Multiple signals and mechanisms that regulate leaf growth and stomatal behaviour during water deficit

We highlight the novel observation that the responses of maize leaf growth to abscisic acid (ABA) signals can be amplified both by mild water deficits and by nutrient stress. Under our experimental conditions these stresses alone had no effect on leaf growth rate. In most cases leaf growth responses were not attributable to changes in the turgors of growing cells, focusing attention on a regulatory role for cell wall biochemistry. Roles for xyloglucan endotransglycosylase (XET), expansins and peroxidases are discussed. An effect of drought on the activity of expansins seems particularly attractive if xylem sap pH is considered as a chemical signal. We show how changes in xylem sap pH can also modify local accumulation of ABA and thereby modify the apparent sensitivity of guard cells to ABA signals

Tidal and subtidal oscillations in a shallow water system in southern Brazil

ABSTRACT Sea level oscillations in time scales between hours and days have a great vertical amplitude regarding the low lying coastal gradient of the beaches in the Rio Grande do Sul coast. However, the mechanism of oscillations is poorly understood since the scarcity of observational data makes it impossible to determine the forces that control sea level oscillations. Therefore, hourly sea level and wind time series with a time period of 650 days were examined. It has been found that the mean tidal and subtidal amplitudes were very similar to each other and that a considerable portion of the energy from sea level oscillations was due to astronomical forces. A new perspective was introduced when high and low frequencies were compared, leading to the comprehension that astronomical tides should be considered in coastal studies in southern Brazil. The sea level time series analyzed in this study showed that the maximum amplitude of the high spring tide was 0.53m, and that the subtidal rise caused by the wind reached up to 0.66m. In general, when large tidal and subtidal amplitudes are added, it can generate extreme events of sea level rise on the coast, which constitute a direct threat to coastal communities and habitats.</div