Canny Martin, Wong Suan Chin, Huang Cheng, Miller Celia
Plant Science Division, Research School of Biology, RN Robertson Building, The Australian National University, Canberra, ACT 0200, Australia.
Centre for Advanced Microscopy, The Australian National University, Canberra, ACT 0200, Australia.
Funct Plant Biol. 2012 Mar;39(2):91-102. doi: 10.1071/FP11172.
Shrinkage of palisade cells during transpiration, previously measured for sclerophyllous leaves of Eucalyptus where cells shrank equally, was compared with shrinkage in thin mesophytic leaves of cotton (Gossypium hirsutum L.). Selected vapour pressure differences (Δe) from 0.6 to 2.7kPa were imposed during steady-state photosynthesis and transpiration. Leaves were then cryo-fixed and cryo-planed paradermally, and images obtained with a cryo-scanning electron microscope (CSEM). Diameters of palisade 'cavity cells' within sub-stomatal cavities, and surrounding palisade 'matrix cells' were measured on CSEM images. Cavity and spongy mesophyll cells shrank progressively down to Δe=2.7kPa, while matrix cells remained at the same diameter at all Δe. Diameters were also measured of cavity and matrix cells quasi-equilibrated with relative humidities (RHs) from 100% to 86%. In leaves quasi-equilibrated with 95% RH, the cavity cells shrank so much as to be almost unmeasurable, while matrix cells shrank by only 6%. These data suggest that there are two distinct pools of water in cotton leaves: cavity plus spongy mesophyll cells (two-thirds of leaf volume) which easily lose water; and matrix cells (one-third of leaf volume), which retain turgor down to relative water loss=0.4, providing structural rigidity to prevent wilting. This phenomenon is probably widespread among mesophytic leaves.
先前已对桉树叶硬叶的栅栏细胞在蒸腾作用期间的收缩情况进行了测量，其细胞收缩程度相同，现将其与棉（陆地棉）薄中生叶的收缩情况进行比较。在稳态光合作用和蒸腾作用期间施加选定的蒸汽压差（Δe），范围为0.6至2.7kPa。然后对叶片进行冷冻固定并进行横向冷冻切片，并用冷冻扫描电子显微镜（CSEM）获取图像。在CSEM图像上测量气孔下腔室内的栅栏“腔细胞”以及周围栅栏“基质细胞”的直径。腔室和海绵叶肉细胞随着Δe降至2.7kPa而逐渐收缩，而基质细胞在所有Δe下直径保持不变。还测量了与相对湿度（RH）从100%至86%达到准平衡状态的腔室和基质细胞的直径。在与95%RH达到准平衡状态的叶片中，腔室细胞收缩得几乎无法测量，而基质细胞仅收缩了6%。这些数据表明，棉花叶片中有两个不同的水分池：腔室加海绵叶肉细胞（占叶片体积的三分之二），它们容易失水；以及基质细胞（占叶片体积的三分之一），在相对失水率=0.4时仍保持膨压，为防止萎蔫提供结构刚性。这种现象可能在中生叶中普遍存在。
