Journal Article

Structural and Functional Vein Maturation in Developing Tobacco Leaves in Relation to AtSUC2 Promoter Activity

Roberts, Alison G., Helle J. Martens, Kathryn M. Wright, Oparka, Karl J., Sauer, Norbert

2003

Overview

Transgenic tobacco (Nicotiana tabacum) plants expressing green fluorescent protein (GFP) from the AtSUC2 promoter were used to study the function of different vein classes in developing leaves. In sink leaves, unloading capacity occurred acropetally, with the class I (midrib) and class II veins becoming functional in phloem unloading before the maturation of the class III veinal network. In contrast, in developing cotyledons and source leaves, loading capacity occurred in a basipetal direction. There was a strong correlation between loading capacity, as assessed by 14C Suc uptake and companion cell expression of AtSUC2-GFP. Developing cotyledons were shown to utilize all available vein classes for loading. A second line of transgenic plants was produced in which GFP, expressed from the AtSUC2 promoter, was targeted to the endoplasmic reticulum instead of the cytoplasm. In these AtSUC2-GFP-ER plants, GFP was unable to traffic into the sieve element and was restricted solely to the companion cells of source leaf tissues. Partial shading of leaves undergoing the sink-source transition demonstrated that the activation of the AtSUC2 promoter in tobacco was influenced by light. Functional and structural maturation of the minor veins required light or a product of light. The activation of the AtSUC2 promoter within major veins appears to be regulated differently from that in the minor veins. The relationship between AtSUC2 activation and the activity of endogenous tobacco Suc transporters is discussed.

• Publisher: American Society of Plant Biologists
• Subject: Arabidopsis Proteins / Arabidopsis Proteins - genetics / Cotyledon / Cotyledon - metabolism / Cotyledons / endoplasmic reticulum / Gene Expression Regulation, Plant / Genes, Plant / Genes, Plant - genetics / genetics / green fluorescent protein / growth & development / leaf development / Leaves / Light / Membrane Transport Proteins / Membrane Transport Proteins - genetics / metabolism / Nicotiana - genetics / Nicotiana - growth & development / Nicotiana tabacum / Phloem / Phloem companion cells / Plant Leaves / Plant Leaves - genetics / Plant Leaves - growth & development / plant proteins / Plant Proteins - genetics / Plant shading / Plant tissues / Plant veins / Plants / Plants, Genetically Modified / promoter regions / Promoter Regions, Genetic / Promoter Regions, Genetic - genetics / Seedlings / Seedlings - genetics / shade / Sieve elements / source-sink relationships / sucrose / tobacco / transcriptional activation / Transgenic plants / transporters / uptake mechanisms / Whole Plant and Ecophysiology