[en] The aim of this study was to investigate pigment degradation, chlorophyll fluorescence diminution, photosynthetic ability and growth reduction in two rice cultivars, in response to either iso-osmotic salt stress or water-deficit stress. Seedlings of rice cultivars RD6 and KDML105 were photo-autotrophically grown in MS media and subsequently exposed to –0.23 (control), –0.40 or –0.67 MPa iso-osmotic NaCl (salt stress) or mannitol (water-deficit stress) for 14 days. The survival percentage of the two rice cultivars reduced dramatically when subjected to –0.67 MPa NaCl treatment. Chlorophyll a (Chla), chlorophyll b (Chlb), total carotenoids (Cx+c), maximum quantum yield of PSII (Fv/Fm) and photon yield of PSII (ΦPSII) in the stressed seedlings were significantly lower when compared to seedlings in the control group (without mannitol or NaCl), leading to low net-photosynthetic rate (Pn) and growth reduction. In addition, the growth characters of plantlets in the salt stress conditions were more sharply reduced, and the physiological changes greater than those in water-deficit stress conditions. On the other hand, non-photochemical quenching in the leaves of stressed plantlets increased significantly, especially in response to iso-osmotic salt stress. In the present study, overall growth performance and physiological characters of KDML105 grown under iso-osmotic stress were better than those of RD6.

[es] El objetivo de este estudio fue investigar la degradaci&oacute;n de pigmentos, la disminuci&oacute;n de la fluorescencia de la clorofila, la capacidad fotosint&eacute;tica y la reducci&oacute;n en el crecimiento de dos cultivares de arroz, en respuesta al estr&eacute;s salino iso-osm&oacute;tico o h&iacute;drico. Se cultivaron de forma foto-autotr&oacute;fica en medio MS pl&aacute;ntulas de los cultivares RD6 y KDML105 y posteriormente se expusieron durante 14 d&iacute;as a NaCl (estr&eacute;s salino) o manitol (estr&eacute;s h&iacute;drico) iso-osm&oacute;tico &ndash;0,23 (control), &ndash;0,40 &oacute; &ndash;0,67 MPa. El porcentaje de supervivencia de los dos cultivares de arroz se redujo dr&aacute;sticamente con el tratamiento de NaCl 0,67 MPa. La clorofila a (Chla), clorofila b (Chlb), carotenoides totales (Cx+c), rendimiento cu&aacute;ntico m&aacute;ximo del PSII (Fv/Fm) y el rendimiento de fotones del PSII (&Phi;PSII) fueron significativamente menores en las pl&aacute;ntulas estresadas respecto a las pl&aacute;ntulas del grupo control (sin manitol o NaCl), lo que les llev&oacute; a una baja tasa de fotos&iacute;ntesis neta (Pn) y a una reducci&oacute;n del crecimiento. Adem&aacute;s, el crecimiento de las pl&aacute;ntulas bajo estr&eacute;s salino se redujo dr&aacute;sticamente y los cambios fisiol&oacute;gicos fueron mayores que bajo estr&eacute;s h&iacute;drico. Por otra parte, el amortiguamiento no fotoqu&iacute;mico (NPQ) en las hojas de las pl&aacute;ntulas estresadas aument&oacute; considerablemente, especialmente en respuesta al estr&eacute;s salino iso-osm&oacute;tico. En este estudio, los caracteres de crecimiento y fisiol&oacute;gicos en conjunto de KDML105 cultivados bajo estr&eacute;s iso-osm&oacute;tico fueron mejores que los de RD6.