Adjustment of photosynthetic activity to drought and fluctuating light in wheat

Drought is a major cause of losses in crop yield. Under field conditions, plants exposed to drought are usually also experiencing rapid changes in light intensity. Accordingly, plants need to acclimate to both, drought and light stress. Two crucial mechanisms in plant acclimation to changes in light conditions comprise thylakoid protein phosphorylation and dissipation of light energy as heat by non-photochemical quenching (NPQ). Here, we analyzed the acclimation efficacy of two different wheat varieties, by applying fluctuating light for analysis of plants, which had been subjected to a slowly developing drought stress as it usually occurs in the field. This novel approach allowed us to distinguish four drought phases, which are critical for grain yield, and to discover acclimatory responses which are independent of photodamage. In short-term, under fluctuating light, the slowdown of NPQ relaxation adjusts the photosynthetic activity to the reduced metabolic capacity. In long-term, the photosynthetic machinery acquires a drought-specific configuration by changing the PSII-LHCII phosphorylation pattern together with protein stoichiometry. Therefore, the fine-tuning of NPQ relaxation and PSII-LHCII phosphorylation pattern represent promising traits for future crop breeding strategies

On a mechanism of intensification of field-aligned currents at the solar chromosphere-quiescent prominence boundaries

Field-aligned electric currents (FAC) are assumed to support various prominence configurations and it is usually supposed that the quiescent prominence (QP) destabilisation can be initiated by some plasma instability. In this work we study another possibility of QP destabilisation connected with FAC changes. Such a destabilisation may occur when FAC flowing along a loop-shaped QP structure are intensified by bouncing surface MHD modes, presumably generated by motions in the photosphere under, or adjacent to, the QP. The MHD disturbances at the prominence "feet" propagate upwards as Alfven waves and surface modes. We study the possibility that the generated MHD modes, which carry FAC, bounce in the loop-shaped QP structure, provided that they undergo multiple reflection at the prominence feet. This is an interesting physical situation leading to intensification of FAC and promising to be another source of QP destabilisation

1999 solar eclipse corona in polarized white light. Preliminary Results

This paper deals with the preliminary results of August 11, 1999 white-light polarization observations carried out in Turkey (Turhal). The corona was photographed in three positions of the polaroid differing by 60°, and the twelve pictures were obtained. All the films are analyzed by means of image processing technique. After coronal holes are identified in Solar Geophysical Data and from the corona observations, distributions of polarization degree and brightness in these holes are obtained and the results are discussed