Acad. M. Popov Institute of Plant Physiology, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 21, Sofia 1113, Bulgaria.
Ann Bot. 2010 Jan;105(1):117-26. doi: 10.1093/aob/mcp274.
Haberlea rhodopensis is a perennial, herbaceous, saxicolous, poikilohydric flowering plant that is able to survive desiccation to air-dried state under irradiance below 30 micromol m-2 s-1. However, desiccation at irradiance of 350 micromol m-2 s-1 induced irreversible changes in the photosynthetic apparatus, and mature leaves did not recover after rehydration. The aim here was to establish the causes and mechanisms of irreversible damage of the photosynthetic apparatus due to dehydration at high irradiance, and to elucidate the mechanisms determining recovery.
Changes in chloroplast structure, CO2 assimilation, chlorophyll fluorescence parameters, fluorescence imaging and the polypeptide patterns during desiccation of Haberlea under medium (100 micromol m-2 s-1; ML) irradiance were compared with those under low (30 micromol m-2 s-1; LL) irradiance.
Well-watered plants (control) at 100 micromol m-2 s-1 were not damaged. Plants desiccated at LL or ML had similar rates of water loss. Dehydration at ML decreased the quantum efficiency of photosystem II photochemistry, and particularly the CO2 assimilation rate, more rapidly than at LL. Dehydration induced accumulation of stress proteins in leaves under both LL and ML. Photosynthetic activity and polypeptide composition were completely restored in LL plants after 1 week of rehydration, but changes persisted under ML conditions. Electron microscopy of structural changes in the chloroplast showed that the thylakoid lumen is filled with an electron-dense substance (dense luminal substance, DLS), while the thylakoid membranes are lightly stained. Upon dehydration and rehydration the DLS thinned and disappeared, the time course largely depending on the illumination: whereas DLS persisted during desiccation and started to disappear during late recovery under LL, it disappeared from the onset of dehydration and later was completely lost under ML.
Accumulation of DLS (possibly phenolics) in the thylakoid lumen is demonstrated and is proposed as a mechanism protecting the thylakoid membranes of H. rhodopensis during desiccation and recovery under LL. Disappearance of DLS during desiccation in ML could leave the thylakoid membranes without protection, allowing oxidative damage during dehydration and the initial rehydration, thus preventing recovery of photosynthesis.
Haberlea rhodopensis 是一种多年生草本石生植物，具有变渗性，在光照低于 30 微摩尔/平方米/秒时能够耐受干燥至风干状态。然而，在 350 微摩尔/平方米/秒的光照下进行干燥会导致光合作用器不可逆的变化，成熟叶片在重新水合后无法恢复。本研究旨在确定高光强下干燥导致光合作用器不可逆损伤的原因和机制，并阐明决定恢复的机制。
比较 Haberlea 在中等光照（100 微摩尔/平方米/秒；ML）和低光照（30 微摩尔/平方米/秒；LL）下干燥过程中叶绿体结构、CO2 同化、叶绿素荧光参数、荧光成像和多肽模式的变化。
在 100 微摩尔/平方米/秒的充分供水植物（对照）中未受损。在 LL 或 ML 下干燥的植物具有相似的失水率。在 ML 下干燥会比在 LL 下更快地降低光系统 II 光化学量子效率，特别是 CO2 同化率。在 LL 和 ML 下，脱水都会导致叶片中应激蛋白的积累。在 LL 植物中，经过 1 周的重新水合后，光合作用活性和多肽组成完全恢复，但在 ML 条件下仍存在变化。电子显微镜观察叶绿体结构变化显示，类囊体腔充满电子致密物质（致密腔物质，DLS），而类囊体膜呈浅染色。在脱水和再水合过程中，DLS 变薄并消失，其时间过程主要取决于光照：在 LL 下，DLS 在干燥过程中持续存在，在晚期恢复过程中开始消失，而在 ML 下，DLS 从脱水开始消失，随后完全消失。
证明了在 LL 下干燥和恢复过程中，DLS（可能是类黄酮）在类囊体腔中的积累，并提出了一种保护 Haberlea rhodopensis 类囊体膜的机制。在 ML 下干燥过程中 DLS 的消失可能会使类囊体膜失去保护，从而在脱水和初始再水合期间允许氧化损伤，从而阻止光合作用的恢复。
