Phytochrome B increases drought tolerance by enhancing ABA sensitivity in Arabidopsis thaliana

Phytochrome B (phyB) can adjust morphological and physiological responses according to changes in the red : far‐red (R:FR) ratio. phyB‐driven acclimation of plants to open environments (high R:FR ratio) increases carbon gain at the expense of increased water loss. This behaviour alleviates stressful conditions generated by an excess of light, but increases the chances of desiccation. Here we evaluated how phyB modulates this drought‐tolerance response by comparing wild‐type Arabidopsis thaliana adult plants to the null phyB in response to water shortage. phyB wilted before the wild type, and this was due to phyB maintaining open stomata under a reduction in soil water availability. Although phyB presented enhanced ABA levels under well‐watered conditions, this mutant was less sensitive than the wild type in diminishing stomatal conductance in response to exogenous ABA application. Reduced sensitivity to ABA in phyB correlated with a lower expression of ABCG22, which encodes a putative ABA influx transporter, and PYL5, which encodes a soluble ABA receptor. Furthermore, the expression of RAB18 and RD29A, both typical ABA‐induced genes, was lower in phyB than the wild type after ABA treatment. We propose that phyB contributes to the acclimation of plants to open environments by enhancing ABA sensitivity when soil water becomes limiting.     

The geographical distribution of populations of the large-billed subspecies of reed bunting matches that of its main winter food

We investigated the effects of resource distribution on the population structure and distribution of a polytypic bird species. We compared the presence of insect remains (mainly dormant larvae) in the winter diet of two reed bunting subspecies, small billed E. s. schoeniclus and large billed E. s. intermedia and studied the distribution of this resource within reed ( Phragmites sp.) stems in seven north Italian localities where the two subspecies breed (three schoeniclus and four intermedia populations). We also tested if the distributions of winter insect resources and breeding populations of the large bill subspecies overlapped. The distribution of the larvae in reed stems matched closely the distribution of large billed breeding populations. The winter diets of the two subspecies were significantly different in terms of frequency of insect remains. These results, when compared to theoretical models of para-patric distribution, suggest that the two subspecies may be subject to ecological (vicariant) selection maintaining their reproductive isolation. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 21–26.