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The use of low [CO 2 ] to estimate diffusional and non‐diffusional limitations of photosynthetic capacity of salt‐stressed olive saplings
Author(s) -
CENTRITTO M.,
LORETO F.,
CHARTZOULAKIS K.
Publication year - 2003
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.2003.00993.x
Subject(s) - photosynthesis , stomatal conductance , rubisco , chemistry , salt (chemistry) , horticulture , cultivar , botany , conductance , photosynthetic capacity , biology , mathematics , biochemistry , combinatorics
In this study it has been shown that increased diffusional resistances caused by salt stress may be fully overcome by exposing attached leaves to very low [CO 2 ] (∼ 50 µ mol mol −1 ), and, thus a non‐destructive‐ in vivo method to correctly estimate photosynthetic capacity in stressed plants is reported. Diffusional (i.e. stomatal conductance, g s , and mesophyll conductance to CO 2 , g m ) and biochemical limitations to photosynthesis ( A ) were measured in two 1‐year‐old Greek olive cultivars (Chalkidikis and Kerkiras) subjected to salt stress by adding 200 m m NaCl to the irrigation water. Two sets of A – C i curves were measured. A first set of standard A – C i curves (i.e. without pre‐conditioning plants at low [CO 2 ]), were generated for salt‐stressed plants. A second set of A – C i curves were measured, on both control and salt‐stressed plants, after pre‐conditioning leaves at [CO 2 ] of ∼ 50 µ mol mol −1 for about 1.5 h to force stomatal opening. This forced stomata to be wide open, and g s increased to similar values in control and salt‐stressed plants of both cultivars. After g s had approached the maximum value, the A – C i response was again measured. The analysis of the photosynthetic capacity of the salt‐stressed plants based on the standard A – C i curves, showed low values of the J max (maximum rate of electron transport) to V cmax (RuBP‐saturated rate of Rubisco) ratio (1.06), that would implicate a reduced rate of RuBP regeneration, and, thus, a metabolic impairment. However, the analysis of the A – C i curves made on pre‐conditioned leaves, showed that the estimates of the photosynthetic capacity parameters were much higher than in the standard A – C i responses. Moreover, these values were similar in magnitude to the average values reported by Wullschleger ( Journal of Experimental Botany 44, 907–920, 1993) in a survey of 109 C 3 species. These findings clearly indicates that: (1) salt stress did affect g s and g m but not the biochemical capacity to assimilate CO 2 and therefore, in these conditions, the sum of the diffusional resistances set the limit to photosynthesis rates; (2) there was a linear relationship ( r 2 = 0.68) between g m and g s , and, thus, changes of g m can be as fast as those of g s ; (3) the estimates of photosynthetic capacity based on A – C i curves made without removing diffusional limitations are artificially low and lead to incorrect interpretations of the actual limitations of photosynthesis; and (4) the analysis of the photosynthetic properties in terms of stomatal and non‐stomatal limitations should be replaced by the analysis of diffusional and non‐diffusional limitations of photosynthesis. Finally, the C 3 photosynthesis model parameterization using in vitro ‐measured and in vivo ‐measured kinetics parameters was compared. Applying the in vivo ‐measured Rubisco kinetics parameters resulted in a better parameterization of the photosynthesis model.