Leaf chlorophyll fluorescence, hyperspectral reflectance, pigments content, malondialdehyde and proline accumulation responses of castor bean (Ricinus communis L.) seedlings to salt stress levels

Chinese castor bean (Ricinus communis L.) cultivation has expanded in coastal saline regions of Yancheng, city in Jiangsu province of China (120 degrees 13'E, 33 degrees 38'N), where salinity is an important factor limiting traditional crops distribution. In order to evaluate the effects of salt stress on Chinese castor bean, we measured response in selected indices to increasing levels of salt stress. These indices included leaf chlorophyll fluorescence, pigments content, hyperspectral reflectance, malondialdehyde (MDA) and proline accumulation in seedlings. In this study, seedlings of Chinese castor bean var. Zi Bi were cultured for a month with half-strength Hoagland nutrient solution, then subjected to four levels of salt stress induced by NaCl for 7 days, namely control (0 mM/L), low salt level (100 mM/L), middle salt level (200 mM/L) and high salt level (300 mM/L). Results show that all stress promoted a continuous increase in F-0, as well as continuous reduction in F-m. F-v/F-m, phi PSII and F-v/F-0 were highest at low salt level and lowest at high salt level. NPQ in stressed plants were all significantly higher than control. Most above indicators were significantly correlated (at the 0.05 and even 0.01 level of significance) to each other. Changes in pigments contents were similar to changes in most Chlorophyll fluorescence parameters. Variations in visible spectral properties (especially 400-680nm region) were proportional to leaf chlorophyll contents whereas reflectance in the infrared range were not. Both the BEP and REP were good indicators for measuring plant response to salt stress in this paper. Compared with control, MDA did not increase significantly while proline accumulation increased at middle salt level. All the above results indicated a certain salt tolerance for short time for this cultivar's seedlings. Furthermore, both chlorophyll fluorescence and hyperspectral reflectance at leaf scale can provide useful tools for non-destructive estimates of photosynthetic function. (C) 2009 Elsevier B.V. All rights reserved.