Marler Thomas E, Cruz Gil N
College of Natural and Applied Sciences, University of Guam, Mangilao, GU 96923, USA.
Plants (Basel). 2020 Apr 17;9(4):517. doi: 10.3390/plants9040517.
The growth of synchronized leaf flushes or male cones on trees is an ephemeral event, and non-structural carbohydrates (NSCs) are likely deployed from stem and root storage tissues to support their construction. The relationships among various stem NSCs and these rapid growth events have not been studied to date. Monosaccharides, disaccharides, and starch were quantified in stem tissue prior to and immediately after the growth of leaf flushes or male cones to determine the influences on the concentration of these carbohydrates. The pre-existing leaves were removed from half of the plants to determine if the elimination of this carbon source would influence the NSC behaviors. Starch and sucrose dominated the NSC profiles, and these two NSCs declined following cone or new leaf growth. Removal of pre-existing leaves generated a greater decline in starch and sucrose for cone growth, and a greater decline in sucrose, but not starch following new leaf growth than in control trees with no leaf removal. The initial differences in starch and sucrose among cortex, vascular, and pith tissues disappeared as the concentrations declined in all three tissue categories to reach similar post-growth concentrations among the stem tissue categories. The fructose, glucose, and maltose behaviors were not consistent, and their concentrations were low such that their influence on the total NSC behaviors was minimal. These results provided indirect evidence that stem NSCs were mobilized to support ephemeral male cone and new leaf growth for this arborescent cycad. Growth of female strobili is slow and lengthy, so we did not include female trees in this study. The contributions of stem NSCs to female strobili growth remain to be studied with alternative methods.
树木上同步的叶芽或雄球花的生长是一个短暂的事件，非结构性碳水化合物（NSCs）可能从茎和根的储存组织中被调动起来以支持它们的构建。迄今为止，尚未研究各种茎部NSCs与这些快速生长事件之间的关系。在叶芽或雄球花生长之前和之后立即对茎组织中的单糖、二糖和淀粉进行定量，以确定对这些碳水化合物浓度的影响。从一半的植株上移除已有的叶片，以确定消除这种碳源是否会影响NSCs的行为。淀粉和蔗糖在NSCs组成中占主导地位，这两种NSCs在球果或新叶生长后下降。移除已有的叶片后，球果生长时淀粉和蔗糖的下降幅度更大，新叶生长后蔗糖的下降幅度更大，但淀粉的下降幅度不如未移除叶片的对照树。随着所有三个组织类别的浓度下降，皮层、维管组织和髓组织之间淀粉和蔗糖的初始差异消失，在茎组织类别中达到相似的生长后浓度。果糖、葡萄糖和麦芽糖的行为不一致，它们的浓度较低，因此对总NSCs行为的影响最小。这些结果提供了间接证据，表明茎部NSCs被调动起来以支持这种树状苏铁短暂的雄球花和新叶生长。雌球花的生长缓慢且持续时间长，因此我们在本研究中未纳入雌树。茎部NSCs对雌球花生长的贡献仍有待用其他方法进行研究。
