The mechanism, or hypothesis, of how a plant might be adapted to drought should strongly influence experimental designs. For instance, an experiment testing for water conservation should be distinct from a damage tolerance evaluation. Here we define four new, general mechanisms for plant adaptation to drought, so that experiments can be more easily designed based upon the definitions. A series of experimental methods are suggested along with appropriate physiological measurements related to the drought adaptation mechanisms. The suggestion is made that the experimental manipulation should match the rate, length, and severity of soil water deficit needed to test the hypothesized type of drought adaptation mechanism.

BackgroundWild crop relatives have been potentially subjected to stresses on an evolutionary time scale prior to domestication. Among these stresses, drought is one of the main factors limiting crop productivity and its impact is likely to increase under current scenarios of global climate change. We sought to determine to what extent wild common bean (Phaseolus vulgaris) exhibited adaptation to drought stress, whether this potential adaptation is dependent on the climatic conditions of the location of origin of individual populations, and to what extent domesticated common bean reflects potential drought adaptation.MethodsAn extensive and diverse set of wild beans from across Mesoamerica, along with a set of reference Mesoamerican domesticated cultivars, were evaluated for root and shoot traits related to drought adaptation. A water deficit experiment was conducted by growing each genotype in a long transparent tube in greenhouse conditions so that root growth, in addition to shoot growth, could be monitored.ResultsPhenotypic and landscape genomic analyses, based on single-nucleotide polymorphisms, suggested that beans originating from central and north-west Mexico and Oaxaca, in the driest parts of their distribution, produced more biomass and were deeper-rooted. Nevertheless, deeper rooting was correlated with less root biomass production relative to total biomass. Compared with wild types, domesticated types showed a stronger reduction and delay in growth and development in response to drought stress. Specific genomic regions were associated with root depth, biomass productivity and drought response, some of which showed signals of selection and were previously related to productivity and drought tolerance.ConclusionsThe drought tolerance of wild beans consists in its stronger ability, compared with domesticated types, to continue growth in spite of water-limited conditions. This study is the first to relate bean response to drought to environment of origin for a diverse selection of wild beans. It provides information that needs to be corroborated in crosses between wild and domesticated beans to make it applicable to breeding programmes.

Limited rainfall is the main constraint to agriculture, making agricultural research to understand plant behaviour that leads to avoidance of soil water deficit a matter of priority. One focus has screened for crop varieties that decrease stomatal conductance under high vapour pressure deficit (VPD), a proxy for the leaf evaporative gradient. However, the link between stomatal closure and physiological consequences in field environments is not yet clear. A field experiment on soybeans demonstrated that considerable variation in leaf temperature relative to air temperature occurred, leading to evaporative gradients differing substantially from VPD. Thus, transpiration is decreased by stomatal closure at high VPD, but to compensate, transpiration is somewhat increased due to higher leaf temperatures. Soil water deficit led to lower stomatal conductance, particularly under low evaporative conditions, not just under hot conditions. Non-stomatal photosynthetic limitations were observed due to combined occurrence of stomatal closure and high temperature under high VPD. Although leaves reached temperatures higher than the threshold for a decrease in maximum photochemical efficiency, and displayed non-stomatal photosynthetic limitations, no photoinhibition or damage was observed by night-time. The results demonstrate that more understanding of physiological strategies for achieving altered water use is needed to avoid trade-offs and heat stress.

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Arch Argent Pediatr 2013;111(2):e46-e49 / e46Presentación de casos clínicos RESUMEN Se presenta el caso de una adolescente con colitis isquémica, patología poco frecuente en este grupo etario, que se agrava ante la presencia del lupus eritematoso sistémico (LES). Una paciente de 20 años, con diagnóstico de LES desde los 6 años, consultó por fiebre, dolor abdominal en el flanco y la fosa ilíaca derecha, y diarrea de 48 hs de evolución. Se asumió como gastroenteritis aguda pero, ante la persistencia del dolor, la aparición de vómitos incoercibles y la distensión abdominal, se decidió su internación. La radiografía de abdomen mostró asas distendidas, abundante materia fecal, sin niveles hidroaéreos. La ecografía mostró erosiones y ulceraciones, edema y hemorragia en la submucosa del colon descendente. La tomografía computarizada (TC) evidenció una lesión isquémica en el colon derecho. La colitis isquémica es una patología grave, infrecuente en los jóvenes. Los signos y síntomas, la TC de abdomen y la colonoscopia son los elementos de elección para el diagnóstico. Palabras clave: adolescencia, colitis isquémica, LES, tomografía computarizada de abdomen. SUMMARYWe present the case of an adolescent with ischemic colitis, an infrequent pathology in this age group, worsened in the presence of systemic lupus erythematosus (SLE). The patient, aged 20, was diagnosed SLE at 6. She consulted for fever, abdominal pain in the side and right iliac fossa and diarrhea lasting 48 hours. It was assumed as acute gastroenteritis but given the persistent pain, incoercible vomiting and abdominal distension she was hospitalized. The abdominal X-ray showed distended loops, abundant feces, without airfluid levels. The ultrasound showed erosions and ulcerations, edema and bleeding in the descending colon submucosal layer. The CT scan evidenced an ischemic lesion in the right colon. Ischemic colitis is a severe condition, infrequent in young individuals. Signs, symptoms, abdominal CT scan and colonoscopy are the elements of choice for the diagnosis.