College of Agricultural and Biological Science, Shanghai Jiao Tong University, China.
Physiol Plant. 2010 May;139(1):93-106. doi: 10.1111/j.1399-3054.2010.01350.x. Epub 2010 Jan 13.
Stomatal closure and metabolic impairment under drought stress limits photosynthesis. The objective of this study was to determine major stomatal and metabolic factors involved in photosynthetic responses to drought and recovery upon re-watering in a C(3) perennial grass species, Kentucky bluegrass (Poa pratensis L.). Two genotypes differing in drought resistance, 'Midnight' (tolerant) and 'Brilliant' (sensitive), were subjected to drought stress for 15 days and then re-watered for 10 days in growth chambers. Single-leaf net photosynthetic rate (A), stomatal conductance (g(s)) and transpiration rate (Tr) decreased during drought, with a less rapid decline in 'Midnight' than in 'Brilliant'. Photochemical efficiency, Rubisco activity and activation state declined during drought, but were significantly higher in 'Midnight' than in 'Brilliant'. The relationship between A and internal leaf CO(2) concentration (A/Ci curve) during drought and re-watering was analyzed to estimate the relative influence of stomatal and non-stomatal components on photosynthesis. Stomatal limitation (Ls %), non-stomatal limitation (Lns %), CO(2) compensation point (CP) and dark respiration (Rd) increased with stress duration in both genotypes, but to a lesser extent in 'Midnight'. Maximum CO(2) assimilation rate (A(max)), carboxylation efficiency (CE) and mesophyll conductance (g(m)) declined, but 'Midnight' had significantly higher levels of A(max), CE and g(m) than 'Brilliant'. Maximum carboxylation rate of Rubisco (V(cmax)) and ribulose-1,5-bisphospate (RuBP) regeneration capacity mediated by maximum electron transport rate (J(max)) decreased from moderate to severe drought stress in both genotypes, but to a greater extent in 'Brilliant' than in 'Midnight'. After re-watering, RWC restored to about 90% of the control levels in both genotypes, whereas A, g(s), Tr and Fv/Fm was only partially recovered, with a higher recovery level in 'Midnight' than in 'Brilliant'. Rubisco activity and activation state restored to the control level after re-watering, with more rapid increase in 'Midnight' than in 'Brilliant'. The values of Ls, Lns, CP and Rd declined, and A(max), CE, V(cmax), J(max) and g(m) increased after re-watering, with more rapid change in all parameters in 'Midnight' than in 'Brilliant'. These results indicated that the maintenance of higher A and A(max) under drought stress in drought-tolerant Kentucky bluegrass could be attributed to higher Rubico activation state, higher CE and less stomatal limitation. The ability to resume metabolic activity (A(max), CE, Fv/Fm and Rubisco) was observed in the drought-tolerant genotype and is the most likely cause for the increased recuperative ability of photosynthesis. Incomplete recovery of photosynthesis upon re-watering could be attributable to lasting stomatal limitations caused by severe drought damage in both genotypes. Promoting rapid stomatal recovery from drought stress may be critical for plants to resume full photosynthetic capacity in C(3) perennial grass species.
在干旱胁迫下，气孔关闭和代谢损伤限制了光合作用。本研究的目的是确定参与光合作用对干旱响应的主要气孔和代谢因素，以及在 C(3)多年生草种肯塔基蓝草（Poa pratensis L.）重新浇水后的恢复情况。两种抗旱性不同的基因型“Midnight”（耐受）和“Brilliant”（敏感）在生长室中经历了 15 天的干旱胁迫，然后再浇水 10 天。在干旱过程中，单叶净光合速率（A）、气孔导度（g(s)）和蒸腾速率（Tr）下降，“Midnight”的下降速度比“Brilliant”慢。光化学效率、Rubisco 活性和激活状态在干旱过程中下降，但在“Midnight”中显著高于“Brilliant”。在干旱和重新浇水过程中，通过分析 A 与内部叶内 CO(2)浓度（A/Ci 曲线）之间的关系，来估计气孔和非气孔成分对光合作用的相对影响。在两个基因型中，随着胁迫时间的延长，气孔限制（Ls %）、非气孔限制（Lns %）、CO(2)补偿点（CP）和暗呼吸（Rd）均增加，但“Midnight”的增加程度较小。最大 CO(2)同化率（A(max)）、羧化效率（CE）和叶肉导度（g(m)）下降，但“Midnight”的 A(max)、CE 和 g(m)水平明显高于“Brilliant”。在两个基因型中，Rubisco 的最大羧化速率（V(cmax)）和由最大电子传递速率介导的核酮糖-1,5-二磷酸（RuBP）再生能力（J(max)）均从中度干旱胁迫下降到严重干旱胁迫，但在“Brilliant”中下降幅度大于“Midnight”。重新浇水后，两种基因型的 RWC 恢复到对照水平的 90%左右，而 A、g(s)、Tr 和 Fv/Fm 仅部分恢复，“Midnight”的恢复水平高于“Brilliant”。重新浇水后，Rubisco 活性和激活状态恢复到对照水平，“Midnight”的恢复速度快于“Brilliant”。重新浇水后，Ls、Lns、CP 和 Rd 值下降，A(max)、CE、V(cmax)、J(max)和 g(m)值增加，且“Midnight”的所有参数变化速度均快于“Brilliant”。这些结果表明，在耐旱肯塔基蓝草中，干旱胁迫下维持较高的 A 和 A(max)可能归因于较高的 Rubisco 激活状态、较高的 CE 和较低的气孔限制。在耐旱基因型中观察到代谢活性（A(max)、CE、Fv/Fm 和 Rubisco）的恢复能力，这可能是光合作用恢复能力增强的最可能原因。重新浇水后光合作用不完全恢复可能归因于两个基因型严重干旱损伤引起的持续气孔限制。促进气孔从干旱胁迫中快速恢复可能是 C(3)多年生草本植物恢复完全光合作用能力的关键。
