Dibley Stephen J, Gear Michael L, Yang Xiao, Rosche Elke G, Offler Christina E, McCurdy David W, Patrick John W
School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia.
Funct Plant Biol. 2005 Sep;32(9):777-785. doi: 10.1071/FP04224.
Correlative physiological evidence suggests that membrane transport into storage parenchyma cells is a key step in determining hexose levels accumulated in tomato (Lycopersicon esculentum Mill.) fruit (Ruan et al. 1997). Expression of three previously identified hexose transporter genes (LeHT1, 2 and 3) demonstrated that LeHT3, and to a lesser extent LeHT1, are the predominant transporters expressed in young fruit (10 d after anthesis; DAA). Expression of both transporters dropped sharply until 24 DAA, after which only LeHT3 expression remained at detectable levels through to fruit ripening. LeHT2 was not expressed substantially until the onset of fruit ripening. For fruit at both 10 and 30 DAA, LeHT3 transcripts were detected in storage parenchyma cells of the outer pericarp tissue, but not in vascular bundles or the first layer of parenchyma cells surrounding these bundles. In contrast to LeHT gene expression, hexose transporter protein levels were maximal between 20 and 30 DAA, which corresponded to the period of highest hexose accumulation. The delayed appearance of transporter protein is consistent with some form of post-transcriptional regulation. Based on these analyses, LeHT3 appears to be responsible for the rapid hexose accumulation in developing tomato fruit.
相关生理学证据表明，向贮藏薄壁细胞的膜转运是决定番茄（Lycopersicon esculentum Mill.）果实中己糖积累水平的关键步骤（阮等，1997）。对三个先前鉴定的己糖转运蛋白基因（LeHT1、2和3）的表达分析表明，LeHT3以及在较小程度上的LeHT1是幼果（开花后天数10天；DAA）中表达的主要转运蛋白。这两种转运蛋白的表达在24 DAA之前急剧下降，之后只有LeHT3的表达在果实成熟前一直保持在可检测水平。LeHT2直到果实成熟开始时才大量表达。对于10 DAA和30 DAA的果实，在外部果皮组织的贮藏薄壁细胞中检测到LeHT3转录本，但在维管束或围绕这些维管束的第一层薄壁细胞中未检测到。与LeHT基因表达不同，己糖转运蛋白的蛋白质水平在20至30 DAA之间最高，这与己糖积累最高的时期相对应。转运蛋白的延迟出现与某种形式的转录后调控一致。基于这些分析，LeHT3似乎负责发育中的番茄果实中己糖的快速积累。
