Plant adaptation to dynamically changing environment: the shade avoidance response.

The success of competitive interactions between plants determines the chance of survival of individuals and eventually of whole plant species. Shade-tolerant plants have adapted their photosynthesis to function optimally under low-light conditions. These plants are therefore capable of long-term survival under a canopy shade. In contrast, shade-avoiding plants adapt their growth to perceive maximum sunlight and therefore rapidly dominate gaps in a canopy. Daylight contains roughly equal proportions of red and far-red light, but within vegetation that ratio is lowered as a result of red absorption by photosynthetic pigments. This light quality change is perceived through the phytochrome system as an unambiguous signal of the proximity of neighbors resulting in a suite of developmental responses (termed the shade avoidance response) that, when successful, result in the overgrowth of those neighbors. Shoot elongation induced by low red/far-red light may confer high relative fitness in natural dense communities. However, since elongation is often achieved at the expense of leaf and root growth, shade avoidance may lead to reduction in crop plant productivity. Over the past decade, major progresses have been achieved in the understanding of the molecular basis of shade avoidance. However, uncovering the mechanisms underpinning plant response and adaptation to changes in the ratio of red to far-red light is key to design new strategies to precise modulate shade avoidance in time and space without impairing the overall crop ability to compete for light.

Estudio retrospectivo sobre las posibles complicaciones maternofetales de la exposición a cabergolina / Retrospective Study of any potencial Adverse Effects of Cabergoline on Pregnancy and Embryofetal Development

Objetivos: Estimar la frecuencia de complicaciones maternofetales en mujeres que se embarazaron durante el tratamiento con cabergolina (CAB). Estimar la frecuencia de patología detectada posnacimiento en los niños producto de dichos embarazos. Material y métodos: Estudio retrospectivo y multicéntrico de 86 embarazos en 78 mujeres con hiperprolactinemia idiopática (7) o tumoral (44 micro y 27 macro), en tratamiento con CAB en el momento de la concepción. Edad: 20 a 45 años; PRL inicial: 30 a 1429 ng/ml; duración del tratamiento previo al embarazo 1 a 120 meses; dosis: 0.125 a 4 mg/semana. El rango de exposición embriofetal a la CAB fue de 3 a 27 semanas, el 96.39% de las pacientes la recibió durante el primer trimestre y el 3.61% hasta el segundo. Resultados: No hubo complicaciones mayores durante el embarazo. Se registraron 7 abortos espontáneos (8.1%) y 75 partos, de los cuales 49 fueron vaginales y 26 cesáreas. Se registraron 69 recién nacidos, 63 fueron a término y 6 pretérmino (8.8%), ninguno bajo peso para la edad gestacional. En 3 (5.2%) recién nacidos se observó: 1 malformación mayor (Síndrome de Down) y 2 menores (hernia umbilical e inguinal). Se obtuvo seguimiento de 42 recién nacidos; se diagnosticó epilepsia refractaria en uno y un trastorno generalizado del desarrollo en otro. No se halló una mayor frecuencia de complicaciones en los embarazos ni en los recién nacidos expuestos a CAB que en la población normal. Sería necesario mayor número de pacientes para concluir sobre la seguridad de CAB durante el embarazo.

Objectives: To assess the rate of any potential adverse effects on pregnancy and embryo-fetal development in women who became pregnant under treatment with cabergoline (CAB). To follow up medical data of children who were born from mothers exposed to Cab in early weeks of gestation. Material and methods: Observational, retrospective and multicenter study on 86 pregnancies in 78 women with idiopathic or tumoral hyperprolactinemia. All patients were under Cab at conception. The average age was 29 (range: 20-45). Pituitary images at diagnosis showed 44 microadenomas, 27 macroadenomas and 7 were normal. Serum PRL at baseline was between 30 and 1429 ng/ml. Duration of therapy before pregnancy ranged from 1 to 120 months. Maternal and fetal exposure to cabergoline and doses ranged from 0.125 to 4 mg/week. The mean serum PRL level under which patients achieved pregnancy was 17 ng/ml. Fetal exposure ranged from 3 to 27 weeks; 96.39% of patients received CAB during the first trimester of pregnancy and 3.61% until the second one. Results: No significant complications during pregnancy were found. Seven women (8.1%) had spontaneous abortions. Term deliveries were recorded in 63/69, preterm in six (8.8%), none of them with low weight for gestational age. Neonatal abnormalities were observed in 3 (5.2%): 1 major (Down syndrome) and 2 minor malformations (umbilical and inguinal hernia). Two out of 42, developed abnormalities during the follow- up, one of them was a refractory epilepsy during the second month of life, the other presented a Pervasive Developmental Disorder diagnosed in the third year of life. Conclusion: No significantly higher frequency of complications was found in pregnancies and/or offspring exposed to CAB than in normal population. Larger series of patients are needed to asses the safety.

Twilight-zone and canopy shade induction of the Athb-2 homeobox gene in green plants.

