Effect of drought stress on the osmotic adjustment, cell wall elasticity and cell volume of six cultivars of common beans ( Phaseolus vulgaris L.)

Abstract

In the southern spring–summer season of 2001–2002 six cultivars (Orfeo, Arroz Tuscola, Barbucho, Coscorrón, Pinto and Tórtola) of common beans ( Phaseolus vulgaris L.) were grown under two frequencies of irrigation in the central zone of Chile. Control plants were irrigated every 7 days and water stress plants were irrigated every 21 days. Leaf water potential ( Ψ W), leaf relative water content (RWC), turgid weight to dry weight ratio (TW/DW), osmotic potential at full turgor ( ψ S 100 ), osmotic adjustment (OA), elasticity module of the cell wall ( ɛ) and cell size of the palisade and spongy tissue were evaluated at 74–76 days after sowing (DAS) in completely developed leaves. Water stressed plants showed lower Ψ W than in control plants in all the varieties with values that averaged −1.4 and −0.9 MPa, respectively. According to the Drought Resistance Index (DRI) calculated from field measurements, among the cultivars studied, Orfeo was the most resistant to water stress and Arroz Tuscola, the most susceptible. A close negative relationship between leaf TW/DW and DRI under water stress conditions was observed ( r 2 = 0.63). Leaf TW/DW decreased considerably with water stress in cultivar Orfeo (15%) but the decrease was higher in Tórtola (22%), and there was also a decrease (although smaller) in Pinto (11%). Arroz Tuscola under stress did not present an important change in TW/DW, but presented one of the highest values of TW/DW. There was a strong negative correlation between DRI and palisade cell size under water stress conditions ( r 2 = 0.85) and a strong positive one between palisade cell size and TW/DW ( r 2 = 0.86) thus higher DRI was associated with small palisade cell size and small TW/DW. The most resistant cultivar Orfeo did not show a decrease in ψ S 100 calculated from the pressure–RWC relationships and its resistance was not associated with maintenance of leaf TW/DW under water stress. ψ S 100 calculated from the pressure–RWC relationships decreased only in the cultivar Coscorrón. Cultivar Orfeo showed a strong decrease (35%) of ɛ, in association to a higher cell wall elasticity (CWE) and as consequence maintained better its cell turgescence but this was also the case of Tórtola (56%) and Pinto (34%) and to a lesser extent of Barbucho (18%). This was not the case for Arroz Tuscola where ɛ and CWE were not changed. These results suggest that CWE and to a lesser extent leaf TW/DW can be important components of the water stress adaptation mechanism in this specie that could contribute to the higher resistance to water stress of Orfeo compared to Arroz Tuscola.