Photosynthetic limitations in two Antarctic vascular plants: importance of leaf anatomical traits and Rubisco kinetic parameters

Abstract

Antarctic vascular plants show restrictions in mesophyll CO2 conductance due to morphological leaf adaptations to deal with the harsh climate. Rubisco kinetic parameters, however, compensate by optimizing photosynthesis and carbon balance.

How do vascular plants perform photosynthesis in extreme environments? An integrative ecophysiological and biochemical story

“…Therefore, plants that are adapted to extremely xeric and warm ecosystems show higher RuBisCO CO 2 affinity and specificity (Galmés et al , ; Galmés et al , ), which may partially compensate for a lower RuBisCO content due to nitrogen limitation. A similar trend has been reported for Antarctic plants, which also show a higher k cat c (Sáez et al , ), leading to an even higher carboxylase catalytic efficiency under air conditions than those reported for species from xeric habitats (Galmés et al , ). Taken together, these results suggest that the combination of extreme temperatures and low CO 2 concentrations inside the chloroplast has strongly shaped RuBisCO evolution in plants living in extreme environments.…”

“…It has also been related to the ultrastructural observation that chloroplasts, mitochondria, and microbodies (peroxisomes) are often observed in close proximity (Lütz, ). Additionally, it has been associated with the plastid protrusions observed in alpine plants (Lütz and Engel, ; Moser et al , ; see Section Photobiochemistry), a phenomenon that is likely related to the lower CO 2 partial pressure and leaf development under low temperatures, which often decrease mesophyll conductance ( g m ) and CO 2 assimilation in alpine plants (Saéz et al , ). However, in the Andes mountains of central Chile, where severe drought conditions are observed at the end of the growing season (Mediterranean‐like climate), photorespiration diminishes with elevation in natural populations of P. secunda , but rises after exposure to in situ warming under open top chambers (OTCs), mainly at a lower elevation (Hernández‐Fuentes et al , ).…”

“…The only two native vascular plants of Antarctica (Figure c) have been extensively studied in terms of temperature, water availability and nutrient deficiency (Sáez et al , , ,b; Clemente‐Moreno et al , , ). Interestingly, for both species, g m is the most important limitation under low temperature, drought and nutrient deficiency, as has been previously reported for species from semiarid‐arid environments (Galmés et al , ).…”

“…A higher electron sink capacity might be attained by an increased ratio of unsaturated fatty acids in thylakoid membranes, leading to the stabilization of transmembrane photosynthetic proteins (Falcone et al , ; Burgos et al , ), and by an increased concentration and activation state of CBC enzymes (Yamori et al , ), specially Rubisco (Savitch et al , ; Yamori et al , ; Jaikumar et al , ). Moreover, adaptations in RuBisCO kinetics through increased k cat c and carboxylation catalytic efficiency ( k cat c / K c ) have been reported in plants inhabiting cold ecosystems (Sage, ; Sáez et al , ). Indeed, the highest k cat c ever reported for a C 3 plant was observed in the Arctic–sub‐Arctic grass Arctagrostis latifolia (Orr et al , ).…”

Beyond Porosity: 3D Leaf Intercellular Airspace Traits That Impact Mesophyll Conductance

“…C3 plants, on the other hand, tend toward 89 smaller cell sizes, which presumably facilitates greater mesophyll surface exposure to 90 the IAS, allowing more efficient carbon fixation by Rubisco (Maxwell et al, 1997; 91 Griffiths et al, 2008). Lower leaf porosity, more typically associated with CAM 92 metabolism but observed in some C3 plants, lowers the conductance to gas diffusion in 93 the airspace, most often through lower exposure of mesophyll cells to the IAS (Galmés 94 et al, 2013;Sáez et al, 2017). Thus, CAM plants must maintain a trade-off that 95 maximizes vacuolar CO 2 storage capacity via tight cell-packing, while avoiding 96 excessive diffusional costs as the IAS simultaneously shrinks.…”