Heat shock response in tomato brassinosteroid mutants indicates that thermotolerance is independent of brassinosteroid homeostasis.

Brassinosteroids (BRs) are plant steroid hormones and, when applied exogenously, they induce physiological responses, including tolerance to heat shock (HS). How endogenous BR content and altered perception of BRs influence thermal tolerance is poorly understood. BR-induced thermotolerance in tomato seedlings with altered BR homeostasis was examined by assessing the survival, ion leakage and lipid peroxidation of seedlings from a BR-deficient mutant (extreme dwarf d(x)), a partially BR-insensitive mutant curl3(-abs) allele (curl3 altered brassinolide sensitivity) and a line overexpressing the Dwarf, BR-biosynthesis gene (35SD). We confirmed that treatment with 1 µM of epi-brassinolide (EBL) induces thermotolerance of wild type seedlings following a HS regime at 45 °C. The curl3(-abs) seedlings had the highest basal tolerance to heat, whereas the EBL-induced thermal tolerance of d(x) seedlings was greatest and responded to lower EBL concentrations. The d(x) and 35SD seedlings had similar thermal tolerance; however, they showed increased signs of oxidative stress. EBL reduced the induction of lipid peroxidation of seedlings after recovery from heat. Highest oxidative stress and peroxidase (POX) activity (EC 1.11.1.7) was in BR-deficient d(x) mutant seedlings. EBL was able of inducing POX activity but not other antioxidant enzymes; however, effects of HS on POX activity of seedlings were absent or less marked. Taking together, results indicate that thermal tolerance is independent of endogenous BR content, but HS-mediated oxidative stress depends on BR levels.

Influencia de la época del año en la respuesta in vitro del cafeto Coffea canephora P Var Robusta / Influence of the time of year on the in vitro response of Coffea canephora P Var Robusta coffee trees

Generalmente, las plantas responden de manera diferenciada a las técnicas de cultivo in vitro, dependiendode la respuesta inicial del cultivo y su capacidad embriogénica del genotipo, el estado fisiológico de la planta yel explante, la edad de la planta donante, los factores físicos, los reguladores del crecimiento y las condiciones nutricionales, así como el cambio estacional. De aquí que el presente estudio se realizó con el objetivo de evaluar la influencia de la época del año en que fue tomada la fuente de los explantes en la respuesta in vitro de genotipos de Robusta. Se realizaron muestreos durante todos los meses del año, los explantes foliares fueron cultivados en un medio contentivo de las sales minerales de Murashige y Skoog (1962) y 0,5 y 2,0 mg.L-1 de 2,4-D y kinetina, respectivamente. Se observó que la época del año en que se tomó la muestra ejerció un marcado efecto en la respuesta de los explantes de los genotipos evaluados. Para las condiciones estudiadas resultó favorable la toma de las muestras foliares en los períodos mayo-junio, enero-febrero y noviembre-diciembre, dados los bajos índices de actividad enzimática peroxidasa, oxidación fenólica y contaminación fúngica, así como un elevado porcentaje de formación de callos y mayor contenido de proteínas totales presentes en los mismos. Se determinó que la actividad enzimática peroxidasa pudiera constituir un importante marcador en la etapa inicial de selección de las muestras.

Plants generally respond in different ways to in vitro cultivation techniques, depending on the crop’s initial response and the embryogenic capacity of its genotype, the physiological state of the plant and the explant, the age of the donor plant, physical factors, growth regulators, nutritional conditions and seasonal change. The present study was thus aimed at evaluating the influence of the time of year during which the source of explants was taken on the in vitro response of Robusta genotypes. Samples were taken during each month ofthe year, foliar explants were cultured in a medium containing Murashige and Skoog mineral salts (1962) and 0,5 and 2,0 mg.L-1 2,4-D and kinetine, respectively. It was observed that the time of the year when a sample was taken exercised as marked effect on the response of the explants from the genotypes evaluated. Taking foliar samples during May-June, January-February and November-December proved favourable in the conditions studied here given the low indices of peroxidase enzymatic activity, phenol oxidation and fungal contamination, as well as the high percentage of callus formation and their greater total protein content. It was determined that peroxidase enzymatic activity could constitute an important marker during the initial stage of selecting samples.