Diffusive and Metabolic Limitations to Photosynthesis under Drought and Salinity in C₃ Plants

Abstract

Drought and salinity are two widespread environmental conditions leading to low water availability for plants. Low water availability is considered the main environmental factor limiting photosynthesis and, consequently, plant growth and yield worldwide. There has been a long-standing controversy as to whether drought and salt stresses mainly limit photosynthesis through diffusive resistances or by metabolic impairment. Reviewing in vitro and in vivo measurements, it is concluded that salt and drought stress predominantly affect diffusion of CO(2) in the leaves through a decrease of stomatal and mesophyll conductances, but not the biochemical capacity to assimilate CO(2), at mild to rather severe stress levels. The general failure of metabolism observed at more severe stress suggests the occurrence of secondary oxidative stresses, particularly under high-light conditions. Estimates of photosynthetic limitations based on the photosynthetic response to intercellular CO(2) may lead to artefactual conclusions, even if patchy stomatal closure and the relative increase of cuticular conductance are taken into account, as decreasing mesophyll conductance can cause the CO(2) concentration in chloroplasts of stressed leaves to be considerably lower than the intercellular CO(2) concentration. Measurements based on the photosynthetic response to chloroplast CO(2) often confirm that the photosynthetic capacity is preserved but photosynthesis is limited by diffusive resistances in drought and salt-stressed leaves.

Differences in photosynthetic performance and its correlation with growth among tomato cultivars in response to different salts

“…Thus, we conclude that stomatal closure and increased mesophyll resistance initially limit photosynthesis due to CO 2 availability, but subsequently, this low CO 2 level can lead to leaf metabolism changes, as suggested by other authors [14]. The mechanisms that down-regulate g m under salinity are still unknown, although they may involve regulation of proteins like aquaporins or carbonic anhydrase.…”

Influência da sanidade e deficit hídrico na germinação de sementes de Carthamus tinctorius L.

“…Além disso, as sementes submetidas aos potenciais de -0,851 e -1,27 MPa não germinaram. Diversos autores (Ulisses et al, 2000;Zhu, 2001;Flexas et al, 2004;Ashraf e Foolad, 2007) de absorção de água e posteriormente uma diminuição na velocidade dos processos fisiológicos e bioquímicos (Flowers, 2004).…”

Physiology of cashew plants grown under adverse conditions

“…This could be due to stomatal closure that, in turn, reduces the availability of CO 2 inside the mesophyll cells, or due to non-stomatal limitations that diminishes the potential capacity of CO 2 assimilation (Lawlor, 2002;Flexas et al, 2004). Nevertheless, stomatal closure appears to be the principal cause of reduced photosynthetic rates (Flexas et al, 2004).…”