWC) only decreased to 0.86 in droughted plants. In summer potassium contributed to the osmotic adjustment. In contrast, under water deficits a decrease of 71% in sodium and, to a lesser but significant extent decreases in phosphorus, magnesium and chlorine was observed. Nitrogen, phosphorus and sulphur showed low concentrations during summer and increased in autumn.Abbrev&tions: D-droughted plots, W-watered plots; RWC-relative water content, W -L e a f water potential; ~P~ -osmotic potential, D W -d r y weight

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