Department of Ecology and Evolutionary Biology, University of Colorado Boulder, CO, USA.
Genomics and Bioinformatics Unit, Agriaquaculture Nutritional Genomic Center Temuco, Chile.
Front Plant Sci. 2014 Feb 6;5:24. doi: 10.3389/fpls.2014.00024. eCollection 2014.
The companion cells (CCs) and/or phloem parenchyma cells (PCs) in foliar minor veins of some species exhibit invaginations that are amplified when plants develop in high light (HL) compared to low light (LL). Leaves of plants that develop under HL also exhibit greater maximal rates of photosynthesis compared to those that develop under LL, suggesting that the increased membrane area of CCs and PCs of HL-acclimated leaves may provide for greater levels of transport proteins facilitating enhanced sugar export. Furthermore, the degree of wall invagination in PCs (Arabidopsis thaliana) or CCs (pea) of fully expanded LL-acclimated leaves increased to the same level as that present in HL-acclimated leaves 7 days following transfer to HL, and maximal photosynthesis rates of transferred leaves of both species likewise increased to the same level as in HL-acclimated leaves. In contrast, transfer of Senecio vulgaris from LL to HL resulted in increased wall invagination in CCs, but not PCs, and such leaves furthermore exhibited only partial upregulation of photosynthetic capacity following LL to HL transfer. Moreover, a significant linear relationship existed between the level of cell wall ingrowths and maximal photosynthesis rates across all three species and growth light regimes. A positive linear relationship between these two parameters was also present for two ecotypes (Sweden, Italy) of the winter annual A. thaliana in response to growth at different temperatures, with significantly greater levels of PC wall ingrowths and higher rates of photosynthesis in leaves that developed at cooler versus warmer temperatures. Treatment of LL-acclimated plants with the stress hormone methyl jasmonate also resulted in increased levels of wall ingrowths in PCs of A. thaliana and S. vulgaris but not in CCs of pea and S. vulgaris. The possible role of PC wall ingrowths in sugar export versus as physical barriers to the movement of pathogens warrants further attention.
在一些物种的叶小叶脉的伴胞（CCs）和/或韧皮部薄壁细胞（PCs）中，当植物在高光（HL）下发育时，其凹陷会被放大，而在低光（LL）下发育时则不会。与在 LL 下发育的植物相比，在 HL 下发育的植物的叶片表现出更高的光合作用最大速率，这表明 HL 适应叶片的 CCs 和 PCs 的膜面积增加可能为促进糖输出的转运蛋白提供更高水平。此外，在 HL 适应叶片中，完全展开的 LL 适应叶片的 PC（拟南芥）或 CC（豌豆）的细胞壁内陷程度在转移到 HL 后 7 天增加到与 HL 适应叶片相同的水平，并且这两个物种的转移叶片的光合作用最大速率同样增加到与 HL 适应叶片相同的水平。相比之下，将普通千里光从 LL 转移到 HL 导致 CC 中的细胞壁内陷增加，但 PC 中没有，并且此类叶片在从 LL 转移到 HL 后仅表现出光合作用能力的部分上调。此外，在所有三种物种和生长光照条件下，细胞外壁内陷的水平与光合作用最大速率之间存在显著的线性关系。对于在不同温度下生长的两个拟南芥生态型（瑞典、意大利），这两个参数之间也存在正线性关系，在较凉爽温度下发育的叶片具有更高的 PC 细胞壁内陷水平和更高的光合作用速率。用应激激素茉莉酸甲酯处理 LL 适应的植物也导致拟南芥和普通千里光的 PC 中的细胞壁内陷水平增加，但在豌豆和普通千里光的 CC 中没有。PC 细胞壁内陷在糖输出中的可能作用与作为病原体运动的物理屏障值得进一步关注。
