PNAS （Proceedings of the National Academy of Sciences of the United States of America）111(16) 今天发表了一篇颠覆植物顶端优势理论的文章。

过去百年来一直认为植物的顶芽的顶端分生组织产生生长素吲哚乙酸，并向下面的组织传输，从而保持自身的生长优势，特别是伸长优势，同时抑制其下端的侧芽的生长。本论文以去掉顶芽做实验，检测生长素和蔗糖的最先动向及其对控制芽休眠的转录调节子BRANCHED1 (BRC1) 的影响，认为蔗糖最先启动并打破休眠而使原先不具有顶端优势的休眠芽开始生长。顶芽对蔗糖的掠夺，使侧芽得不到蔗糖生长，是顶端优势的最初动因。

本人尚未认真看文章的细节，但是有个疑问，即：在植物组织培养方面，增加培养基蔗糖浓度经常是抑制顶芽的生长。例如体细胞胚胎发生、小孢子胚胎发生和幼胚培养时，经常为了防止顶芽的过早萌发而增加培养基的蔗糖浓度（一般蔗糖浓度在100——200g/L)。这似乎与该文所述的人为增加蔗糖浓度可以打破被抑制生长的休眠芽的结果不符。是否在体和离体条件下存在不同的机制尚需验证。

见原文评论和摘要：

Sugar demand, not auxin, is the initial regulator of apical dominance

Michael G. Masona, John J. Rossb, Benjamin A. Babstc, Brittany N. Wienclawc, and Christine A. Beveridgea,1

Author Affiliations

A School of Biological Sciences, The University of Queensland, St. Lucia, QLD 4072, Australia;

B School of Plant Science, University of Tasmania, Sandy Bay, TAS 7005, Australia; and

C Biosciences Department, Brookhaven National Laboratory, Upton, NY 11973-5000

Edited by Deborah P. Delmer, University of California, Davis, CA, and approved March 14, 2014 (received for review November 25, 2013)

Significance

It is commonly accepted that the plant hormone auxin mediates apical dominance. However, we have discovered that apical dominance strongly correlates with sugar availability and not apically supplied auxin. We have revealed that apical dominance is predominantly controlled by the shoot tip’s intense demand for sugars, which limits sugar availability to the axillary buds. These findings overturn a long-standing hypothesis on apical dominance and encourage us to reevaluate the relationship between hormones and sugars in this and other aspects of plant development.

Abstract

For almost a century the plant hormone auxin has been central to theories on apical dominance, whereby the growing shoot tip suppresses the growth of the axillary buds below. According to the classic model, the auxin indole-3-acetic acid is produced in the shoot tip and transported down the stem, where it inhibits bud growth. We report here that the initiation of bud growth after shoot tip loss cannot be dependent on apical auxin supply because we observe bud release up to 24 h before changes in auxin content in the adjacent stem. After the loss of the shoot tip, sugars are rapidly redistributed over large distances and accumulate in axillary buds within a timeframe that correlates with bud release. Moreover, artificially increasing sucrose levels in plants represses the expression of BRANCHED1 (BRC1), the key transcriptional regulator responsible for maintaining bud dormancy, and results in rapid bud release. An enhancement in sugar supply is both necessary and sufficient for suppressed buds to be released from apical dominance. Our data support a theory of apical dominance whereby the shoot tip’s strong demand for sugars inhibits axillary bud outgrowth by limiting the amount of sugar translocated to those buds.

Keywords: shoot branchingsink demanddecapitationgirdlinglong-distance signaling

原文：http://www.pnas.org/content/111/16/6092.abstract.html?etoc