C₃ photosynthesis in the desert plant Rhazya stricta is fully functional at high temperatures and light intensities

Abstract

Summary The C3 plant Rhazya stricta is native to arid desert environment zones, where it experiences daily extremes of heat, light intensity (PAR) and high vapour pressure deficit (VPD). We measured the photosynthetic parameters in R. stricta in its native environment to assess the mechanisms that permit it to survive in these extreme conditions. Infrared gas exchange analysis examined diel changes in assimilation (A), stomatal conductance (gs) and transpiration (E) on mature leaves of R. stricta. A/ci analysis was used to determine the effect of temperature on carboxylation capacity (Vc,max) and the light‐ and CO2‐saturated rate of photosynthesis (Amax). Combined chlorophyll fluorescence and gas exchange light response curve analysis at ambient and low oxygen showed that both carboxylation and oxygenation of Rubisco acted as the major sinks for the end products of electron transport. Physiological analysis in conjunction with gene expression analysis suggested that there are two isoforms of Rubisco activase which may provide an explanation for the ability of R. stricta to maintain Rubisco function at high temperatures. The potential to exploit this ability to cope with extreme temperatures is discussed in the context of future crop improvement.

Analysis of transcriptional response to heat stress in Rhazya stricta

“…Sugar phosphates are known for their action in retarding photosynthesis as they bind to Rubisco and prevent the carbamylation process [42]. The results of the present study support the results of Lawson et al [39] because we detected a gene encoding rubisco subunit binding-protein alpha that was upregulated in the two leaf types during midday (Fig. 5).…”

“…Lawson et al [39] found evidence for thermotolerance while studying photosynthetic capacity in R. stricta at the same time period and under the same field conditions as our study. The evidence involved the occurrence of a maximum in vivo carboxylation capacity of the thermostable Rubisco [40] (up to 50 °C).…”

Time-Series Transcriptomics Reveals That AGAMOUS-LIKE22 Affects Primary Metabolism and Developmental Processes in Drought-Stressed Arabidopsis

“…In addition, maximum and operating efficiencies of photosystem II photochemistry ( Figure 2B), photochemical and nonphotochemical quenching (Supplemental Figure 1D), were maintained throughout the drying period despite a decline in carbon assimilation (Figures 1D), indicating very little stress on photosystem II. This suggested that an alternative electron sink, most likely photorespiration (reviewed in Chaves et al, 2003;Lawson et al, 2014), must have been operating under drought stress, and increased gene expression in the photorespiratory pathway supports this notion ( Figure 5C). …”

Description and Validation of the Simple, Efficient, Dynamic, Global, Ecological Simulator (SEDGES v.1.0)

“…Lawson et al, 2014). Moreover, its (ordinary) daily photosynthetic rates are nearly as high as those of common C3 agricultural crops, in spite of living under natural conditions of much higher vapor pressure deficit and presumably much drier soil (Lawson et al, 2014), which reduce productivity. Similar results as for Rhazya stricta have been found for the C3 desert 5 shrub, Larrea divaricata (Mooney et al, 1978).…”