Rostaminedjad Mehri, Askari Hossein, Zakavi Maryam, Nadjafabadi Masood Soltani, Farrokhi Naser
Department of Cell and Molecular Biology, Faculty of Life Sciences and Biotechnology, Shahid Beheshti University G. C., Evin, Tehran, Iran.
Department of Plant Sciences and Biotechnology, Faculty of Life Sciences and Biotechnology, Shahid Beheshti University G. C., Evin, Tehran, Iran.
Iran J Biotechnol. 2019 Jan 11;17(1):e1734. doi: 10.21859/ijb.1734. eCollection 2019 Jan.
Root to shoot connection and transfer of information seems to be taken place mostly via the transmissions of signal molecules, secondary metabolites, amino acids, hormones and proteins, through xylem sap. Examination of earlier reports is indicative of relatively high levels of conservation in xylem sap protein compositions. Apparently these protein molecules are being synthesized in roots in response to environmental changes and get transported to aerial plant parts after secretion into xylem sap.
In order to comprehend this so-called passive signaling, some questions need to be answered: 1) Do these proteins have the capability to act as signals? 2) How much energy does root spend for the biosynthesis of the secreted proteins? How similar is the amount of energy that root cells spent for the biosynthesis of intra- and extra-cellular proteins?
Reported xylem sap proteins curated from Arabidopsis, maize and soybean. Their sequences were put under scrutiny in terms of considering their mobility, and physical and chemical properties. Metabolic energy required for their biosynthesis along with the energy hidden in their peptide bonds were calculated and compared with random non-xylem sap proteins as control.
Xylem sap proteins were significantly smaller than the root proteins, while they were bigger in size when compared to the leaf group. Xylem protein pIs were significantly higher than the control proteins in different plants. Similarly, the protein stability was higher for xylem sap proteins in comparison with roots and leaves in all analyzed plants, except for soybean that the stability was indifferent between xylem and root. The data were suggestive a significantly lower energy consumption for the synthesis of xylem sap proteins.
Lower energy consumption may suggest an economical route of communication between roots and shoots in plants that mainly rely on symplastic signaling.
根与地上部分的连接以及信息传递似乎主要通过信号分子、次生代谢产物、氨基酸、激素和蛋白质在木质部汁液中的运输来实现。对早期报告的研究表明，木质部汁液蛋白质组成具有较高的保守性。显然，这些蛋白质分子是根在响应环境变化时合成的，分泌到木质部汁液后被运输到地上植物部分。
为了理解这种所谓的被动信号传导，需要回答一些问题：1）这些蛋白质是否有能力充当信号？2）根在分泌蛋白的生物合成上花费多少能量？根细胞用于细胞内和细胞外蛋白质生物合成的能量量有多相似？
整理来自拟南芥、玉米和大豆的已报道的木质部汁液蛋白质。从它们的迁移率以及物理和化学性质方面对其序列进行仔细研究。计算它们生物合成所需的代谢能量以及它们肽键中隐藏的能量，并与作为对照的随机非木质部汁液蛋白质进行比较。
木质部汁液蛋白质明显小于根蛋白质，而与叶组相比则更大。不同植物中木质部蛋白质的等电点明显高于对照蛋白质。同样，除大豆外，在所有分析的植物中，木质部汁液蛋白质的稳定性高于根和叶，大豆中木质部和根之间的稳定性无差异。数据表明木质部汁液蛋白质合成的能量消耗明显更低。
较低的能量消耗可能表明在主要依赖共质体信号传导的植物中，根与地上部分之间存在一种经济的通讯途径。
