No abstract

Brassinosteroids (BS) application is associated with the increase of tolerance to some kinds of stresses, such as those induced by the infection of pathogens, temperature, salt and water deficiency. In this work, the influence of a spirostanic analogue of brassinosteroid (SAB) in the leaves of papaya Golden and UENF/CALIMAN 01 (UC 01) was tested to evaluate alterations in the content of chlorophyll in plants submitted to drought stress (DS). When plants were 70 d old, SAB was applied (0,1 mg L-1) for five consecutive days in half of the plants meant for the experiment. The treatments were: control irrigated (I), I with SAB (IB), DS and DS with SAB (DSB). The evaluated leaves were marked in accordance to the age: LEAF 1 (youngest expanded leaf), LEAF 2 (insertion immediately below LEAF 1) and LEAF 3 (insertion immediately below LEAF 2). The same leaves were used throughtout the experimental period. After the thirteenth day, the chlorophyll contents of DSB (Golden and UC 01) were always lesser than the treatment DS in LEAF 2. The irrigation was restarted in stressed plants on the fifteenth day, followed by new application of SAB (IB and DSB treatments). In Golden plants, DSB showed the lowest values of chlorophyll contents after re-watering, while in UC 01, differences in chlorophyll contents between treatments DS and DSB had not occurred. Alterations in F v /F m relation did not occur among the treatments during stress. In genotype UC 01, the irrigated plants showed minor values of F v /F m at the end of the experiment, whereas the plants submitted to DS presented increments in this relation in this same time. These results indicate that SAB might have contributed to accelerate the rate of leaf senescence of the oldest leaves of stressed plants, redistributing photoassimilates and other compounds for the youngest leaves.

La salinidad del suelo es una de las principales limitaciones que afectan la producción de arroz en todo el mundo. Se espera que este estrés se intensifique cada vez más debido al cambio climático que se está presentando a nivel global. El arroz es uno de los cereales más importantes y alimenta a más del 50 % de la población mundial. Para satisfacer la demanda del aumento de la población la producción de arroz debe mejorarse continuamente y para ello, una de las estrategias para reducir los daños que provoca la salinidad es el uso de productos bioactivos que sean amigables con el medio ambiente. La presente revisión recopila información actualizada sobre los efectos que el estrés salino provoca en las plantas de arroz, haciendo énfasis en su influencia en el sistema radical de estas plantas, teniendo en cuenta las múltiples funciones que las raíces desempeñan; además, se discuten las potencialidades de los oligogalacturónidos como posibles protectores de las plantas al estrés por salinidad. Estos compuestos, que se obtienen a partir de la pectina de la corteza de los frutos, han demostrado su efecto estimulante en el enraizamiento, el crecimiento y la diferenciación de diferentes especies vegetales.