We present evidence that a novel phytochrome (other than phytochromes A and B, PHYA and PHYB) operative in green plants regulates the "twilight-inducible" expression of a plant homeobox gene (Athb-2). Light regulation of the Athb-2 gene is unique in that it is not induced by red (R)-rich daylight or by the light-dark transition but is instead induced by changes in the ratio of R to far-red (FR) light. These changes, which normally occur at dawn and dusk (end-of-day FR), also occur during the daytime under the canopy (shade avoidance). By using pure light sources and phyA/phyB null mutants, we demonstrated that the induction of Athb-2 by changes in the R/FR ratio is mediated for the most part by a novel phytochrome operative in green plants. Furthermore, PHYB plays a negative role in repressing the accumulation of Athb-2 mRNA in the dark and a minor role in the FR response. The strict correlation of Athb-2 expression with FR-induced growth phenomena suggests a role for the Athb-2 gene in mediating cell elongation. This interpretation is supported by the finding that the Athb-2 gene is expressed at high levels in rapidly elongating etiolated seedlings. Furthermore, as either R or FR light inhibits cell elongation in etiolated tissues, they also down-regulate the expression of Athb-2 mRNA. Thus, these data support the notion that changes in light quality perceived by a novel phytochrome regulate plant development through the action of the Athb-2 homeobox gene.

Ectopic expression of the Arabidopsis transcriptional activator Athb-1 alters leaf cell fate in tobacco.

The Arabidopsis thaliana Athb-1 is a homeobox gene of unknown function. By analogy with homeobox genes of other organisms, its gene product, Athb-1, is most likely a transcription factor involved in developmental processes. We constructed a series of Athb-1-derived genes to examine the roles of Athb-1 in transcriptional regulation and plant development. Athb-1 was found to transactivate a promoter linked to a specific DNA binding site by transient expression assays. In transgenic tobacco plants, overexpression of Athb-1 or its chimeric derivatives with heterologous transactivating domains of the yeast transcription factor GAL4 or herpes simplex virus transcription factor VP16 conferred deetiolated phenotypes in the dark, including cotyledon expansion, true leaf development, and an inhibition of hypocotyl elongation. Expression of Athb-1 or the two chimeric derivatives also affected the development of palisade parenchyma under normal growth conditions, resulting in light green sectors in leaves and cotyledons, whereas other organs in the transgenic plants remained normal. Both developmental phenotypes were induced by glucocorticoid in transgenic plants expressing a chimeric transcription factor comprising the Athb-1 DNA binding domain, the VP16 transactivating domain, and the glucocorticoid receptor domain. Plants with severe inducible phenotypes showed additional abnormality in cotyledon expansion. Our results suggest that Athb-1 is a transcription activator involved in leaf development.

The Arabidopsis Athb-2 and -4 genes are strongly induced by far-red-rich light.

The isolation and characterization of the Athb-2 gene, which codes for a HD-Zip protein in Arabidopsis thaliana is reported. Interestingly, Southern analysis has established that the Arabidopsis genome contains sequences which are highly related to the Athb-2 HD-Zip coding region. One of these genes, designated Athb-4, has been cloned and partially sequenced. Amino acid sequence comparison revealed that Athb-2 and -4 are members of a small family of HD-Zip related proteins. Athb-2 mRNA analysis showed that this gene is expressed during the vegetative and reproductive phases of plant growth. A significant increment in the amount of Athb-2 transcripts was observed in flowering plants. A higher steady-state level of the Athb-2 mRNA was also found in dark-adapted plants. Remarkably, far-red-rich light treatment of Arabidopsis plants results in a rapid and strong induction of the Athb-2 expression. This light treatment also induces the accumulation of Athb-4 transcripts, suggesting a similar role for the two members of this HD-Zip family.

[Enteroparasitoses in the V Region, Chile. A study of rural school children from Santo Domingo, 1987]. / Enteroparasitosis en la V Región, Chile. Estudio en escolares rurales de Santo Domingo, 1987.

The results of a new enteroparasitological survey carried out by the authors are analyzed with the aim of contributing to the knowledge of the situation of these infections in the V Region, Chile. In 1987 the children of five rural schools of Santo Domingo were studied by means of the modified Telemann method, the Ziehl-Neelsen stain and seried Graham test. The parasites more frequently found were: E. vermicularis (50.4%) and G. lamblia (10.8%). No E. histolytica was found in these children. The most frequent commensal was E. nana (21.9%). Cryptosporidium sp. presented a low frequency (0.9%), a figure that in these asymptomatic subjects is in accordance with that found in outpatients with chronic diarrhea in Valparaíso, V Region.

[Cryptosporidiosis in the V Region Chile. III. Study of malnourished patients, 1985-1987]. / Cryptosporidiosis en la V Región, Chile. III. Estudio en pacientes desnutridos, 1985-1987.

Frequency of infection by Cryptosporidium sp. in 1,039 faecal smears stained by Ziehl-Neelsen, obtained from undernourished patients of a Nutritional Recovery Center and an ambulatory undernourished center from the Fifth Region, Chile, were studied. All underwent a coproparasitological examination by the modified Telemann method. Thirty eight (3.7%) patients infected by the parasite were detected, with an overall frequency of 8.5% among patients of the Nutritional Recovery Center and 1.9% among the ambulatory patients; this difference was statistically significant. The highest percentage of positive results were detected among the younger milk feeding infants. Also the percentage of difference among these and the older milk feeding infants (3.7%) was statistically significant. Association of Cryptosporidium sp. and Giardia lamblia was observed in 6 ambulatory patients (2.3%).