The oxygen status of the developing seed

Summary Recent applications of oxygen‐sensitive microsensors have demonstrated steep oxygen gradients in developing seeds of various crops. Here, we present an overview on oxygen distribution, major determinants of the oxygen status in the developing seed and implications for seed physiology. The steady‐state oxygen concentration in different seed tissues depends on developmental parameters, and is determined to a large extent by environmental factors. Photosynthetic activity of the seed significantly diminishes hypoxic constraints, and can even cause transient, local hyperoxia. Changes in oxygen availability cause rapid adjustments in mitochondrial respiration and global metabolism. We argue that nitric oxide (NO) is a key player in the oxygen balancing process in seeds, avoiding fermentation and anoxia in vivo. Molecular approaches aiming to increase oxygen availability within the seed are discussed. Contents Summary 17 I. Introduction 17 II. Oxygen diffusion and the barriers to gas exchange 18 III. Metabolic indicators of seed hypoxia 19 IV. High‐resolution mapping of oxygen distribution in the developing seed 20 V. The effect of environmental factors on steady‐state oxygen concentrations 23 VI. Gene expression and metabolism under low oxygen 24 VII. Mechanisms of oxygen sensing and balancing in seeds 25 VIII. Might low internal oxygen levels be advantageous for seed development? 27 Acknowledgements 27 References 28