Sheue Chiou-Rong, Liu Jian-Wei, Ho Jia-Fang, Yao Ai-Wen, Wu Yeh-Hua, Das Sauren, Tsai Chi-Chu, Chu Hsiu-An, Ku Maurice S B, Chesson Peter
Department of Life Sciences & Research Center for Global Change Biology, National Chung Hsing University, 250 Kuo Kuang Rd., Taichung 40227, Taiwan.
Department of Biological Resources, National Chiayi University, 300 Syuefu Rd., Chiayi 60004, Taiwan.
Am J Bot. 2015 Apr;102(4):500-11. doi: 10.3732/ajb.1400485. Epub 2015 Apr 9.
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Chloroplast development and structure are highly conserved in vascular plants, but the bizonoplast of Selaginella is a notable exception. In the shade plant S. erythropus, each dorsal epidermal cell contains one bizonoplast, while other cells have normal chloroplasts. Our quest was to (1) determine the origin of bizonoplasts, (2) explore developmental plasticity, and (3) correlate developmental changes with photosynthetic activity to provide insights unavailable in other green plants with more constrained development.•
Bizonoplast development was studied in juvenile prostrate and older erect shoots of S. erythropus. Plastid plasticity was studied in plants cultivated under different light conditions. Chlorophyll fluorescence was measured and correlated with photosynthetic activity.•
The bizonoplast originates from a proplastid, forming a distinctive upper zone rapidly after exposure to low light. In the prostrate shoots, the proplastid develops through early stages only. When the shoot becomes erect, the proplastid soon develops into a mature bizonoplast. Erect shoots have significantly higher photosynthetic efficiency than prostrate shoots. No bizonoplasts were found in the plants growing in high light, where 2-4 spheroidal chloroplasts formed, or with light from below.•
The upper zone develops above a normal-looking chloroplast structure to produce a bizonoplast. Bizonoplast developmental plasticity suggests that regular lamellar structure and monoplastidy are adaptations to deep shade environments. Such novel variation in S. erythropus is in stark contrast to known plastid development in other vascular plants, possibly reflecting retention of developmental flexibility in the basal clade, Lycophyta, to which it belongs.
叶绿体的发育和结构在维管植物中高度保守，但卷柏的双区质体是一个显著例外。在阴生植物红枝卷柏中，每个背表皮细胞含有一个双区质体，而其他细胞具有正常叶绿体。我们的研究旨在：（1）确定双区质体的起源；（2）探索发育可塑性；（3）将发育变化与光合活性相关联，以提供在其他发育受限的绿色植物中无法获得的见解。
在红枝卷柏的幼年匍匐茎和较老的直立茎中研究双区质体发育。在不同光照条件下培养的植物中研究质体可塑性。测量叶绿素荧光并将其与光合活性相关联。
双区质体起源于前质体，在暴露于弱光后迅速形成一个独特的上部区域。在匍匐茎中，前质体仅通过早期阶段发育。当茎变为直立时，前质体很快发育成成熟的双区质体。直立茎的光合效率明显高于匍匐茎。在高光下生长的植物中未发现双区质体，在高光下形成2 - 4个球状叶绿体，或在底部有光照的情况下也未发现双区质体。
上部区域在看似正常的叶绿体结构上方发育以产生双区质体。双区质体的发育可塑性表明规则的片层结构和单核质体是对深荫环境的适应。红枝卷柏中这种新的变异与其他维管植物中已知的质体发育形成鲜明对比，可能反映了它所属的基部类群石松纲在发育灵活性方面的保留。
