Hydrotropism mechanisms and their interplay with gravitropism.

Plants partly optimize their water recruitment from the growth medium by directing root growth toward a moisture source, a phenomenon termed hydrotropism. The default mechanism of downward growth, termed gravitropism, often functions to counteract hydrotropism when the water-potential gradient deviates from the gravity vector. This review addresses the identity of the root sites in which hydrotropism-regulating factors function to attenuate gravitropism and the interplay between these various factors. In this context, the function of hormones, including auxin, abscisic acid, and cytokinins, as well as secondary messengers, calcium ions, and reactive oxygen species in the conflict between these two opposing tropisms is discussed. We have assembled the available data on the effects of various chemicals and genetic backgrounds on both gravitropism and hydrotropism, to provide an up-to-date perspective on the interactions that dictate the orientation of root tip growth. We specify the relevant open questions for future research. Broadening our understanding of root mechanisms of water recruitment holds great potential for providing advanced approaches and technologies that can improve crop plant performance under less-than-optimal conditions, in light of predicted frequent and prolonged drought periods due to global climate change.

Distinct effects of two separately applied stressors on behavior in the red flour beetle.

Stress is ubiquitous in nature and organisms have evolved mechanisms to cope with it. Stress responses nevertheless vary based on the type of stress, its duration, magnitude, and the organism's physiological status. We studied here the effect of two separately applied stress types, differing also in their duration, on various behavioral responses of the red flour beetle (Tribolium castaneum). The two stress types applied were short-term cold stress and long-term low protein stress. The behavioral response variables were movement activity, preference to move along the test arena edges, latency to emerge from shelter, and preference for dark microhabitat, measured at two stages of the beetles' lives, as young adults after eclosion and one month later. Behavioral responses were stress-specific. Cold-stressed beetles moved over the longest distances but were also the most reluctant to leave an accessible shelter. We interpret this to mean that cold-stressed beetles were the most active under unfavorable conditions and least bold under more favorable, protected conditions. As beetles aged, their movement activity decreased and latency to emerge from shelter increased. Non-stressed beetles were the most consistent in their behavior across all behavioral tests. This finding is similar to those in previous studies and suggests that moderate stress reduces behavioral consistency. While all beetles gained mass during the study period, the two stress types led to different patterns of body mass increase, which was more moderate for cold-stressed than for protein-stressed beetles.

The negative effect of starvation and the positive effect of mild thermal stress on thermal tolerance of the red flour beetle, Tribolium castaneum.

The thermal tolerance of a terrestrial insect species can vary as a result of differences in population origin, developmental stage, age, and sex, as well as via phenotypic plasticity induced in response to changes in the abiotic environment. Here, we studied the effects of both starvation and mild cold and heat shocks on the thermal tolerance of the red flour beetle, Tribolium castaneum. Starvation led to impaired cold tolerance, measured as chill coma recovery time, and this effect, which was stronger in males than females, persisted for longer than 2 days but less than 7 days. Heat tolerance, measured as heat knockdown time, was not affected by starvation. Our results highlight the difficulty faced by insects when encountering multiple stressors simultaneously and indicate physiological trade-offs. Both mild cold and heat shocks led to improved heat tolerance in both sexes. It could be that both mild shocks lead to the expression of heat shock proteins, enhancing heat tolerance in the short run. Cold tolerance was not affected by previous mild cold shock, suggesting that such a cold shock, as a single event, causes little stress and hence elicits only weak physiological reaction. However, previous mild heat stress led to improved cold tolerance but only in males. Our results point to both hardening and cross-tolerance between cold and heat shocks.

Space-time completion of video.

This paper presents a new framework for the completion of missing information based on local structures. It poses the task of completion as a global optimization problem with a well-defined objective function and derives a new algorithm to optimize it. Missing values are constrained to form coherent structures with respect to reference examples. We apply this method to space-time completion of large space-time "holes" in video sequences of complex dynamic scenes. The missing portions are filled in by sampling spatio-temporal patches from the available parts of the video, while enforcing global spatio-temporal consistency between all patches in and around the hole. The consistent completion of static scene parts simultaneously with dynamic behaviors leads to realistic looking video sequences and images. Space-time video completion is useful for a variety of tasks, including, but not limited to: 1) Sophisticated video removal (of undesired static or dynamic objects) by completing the appropriate static or dynamic background information. 2) Correction of missing/corrupted video frames in old movies. 3) Modifying a visual story by replacing unwanted elements. 4) Creation of video textures by extending smaller ones. 5) Creation of complete field-of-view stabilized video. 6) As images are one-frame videos, we apply the method to this special case as well.