Overexpression of a Plasma Membrane Aquaporin in Transgenic Tobacco Improves Plant Vigor under Favorable Growth Conditions but Not under Drought or Salt Stress

TLDR

Aquaporins mediate most symplastic water transport in plants, yet their contribution to plant water status under favorable growth and abiotic stress remains unclear. The study aimed to test whether constitutive overexpression of Arabidopsis PIP1b in tobacco would alter plant water transport and vigor. Transgenic tobacco plants were engineered to constitutively express the plasma‑membrane aquaporin PIP1b. PIP1b overexpression enhanced growth, transpiration, stomatal density, and photosynthetic efficiency under favorable conditions, but had no benefit under salt stress and accelerated wilting under drought, showing that increased symplastic water transport improves vigor only when water is plentiful.

Abstract

Most of the symplastic water transport in plants occurs via aquaporins, but the extent to which aquaporins contribute to plant water status under favorable growth conditions and abiotic stress is not clear. To address this issue, we constitutively overexpressed the Arabidopsis plasma membrane aquaporin, PIP1b, in transgenic tobacco plants. Under favorable growth conditions, PIP1b overexpression significantly increased plant growth rate, transpiration rate, stomatal density, and photosynthetic efficiency. By contrast, PIP1b overexpression had no beneficial effect under salt stress, whereas during drought stress it had a negative effect, causing faster wilting. Our results suggest that symplastic water transport via plasma membrane aquaporins represents a limiting factor for plant growth and vigor under favorable conditions and that even fully irrigated plants face limited water transportation. By contrast, enhanced symplastic water transport via plasma membrane aquaporins may not have any beneficial effect under salt stress, and it has a deleterious effect during drought stress.