3.2.1. Gas Exchange Attributes

Analysis of variance showed that TU priming significantly influenced the physiological parameters under different environmental conditions (Table 2). Among the gas exchange attributes, photosynthetic rate and stomatal conductance were decreased, while transpiration and intercellular CO2 rates were increased under heat stress conditions as compared to control–no stress. The photosynthetic rate was decreased by 41.2% in 8046 and 49.2% in 7126, respectively, while stomatal conductance was decreased by 19.4% in 8046 and 34.6% in camelina under heat stress over control–no stress. Maximum photosynthetic rate (6.94 μmol CO2 m−<sup>2</sup> s−1) and stomatal conductance (0.079 mol H2O m−<sup>2</sup> s−1) were noted with osmopriming, while a lower value of these attributes (2.04 μmol CO2 m−<sup>2</sup> s<sup>−</sup>1, and 0.04 mol H2O m−<sup>2</sup> s<sup>−</sup>1, respectively) was noted with control–no priming. Nevertheless, photosynthetic rate was improved by 44.3% in 8046 and 42% in 7126 with TU priming compared to control–no TU. Transpiration rate (0.68 mol H2O m−<sup>2</sup> s<sup>−</sup>1) was increased, and internal CO2 rate (344.4 μmol CO2 mol<sup>−</sup>1) was decreased with TU seed priming compared to control–no TU. In relation to camelina varieties, the 8046 variety was more tolerant to heat stress conditions compared to 7126 variety (Table 2). Among the varieties, higher values of photosynthetic rate (5.11 μmol CO2 m−<sup>2</sup> s−1) were noted in 8046, while lower values (3.67 μmol CO2 m−<sup>2</sup> s<sup>−</sup>1) were noted in 7126. Maximum values of gas exchange attributes including photosynthetic rate (7.45 μmol CO2 m−<sup>2</sup> s<sup>−</sup>1) were observed at TU2 (TU priming), T1 (22 ◦C), and V2, while minimum values of gas exchange attributes including photosynthetic rate (2.05 μmol CO2 m−<sup>2</sup> s<sup>−</sup>1) were observed at TU0 (control–no priming), T2 (32 ◦C), and V1 (7126). Among the seed priming, hydro-priming showed an increase of 18.07% in photosynthetic rate and TU–seed priming showed an increase of 43.3% in photosynthetic rate as compared to control–no priming



Values (mean ± standard error, *n* = *3*), TU0 = No thiourea priming, TU1 = Water priming, TU2 = Thiourea priming; LSD = least significant difference; values sharing same case letter or without lettering for a parameter do not differ significantly (*p* ≤ 0.05) by the LSD test.

> Among the interactions, all interactions were significant for the photosynthetic rate. TU × T was significant for photosynthetic rate and intercellular CO2 rates. The T × V interaction remained significant for intercellular CO2 rates. The higher-order interaction TU × T × V was significant for stomatal conductance.

### 3.2.2. Water Relations

Seed priming significantly affected the plant water relations under heat stress (Figures 1 and 2). Heat stress reduced the plant water relations including water potential, osmotic potential, pressure potential, and relative water content as compared to control–no stress. Water potential decreased by 30% in 8046 and 33.7% in 7126, respectively, and leaf relative water content was decreased by 25.6% in 8046 and 35.9% in 7126, respectively, under heat stress over control–no stress. High values of water potential (−0.80 MPa), osmotic potential, (−1.33 MPa), pressure potential (0.48 MPa), and relative water content (86.5%), respectively, were noted with osmo-priming (TU priming) compared to control–no TU applied (Figures 1 and 2). Nevertheless, the relative water content was improved by 13.6% and pressure potential was increased by 29.5% with TU priming compared to control–no TU. In relation to camelina varieties, the 8046 variety was more tolerant to heat stress conditions compared to 7126 variety (Figures 1 and 2). In addition, higher values of water potential (−1.00 MPa) were noted in 8046, while lower values (−1.09 MPa) were noted in 7126. Maximum values of gas exchange attributes including water potential (−0.79 MPa) were observed at TU2 (TU priming), T1 (22 ◦C) and V2, while minimum values of water relations including water potential (−1.32 MPa) were observed at TU0 (control–no priming), T2 (32 ◦C), and V1 (7126). Among the seed priming, hydro-priming showed an increase of 15.05% in relative water content and TU–seed priming showed an increase of 60.9% in relative water content as compared to control–no priming.

Among the interactions, TU × T was significant for osmotic potential. The T × V was significant for water potential and relative water content. The higher-order interaction TU × T × V was significant for water potential.
