Phenotypic plasticity of field pea (Lathyrus oleraceus L.) nodule morphology and cell-wall lignin in response to water and photothermal regimes.

Abstract

Legume plants associate symbiotically with Rhizobium and Bradyirhizobium bacteria that fix atmospheric nitrogen. Despite the well-documented effects of water regime on nodule establishment and functionality, little is known about its influence on nodule morphology after establishment. We grew Lathyrus oleraceus L. plants in a factorial experiment combining two growing conditions (winter and spring) and three levels of plant available water (PAW) in soil: 60 %, 85 %, and 100 %. Plant growth traits were measured. Nodules were analyzed with optical and confocal microscopy, using fluorescence lifetime imaging microscopy for lignin autofluorescence analysis. High water availability increased shoot biomass, as well as number and size of nodules compared to low water availability, with stronger effects in spring than in winter. The typical indeterminate nodules of field pea exhibited phenotypic plasticity whereby plants in dry soil had smaller and rounder nodules compared to plants grown at 100 % PAW. Lignin content of nodule cortex cells also varied with water and growing condition, being higher for 100 % PAW in winter and 60 % PAW in spring. Lignin content and morphological plasticity of field pea nodules may have implications for adaptation to water and photothermal variations.