After measurement, the seed is dissected along the measurement transect to identify each of the structurally distinct zones of the seed (seed coat, vacuole, embryo, endosperm). This is necessary to relate measurements of oxygen concentration with each physiologically and functionally distinct portion of the seed.Following this general procedure, oxygen maps have been created for the seeds of soybean [17], pea and broad bean [18,19], maize [20], barley [21], sunflower [22] and oilseed rape [6]. Some examples are shown in Figure 1. For wheat, only single location measurements [23], but no oxygen profile across the seed, are as yet available. Complete oxygen maps have established the reality of localized hypoxia within the seed, covering the major part of the maize and barley endosperm and the pea embryo (Figure 1).

Figure 1.Characteristic oxygen profiles measured in seeds of maize, barley and pea (left, middle and right panel, respectively). Oxygen was measured using microsensors along the x-axis. Oxygen concentration is given in % of atmospheric saturation (100% corresponds …The maps accord well with inferences based on biochemical assays and growth experiments [1-5]. Seed oxygen concentrations are developmentally regulated, and, for chlorophyll-bearing seeds, are also influenced by ambient light intensity [6]. Sensitivity to these factors is species-dependent. Moreover, microsensor-based oxygen mapping has allowed for the identification of regions having a high diffusional impedance for gas exchange – one example is the outer suberin-containing aleurone layer of the maize caryopsis, across which there is a substantial oxygen concentration gradient (Figure 1, left panel).

It has further become possible to characterize certain gas diffusion pathways [20] as well as to quantify localized photosynthetically induced oxygen release [21]. The high photosynthetic activity of the pericarp chlorenchyma in the barley caryopsis allows for the build-up of significant endogenous oxygen levels in the tissue, reaching almost double the atmospheric concentration (Figure 1, middle panel). Thus, microsensor-based mapping can also identify regions which underly hyperoxic (stress) conditions which is physiologically quite different from hypoxic stress. In brief, oxygen mapping in seeds has provided a wealth of information regarding endogenous oxygen status, and has facilitated the association of oxygen gradients with specific regions of the seed.4.?Monitoring Environmental Effects on Steady-state Carfilzomib Oxygen Concentrations within the SeedMost seeds are photosynthetically active during at least some stages of development.