Methods of Comparative Study

In most plants there is a continuum of gas-filled intercellular space which can serve for the transport of atmospheric or photosynthetic oxygen from shoot to root. Despite this, the lack of oxygen in flooded soils will often restrict root growth, but the development of aerenchyma can substantially improve transport leading to deeper rooting, a greater degree of rhizosphere oxygenation and improved nutrient acquisition. In roots, gas-phase transport is chiefly by diffusion and within the cortex; in aerial parts and rhizomes, in addition to diffusion there may be a large convective component operating in both pith and cortex. Aerenchyma is formed either by wall separation and cell collapse (lysigeny) (Figure 3.1a) or by cell separation only (schizogeny) (Figure 3.1b); lysigeny may be stimulated by ethene, low oxygen and nutrient deficiency.