Abstract

 

It is well known that green tea made from fully developed leaves located at the base of young shoots is of lower quality than that made from the still developing leaves located on the top of the shoot. It has additionally been shown that plant shading can significantly improve green tea quality. Here, we aimed to get more insight into the effects of shading on the overall metabolome in different parts of the tea shoots. To do this, field-grown tea plants were shaded by coverage with either a straw layer or a black net, both blocking the daylight intensity for more than 90%. Both the first (i.e. still developing) leaf and the fourth (i.e. fully developed) leaf, as well as the stem of young shoots were harvested and subjected to complementary untargeted metabolomics approaches, using accurate mass LC-Orbitrap-Fourier transform mass spectrometry (FTMS) for profiling both semi-polar and lipid-soluble compounds and GC-TOF-MS for profiling polar compounds. In total, 1419 metabolites were detected. Shading resulted in a decreased ratio of polyphenols to amino acids (which improves the quality of green tea) and lower levels of galloylated catechins in the shoots. The positive effect of shading on the amino acid/catechin ratio was more pronounced in the fully developed (fourth) than in the developing (first) leaves. Furthermore, many metabolites, especially organic acids, carbohydrates and amino acids, showed differential or opposite responses to the shading treatments between the three shoot tissues investigated, suggesting a within-plant spatial regulation or transport/redistribution of carbon and nitrogen resources between the tissues of the growing young shoots. This work provides new insight into the spatial effects of shading on tea plants, which could further help to increase tea quality by improving cultivation measures for plant shading.

Highlights

• Using complementary untargeted metabolomics approaches, 1419 metabolites has been detected in three young tea shoot tissues (stem, first and fourth leaves) and their responses to two plant shading treatments determined.
• In contrast to its marked increase in both first and fourth leaves, the key tea quality-related amino acid theanine significantly decreased in the stems under shading.
• The positive effect of shading on the amino acid/catechin ratio was more pronounced in the fully developed (fourth) than in the young still-developing (first) leaves.
• Differences in shading-induced changes in metabolites (e.g. organic acids, carbohydrates and amino acids) between the three young shoot tissues (suggest a within-plant spatial redistribution of carbon and nitrogen resources.

中文翻译：

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猩红橡树光合作用和叶片性状的季节性趋势

摘要

 

众所周知，由位于嫩芽底部的完全发育的叶子制成的绿茶质量低于由位于嫩芽顶部的仍在发育的叶子制成的绿茶。另外还表明，植物遮荫可以显着提高绿茶质量。在这里，我们旨在更深入地了解阴影对茶芽不同部位整体代谢组的影响。为此，田间种植的茶树用稻草层或黑网覆盖遮荫，两者都阻挡了 90% 以上的日光强度。收获第一片（即仍在发育的）叶子和第四片（即完全发育的）叶子以及嫩芽的茎，并进行互补的非靶向代谢组学方法，使用精确质量 LC-Orbitrap-傅立叶变换质谱 (FTMS) 分析半极性和脂溶性化合物，使用 GC-TOF-MS 分析极性化合物。总共检测到 1419 种代谢物。遮荫导致多酚与氨基酸的比率降低（这会提高绿茶的质量）和芽中没食子酰化儿茶素的含量降低。阴影对氨基酸/儿茶素比率的积极影响在完全发育的（第四）叶子中比在发育（第一）叶子中更明显。此外，许多代谢物，尤其是有机酸、碳水化合物和氨基酸，对所研究的三种芽组织之间的遮荫处理表现出不同或相反的反应，表明植物内空间调节或碳和氮资源在生长幼枝组织之间的运输/重新分配。这项工作提供了对遮荫对茶树的空间影响的新见解，这可以通过改进植物遮荫的栽培措施进一步帮助提高茶质量。

强调

• 使用互补的非靶向代谢组学方法，在三种年轻的茶树芽组织（茎、第一和第四叶）中检测到 1419 种代谢物，并确定了它们对两种植物遮荫处理的反应。
• 与第一叶和第四叶显着增加相反，遮荫下茎中与茶质相关的关键氨基酸茶氨酸显着降低。
• 阴影对氨基酸/儿茶素比率的积极影响在完全发育的（第四）叶子中比在年轻的仍在发育（第一）叶子中更明显。
• 三种幼枝组织之间由遮荫引起的代谢物（例如有机酸、碳水化合物和氨基酸）变化的差异（表明碳和氮资源在植物内的空间重新分布）。