Due to their robustness, reliability and long term stability microoptodes today are widely used in various biotechnological applications, like tissue engineering [11].Fiber optic sensors display the following advantages over microelectrodes:Affordable price,Measures oxygen in liquid as well as in the gas phase,Sensor signal independent of flow velocity,No time for polarization required, unlike the electrochemical electrode,No consumption of oxygen molecules while measuring, unlike the electrode that consumes oxygen molecules,No cross-sensitivity and no interference to carbon dioxide (CO2), hydrogen sulfide (H2S), ammonia (NH3), pH, and any ionic species like sulfide, sulfate or chloride. Oxygen microoptodes are only affected by gaseous sulfur dioxide (SO2) and gaseous chlorine (Cl2),Measurement range from 1 ppb up to 22.

5 ppm dissolved oxygenFast response times (t90 up to 1 s in the liquid and < 0.2 s in the gas phase).While there are a number of good reasons for using optical sensors, there have one disadvantage: microoptodes have a tip size of approximately 50 ��m, which is relatively big as compared to microelectrodes (10 ��m and less). This hampers studies where a very high spatial resolution is needed, e.g. to map gradients in oxygen concentration over a few cell layers. However, microoptodes allow spatial resolutions of slightly below 50 ��m, which is sufficient for most applications.3.?Oxygen Mapping in Plant SeedsOxygen-sensitive microsensors have enjoyed a long history of use in plant biology with focus on roots and its nodules [12-15].

The first (albeit indirect) attempt on seeds was done by Porterfield et al. [16] using miniature glass electrodes. By assessing the endogenous oxygen status within the siliques of both thale cress (Arabidopsis thaliana) and oilseed rape (Brassica napus) it was proposed that oxygen deficiency is an important determinant of the process of seed development. A series of studies followed, in which direct estimates of endogenous oxygen concentrations were made using relatively robust oxygen probes (microoptodes; Presens GmbH Germany). The procedure for oxygen profiling in seeds has since been standardized into the following four steps:The fruit (containing the intact seed) is fixed in a horizontal plane and, if necessary for the access of the microsensor, interfering material of the fruit is removed (e.g.

a small window is cut into the pod wall of a leguminous species, while in maize, the husk is discarded).Correct Brefeldin_A positioning of the microsensor on the seed surface is aided by a microscope. In some cases, the sealing of the microsensor entry point is necessary to prevent the diffusion of oxygen into the seed via the micro-channels formed by the probe. Often this is achieved by the application of silicone grease.The microsensensor is driven, in a series of timed steps, into the seed using a micromanipulator.