Stomata control the gas exchange of terrestrial plant leaves, and are therefore essential to plant growth and survival. We investigated gas exchange responses to vapor pressure deficit (VPD) in two gray poplar (Populus × canescens) lines: wild type and abscisic acid-insensitive (abi1) with functionally impaired stomata. Transpiration rate in abi1 increased linearly with VPD, up to about 2 kPa. Above this, sharply declining transpiration was followed by leaf death. In contrast, wild type showed a steady or slightly declining transpiration rate up to VPD of nearly 7 kPa, and fully recovered photosynthetic function afterward. There were marked differences in discrimination against 13CO2 (Δ13C) and C18OO (Δ18O) between abi1 and wild-type plants. The Δ13C indicated that intercellular CO2 concentrations decreased with VPD in wild-type plants, but not in abi1 plants. The Δ18O reflected progressive stomatal closure in wild type in response to increasing VPD; however, in abi1, stomata remained open and oxygen atoms of CO2 continued to exchange with 18O enriched leaf water. Coupled measurements of Δ18O and gas exchange were used to estimate intercellular vapor pressure, e i In wild-type leaves, there was no evidence of unsaturation of e i, even at VPD above 6 kPa. In abi1 leaves, e i approached 0.6 times saturation vapor pressure before the precipitous decline in transpiration rate. For wild type, a sensitive stomatal response to increasing VPD was pivotal in preventing unsaturation of e i In abi1, after taking unsaturation into account, stomatal conductance increased with increasing VPD, consistent with a disabled active response of guard cell osmotic pressure.

中文翻译：

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蒸气压不足对野生型和脱落酸不敏感植物气体交换的影响。


气孔控制着陆地植物叶子的气体交换，因此对于植物的生长和生存至关重要。我们研究了两种灰杨（Populus × canescens）品系对蒸气压不足（VPD）的气体交换反应：野生型和气孔功能受损的脱落酸不敏感（abi1）。 abi1 中的蒸腾速率随 VPD 线性增加，最高可达约 2 kPa。高于此值，蒸腾作用急剧下降，随后叶片死亡。相比之下，野生型在VPD接近7kPa时蒸腾速率稳定或略有下降，随后完全恢复光合功能。 abi1 和野生型植物对 13CO2 (Δ13C) 和 C18OO (Δ18O) 的辨别力存在显着差异。 Δ13C 表明，在野生型植物中，细胞间 CO2 浓度随着 VPD 的增加而降低，但在 abi1 植物中则不然。 Δ18O 反映了野生型中随着 VPD 的增加而逐渐关闭的气孔；然而，在 abi1 中，气孔保持开放，CO2 的氧原子继续与富含 18O 的叶水交换。 Δ18O 和气体交换的耦合测量用于估计细胞间蒸气压 ei 在野生型叶片中，没有证据表明 ei 不饱和，即使在 VPD 高于 6 kPa 时也是如此。在abi1叶片中，ei在蒸腾速率急剧下降之前接近饱和蒸汽压的0.6倍。对于野生型，对 VPD 增加的敏感气孔反应对于防止 ei 不饱和至关重要。在 abi1 中，考虑不饱和度后，气孔导度随着 VPD 增加而增加，与保卫细胞渗透压的禁用主动反应一致。